.vgreamosimemew

CIE Nol MONTHLY FOR THE ELECTRONICS & MUSIC HOBBYISI

PROJECTS, FEATURES, NEWS & REVIEWSIN ELECTRONICS & ELECTRO-MUSIC

HI-FI SUB -BASS WOOFERLOOKING AT MICROPHONESCAR BATTERY MONITORBALANCED LINE SYSTEMCONTINUITY TESTER

TWO SPECIALOFFERS !!

BBC R4D1OPHONICWORKSHOP -21

MARCH 198165p

HOME WORKSHOP VEHICLE EDUCATION COMPUTERS ELECTRO -MUSK1,*

Here are just a fewof our enclosures...

...to find out more...see our Retail Catalogue, price 40p, for thecomplete range of Vero Products available tothe Electronics Hobbyist.

The Retail Department, Vero Electronics limitedIndustrial Estate, Chandler's Ford, Hampshire S05 3ZR

Tel (04215) 62829

"LEO nicskennic____Rween

First Issue 100 Pages for the Electronics and Music Hobbyist!EditorMike BeecherTechnical EditorChris JordanArt EditorPeter BlackmoreEditorial SecretarySue ForsterTechnical IllustratorsJohn DudleyRoy SmithPhotographyIan JamesPaul Mellor

Consultants

ProjectsRobert PenfoldCircuit DesignChris LareElectro-MusicVince S. HillMicroprocessorsPeter KershawMusic SynthesisTim SousterStudio RecordingMark AndrewsEducationSteve LeverettHi-FiJeff MacaulayTV & VideoAndy EmmersonStage EquipmentBen DuncanOrgan ElectronicsKen Lenton-SmithGuitar ElectronicsAdrian LeggPercussion ElectronicsLloyd RyanElectronics NewsMark SpaceBook ReviewsNigel FawcettMicrocomputersGraham KnightSoftwareGraham DaubneyCourse WritersNorman ButlerGraham HallTechnical LabBob KirschDave GoodmanStudio TechnicianGlenn Rogers

Editorial Offices282 London RoadWestcliff-on-SeaEssex SSO 7JGTel: (0702) 338878

Advertisement ManagerTerry Day

Classified ManagerDennis Hill

Advertisement OfficesElectronics & Music MakerHillcroft House16 The AvenueHighams ParkLondon E4 9LDTel: 01-527 3376

Published byMaplin Publications282 London RoadWestcliff-on-SeaEssex SSO 7JGTel: (0702) 338878

Distributed byCemas Limited24 Bridge StreetSt IvesHuntingdonCambridgeshire PE17 4EGTel: (0480) 63942

Printed byEden Fisher (Southend) Limited

Typeset byQuillset Typesetting

SubscriptionsRates for 12 issues:UK & Overseas Surface: £9.90Europe: £11.64Airmail: £25.20

CopyrightAll material is subject to world wideCopyright protection, and reproductionor imitation in whole or part is expresslyforbidden. All reasonable care is taken toensure accuracy in preparation of themagazine but Maplin Publications cannotbe held legally responsible for its contents.Where errors occur corrections will bepublished as soon as possible afterwards.All prices and data contained inadvertisements are as ascertained to becorrect at the time of going to press.Permission to reproduce printed circuitboard layouts commercially or marketingof kits must be sought from the Publisher.© Copyright 1981 Maplin Publications.

CONTENTS

ELECTRONICSThe Matinee OrganICs for Electro-Music Charles Blakey 12The Spectrum Synthesiser Chris Jordan 16Starting Point Robert Penfold 12Continuity Tester Robert Penfold 26Hi-Fi Sub -Bass Woofer Jeff Macaulay 30Circuit Maker 36Balanced Line System Chris Lare 38Circuits and Standards 42Car Battery Monitor David Hough 44

COMPUTINGUsing MicroprocessorsSharp MZ-80K - the Melody Micro Graham KnightBasically BASIC Graham Hall

ELECTRO-MUSICWorking with Video Andy Emmerson 57Guide to Electronic Music Techniques Vince S. Hill 59Instrument Review - Yamaha SK20 Synthesiser 60Advanced Music Synthesis Chris Jordan 63Hot Wiring Your Guitar Adrian Legg 67Discotek Ben Duncan 68Radiophonic Workshop 70Hi-Fi Jeff Macaulay 73Looking at Microphones Chris Lare 74Get Organised! Ken Lenton-Smith 77

Page

6

Peter Kershaw 485154

NEWSNew Products 78Music Maker Equipment Scene 79E&MM Subscriptions and T -Shirts 79America Ian Waugh 81Record Reviews 82Book Reviews 83Patents 85Education Steve Leverett 87Breadboard Exhibition Report 89Industry Profile - Vero Electronics 90Citizens Band 93Events 93Next Month 95Special Offers 95Quo Zog? Stichos 96Advertisers Index 96E&MM Cassette Service 96

E&MM MARCH 1981 1

NEW REDUCEDPRICES

8K £39916K £44932K £499RRP £795 for 32K

41111111.111144pip

The PEDIGREE PETS homepopular Ice

ome & business.,se. 8K Microsoft Basic in ROM 8K Pet 32K & 16K withew improved keyboard All with green screen.

Cassette Deck £55 extra Full range of software avan;abs

Interface PET IEEE - Centronics Parallel

Decoded £77.00 + VAT

We give a full one year'swarranty on all our products.

,G0.; GET YOURSELF Asi''',00` PRINTER FOR

S' YOUR PET AND SAVEA FORTUNE

only £299 + VAT

Interface Cards for Apple,Pet, TRS80, Nascom andCompukit - £49 + VAT

Full Pet Graphics includingcables. Ready to go. EX -STOCK.

NASCOM 2 DISC DRIVESAdd a powerful, double

density, mini floppy disc toyour Nascom system.

Disc Controller Card (includesNasbus 6 S100 interface Will control 4 Drives. CPM operating system. Extended Disc BasicCompiler. Power supply included

One Disc System - £499 + VATAdditional Disc Unit - £299 r VAT

NASCOM 2 GAMES TAPEfeaturing Space Invaders and Android Nim, Re -numbering

program and other goodies!

£7.50 ± VAT

NECSPINWRITER

only£1350

+ VAT

NEC's high quality printer uses a print "thimble" that hasless diameter and inertia than a daisy wheel, giving a quieter,faster, more reliable printer that can cope with plotting andprinting 1128 ASCII characters) with up to five copies, fric-tion or tractor fed. The ribbon and thimble can be changed inseconds. 55 characters per second bidirectional printing -with red/black, bold, subscript, superscript, proportionalspacing, tabbing, and much, much more.

TEACDISK

DRIVES

TEAC FD -50A has 40 tracks giving 125K Bytesunformatted single density capacity.The FD -50A can be used in double density recordingmode.The FD -50A is Shugart SA400 interface compatible.Directly compatible with Tandy TRS80 expansioninterface.Also interfaces with Video Genie, SWTP, Heathkit,North Star Horizon, Superbrain, Nascom, etc, etc.Address selection for Daisy chaining up to 4 Disks.Disks plus power supply housed in an attractive greycase.

Single £2254 -VAT Double £3894_ VATDisk Drive Disk Drive

COMP POCKET COMPUTERGREATEST BREAKTHROUGH

YET

seen"tosetTssw\

C.51:1'" 101111."-J,Jv COMPUTERPOWER THAT

ONCE FILLED A ROOMCAN NOW BE CARRIED IN YOUR POCKET'

Programs in BASIC "QWERTY" AlphabeticKeyboard 1.9K Random Access Memory Long Battery Life.

Computer power that once filled a room can now be carriedin your pocket! It's easy to load with ready -to -run softwarefrom cassette tape (interface and recorder optional) orprogram it yourself in easy -to -learn BASIC. 24 -characterliquid crystal readout displays one line at a time. Specialfeature is advanced non-volatile memory allows you topower on and off without losing the contents of memory.Note: Memory must be transferred to tape before changingbatteries. Automatic statement compaction squeezes everyounce of memory space. Features power -off retention ofprograms and data. Powerful resident BASIC languageincludes multiple statements, math functions, editing,strings, arrays and much more. Multiple program loadingcapability subject to RAM availability. Carrying case andbatteries included.

FOR FILE HANDLING

ACULABFLOPPY

TAPEThe tape that behaves

like a disc, forTRS-80 LEVEL 2.

only £169 + VATThe Aculab Floppy Tape for the TRS-80 and Video Genie is ahighly reliable digital storage system that provides many ofthe advantages of floppy disks at less cost. Automaticdebounce routine for the Level 2 keyboard.Connects directly to TRS-80 Level 2 Keyboard. Operatingand file handling software in ROM. 8 commands add 12powerful functions to Level 2 BASIC.

THE VIDEO GENIE SYSTEMIdeal for small businesses, schools, colleges, homes, etc.Suitable for the experienced, inexperienced, hobbyist,eacher, etc.

16K£289

EG3000Series

WITHNEW

EXTRAKEYS!

16K user RAMplus extended 12K Microsoft

BASIC in ROM Fully TRS-80 Level IIsoftware compatible Huge

range of software already available Self contained, PSU,UHF modulator, and cassette Simply plugs into videomonitor or UHF TV Full expansion to disks and printer Absolutely complete - just fit into mains plug.The Video Genie is a complete computer system, requiringonly connection to a domestic 625 line TV set to be fullyoperational; or if required a video monitor can be connectedto provide the best quality display. 51 key typewriter stylekeyboard, which features a 10 key rollover. Supplied withthe following accessories:- BASIC demonstration tape; Video lead; Second cassetee lead; Users manual BASIC manual; Beginners programming manual. Writ,.useful programs in the BASIC computer language yourself.

VIDEO GENIE EXPANSION BOX.NOW IN SHOP

only £325 'A

TRS80LEVEL 2 16K

Fully converted to UK T V Standard. Comes complete witheasy to follow manuals. UK Power Supply - Cassette Leads- Sample tapes. Special box to enable you to plug into yourown TV. Recommended for first time -buyers. Just plug inand go. Full Range of Software Available

Interface to Centronics Parallel for TRS80 £75.00 + VAT

only £295 - VA' TRS80Expand your T R S80 bY EXPANSION32K.32K Memory on board + INTERFACECentronics parallel portDisk controller card. Realtime clock. Requires LevelII Basic. Interface for 2cassette decks complete

with power supply

YOU NEED NEVER MISS ANIMPORTANT CALL AGAIN

TWO CORDLESS TELEPHONESYSTEMS - DIRECT FROM USA

THE ALCOM only £147 + VATBase station connects to your telephone line. Remotehandset clips to your belt and gives you push-button dialling- Bleeps when call arriving - Nicad rechargeable batteries.Charger in base unit.

LOW COST TELEPHONE only

ANSWERING MACHINE £V99. 95AT

Microprocessor controlled answering machine. Plug intoyour phone line. Records any phone call messages. Remotebleeper enables you to listen to your messages fromanywhere in the world. Uses standard cassettes. Comescomplete with mains adaptor, microphone, remote bleeper,base unit, cassette with 30 sample pre-recorded messages.

COMMERCIALEXPANDABLE COMPLETE

TRS 80 MODEL II

64K1 -Disk

Model II£1995.00

RRP £2250.00

The Model III is now in our showroomThis new unit from the world's most successful microcompany is now available immediately with software.The basic unit comes complete with 64 thousand characters(bytes) of Memory. The built in 8" Floppy disc adds another1/2 million extra characters including the disc operatingsystem. More disc expansion is now available.The Model II is a complete unit with a full keyboard including anumeric pad and 12" screen which gives 24 lines of 80characters. The computer is supplied with both the discoperating system and the Level III Basic.A full self test routine is written into the power up procedureto eliminate incorrect operation. Both serial and parallelexpansion sockets are standard. A printer is a plug-inoperation.Both hardware and software necessary to talk to a mainframeare included. Terminal usage is very possible. With theaddition of CPM2 you can operate with COBOL, FORTRAN,MBASIC, CBASIC in which languages are many otherapplications packages i.e. accounting, payroll stock etc.

CP/M2 £95.00 M BASIC £155.00CIS COBOL £400.00 FORTRAN £220.00C BASIC 05.00 WORDSTAR £255.00

is ear III 0a 4I 80,4, 46 , 40

/i410,11 i 40 t!

COMP PRO MIXERProfessionalaudio mixer

that you canbuild yourself

and saveover £100.

Only

£99.90plus VAT forcomplete kit.

Plus FREEpower supply

valued at

FULL RANGE OF £25.00

ACCESSIT AUDIO ADD-ONS*************************************************************

WITH ORDERS OVER f100.00 -ENCLOSE THIS COUPON WITH ORDER*************************************************************

2 MARCH 1981 E&MM

:e FREE 10 C-12 CASSETTES

£99.90+ VAT

CD

53 U)

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CD

12) 0IT )-o W

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5 a-0 3

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CDco 2

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RRP£540 only

£399

ANADEXDP8000

Super Quality - Low cost t, t, Tractor Fe,": .,,I 96ASCII character set. Accepts RS232C at band rates between

100 and 9600 and Parallel Bit data.Attaches either directly or through interfaces to Pet, Apple,

TRS80, Sorcerer, Nascom, Compukit etc.

THE NEW ANADEXDP9500 and DP9501

A PROFESSIONAL PRINTERBi-directional printing

Up to 220 chars/line. with 4 print densities

500 char buffer RS232C and Centronics

irk Parallel interface built in Full software control of matrix

needles allowing graphics capability 200 chars/sec Adjustable width tractor feed.

DP9500 - ONLY £795 + VATDP9501 - ONLY £845 VAT

THE ATARI VIDEO COMPUTERGAMES SYSTEM 00

Atari's Video Computer System Vnow offers morethan 1300 different gamevariations and options in twentyGame ProgramTM cartridges!

Most Carriages only 13.90 VAPrices may vary with special

editions Basic Maths, AirseaBattle, Black Jack, Breakout,Surround, Spacewar, Video

Olympics, Outlaw, Basketball,Hunt & Score', Space War,Sky Diver, Air Sea Battle,

Codebreaker*, Miniature Golf.

Extra Paddle Controllers Keyboard Controllers- £14.90 + VAT - £16.90 + VAT

SPACE INVADERS NOW IN STOCK £25

EUROPE'S FASTEST SELLING ONE BOARD COMPUTER

OMPUKIT UK101* 6502 based system - best value for money on the market. * Powerful 8K

Basic - Fastest around * Full Qwerty Keyboard * 4K RAM Expandable to 8Kon board. * Power supply and RF Modulator on board. * No Extras needed -Plug-in and go. * Kansas City Tape Interface on board. * Free Sampler Tapeincluding powerful Dissassembler and Monitor with each Kit. * If you want to

learr about Micros, but didn't know which machine to buy then this is themachine for you.

40 pin Expansion Jumper Cable for Compukit expansion £8.50 + VAT I

Buld, Undo bland and Program your ownComputer for only a small outlay

KIT ONLY £179 VAT

NO EXTRAS NEEDED

Available ready assembled, tested & e dy to go 1:229 + VAT.

NEW MONITOR FOR COMPUKIT UK101 In 2K Eprom 2716 Allows screen editing Saves data on tape Flashing cursor Text scrolls down E22.00 VAT

Special Bonus SAVE £22. New Super Monitor inc. in each kit or sold separately for E22 + VAT.

FOR THE COMPUKIT

Assembler/ Editor

Game Packs

E14.90 1. Four Games

Screen Editor Tape

Super Space Invaders toldSpace Invaders

£5.00 Chequers

E5.90 2. Four Games

All Prices exclusive VAT

£5.50

E5.00

£3.00

E5.00 Real Time Clock

3. Three Games 8K only

3.00E5.00 Case for Compukit E29.50

HITACHIPROFESSIONAL

MONITORS9" - £99.9512" - fad £149

Reliability Solid state circuitry using an IC and silicontransistors ensures high reliability. 500 lines horizontalresolution Horizontal resolution in excess of 500 lines isachieved in picture center. Stable picture Even playedback pictures of VTR can be displayed without jittering. Looping video input Video input can be looped throughwith built-in termination switch. External sync opera-tion (available as option for U and C types) Compactconstruction Two monitors are mountable side by side in a

standard 19 -inch rack.

MEMORY UPGRADES16K (8 x 4116) £17.90 - VAT

4K Compukit (8 x 2114) £17.90 . VAT

ENGLISH COLOUR TV/AMERICAN NTSC

COLOUR MONITORSuitable for Apple, Atari and Texas 99/4 £295 VAT

8MHz Super Quality Modulators £4.90

6MHz Standard Modulators E2.90

C12 Computer Grade Cassettes 10 for £4.00

Anadex Printer Paper - 2000 sheets £25.00

Floppy Discs 5 1/4" Hard and Soft Sectored E3.50

Floppy Disc Library Case 51/4" £3.50

Verocases for Nascom 1 & 2 etc. £24.90

Keyboard Cases £9.90

NEB TV GAME BREAK OUTHas got to be one of the world's greatest TV games. You reallyget hooked. As featured in ETI. Has also 4 other pinball garnetand lots of options. Good kit for up -grading old amusementgames.MINI KIT - PCB, sound & vision modulator, memory chipand de -code chip. Very simple to construct. £14.90 VAT

'OR PCB £2.90 MAIN LSI £8.50 Both plus VAT

WE ARE NOW STOCKING THEAPPLE II AT

REDUCED PRICES

3

16K

£649

48K £659Getting Started APPLE II is faster, smaller, and mo epowerful than its predecessors. And it's more fun to use toobecause of built-in features like: BASIC - The Language that Makes Programming Fun. High -Resolution Graphics lie a 54,000 -Point Array) forFinely -Detailed Displays. Sound Capability that BringsPrograms to Life. Hand Controls for Games and OtherHuman -Input Applications. Internal Memory Capacity of48K Bytes of RAM, 12K Bytes of ROM; for Big -System Per-formance in a Small Package. Eight Accessory ExpansionSlots to let the System Grow With Your Needs.

You don't need to be an expert to enjoy APPLE II. It is acomplete, ready -to -run computer. Just connect it to a videodisplay and start using programs for writing your own) thefirst day. You'll find that its tutorial manuals help you make ityour own personal problem solver.

SPECIAL OFFERWe will part exchange

your Sinclair ZX80 forany of our products.

Refurbished ZX80's - fully guaranteed +

Refurbished MicroAces - £69.90 VAT

(Supply dependant upon stocks).

We have one of the largest collections of Computer Books under one roof, along withracks of software for the PET and TRS80.

Come and see for yourself.

OUR HESHOWROOM Et

SALES CENTRE AT311 Edgware Road,

London W2.Telephone: 01-262 0387

APPLE DISC IIDisc with Controller

£349 + VAT

Additional Drives£299 ' VAT

Powerful Disk Operating Software Supports up to 6drives Name Access to Files for Ease of Use BASICProgram Chaining to Link Software Together Randomor Sequential File Access to Simplify Programming Dynamic Disk Space Allocation for Efficient Storage Individual File Write -Protection Eliminates AccidentalFile Alterations Loads an 8K Byte Binary Image in 6.5sec. 11.2 sec. in Pascal) Storage Capacity of 116Kilobytes 1143K Bytes with Pascal) on Standard 51/4"Diskettes Powered Directly From the APPLE (Up to 6Drives) for Convenience and High Reliability Packagedin Heavy -Duty, Colour -Coordinated Steel Cabinet

A SELECTION OF APPLE INTERFACESARE NOW AVAILABLE AT OUR NEW

SHOWROOM.

"Europes Largest DiscountPersonal Computer Stores"

Delivery is added at cost.. Please make cheques and postal orders payable to COMPSHOP LTD., or phone your orderquoting BARCLAYCARD, ACCESS, DINERS CLUB or AMERICAN EXPRESS number.

CREDIT FACILITIES ARRANGED - send S.A.EMAIL ORDER AND SHOP:14 Station Road, New Barnet, Hertfordshire, EN5 1QW (Close to New Barnet BR StationTelephone: 01-441 2922 (Sales) 01-449 6596 Telex: 298755 TELCOM GOPEN (BARNET) - 10am - 7pm - Monday to SaturdayNEW WEST END SHOWROOM:311 Edgware Road, London W2. Telephone: 01-262 0387OPEN (LONDON) - 10am - 6pm - Monday to Saturday* IRELAND: 80 Marlborough Street, Dublin 1. Telephone: Dublin 749933* COMPSHOP USA, 1348 East Edinger, Santa Ana, California, Zip Code 92705

Telephone: 0101 714 5472526

BARCLAYCARD

VISA

for application form.

- Moorgate Line).

COMPCOMPUTERCOMPONENTS

(Part of the Compshop Ltd. Group)

9*4- FREE 10 C-12 CASSETTESWITH ORDERS OVER f100.00 -ENCLOSE THIS COUPON WITH ORDER*************************************************************

E&MM MARCH 1981 3

TRANSCENDENT POLYSYNTHBy brilliant design work and the use of high technology components thePolysynth brings to the reach of the home constructor a machine whoseversatility and range of sounds is matched only by ready built equipment costingthousands of pounds. Designed by synthesiser expert Tim Orr and beingfeatured in Electronics Today International, this latest addition to the famousTranscendent family is a 4 octave (transposable over 71/2 octaves) polyphonicsynthesiser with internally up to 4 voices making it possible to playsimultaneously up to 4 notes. Whereas conventional synthesisers handle onlyone at a time.

The basic instrument is supplied with 1 voice and up to 3 more may be pluggedin. A further 4 voices may be added by connecting to an expander unit, themetalwork and woodwork of which is designed for side by side matching with the

Cabinet size 31.1" x 19.6" x 7.6" rear 3.4" front

Kit also available as separate packs

ADSR ICCEM 3310 £4.00

VCO ICCEM 3340

ICs and details of allpacks in our

FREECATALOGUE

main instrument. Each voice is a complete synthesiser in itself with 2 VC0s, 2ADSRS, a VCA and a VCF (requiring only control voltages and a power supply, thevoice boards are also suitable for modular systems). One of these voices isautomatically allocated to a key as it is operated. There are separate tuningcontrols for each VCO of each voice. All other controls are common to all thevoices for ease of control and to ensure consistency between the voices.

Although very advanced electronics the kit is mechanically very simple withminimal wiring, most of which is with ribbon cable connectors. All controls arePCB mounted and the voice boards fit with PCB mounted plugs and sockets. Thekit includes fully finished metalwork, solid teak cabinet, professional qualitycomponents (resistors 2%, metal oxide or metal film of 0.5% and 0.1%), nuts,bolts, etc.

Pack Price

POLY 1 Pair of PCB's for multiplex cct. K.B. contacts£9.50POLY 2 IC's IC sockets, Rs, Cs, for multiplex cct. ... £8.20POLY 3 Superior quality keyboard £32.25POLY 4 Contacts and bus bars £12.00POLY 5 Double sided plated through PCB for digital

control and pitch/gate generator cct. £17.25POLY 6 Rs, Cs, heat sink for fitting to Pack 5 £10.50

£6.00 POLY 7 IC's IC sockets, diodes for fitting to Pack 5£31.30POLY 8 Double sided mother board

(for plug-in voices) £18.90POLY 9 Rs, Cs, connectors for mother board .. £14.10POLY 10 IC's IC sockets, Trs, heat sinks for

mother board £13.10POLY 11 PCB for master controls

(left of section marked VOICES) £18.80POLY 12 IC's IC sockets, diodes, Trs, Rs, Cs for

master control PCB £9.30POLY 13 Pots, Switches for master control board... £11.80POLY 13 Pots, Switches for master control board... £11.80POLY 14 PCB for VOICE controls £6.80

POWERTRANPRICE STABILITY: Order with confidence. Irrespective of any price changes wewill honour all prices in this advertisement until May 31st 1981 if this month'sadvertisement in Electronics & Music Maker is quoted with your order. Errorsand VAT rate changes excluded.

EXPORT ORDERS: No VAT. Postage charged at actual cost plus £1.00 handlingand postal documentation.

U.K. ORDERS: Subject to 15%* surcharge for VAT. No charge is made forcarriage, or at current rate if changed.

EXPANDABLEPOLYPHONIC

SYNTHESISER

COMPLETE KITONLY

£320.00+ VAT!

(single voice)

Plug in extraVoices - Kit price f52 + VAT(f48 - + VAT if ordered with kit)

Pack Price

POLY 15 Pots, switches, diodes, Cs for VOICE PCB £4.80POLY 16 PCB for plug in voice £8.20POLY 17 Rs, Cs, presets, connectors for one voice £16.30POLY 18 IC's, IC skts, diodes for one voice £27.50POLY 19 Transformer 0-120-240, 17-0-17, 0-7.7 £6.30POLY 20 Pitch bend control £3.90POLY 21 Misc parts e.g. jack sockets, knobs,

mains switch etc. £13.00POLY 22 Ribbon cable, ribbon cable connectors,

mains cable £8.45POLY 23 Fully finished metalwork and fixing parts £25.60POLY 24 Solid teak cabinet £25.80POLY 25 Construction manual £1.50Total cost for individually purchased packs for single

voice instrument £355.15Special kit for 4 voice expander kit includingconnectors £295.00

ALL PRICES VAT EXCLUSIVE

OUR CATALOGUE IS FREE! WRITE OR PHONE NOW!

POWERTRAN ELECTRONICSPORTWAY INDUSTRIAL ESTATE ANDOVERANDOVER, HANTS SP10 3WW (STD 0264) 64455

SECURICOR DELIVERY: For this optional service (U.K. mainland only) add£2.50 (VAT inclusive) per kit.

SALES COUNTER: If you prefer to collect your kit from the factory call at SalesCounter Open 9 a.m. - 12 noon, 1 -4 p.m. Monday -Thursday.

MANY MORE KITS ON PAGES 29 & 56

4 MARCH 1981 E&MM

Few people today can ignorethe presence of electronicsand music in their everyday

lives. Within the home: Hi-Fi, elec-tronic musical instruments, tele-vision, video and the micropro-cessor provide leisure activitieswhich have direct links with mak-ing electronics and music. Formany people, the results of theseactivities extends still further intobusiness, outdoor recreation andthe entertainment industry.

Why Electronics & MusicMaker? Because there is a hugepublic who need to be informedabout today's electronic and elec-tro-music developments. This islargely achieved by practicalbuilding projects submitted byleading authors in electronics whoalso have a special interest inmusic. In addition, there will befeatures, news and new -style re-views that will directly link for thefirst time commercial electro-music to the hobbyist market.

Electro - music defines thewhole field of musically orientatedelectronic equipment. Its rangeincludes H i-Fi, car sou nd systems,micro - computers, electronic

,ELEC.1, 11111CSWITUDIC_-.11110,1K61);A special magazine for the hobbyist!by Mike Beecher, EditorElectronics & Music Maker.

musical instruments and soundprocessors. Thus Electronics &Music Maker has a vast market inD -I -Y Electronics, musicians at alllevels, audiophiles, teachers andstudents plus anyone involved inelectronics, computing and themusic industry.

Music today depends to agreat extent on electronics - forinstrument design from the elec-tronic organ to the sophisticatedmicro -based synthesizer, and forsound recording and reproduc-tion - there can be no moreimportant time for launching our

magazine.In schools and colleges, the

enormous potential of computers,electronic musical instrumentsand other new electronic aids ismore than evident. Pupils try outthese educational tools with aneagerness that urges the teacherto acquire more knowledge. Elec-tronics & Music Maker's editorialpolicy will be authoritative in itsinformation to education.

Boosted sales of electronicsmagazines when featuring musi-cal building projects confirm aneed for Electronics & MusicMaker. The lack of practical infor-mation in leading music magaz-ines equally points to the need foran electronics and music publica-tion, and these cost -sensitive eco-nomic times lead many people tothe do-it-yourself periodical.

For the layman, Electronics &Music Maker gives the chance toenterthe exciting world of electro-music, with regular features intro-ducing the beginnerto electronicsalong with practical step-by-stepconstructional projects that havebeen thoroughly tested and arenot only enjoyable, but useful to

build. Important aspects such aswhere to buy components, ready-made circuit boards and cleardescriptions in both electronicand musical terms will be pro-vided.

For the musician, Electronics& Music Maker enables a vitalupdating of electronic music de-velopments, particularly in termsof practical projects, reviews inour electro-music studio, provenand tested projects from our tech-nical lab, and also encouragesreaders to contribute their ideasand experiences of electronicmusic making, whether for home,school, disco, stage or studio.

For the electronic hobbyist,Electronics & Music Maker offerspractical projects and features forhome, workshop, vehicle, educa-tion, computer and making music.

Above all, the editorial policyof the magazine will be to presentan informative publication thatbrings together the 3 main areas ofleisure interest for the future -electronics, computing and music.

Atteri Send to: Reader's Letters, Electronics & Music Maker282 London Road, Westcliff-on-Sea, Essex SSO 7JG.

Dear Editor,

We have read with interest Elec-tronics & Music Maker, and wouldadvise you that we feel there isscope for this magazine, espec-ially in the future of music usingelectronic and micro computertechniques. Obviously Roland, asa company which is in the fore-front of electronic music, will verymuch look forward to seeing amagazine of this nature on themarket, and we will do our best togive you all the technical assis-tance that we can.

In the meantime, we wish youevery success.

Yours sincerelyF. R. MeadSales Director

Brodr Jorgensen (UK) Ltd.

Dear Editor,

Vero Electronics would like totake the opportunity of wishingyou every success with Electron-ics and Music Maker.

Having had the opportunity topreview the publication we lookforward with great interest to theeducational and project features.These are areas on which VeroElectronics have laid particularemphasis for many years and weare pleased to be associated withthe first edition of your newmagazine.

Best wishes for a successfullaunch,

John Burns,Commercial Sales ManagerVero Electronics Ltd.

Essex County Council..leg"Ps.40"11

After a period of successfulteaching in this Authority andelsewhere, Mike Beecher nowseeks to promulgate through thispublication those lessons whichhe himself learnt in the classroomand beyond.

Thisself-styled 'Electro-Musi-cal' approach combines soundmodern educational practice withthe practice of modern sounds ineducation.

We wish him every success in.this exciting new venture at a timeof innovation and experiment inthe teaching of music.

Eric StapletonSenior Inspector for Music (Essex)

I would like to wish your newmagazine every success, and I

am sure your entry into the tech-nical music and electronicsmarket will further stimulate thegrowth of synthesis as a mediumfor music. We look forward to thegreater understanding of sciencein music which we feel will be thecontinuing theme in 1981 and1982.

Yours sincerelyJim WilmerMarketing ManagerRose, Morris & Co Ltd

There has long been a need forthis particular type of magazine.It should be welcomed by all thoseinterested in the creative use oftechnology in education and bythe professional and amateurmusician.

Desmond BriscoeBBC Radiophonic Workshop

MARCH 1981 E&MM5

ELECTRONICS

13§E MiTINEEPART 1 OF A SERIES SHOWING YOU HOW TO BUILD A COMPLETE

ELECTRONIC ORGAN AND SAVE YOURSELF HUNDREDS OF POUNDS

In the early part of this centuryalmost every home had a piano,but the advent of recorded musicand hi-fi turned most people awayfrom making their own music andthousands of pianos were scrap-ped. Today we are witnessing arenaissance in home musicmaking, brought about by thearrival at an affordable price ofthe easy -to -play home entertain-ment organ.

Home entertainment organsare now available in the shops atprices ranging from a few hun-dred pounds to several thousandpounds. A careful study, however,shows that ready-made organs

6

selling in the £700 to £1,000price range are a "best buy" forhome entertainment.

Organs priced at under £700are rather basic and although onthe face of it, ideal for the begin-ner, their limited range can soonrestrict the more ambitiousplayer. Organs priced at over£1,000 have extra facilities, butapart from orchestral voicing,string and brass chorales, theextra features have a limited use-fulness and unless you are ahighly proficient musician theyare not worth the extra price.Certainly, if you can afford it,orchestral voicing, string andbrass chorales are worth having,

but they are still rather expensive.The organs in our "best buy"

price range have four main fea-tures: two manuals, a 13 -notepedalboard, a rhythm unit and asimplified chord playing facilitycommonly known as single fingerchording. Table 1 shows how theMatinee compares with twelve ofthe most popular ready-madeorgans in the shops at themoment. Naturally it was not pos-sible to compare every switch andfacility, and all the organs in thesurvey did have other featureswhich are either shared by theMatinee or restricted to a particu-lar manufacturer. The Matineetoo has some features not found

on the other organs in the surveyas a close examination of thespecification will show.

You will see from Table 1 that.the Matinee compares very fav-ourably with the commercialorgans and the fact that it hasdrawbar voicing, more than over-comes any apparent deficiency inupper manual voices, becausehaving all the voices on drawbarsallows an almost infinite variationof sound, greatly surpassing any-thing possible with fixed volumestops.

The one stand -out feature onTable 1 is of course the price, butnone of the saving is due to a lackof quality or to inferior circuits.

MARCH 1981 E&MM

ELECTRONICS

The organ sounds every bit asgood as the commercial organsand it looks as good as well.Ready - made punched andprinted front panels are availableand a complete cabinet of equalquality to those found on the otherorgans in the survey is included inthe price. For those who wish tobuild their own cabinet, we shallpublish full cutting and construc-tion details in the last part of thisseries and this could save youanother £70 or £80 as the pricefor everything except the cabinetis only £299.95.

Some of the price saving cer-tainly comes from the fact thatyou have to build the organ your-self, but much of the saving is theresult of a major technologicaladvance in integrated circuitsdesigned for electronic organs.

In 1978, a young graduate fromthe University of Bologna in Italy,Mr Giuseppe Ravaglia joinedSGS-Ates, a company that wasalready actively involved in thedesign of integrated circuits forthe electro-music scene. Mr Rav-aglia has the rare distinction ofhaving not only a degree in elec-tronic engineering, but also ofhaving studied music theory atthe Muncipal School of Music.Since he joined SGS-Ates, he hasbeen working at their head-quarters near Milan in Italy on the

of microprocessor

PARTS LIST

controlled organs with program-mable voicing and specification.

The first step towards this goalwas to integrate on one chip whatmight be considered the heart ofan organ - the tone generationand gating system. By late 1979he and the team of SGS DigitalIC's Applications Group had aworking breadboard of such asystem. It consisted of over 300CMOS integrated circuits and yetby mid -1980 every part of thishad been condensed onto oneintegrated circuit chip measuringless than two tenths of a milli-metre.square. They called theirbaby, the M108.

Not a very exciting name, butdefinitely a very exciting chip. Tofully appreciate their achieve-ment, it is necessary to lookbriefly at the way the silicon chiphas been advancing on the elec-tronic organ over the past fewyears.

During the 1960's, an organwith an integrated circuit in itwould have been a rarity, but bythe late 60's the first IC speci-fically designed for electronic or-gans was on the market. It was atop octave synthesiser IC thatallowed the twelve musical notesof the top octave of an organ to begenerated from one very highfrequency. In earlier years elec-tronic organs had to have sepa-rate generators for each note in

Resistors - all 5% carbon unless specified

R368, 371-2, 374, 380R369, 375-6R370R373. 377, 381R378R382R383RV28, 30RV29RV31RV32

CapacitorsC122C123C124,205C125C126C127C128C203

SemiconductorsIC35IC36IC37TR36-38TR390133-136, 138D137

MiscellaneousS20, 21S31S36

10k4 k768k1k100k47R47k22k Drawbar lin., red220k Hor. S -min preset1k Hor. S -min preset22k Hor. S -min preset

luF carbonate10uF 25V axial elect.100nF min. disc ceramic33uF 16V axial elect..22uF 10V axial elect.100pF ceramiclOOnF carbonate3n3 polystyrene

1458C4001 BE4013BEBC548BSX20,1N41486V8 400mV zener diode

Tablet rocker, redLatchswitch, 4 -poleSwitched swell pedal

5 off (MIOK)3 off (M4K7)

(M68K)3 off (M I KO)

(MIOOK)(M47R)(M47K)

2 off (BR41U)(WR62S)(WR55K)(WR59P)

(WW53H)(FB22Y)

2 off (YR75S)(FB35Q)(FB29G)(WX56L)(WW41U)(BX62S)

3 off

5 off

(QH46A)(QX01 B)(QX07H)(QB73Q)(QF32K)(QL808)(QH1OL)

2 off (BH51F)(FH68Y)(XY89W)

All parts will be available as a complete kit from Maplin ElectronicSupplies Ltd in mid -April (when Part 3 is published).

Table 1. Comparison Chart

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PRICE 399 725 875 695 750 995 965 855 799 975 819 930 899KEYBOARD SIZE (NOTES) 49 44 44 44 44 44 44 37 44 44 44 44 4413 -NOTE PEDAL BOARD V V V V V V V V V V V V VDRAW BAR VOICING ,/ VORGAN VOICES UPPER 7 9 5 6 6 7 9 6 12 7 9 6 8ORGAN VOICES LOWER 5 5 2 4 4 3 4 3 5 3 3 4 3ORGAN VOICES PEDALS 2 2 2 2 2 1 2 1 4 2 2 2 2BASS GUITAR PEDALS V ./FOOTAGES UPPER 3 3 5 3 3 4 4 3 3 4 3 3 3FOOTAGES LOWER 3 1 2 2 1 1 1 1 2 1 1 1 1

FOOTAGES PEDALS 2 2 2 2 2 1 2 1 3 2 2 2 2PRESET STOPS (INCLUDING PERCUSSION) 5 2 2 4 8 5 5 3 1 4 7 6 4UPPER MANUAL SUSTAIN V V V V V V V V V V V VLOWER MANUAL SUSTAIN V V

PEDAL SUSTAIN V V V V V V ' V V V V V VVIBRATO V V V V V V V' V V V V VDELAY VIBRATO V V V V V V V VROTOR SOUND V V V V V i v v J vREVERB V V V V V v vWAH WAH V V VGLIDE V V V

vV V V

rVREPEAT r ,, v vRHYTHMS 30 12 15 15 8 8 10 10 14 12 8 8 12

SINGLE FINGER CHORD V V V V V V V V V V VMEMORY V V V V V V V V V V

Table 2. The Equal Tempered Scale

Octave 1(C1 to B1)

Octave 2(C2 to B2)

Octave 3(C3 to B3)

Octave 4(C4 to B4)

Octave 5(C5 to B5)

Octave 6(C6 to B6)

Octave 7(C7 to B7)

C 32.7 65.4 130.8 261.6 523.3 1046.5 2093C# 34.6 69.3 138.6 277.2 554.4 1108.7 2217.5D 36.7 73.4 146.8 293.7 587.3 1174.7 2349.3D# 38.9 77.8 155.6 311.1 622.3 1244.5 2489.7E 41.2 82.4 164.8 329.6 659.3 1318.5 2637F 43.7 87.3 174.6 349.2 698.5 1396.9 2793.8F# 46.2 92.5 185 370 740 1480 2960G 49 98 196 392 784 1568 3136G# 51.9 103.8 207.7 415.3 830.6 1661.2 3322.4A 55 110 220 440 880 1760 3520A# 58.3 116.5 233.1 466.2 932.3 1864.7 3729.3B 61.7 123.5 246.9 493.9 987.8 1975.5 3951.1

Pedaiboardand16ft C2

8ft and C3Lower Manual (Accompaniment)16ft and C58ft and C64ft and C7Upper Manual (Solo)16ft and C68ft and C74ft

and C8 (4186Hz)

RANGES: All frequencies in Hz. Scale based on A=440Hz.

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ELECTRONICS

the top octave with the result thatone oscillator could go out oftune, making one note sound flator sharp in every octave on thekeyboard and you had to take thewhole organ to pieces to cure thefault. The top octave synthesiserIC's eliminated this problemsince all the frequencies could beadjusted from one control to pullthe whole organ into tune inseconds.

Every note on the organ canthen be created by dividing eachtop octave note by two, severaltimes. For example, the C belowtop C is exactly half the frequencyof top C and so on down to bottomC (see table 2).

The second advance came inthe integration of rhythm genera-tor IC's. For some years now, allpopular electronic organs havehad rhythm generators, mostlycoupled with some form of simpli-fied left-hand playing facility suchas single finger chording. Theearly rhythm generators wereboards of digital IC's and earlychord generators were built frombanks of diodes. In the mid -70's,both the rhythm and chord gen-erators were condensed onto oneIC or in some cases a two IC set.

The new M108 IC combinesthe top octave generator, thedividers, the rhythm generatortiming, the chord generator andall the gating. It is the inclusion ofthis latter item that eliminatesmost of the tedious wiring andmakes this a really easy organ tobuild. Instead of each keyboardneeding 200 wires, the Matineekeyboards need just 17! Thisrepresents a saving of well over80% in wiring the whole organ.

The gating is one of the mostimportant features of an organ.What we mean by gating is switch-ing the raw frequency to the mainbus bars. For example, if middle Cis pressed, we need 261.6Hz to beswitched to the 8 foot voices,523.3Hz to be switched to the 4foot voices and 130.8Hz to beswitched to the 16 foot voices.Then, if for example the 8 footFlute stop is pressed, any fre-quency switched through to the8 foot voices will pass through theFlute filters and the characteristicFlute tone will be heard at thecorrect frequency.

Various forms of gating areavailable. The simplest is themechanical switch fitted underthe key, or in our case with threefootages we would need threeseparate contacts under eachkey. This is mechanically difficultand expensive and a great deal ofwiring is required; 3 wires foreach key if there are 3 footages. Inaddition, if envelope shaping isrequired, a further contact wouldbe needed as a key -down detec-tor, generating even more wiring.

The other most commonlyfound form of gating is the diodeor transistor switch. This has theadvantage of needing only onecontact under each key regard-less of how many footages thereare. However, it still needs thesame number of wires eventhough most are no longer con-nected to the key switches. Onemajor advantage is that the attackand decay can be set individuallyfor each key, though this is expen-sive to do and is not found onorgans in the £700 to £1,000price range. The disadvantagesare that there are lots of com-ponents and the output is notsymmetrical, so if a fast attackwas required there would be anaudible thump in the output(caused by the average DC levelsuddenly changing). Another dis-advantage is that some of thesignal leaks through a semicon-ductor switch even when it is fullyoff because of the inherent capa-citance of a diode or transistor. Itis a very tiny signal, but in anorgan with lots of footages therewill be hundreds of switches inparallel all adding their little bit.The result is a just audible broad-band noise that is generallyreferred to as "singing".

The gating in the M108 isperformed by MOS switcheswhich unlike diodes and ordinarybipolar transistors do not allowany signal to pass when they areoff and thus there is no singing inthe Matinee organ. Also the out-put of the M108 is perfectlysymmetrical, however manynotes are played simultaneously.And finally the biggest advantageof all, of course, is that massivesaving in wiring. Only 17 wires arerequired for each keyboard andonly one simple contact is neededunder each key, including thekey -down detector.

The key -down detector is re-quired so that we can provideenvelope -shaping of some of thevoices. In early electronic organs,the raw tones were simply filteredto produce the correct wave -shapes to simulate the charact-eristic sound of an instrument.However, the voices did not soundvery realistic, because one of themost fundamental characteristicsof the sound of an instrumentwere missing. This characteristicwas the way in which the volumeof the sound changed with time,in particular at the beginning andend of a note.

If a key is struck on a piano, forinstance, the volume of the soundreaches a maximum almost in-stantaneously, whereas if anaccordion starts to play the soundit takes a whole second or more toreach full volume. We say that apiano has a fast attack; its en-velope opens and reaches a maxi -

SPECIFICATIONTwo 49 -note manuals.13 -note pedalboard.Solo voices all on drawbars: Flute 4ft, String 4ft,

Flute 8ft, String 8ft, Clarinet 8ft, Flute 16ft,Cello 16ft, Sustain (3 seconds approx.).

Solo preset voices: Accordion, Banjo, Banjo Repeat,Harpsichord, Piano, Manual and Auto Wah,Percussion.

Accompaniment voices all on drawbars: Flute 4ft,String 4ft, Flute 8ft, String 8ft, Flute 16ft,Sustain (3 seconds approx.).

Pedal voices all on drawbars: Bass Guitar 8ft,Organ Bass 8ft, Organ Brass 16ft.Sustain (3 seconds approx.).

Other effects: Vibrato, Delayed Vibrato, Rotor Soundfast and slow, Strings Direct, Add Drawbarsto Effects, Rhythm Tempo, Glide or PianoSustain (control on swell pedal). Swell Pedalbecomes Wah control when Manual Wah selected.

Controls: Vibrato Rate, Vibrato Depth, Reverberation,Rhythm Volume, Presets Volume.

Rhythm and Auto -AccompanimentControls:

Rhythm stop/startAuto -rhythm stop/startAuto -chordChord vampMemoryVariable tempoCountermelody30 Rhythms each a full 2 bars long.

Other Features:Eight instruments: Bass drum, low bongo, highbongo, conga drum, claves, snare drum, shortcymbal, long cymbal.Alternating Bass or Walking Bass dependent onrhythm chosen.Major, minor and seventh chords available.Minor and seventh chords controlled frompedalboard in automatic mode.Indicator flashes red on downbeat, green on theother beats in the bar.

Internal amplifier and 12 inch full range loudspeaker.Headphone socket.

mum very quickly, whereas theaccordion has a slow attack. If wehave an amplifier whose gain wecan control, we can simulatethese attack rates by switching aparticular preset volume changeto the amplifier gain control whena given stop is pressed. All weneed to know is when to start thevolume change and hence theneed for a key -down detector.

Similarly the amplifier couldbe set to close down the volumequickly or slowly when the noteends. Again different instrumentsstop sounding at differing speeds.For example an undamped stringinstrument will carry on soundingfor a long time after the string isplucked; the volume graduallybecoming less and less, whereasa wind instrument stops soundingalmost the instant the musicianstops blowing. We say that un-damped stringed instrumentshave a slow decay whereas windinstruments have a fast decay.Again, the key -down detector is

used to signal when the last key isreleased.

For example, on the Matineethe piano voice has a very fastattack and a fairly slow decay ifthe keys remain held down. How-ever, if the keys are released thena fast decay is set in motion inorder to correctly simulate theaction of the dampers on a realpiano. In addition, a control isprovided that works like a "loudpedal" to sustain the notes for along time or in other words to givea very slow decay. Although thebasic tone of the piano voice onthe Matinee sounds like a piano,the addition of this envelopeshaping transforms the voice andmakes it dramatically realistic.The other voices on the Matineeare treated similarly to addrealism to the sounds.

The M108 makes all this pos-sible very easily and it is this thathas led to the low price andsimplicity of construction. In fact

E&MM MARCH 1981 9

ELECTRONICS

+6V

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the only qualification you need tosuccessfully build the Matinee isthe ability to solder correctly.Virtually all the electronics arebuilt on one large printed circuitboard with only the main powersupply located elsewhere. All thewiring is via simple PCB plugs andsockets so that everything justplugs together for absolutesimplicity of construction. All thefixings, metalwork and woodworkare available for you to just bolttogether if you wish, guaranteeingyou a first class finish that willgrace any living room.

Although we shall be goinginto the circuitry of the Matinee indepth, we wish to make it quiteclear at this point that you do notneed to read or understand anypart of these technical descrip-tions to successfully build thisorgan. In fact many of the termsused may be a mystery to you, butanyone reading our beginnerscourse that commences else-where in this first issue of E&MMwill quickly gain an understand-ing of these descriptions.

Two M108 IC's are used in theMatinee, one for each keyboard.For the pedalboard a different ICis used: the M147 which will bedescribed later. At this stage it issufficient to know that the M108'srequire a master frequency of1,000,120Hz to generate all thenotes of the keyboard and carryout all their other timing func-tions, and the M147 requires amaster frequency of 500,060Hz.In Fig. 2 we show the circuit of themaster oscillator used in theMatinee from which all the tonesand timing throughout the wholeorgan are derived.

The main oscillator is formed

by IC36, a CMOS device contain-ing four separate NOR gates.When power is applied, thevoltage at the input to IC36c islow, at -6V, because C127 isuncharged. Since the input is low,the output of gate 'c' is high. Simi-larly the output of gate 'b' is lowand gate 'a' high also. Gates 'a'and 'b' and R378 form a Schmitttrigger that greatly improvesthe sharpness of the edges ofthe waveform. The output of 'a'being high, now charges C127 ata rate set by RV32 which shouldbe adjusted so that middle A onthe keyboard produces 440Hz.When this is the case the fre-quency of the oscillation at thispoint will be exactly 2.00024 MHz.

When C127 is charged theinput to gate 'c' will be high andhence the output now goes low.The outputs of gates 'b' and 'a' arenow also forced to change stateand the output of 'a' being lowdischarges C127 until the inputat 'c' is low again. This processrepeats itself continuously twomillion times every second. Thisoscillation is then presented togate 'd' which simply acts as abuffer for the square wave output.

IC35 is a dual op -amp whichproduces an oscillation in muchthe same way as IC36 except thatit is a triangular waveform and at avery low frequency. RV28 is thevibrato rate drawbar and sets thefrequency between 2Hz and20Hz. The amount by which thevibrato changes the frequency ofoscillation of IC36 is set by thevibrato depth drawbar RV30.

With the vibrato switch SW20off, the output of IC35 is shortcircuited to ground, but whenswitched on the output is coupled

through the DC blocking capaci-tor C123 to the base of TR38. Thistransistor is supplying the mainpositive DC voltage that allowsIC36 to operate. As the supply railvoltage changes under the con-trol of the vibrato oscillator, so thepoints at which the switch -overthresholds in IC36 occur, changeand the frequency of oscillationalso changes slightly.

When the delay vibrato switch,SW21 is on and no key is pressedon the keyboard, C126 is chargedand TR36 fully on, short circuitingthe output of IC35. When a key ispressed, the positive voltage onD135, D136 is removed and C126discharges slowly through RV29.This preset adjusts the length ofthe delay before C126 is suf-ficiently discharged to allow TR36to turn off. As it does so the outputof the vibrato oscillator is nolonger inhibited. At the next in-stant when no keys are pressedon the keyboard, C126 chargesagain ready for the next key to bepressed.

A glide switch is fitted on thefoot pedal to give Hawaiian Guitareffect. When the switch isoperated the current throughTR37 changes slightly over ashort period set by the position ofRV31. The effect of this is muchthe same as changing the voltageon the base of TR38: the fre-quency of the main oscillator ischanged. The change is set byR375 and R376 to give a onesemitone change on the key-boards. When the switch is re-leased the current through TR37returns to normal at the rate setby C128.

Because the main voltage railto IC36 is used to produce the

organ's vibrato and glide effectsthe output of gate 'd' can undercertain circumstances reach volt-age levels that are insufficient tocorrectly drive IC37. TR39 istherefore provided to apply suf-ficient amplification to the outputof gate 'd' to ensure that IC37 iscorrectly driven in all conditions.

IC37 is a CMOS IC containingtwo D -type flip-flops that are con-nected here to function as fre-quency dividers. The main oscil-lator frequency of 2.00024 MHz isapplied to pin 3, the input to thefirst flip-flop. The output at pin 1is exactly half this frequency:1.00012 MHz, the frequency re-quired by the M108's. As well asbeing connected to the clockinput of the M108's it is alsoconnected to pin 11 on IC37, theinput to the second flip-flop. Theoutput at pin 13 is exactly half thefrequency on pin 11:500,060Hz,the frequency required by theM147.

It may seem strange at firstsight that we have set the mainoscillator to run at 2MHz when thehighest frequency used is 1MHz.There are, however, several ad-vantages in starting with a higherfrequency than that required.Firstly the higher frequency givesbetter accuracy and the Schmitteffect of IC36 gives excellent longterm stability and secondly the4013 generates an excellentsquare wave shape whose mark/space ratio is exactly 1:1. Thiscircuit, then, provides an idealwaveform to drive the clock inputson the M108's and M147.

Next month, we shall begin theconstruction details of the Matineeorgan and continue the descrip-tion of the circuits used. E&MM

10 MARCH 1981 E&MM

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E&MM MARCH 1981 11

ELECTRONICS

ICs FOR ELECTRO-MUSICCharles Blakey, Digisound

0 verheard at a recent meetingwas a comment to the effectthat if cars had made the same

technological progress as electronicsthen a certain well known make wouldnow cost 1.75p and do three millionmiles to the gallon. We will not go intothe logicofthiscomparison butat leastit puts the progress of our industry inperspective. Just one of the spin-offs isthat it is now practical to producespecialised integrated circuits in rela-tively small quantities and end up witha product which is much cheaperthanthe equivalent circuit based on dis-crete components and having thesame performance. In the last fewyears there has been a steady growthof IC's specifically designed for elec-tronic music applications which inturn have made a large impact on thedevelopment of voltage controlledsynthesisers. The designer can nowreadily apply his skills to producingcompact units essential for both leadsynthesisers and for polyphonicsystems; to offering equal perform-ance at a lower cost; or greaterperformance capabilities at anacceptable cost.

The object of this series of articlesis to look inside these 'black boxes' soas to provide a greaterof their function and application. Donot be put off by an occasionalmathematical expression dottedaround the pages since this is alwaysfollowed up by a practical solution. Wealso hope that the series will stimulatereaders to experiment with these newproducts and share their ideas anddesigns with others interested in thefield of electro-music.

The Spectrum Synthesiser projectcommencing in this issue utilisesintegrated circuits produced by CurtisElectromusic Specialities and I shallbe dealing with some of this com-pany's product line, includingtheCEM3310 Voltage Controlled EnvelopeGenerator, CEM 3320 Voltage Con-trolled Filter, CEM 3330 Dual VoltageControlled Amplifier, and CEM 3340Voltage Controlled Oscillator. One ofthe features which makes these IC'sideal for electronic music is that theirvoltage control response is exponen-tial, that is, for a unit increase involtage there is a doubling of theoutput. Refer to Figure 1 for the shapeof this response. In the case of theoscillator this results in a doubling offrequency and this exponential rela-tionship is a perfect match for theequally tempered musical scale. Theuse of an exponential VCO greatlysimplifies keyboard electronics sinceone merely has to generate equalvoltage intervals between notes; itallows the complete audio frequencyrange to be covered withoutswitching;and it also means that two or moreoscillators may be transposed in pitchwhile maintaining the preset fre-quency relationship. Exponential con-trol is also necessary forthefilter since

Limited

MULTIPLIER CGAIN 14N

nir'" Cf

PULSE OUT E

CONTROL E

,".°A"".

CURRENTo.

gtr'" E

P EC.410111.11PLIE

EFNEOUENCY

CEM 3340 V.C.O.

in many instances the keyboard con-trol voltage will be used to adjust thecut-off frequency of the filter and thelatter must therefore track the oscil-lator to maintain the same harmoniccontent irrespective of pitch. For thevoltage controlled amplifier the ex-ponential response is used to com-pensate for the design of the humanear which reacts to sound intensity in alogarithmic manner. Finally for theenvelope generator the production ofexponential contours is not unusualsince use is frequently made of thecharacteristic charging/dischargingresponse of a capacitor. By using,however, an exponential voltage con-trol for the attack, decay and releasetime constants one is able to achieve a50,000:1 range, say 2 milliseconds to100 seconds, with a single control andwith the most useful range utilising ahigh proportion of the potentiometerscale.

Other common features of the CEMdevices include housing in standardplastic 16 or 18 pin DIL packages andtheir ability to operate from a widerange of power supplies. The latterincludes the widely adopted ±15Vsupplies as well as the increasinglypopular +15V, -5V supplies used insynthesisers incorporating CMOSlogic controllers.

CEM 3340 VoltageControlled Oscillator(VCO)

We will plunge straight in at theheart of the synthesiser, the VCO,since by dealing with the most criticalpart first we can avoid spending timeon some simpler aspects later. Wehave extolled the virtues of exponen-tial control but how is it achieved andhow does one get the scale accurateover a wide range coupled with goodtemperature stability? Such genera-tors make use of the fact that the

COLLECTORCURRENT, lc

lc

VBE

18 36 54 72 90BASE-EMITTER VOLTAGE VBE (mV)

Figure 1. The exponential characteristic of a transistor junction.

Figure 2. A typical exponential generator using discrete components.

current, !,, flowing into the collector ota transistor is an exponential functionof the base -emitter voltage, VBE,

namely the difference between thevoltage at the base and at the emitter ofthe transistor. Hence I, = Fe(VBE/VT)and a curve of VBE versus lb is shown inFigure 1. Unfortunately one of thecomponents of F, namely the emittersaturation current, doubles for every10°C rise in temperature and the firststep is to cancel out this term by usinga dual transistor, preferablycontainedon a single chip toensure temperatureequalisation. The front end of a typicalVCO then becomes like Figure 2. IC1 isa standard inverter and its invertinginput provides a summing nodefortheinput voltages via resistors R1 and R2(any number of resistors may beadded). The gain of theopamp is set byR3 plus R4. Most synthesisers adopt ascale of 1 volt/octave, that is, one voltapplied to RI, assuming thatthis istheresistor connected to the keyboardvoltage, will double the frequency ofthe VCO. To achieve this with thearrangement of Figure 2 the com-ponent values are chosen to obtain an18mV change at the base of Trl foreach increment of one volt applied toRl. So that we are operating in themost accurate range of TR1 we need toapply a reference current to its col-lector and this is obtained from R7

connected to a positive referencevoltage. The function of IC2 is to sinkexcess current from the emitters ofTR1 and TR2. The output current, .1b,taken from the collector of TR2 thenusually goestosomeswitch ingdevice,such as a FET,tocharge and dischargea capacitor and generate a waveform.

The circuit will now give ICe- (Vb/VT), where VT is equal to about26mV at 20°C with the emphasis beingon the temperature. If the temperatureof the transistor changes from 20°C,as it surely will, then the 1/T com-ponent willalter by 0.33% for everyonedegree Centigrade change and thiswould certainly not be acceptableforasynthesiser oscillator. To counteractthis we haveto alter Vb byan equivalentamount and the usual technique is toemploy a special temperature com-pensating resistor either in the feed-back loop of IC 1 or in place of R6.

Now turn to the functional blockdiagram of the CEM 3340 shownabove and also refer back to Figure2 where the numbers in bracketsrelate to the pin numbers on the CEM3340. The similarity is apparent. Thefirst step is to set the scale of the VCOand a 1k8 resistor to ground from pin14 provides greatest multiplier accu-racy. To obtain the widely used 1V/octave scale a 100k resistor is con-nected tothefrequencycontrol pin 15.

12 MARCH 1981 E&MM

ELECTRONICS

As already mentioned this latter pin isa summing node and soany numberofresistors may be connected to thispoint. For example, supposewe wish toadd a fine frequency control of ±0.5octaves whose voltage is obtainedfrom a potentiometer connected be-tween ±15V then a resistor of 3M0(3M3 would be near enough) connec-ted to pin 15 would achieve this.Likewise a resistor or a variable re-sistor, or both, may be connectedbetween the positive supplyand pin 15to settheoscillatoratthedesired initialfrequency, i.e., the frequency with nokeyboard or other external voltagesapplied. The reference current istaken to pin 13 and for the CEM 3340the current should be in the range of3uA to 15uA, so let us use 10uA whichrequires a 1M5 resistor connected to a+15V supply. Next connect the timingcapacitor to pin 11 and this should bechosen to keep the current within therange of 50nA to 100uA and thefrequency is given by f = 31 EG(Vcc.CF)where IEG istheoutput current from the

higher currents and so causes theoscillator to go flat at higher frequen-cies. In the CEM 3340 pin 7 outputs acurrent which is a quarter of theexponential generator current. Thiscurrent is converted to a voltage byconnecting it to a grounded trimmer(10k) and taking part of the voltagefrom the wiper back to the inputsumming node, pin 15, via a resistor(say, IMO) and then usingthe trimmerto cancel out the bulk resistance effectby an additional calibration at highfrequency, i.e., about 10kHz.

While the number of external com-ponents around the exponential gene-rator have been kept to a minimumconsistent with freedom for the de-signer the following rules should beobserved in order to retain the accu-racy of the device.1. The positive supply is used as areference voltage to generate thereference current and also possibly toset the initial frequency. This requiresthat the positive supply for the VCO isextremely stable in respect of both

(a) SIGNALINPUT

1k0

10nF

I Rc

( b) LINEARCONTROL

INPUT

( c )

+15V (13)

RCvFAP mi

-15V

4

(d) SIGNALINPUT

Figure 3.

1

2 3

5k6

-=--1-1-24k10k

Figure 4. Scale trim for CEM 3340.

exponential generator, Vcc is, as usual,the positive supply voltage and CF thevalue of the capacitor at pin 11. Thus ifthe most accurate range for the VCO isto be 10Hzto lOkHzthenthecapacitorshould be 1nF.

Where the CEM 3340 differs sub-stantially from Figure 2 is in its uniquemethod for compensating for thetemperature dependence of the VTterm discussed earlier. Within the IC isa Tempco Generator wh ich prod uces atemperature corn pensati ng offset andis generated by the same mechanismwhich causes the temperature depen-dence within the exponential gene-rator. The cancellation of the latter istherefore nearly perfect. It meanshowever that precise adjustment ofthe volts/octave scale is different tothat expected from Figure 2 and so thearrangement of Figure 4 should beused, in which the 10k preset poten-tiometer provides for accurate adjust-ment of the scale.

One further problem with theseexponential generators is the bulkresistance of the base -emitter junc-tion which becomes significant at

time and temperature.2. All of the resistors should be metalfilm, or similar, with a temperaturecoefficient of 100ppm/°C, or better,and the trimmers should be cermettypes. Resistor accuracy of 1% isadequate so long as only one of thefrequency control input resistors isrequired for precise frequency con-trol, namely from the keyboard. Do nothave any inputs to pin 15 wherevibration or a small change in tem-perature are likely to affect the fre-quency unless some means of isolat-ing them when not in use is alsoinstalled.3. Pins 13 and 15 require compen-sation components of a 470R resistorin series with a lOnF capacitor con-nected to ground.4. The timing capacitor should be alow loss, low leakage type such assilver mica, polystyrene or, for largervalues, polycarbonate. It is also worthnoting that at low frequencies thecurrents are only a few nanoamps andleakagethrough residual solder fluxorgeneral dirt can create problems. It isgood practice to clean the foil side ofthe PCB after soldering with a proprie-tary solvent and then apply a PCBvarnish.

Next we turn to the subject of FM(frequency modulation) of the VCO.Pin 13 is referred to as linear controland sometimes as linear FM input. It isa summing node and so an additionalresistor may beconnectedtothis pointto obtain linear FM using an ACwaveform. Take note of what is hap -

TRIANGLE

OUTPUT

SAWTOOTH

OUTPUT

PULSE

OUTPUT

SYNC.

INPUT

ZfZ:zizfziz

Figure 5. Hard synchronisation capabilities.

pening in these circumstances,namely, one is effectively increasingand decreasing the reference current.The first effect is that if the currentdeveloped at this input were to exceedthe reference current then the oscil-lator will be gated off (you may wish touse this fact in some application).Suppose, however, that we keep the1 M5 resistorconnectedto+l5Vforthereference current and add a 1M0resistor for a linear FM input. This willgive us about a 10% change in fre-quency for a one volt change in input,i.e., a ±50% frequency change for a±5V waveform. There are two mainuses for such an input. First to providesome dynamic timbre modulationusing an envelope shaper (ADSR plusVCA) to shape the modulating wave-form. Secondly, if a modulating wave-form is applied tothe linear FM inputoftwo or more oscillators set to differentintervals then a type of chorusingeffect will be obtained since thetracking of the oscillators has beenaffected. The more usual FM effect isvibrato and one usually requires adeeper modulation as well as main-taining a constant depth over the fre-quency range and tracking betweenoscillators. Vibrato is therefore ob-tained with a modulating waveformapplied to the exponential controlinput, pin 15, via an appropriatepotentiometer and resistor network.

The CEM 3340 provides threesimultaneous waveforms: sawtooth,triangle and pulse. They are nominallyreferenced to OV and their amplitudeis determined by the positive supplyvoltage, being: two thirds of the supplyfor the sawtooth; one third for thetriangle; and 1V5 below the supply forthe pulse. A particular point to note isloading of the triangle outputwill lowerthe VCO frequency since the output isalso connected to an internal com-parator. Even into a 100k load thefrequency may drop by 0.15% and inany event the output should notdirectly drive a load of less than 10kand/or more than 1nF to ground. Onthe other hand the pulse output is anopen NPN emitter and requires a pulldown resistor to ground or a negativevoltage. This output may be readilyclamped to a lower voltage using azener diode. The amplitude of thesignals and whether they are groundreferenced or AC is the free choice ofthe designer. For example, if a rotaryswitch is used to output one waveformat a time and the desired amplitude is,say ±-5V, then this is easily accom-

plished by switching into an op ampinverter and selecting the appropriateinput resistors to obtain the requiredgain for the different waveforms andthen place a capacitor in the outputline.

Pulse width may be varied from Oto100% duty cycle by 0 to +5V (Vcc .15V)applied to pin 5. The +5V may bederived from the positive supply usinga resistive divider and a trimmer i n thisnetwork may be desirable if it isessential that the pulse does notcompletely disappear at the extremeends.

The remaining facilities on theCEM 3340 VCO are for synchroni-sation. The hard synchronisation in-put, pin 6, may be configured inseveral ways but in its simplest form aln F capacitor connected to pin 6 willrespond to inputs of both positive andnegative pulses. The effect is illu-strated in Figure 5 which shows that apositive pulse causes waveform re-versal only during its rising portionwhereas a negative pulse causesreversal during the falling portion ofthe waveform. Clearlythistechnique isonly applicable to two or more oscilla-tors. The oscillator of lowestfrequencyis referred to as the 'master' oscillatorand the other(s) as 'slave' oscillator(s)and the pulse output from the masteris used for synchronising the otheroscillator(s). The complex waveformswhich result are capable of yieldingsome pleasing timbral effects espe-cially when only the slave oscillatorsare frequency modulated. Soft syn-chronisation requires negative pulsesof about -5V amplitude and coupledvia a 1nF capacitor to pin 9. Theoscillators in this instance will usuallybe connected to a soft sync. bus andwhen one oscillator discharges itssync. pulse will cause prematuredischarge of other oscillators in such amanner that their oscillation period isan integral multiple of the reset pulseperiod.

The final but important point relat-ing to the CEM 3340 concerns thenegative supply voltage. If this isgreater than -7V5 then a currentlimiting resistor must be placed be-tween the negative supply line and pin3. The value of the resistor is deter-mined by (VEE -7.2)/0.008 which for-15V gives a nominal 975 ohms and apractical choice of 910 ohms.

Next month I shall continue thislook at the Curtis range of IC's, startingwith the CEM 3320 Voltage ControlledFilter. E&MM

E&MM MARCH 1981 13

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14 MARCH 1981 E&MM

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£20.63STA15. 15 watts per channel Stereo Amplifier

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E&MM MARCH 1981 15

ELECTRONICS

SPECTRUMSYNTHESISER* Low Cost* Easy to Construct* Four Octave Keyboard* Performance Controller

* FM and Sync.* Sequencer Effects* Stereo Outputs* Interface Facilities

The Spectrum is a monophonic two oscillator switch -linkedsynthesiser featuring advanced specification, constructionalsimplicity and low cost. Modulation, timbre control, and interface

facilities not found on any comparable synthesiser make it extremelypowerful and versatile for keyboard playing, sound effects and manyother home, stage, or studio applications. Construction is simplified bythe use of integrated circuits that each perform major synthesiserfunctions with few external components. Error -prone control wiring iseliminated by the use of a single PCB mounted behind the panel andholding the pots (PCB mounting) and switches. No glueing of contactblocks or bending of gold wires is needed to assemble the keyboardcontacts - a new contact system only requires soldering of thecontacts and drilling of the chassis to mount the contact PCB. This alsocontributes to the low cost - the Spectrum can be built for around£200 including metalwork and PCB's, but not including the case.

DescriptionFigure 1 shows a block diagram of the synthesiser and the front

panel legending is reproduced below. Modulation routing is

accomplished by source and function switches and depth controls,rather than the usual method of providing each source with its owndepth for each controlled function found on some small synthesisers.Switching is most suitable for a large number of sources as here, andallows fast selection of source and selection of modulation effects withpreset depths, in favour of simultaneous modulation of one parameterby more than two signals. Six modulation signals are available:keyboard, controller, low frequency oscillator (LFO), noise generatorand external. The keyboard is of the highest note priority type and has aglide which always completes even after the key is released - this

INTERFACE

KEY CV VCO CV0 0OUT IN

KEY GATE GATE

0OUT IN

CONTROLLERCV

PRE-VCFSIGNALO 0

IN/OUT IN

POST- VCAVCO1 RAMP SIGNALO 0

OUT IN

E&MMSPECTRUMSYNTHESISER

KEYBOARD5

4

40 4

3

1 0 973

2

8

2 2

- 5 5 -1-

TUNE0 10

GLIDE

LOW FREQUENCY OSCILLATOR

3

2

9

8

O

- RNOREG

WAVEFORM

by Chris Jordan

makes the keyboard much more useful as a controller for effectssounds. The joystick controller routes a voltage dependent on the side -to -side position of the stick to various voltage controlled circuits,allowing it to be used to control the pitch (pitch bend), timbre, or both(see later). The external voltage fed into the controller jack canoverride or add to the joystick voltage for control by additionalsynthesiser equipment, or a pedal can be plugged in and used forcontrol by attenuating a fixed joystick voltage.

The low frequency oscillator generates random and regular sampleand hold effects in addition to the four common waveforms. Theregulator S/H option allows rising and falling scales, rising and fallingrepeating groups of two, three or more notes, and other sequencer -likeeffects, with the pattern controlled by the LFO rate. An LED displays theLEO cycle and the joystick's vertical position determines the amplitudeat the LFO manual output. The envelope generator is of the exponentialADSR type and like the LEO has + and - outputs that can be separatelyselected for each controlled parameter. The envelope generatorshares its gate signal with the envelope shaper, which determines theloudness contour of each note. 'Single' on the gate selector switchcauses gating each time a first key is depressed; 'Multiple' retriggerswhen any new note is played, allowing fast runs without 'missed' notes.'Hold' keeps the gate high for continuous effects, and 'LEO' causesgating on each LEO cycle. In the 'Repeat' position the envelopegenerator retriggers at the end of the decay period, acting as anadditional LFO with variable symmetry. This allows complex rhythmic

VOLTAGE CONTROLLED OSCILLATOR 164 20

2530

32

-16'

NI4d- 4'5

- 8'

RANGE2'

15

10

0% 50%

PULSE WIDTH

35

40

45

vA

--- LA- 1/1

OFF

- LI1SUB

WAVEFORM

VOLTAGE CONTROLLED OSCILLATOR 264'

1

01

RANGE

32' 2

- 16'

4'

2'

3

4

- 5 5

TUNE

4

3

01 - LA-- OFF

-L11WAVEFORM SUB

SOURCE

OSCILLATOR MODULATIONLEO

MAN+LEO

- -LEO

+EG

- -EGNOISE

2

3

PW

OFF

VCO- 1+2

VC01

FUNCTIONVCO 2

16 MARCH 1981 E&MM

ELECTRONICS

KEYBOARD

JOYSTICK

LOWFREQUENCYOSCILLATOR

ENVELOPEGENERATOR

r- -1

--7-j- VOLTAGErlCONTROLLED

I OSCILLATOR.1I , ai 1

t_ _ _ _

II

ILy

L

rly

VOLTAGE -CONTROLLEDOSCILLATOR.2

II

RINGMODULATOR

VOLTAGECONTROLLED

FILTER

4

VOLTAGECONTROLLED

AMPLIFIER

II I

NOISEGENERATOR

MODULATION ROUTING

- AUDIO GATE

ENVELOPEGENERATOR

-r- -

VOLTAGECONTROLLED

AMPLIFIER

VOLTAGECONTROLLED

PAN

OUTPUTS

Figure 1. Block Diagram of the Spectrum Synthesiser.

effects when used with the LFO, and gives great scope for 'backdrop'sounds based around complex S/H patterns with periodic timbresweeping effects derived from the EG. 'Key Repeat' brings in the repeatonly when a key is held, allowing key -synchronised repeating notes anddelayed modulation (the delay determined by the attack time). An LEDindicates the EG's attack segment.

The voltage controlled oscillators (VCO's) each have five switchedoctave ranges and five waveforms. The sub -octave output is a pulsewave with a square wave added an_octave below, making the soundfuller and richer. The tuning LED detects the beats between theoscillators, and indicates when the pitches are in simple musicalintervals, useful for tuning without sounding a note (e.g. on stage). Thepulse width of VCO 1 is variable, and VCO 2 has a tune control with a ±one fifth range.

The VCO's can be used together to provide a vast range of soundsnot possible with basic synthesisers having only waveform, shape, VCFcutoff and VCF resonance as the controls affecting basic timbre. This isdone by frequency modulation and synchronisation - special featuresof this design. FM uses the triangle output of VCO 1 to modulate thefrequency of VCO 2 up to ±100% giving a whole range of non -harmonictones for bell, gong, chime sounds etc. Synchronisation gives variouswaveforms from VCO 2 (see Figure 2) which have particular bands ofharmonics emphasised for strong, voice -box -like sounds. This isachieved by resetting the output of VCO 2 upon each cycle of VCO 1, sothe tones generated are always harmonic. Two modes of sync. areprovided: Sync. I is that normally found on rampwave oscillators, theVCO 2 waveform beginning in the same way after each reset; Sync. II is

NOISE 8- RM1

0

404

2 2

5 5

NOISE mix RM

3

4

3

2.I

1 \ \ 9

0 10

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3

110MAN +150 -IR ON +EG -EG

I 1-

SOURCE

3

2

VOLTAGE CONTROLLEDFILTER 4 5

3

RESPONSE

7

9

2

8 2

0 10

KEYBOARD FOLLOW

NOISE

-EG

EG -

-LEO -

+ISO

tIOMAN SOURCE

0 10

FREQUENCY

7

9

3 1r 7

0 10

RESONANCE

54

2 300 10

DEPTH

9

8

8

GATEED

APT

AP

SINGLE -

INUIT -

OL

APS

D

MODE

(a)

ICI //.///////(d)/////

Figure 2. Sync. Waveforms. (a) Sync. Pulses.(b) Sync. I. (c) Sync. II. (d) Sync. IIwith decreased VCO1 frequency.

something totally new - the triangle output is set to mid way each timebut then carries on in the same direction in the new cycle. VCO 2 lockson to VCO 1 harmonics with the change from one harmonic to the nextemphasised by a sharp change in tone. This enables automaticarpeggiation and incredible tone sweeps to be obtained since VCO 2now is effectively a voltage controlled waveform generator/frequencymultiplier. The sync. control attenuates the pulses fed to VCO 2 so thatit only resets if the wave form is above a certain threshold, resulting inthe oscillators being locked together in musical intervals (3rds,5ths etc.). Simultaneous sync. I and FM produces harmonic tones withthe shape of FM-ed waveforms within each cycle.

The ring modulator uses triangle and square VCO waveforms toprovide further complex tones. Its output is mixed with the noise signaland fed into a special voltage controlled amplifier (VCA). This can becontrolled by the LEO or EG, and gives the signals their own loudnesscontours. Hence noise 'chiffs' can be added to notes, or ringmodulation set to swell in as a note decays.

The VCA output is fed to the voltage controlled filter (VCF) mixed withthe VCO outputs. The VCF offers the two most useful responses, lowpass and band pass, plus an intermediate response for bright soundsthat remain strong in lower harmonics. Cutoff frequency andresonance controls perform their normal functions and a keyboardfollow control determines how the cutoff frequency varies over thekeyboard range.

After envelope shaping, the signal is fed to the voltage controlledpan circuit which can modulate the location of the sound in the stereofield by the LEO or EG signals. The stereo outputs can also be -used for

-10PAN

+ESPAN

P- AN

LSO

PAN

- m11)61

-,m5(1)8

FUNCTION

E&MM MARCH 1981 17

ELECTRONICS

04- -0 68

02

610 611 R12

J. 1

T

E &MM

R13 R14 R15 R17 618 R19

Rl 1 1 116

T r T T T T

KEYBOARD CONTACT ASSY GA 09K 1241

R20 R21

1 1

T T

262[1)

R23 R24 R25 R26 R27 R28J. 1, .1 .L 1 1

0630 0

31

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0

rfir NT:k ran rrNri rd.!!!

e D2,LI; e

Figure 5. Keyboard printed circuit board.

voltage control of the depth of external effects such as reverb, phase,and echo, by routing one signal via the effects unit and one direct to theamplifier. A mono output is also provided, and the pan VCA can also beused for additional amplitude modulation with the LFO as source (fortremolo and other effects).

The interface jacks allow connection to external devices such assequencers, additional VCO banks, waveform processors etc, anddesigns for these will be published in the future. The SpectrumSynthesiser and future equipment will use the 1V/octave CV standard,and can be interfaced to any other exponential CV synthesiser.

KeyboardThe Spectrum uses a unique key contact system which is cheaper,

more reliable, and easier to construct than alternatives using gold-plated wire and contact blocks. A single moving contact is used foreach key with all contacts and their associated divider chain resistorsheld on a PCB (in two parts) fixed to the keyboard chassis.

The moving contacts are silver plated springs, each fixed at one endand moved at the other by the plunger of the respective key such thatthe spring makes contact with two palladium ba'rs when the key isdepressed (Figure 1). The first bar is connected to the sample and holdcircuit which stores the voltage representing the last key depressed,and the second to a circuit which generates a gate signal for the S/Hand the envelope generators. The moving contacts connect to thedivider chain (see Figure 2). These functions are usually carried oul byseparate contact pairs, where unless the contacts are precisely set up,note -jumping will occur when the envelope is gated before the S/Hreceives the new key voltage. The system used here is immune fromthis since the construction ensures the correct sequence of operation,and no initial setting up is required. The keyboard recommended in theparts list has removable key plungers so that cleaning the contacts ismuch easier too. Unclipping a plunger allows access to the sides of thebars and springs that meet.

Keyboard constructionUse the printed circuit board as a template to mark the fixing holes

on the underside of the keyboard chassis. Mark them such that theedge of the board holding the bars will be about 5mm from theplungers and then drill for 6BA clearance. Fit the 48 divider resistorson the component side of the board along with the 12 veropins andsolder in place. Cut the palladium bars to length and fit them to thetrack side using small loops of wire passed over the bar, through the

Figure 3. Key contact construction.

R8 R9 610 To R54 R5547R 47R 47R 47R 47R

Figure 4. Circuit of key contact assembly.

mounting holes and twisted on the component side. Make sure eachbar is well seated before soldering at each loop position on both sides.Cut each plunger to length, leaving the nearest slot to the key end for thecontact. Tin 5mm of both ends of the contact springs and fit each oneby passing the thin end through the detached plunger and soldering itto the pad on the PCB. If you've marked the PCB mounting holes cor-rectly then for proper operation the end of the spring should be about2mm from the far edge of the pad. The positioning of the PCB and thesprings on the PCB is not critical as long as when the PCB is mountedand the plungers clipped on, the springs are under slight tension to en-sure positive contact. Mount the PCB to the chassis using 6BA bolts, 1/7"spacers and nuts, and washers to separate them further. The keysopposite the mounting positions will have to be temporarily removed tofit the bolts, and this should be done before drilling if a hand-held drillis used, to avoid the possibility of damage to the keys. Again, thespacing is not critical so long as all the contacts normally clear bothbars and make contact with both when their keys are depressed.

KEYBOARD PARTS LISTResistorsR8-55

Miscellaneous

47R 2 48 off

49 -note C -C keyboardContact springs 49 offPalladium bars, 1.2mm k 330mm Set of 424 -contact PCB25 -contact PCB6BA 1" bolts68A 1/2" spacers6BA washers6BA nutsVeropins

(X47R)

(X13171-)(QYO7H)

(GAO9K)(GA1OL)(BF67H)(FW35Q)(BF22Y)(BF18U)(FL248)

A view of the key contacts before mounting of the board.

18 MARCH 1981 E&MM

ELECTRONICS

0R32

0

R34 R35 R36 R37 R381 1 1 1

T T T

E &MM

R39

j" 40 (1

R41

iiR42 R43

1

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KEYBOARD CONTACT ASSY

R44

-r

R45

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R47

T

R48.1.

R49

T T

GA 10 L 1251

R50 851

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r

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A1/2" spacer and one nut were found to be about right, though washerscould be used if a high or low action to the keys is preferred.Connect the two halves of the board together using short wire linksacross the veropin pairs. This completes the keyboard construction.

The assembly can be tested on its own by connecting a multimeterset on the low resistance range across pins 1 and 3. Depressing thebottom key should give zero resistance, and the top key about 2.4K.Check that all the other keys give intermediate readings and repeat forthe other bar with the meter across pins 1 and 4.

Power Supply UnitThe proper operation of synthesiser circuits requires a stable,

noise -free supply, so it is important that the Power Supply Unit (PSU) iswell -regulated and has current in reserve. The Spectrum PSU usesmonolithic regulators and low temperature coefficient components ina dual design to provide ± 15V at 270 mA maximum.

The completed PSU fitted to the back plate.

PSU CircuitThe Power Supply Unit consists of two identical circuits providing

the positive and negative supplies, driven by a dual secondarytransformer. Each secondary produces about 21V when the AC signalis rectified and smoothed, and is fused for protection in the event of apower supply fault. Regulation is carried out by the well-known uA723regulator IC which is used with an external power transistor in seriespass mode to provide the required current. This current limits at270 mA when the voltage across series resistor R1 (R2 in the -ve side)reaches 0.6V. RV1 (RV2) allows the rail voltage to be adjusted to exactly15V, and D1 (D2) protects against reverse polarity, again in the event ofa fault. The +15V regulated output of the side based around IC2 isconnected to OV of the IC1 side, giving the -15, 0, +15V supply rails.

PSU ConstructionThe prototype PSU was mounted on an aluminium panel along with

the mains cable, switch, and fuse. This was then fixed by screws tothewooden back of the synthesiser allowing the PSU to be separatelyassembled and easily removed if necessary (see photograph).

All components except the transformer fit on the PCB. Assemblethe components onto the printed circuit board, starting with theresistors, diodes, polystyrene capacitors and IC sockets. These can allbe inserted and soldered in together, before the large components arefitted. Note the orientation of the diodes, particularly in the bridgerectifiers (D1-8).

Use 4BA bolts and nuts to fix the chassis fuse holders, and connect

POWER SUPPLY UNIT PARTS LISTResistors - all 5% 1/2)A/ carbon unless specified.R1,2 2R2 1/2WR3,4 3k3 1%R5,6 3k0 1%R7 330RRV1,2 1k cermet preset 2 off

CapacitorsC1,2C3,4,7,8C5.6

SemiconductorsIC1,2TR1,2DI -D10

MiscellaneousT1S1FS1

FS2,3

2200uF 25V axial elect.2u2 63V PC elect.100pF polystyrene

uA723 14 -pin OILBD1351N4001

240V prim. 0-15, 0-15 sec. 10VADPST rocker switch with neon20mm 500mA quick blow fuse20mm panel fuseholder20mm IA quick blow fuse20mm chassis fuseholder14 -pin DIL socketPrinted circuit board3A 3 -core mains cable 2m13A mains plug6BA 1" bolts6BA 1/2" spacers6BA nuts4BA 1/2" bolts4BA nuts4BA solder tagsCable grommetVeropins

2 off2 off2 off

2 off4 off

2 off2 off10 off

2 off2 off2 off

(S2R2)(T3K3)(T3K0)(M330R)(WR40T)

(F390X)(FFO2C)(BX28F)

(QL21X)(QF06G)(QL73Q)

(LY03D)(YR70M)(WRO2C)(RX96E)(WR03D)(RX49D)(BL18U)(GAO3D)(XR01B)(HL58N)(BFO7H)(FW35Q)(BF18U)(BFO3D)(BF17T)(BF28F)(LR48C)(FL24B)

them using veropins through the tag holes. Insert and solder in thecermet presets and electrolytic capacitors, followed by the two powertransistors. The leads leave the transistors quite close together andshould be bent apart about 'A" from the package before putting them inplace. Check that you have put them in the right way round, with themetal sides facing the nearest board edge. Solder in theeight remainingveropins and check the orientation of the electrolytic capacitorsdiodes, and transistors. Fix the PSU board to the back panel, orwhatever else you are using, using 6BA bolts with spacers. Fit themains switch, fuseholder, and transformer to the panel, using 4BAbolts for the latter and including two solder tags on one side for the

Figure 8. PSU and mains wiring.

E&MM MARCH 1981 19

ELECTRONICS

Lt

N

IC1,2uA 723

TOPVIEW

S1b

7

14

T

01-101N 4001

a

k c e

TR 1.2BD135

5

0

15V

OV

1FS 20 =

2

30

4

14

C12200uF

12 11

510

2-6 3

u=1 IC1

C32u2 4

7 13

-I I-C R5100pF

II. RV11k

2S

3k0

..=

R1

E-1 502R2

I

R33k3

D9

FS 3

14

R7330R

6 T

C2 =2200uF

TR2

12 1110

20- 6 3

+=C4

2u2

IC2

7 13

C6100pF

R2

2R2

+15V

C7 2u2

OV

R43k3

RV21k

R63k0

7!1310

60

+ C8 2u2

BOARD P1OUTLINE

7o-15V

Figure 6. Circuit of the Power Supply Unit.

Figure 7. PSU printed circuit board.

earth connections. Strip back a length of the mains cable and cut offsome of each core for connecting the switch, fuse, transformer andPCB. Connect these as shown in Figure 7, and then connect the mainscable and secure it with the grommet. The fuse is wired on the supplyside of the switch, so that the switch neon will go out if the fuse blows.Fit a mains plug with a 3amp fuse and then check the wiring beforegoing on to the next stage.

PSU Setting UpBefore inserting FS2, 3 or IC1, 2 first insert FS1, plug in, switch on,

and measure the voltage across each secondary. This should bearound 15V RMS. Now fit FS2 and 3 with the power off, switch on, andmeasure the voltage across Cl and 2, each of which should be about21V. Switch off again, insert IC1 and 2, switch on, and measure the

output voltages (across points 6,5 and 7,6). If you are confident in yourconstructional abilities, you can leave these checks and try the PSUwith all the fuses and IC's in first time. Either way, the rail voltagesshould be measured and RV1 (+ve) and RV2 (-ve) adjusted so that theyare exactly 15V. An oscilloscope will probably be more accurate for thisthan a cheap multimeter, though use a digital multimeter or a goodmechanical meter if one is available.

Digisound Ltd. will be offering a full set of the CEM IC's used in thisproject at the special reduced price of £29.00 inc. VAT and postage.Ready-made metalwork and PCB's will be obtainable from MaplinElectronic Supplies. A cassette demonstratingtheSpectrum'sfacilitieswill be made available from E&MM. E&MM

20 MARCH 1981 E&MM

CONTROLLL

SPEEDDRIS

DRILL CONTROLLERElectronically changes speedfrom approximately 10 revs tomaximum. Full power at allspeeds by finger-tip control.Kit includes all parts, case,everything and full instructions.

£3.45Made up model £2.00 extra

SIX DIGIT COUNTERSOne pulse moves one digit --Type I for 230v AC or 100v DCnot resettable. Price 80p -Type 2for 48v DC or 115v AC and re-settable £1.115.

COMPONENTS BARGAINRef. W0998. Modern fibre glass board, contains a multitudeof very useful parts, some of which are: SCR ref. 2N 5060/2,35 asserted rectifiers including four 3 amp 400v types (madeup in a bridge) 8 transistors type BC 107 and 2 type BEY 51electrolytic condensers. 250uf 100y DC and 100uf 25v DC andover 100 parts including variable, fixed and wire woundresistors, electrolytics etc. Don't miss this snip at £1.15.

SIREN OR BLEEPERAmerican Delta mechanical type,works on 6 to 12v to DC or 12 to24v AC. Price 75p or £60 per 100.Electronic Bleeper TH3S emitshigh pitched wailing note ofvarying pitch. In red plasticcase with fixing bracket, £5.00.

CASSETTE PLAYER/RECORDERSWith record and playback heads, all electronics, switchesand speaker. Price £9.05 (surely this must be the bargain ofthe year). Music centre replacement stereo with heads butnot electronics. £14.95.

DESOLDERING PUMPIdeal for removing components fromcomputer boards as well as for `iservice work generally. Price £6.35.

INTERCOM OUTFITBrand new intercoms with 50' inter -connecting lead. Masterand sub, in neat plastic cases suitable for office or home oras a baby alarm etc. These are new stock but please expecta little fault. Offered at less than the price of the 2 speakers,switches and cases. Only £3.74 the pair.

HEADPHONE AMPLIFIER (STEREO)With volume, tone andbalance control 9v operation.All made up ready to go.Price £4.50. -Y-4-14111,1F

MAINS SOLENOIDSAll have powerful pull.TT2 size 1.i" 21" r 2". Price £2.95TT6 size 2i" 2". Price £3.50TT10 size 3" 2l" 2". Price £416

ELECTRONICJIGSAW PUZZLEOne of the many things you canmake with this miniature uni-selector. We give the circuitfree when you order. Price £3.45.

MAINS OPERATED VALVESMade by Asco. Two models available both suitable for waterand non -corrosive liquids, both for normal mains Operation.Ref. VI for 1" pipes and low pressure operation. V2 is for1" pipe and high pressure operation.

VERSADRILLA 12 volt battery operated power f--drill,not just suitable for printedcircuit boards but will do all thejobs and is powerful enough toperform all the functions andoperations normally expected ofBlack 6 Decker and other mainsdrills. Its chuck accepts up to 1"drills. Size approx. 150mm x50mm. Price £1675.

3 -CHANNEL SOUND TO LIGHT KITComplete kit of parts for a three -channel sound to light unit controlling over 2,000watts of lighting. Use this at home if you wish but it is plenty rugged enough forDisco work.The unit is housed in an attractive two-tone metal case and has controls for eachchannel, and a master on/off. The audio input and output are by 'A" sockets andthree panel mounting fuse holders provide thyristor protection. A four -pin plug andsocket facilitate ease of connecting lamps. Special snip price is £14.95 in kit formor £19.95 assembled and tested.

DELAY SWITCHMains operated - delay can be accuratelyset with pointers knob for periods of up to21/2 hrs. 2 contacts suitable to switch 10amps - second contact opens a fewminutes after 1st contact.

VENNER TIME SWITCH mains operatedwith 20 amp switch. one on and one off per24 hrs. repeats daily automaticallycorrecting for the lengthening or shorteningday. An expensive time switch but you canhave it for only £2.95. These are new butwithout case, but we can supply plasticcases (base and cover) f 1.75 or metal casewith window £2.95. Also available isadaptor kit to convert this into a normal 24hr. time switch but with the addedadvantage of up to 12 on/offs per 24 hrs.This makes an ideal controller for theimmersion heater. Price of adaptor kit isf 2.30.

FLUORESCENT TUBE INVERTERFor camping - car repairing -emergency lighting from a 12vbattery you can't beat fluorescentlighting, it will offer plenty of welldistributed light and is economi-cal. We offer Phillips inverter for12" 8 watt miniature tube for only£2.75 with tube and tube holdersas well.

SUPER HI-FI SPEAKERCABINETS

Made for an expensive Hi-Fi outfit - willsuit any decor. Resonance free cut -Outs for8" woofer and 4" tweeter. The frontmaterial is carved Dacron, which is thickand does not need to be stuck in and thecompleted unit is most pleasing. Colourblack. Supplied in pairs, price £6.90 perpair (this is probably less than the originalcost of one cabinet) carriage £3 the pair.

CHASSIS BARGAIN3 wave band radio with stereo amplifier.Made for incorporation in a high-classradiogram, this has a quality of outputwhich can only be described as superb. It istruly hi-fi. The chassis size is approximately14". Push buttons select long, medium,short and gram. Control are balance.volume, treble and bass. Mains powersupply. The output is 6 +6 watts. Brand newand in perfect working order, offered at lessthan value of stereo amp alone, namely£6.90. Post £2.00.

DOOR SWITCHNeat tubular pattern for letting into door frame. This is achangeover switch so can be used in opening or closingcircuits. Price 57p. D.I.Y. burglar alarm parts available,request diagram and price list of our mains operated system.

THIS MONTH'S SNIPTHERMOSTAT ASSORTMENT 10 different thermostats. 7 bi-metal types and 3 liquid types. There are the current stats which willopen the switch to protect devices against overload, short circuits,etc, or when fitted say in front of the element of a blower heater, theheat would trip the stat if the blower fuses; appliance state, one forhigh temperatures, others adjustable over a range of temperatureswhich could include 0-100°C. There is also a thermostatic podwhich can be immersed, an oven stat, a calibrated boiler stet, finallyan ice slat which, fitted to our waterproof heater element, up in theloft could protect your pipes from freezing. Separately, thesethermostats would cost round about £15.00 - however, you canhave the parcel for £2.50.

V3 MICROSWITCHESOver 50,000 in stock, all 250 AC working, all with 3 silvercontacts for c/o circuits. 10 amp 25p each or £20 per 100,15 amp 35p each or £30 per 100.

TANGENTIAL BLOWERMetal bladed Smiths made super silent with dozens of appli-cations, cooker hoods, fume extractor -blower heater freshair impeller etc. Air outlet is rectangular size approx. 101" x2)" £4.95. Post L1 .50.

MULLARD UNILEXA mains operated 4+4 stereosystem. Rated one of thefinest performers in the stereofield this would make a won-derful gift for almost anyone.'In easy -to -assemble modularform this should sell at about£30 -but due to a special bulk buy and as an incentive foryou to buy this month we offer the system complete at only£16 including VAT and postage.FREE GIFT -Buy this month and you will receive a pair ofGoodman's elliptical 8"x 5" speakers to match this amplifier.

II BATTERY MOTORSFor model makers, smallest is about as big as a thimbleand the biggest is powerful enough for a drill, £2 the 8.12V MOTOR BY CROUZETA powerful motor virtually impossible to stop by hand,size approx. 21" long and 21" dia. permanent magnet soreversible simply by changing polarity and has a relativelyconstant speed with or without load. Fitted with a splinedshaft which could directly engage a toothed wheel or to whicha pulley could be attached. Ideal for large models, or smallmachines etc. Priced £4.25.MAINS OPERATED LOW SPEED MOTORSProgrammer type as used in time switches etc. The followingfinal speeds in stock: -1r 24 hrs - 1r 8 hrs - lr 4h -1rh -2 rh - erh - 4rh -12 rh -20 rh - 30 rh -1r min - 2rm -4 rill -8 rm -15 rm- 25 rm -30 rm - 200 rm - all at £3.50 each.SPIT MOTORSThese are powerful mains operated induction motors withgear box attached with easy to fix to, squared shaft, finalspeed is approx. 5 revs. per min., price £5.25 -similar motorbut with final speed 110 rpm, 80 rpm £5.15.

INDUCTION MOTORS Mains working asused in record players, fans, etc. Speedusually 1,400. All have ample spindlelength for coupling fan blade, pulley etc.Power depends on stack size. 1/2" stack£2.00; 3/4" stack £2.50;'/s" stack £3.00; 1"stack £3.50; 11/2" stack £4.50. Add 25p tototal motor cost to cover postage and thenadd 15% VAT.

8 POWERFUL BATTERYMOTORSFor models, Meccanos, drills, remotecontrol planes, boats. etc. £2.

MINI -MULTI TESTERDeluxe pocket size precision moving coil instrument,jewelled bearings - 2000 o.p.v. mirrored scale. 11instant ranges measure: DC volts 10, 50, 250, 1000. ACvolts 10, 50, 250, 1000. DC amps 0-100 mA. Continuity.nd resistance 0-1 meg ohms in two ranges. Completewith Test Prods and instruction book showing how tomeasure capacity and inductance as well. Unbelievablevalue only £6.75 + 50p post and insurance.FREE Amps ranges kit to enable you to read DC current from 0-10 amps, directly onthe 0-10 scale. It's free if you purchase quickly but if you already own a mini testerand would like one, send £2.50.

Terms: Cash with order - but orders under f 10 must add 50p to offset packing, etc.B4 LK ENQUIRIES INVITED. - PHONE HAYWARDS HEATH 54563

ACCESS & BARCLAYCARD WELCOMED

J. BULL (Electrical) LTD.(Dept. EME, 34-36 AMERICA LANE

HAYWARDS HEATH, SUSSEX RH16 3QU

IT'S FREEOur monthly Advance Advertising Bargains List givesdetails of bargains arriving or just arrived -often bargainswhich sell out before our advertisement can appear -it'san interesting list and It's free -just send S.A.E. Beloware a few of the ,Bargains still available from previouslines.DUE TO THE HIGH 6 RISING PRICES OF FUEL manycompanies and probably many householders are lookingaround for ways of saving some of this cost. One Companybought a number of fans from us and fitted these on the ceilingof their workshops where the hot air tends to collect and theyblow this hot air downwards. Another Company has boughtfens from us to suck tits exhaust from their oil fired centralheaters through a zig zag of asbestos pipes, the asbestospipes being in a separate chamber which becomes a hot airchamber, the hot air from this is blown through ducting towhere ever It is needed. Basically, they have cut out the normalchimney and replaced this with one of our high power extrac-tor fans, If you have any other good ideas on heat cost saving,let us know and we will pass it on to other readers.

EXTRACTOR FANSEx -Computer made by Woods of Colches-ter, ideal also as blower; central heatingsystems, fume extraction etc. Easy fixingthrough panel, very powerful 2,500 r.p.m.but quiet running. Choice Of 2 sizes, 5"£5.50, 6" £11-50; post £1 per fan,

PING PONG BALL BLOWER -UPPERS Have you got toorganise a Party or Charity Fund -Raising Event?Then one always popular way is to have ping pong balls goingup and down and being caught. We have some powerfulblowers and these should be ideal for this, and of course formore serious purposes. They are 4 stage blowers, coupled tosynchronised AC mains motors of approximately 1 h.p. Theyhave a terrific suction as well as a high velocity blow. Ex com-puters, price £2600.TRANSMITTER SURVEILLANCETiny, easily hidden but which will enable conversation tobe picked up with FM radio. Can be made in a matchbox -allelectronic pails and Circuit. E2.30.RADIO MIKEIdeal for discos and garden parties, allows complete freedomat movement. Play through FM radio or tuner amp, £5.90.SAFE BLOCKMains quick connector will save you valuable time. FeaturesInclude quick spring connectors, heavy plastic case and autoon and off switch. Complete kit E1.95.LIGHT CHASERGives a brilliant display -a psychedelic light show for discos,Parties and pop groups. These have three modes of flashing,two chase -patterns and a strobe effect. Total output power 750watts per channel. Complete kit. Price £16. Ready made up£4 extra.FISH BITE INDICATOR enables anglers to set up severallines then sit down and read a book. As soon as one has abite the loudspeakers emits a shrill note. Kit, Price £4-90.

WAVEBAND SHORTWAVE RADIO KITBandspread covering 13.5 to 32 metres. Based on circuit whichappeared in a recent issue of Radio Constructor. Complete kit.Includes case materials, six transistors, and diodes, con-densers, resistors, inductors, switches, etc. Nothing else tobuy, If you have an amplifier to connect It to on a pair of highresistance headphones. Price E11 95.SHORT WAVE CRYSTAL RADIOAll the parts to make us the beginner's model. Price £2.30.Crystal earpiece 650. High resistance headphones (give beetresults) Ern. Kit includes chassis and front but not case.RADIO STETHOSCOPEEasy to fault find -start at the aerial and work towards thesneaker - when signal stops you have found the fault. Corn -piste kit E4 05,INTERRUPTED BEAM KITThis kit enables you to make a switch that will trigger when asteady beam of infra -red or ordinary light Is broken. Maincomponents -relay. photo transistor, resistors and caps etc.Circuit diagram but no case, Price £2.30.OUR CAR STARTER AND CHARGER KIT has no doubtsaved many motorists from embarrassment in an emergencyyou can start car off mains or bring your battery up to fullcharge In a couple of hours. The kit comprises: 250w mainstransformer, two 10 amp bridge rectifiers, start/charge switchand full instructions. You can assemble this in the evening,box It up or leave it on the shelf in the garage, whichever suitsyou best. Price EH -50 + £2.50 post.G.P.O. HIGH GAIN AMP/SIGNAL TRACER. In casemeasuring only 51in , 31in x 11in is an extremely high gain(70DB) solid state amplifier designed for use as a signaltracer on GPO cables etc. With a radio it functions very wellas a signal tracer. By connecting a simple coil to the Inputsocket a useful mains cable tracer can be made. Runs onstandard 44v battery and has input, output sockets and on -offvolume control, mounted flush on the top. Many other usesInclude general purpose amp, cueing amp, etc. An absolutebargain at only £1.115. Suitable 80 ohm earpiece 69p.VU METEREdgewise mounting, through hole size 1.4" x 4" approx.These are 100 micro amp f,s.d. and fitted with Infernal 6 voltbulb for scale illumination, also have zero reset. The scale isnot calibrated but has very modern appearance. Price E2110.BALANCE METEREdgewise mounting 100 UA centre zero. Price E2 -30p.

METEREagle full vision plastic front, 50 UA, Price £4.110p 1 mAPriceWATERPROOF HEATING WIRE60 ohms per yard. This is a heating element wound on a fibreglass coil and then covered with p.v.c. Dozens of uses -around water pipes, under grow boxes in gloves and socks.23p metre.DIAL INDICATORAs used In tool making and other precision measuring op-erations, the famous John Bull accurately shows differencesof 0.1mm. A beautifully made precision instrument, price Inpmroicriet tginsphops would be £12-£15. We have a fair quantity.

COMPONENT BOARD Ref. W0961,This is a modern fibre glass board which contains a multitudeof very useful parts, most Important of which are: 35 assorteddiodes and rectifiers Including four 3 amo 400v types (made upIn a bridge) 8 transistors type BC 107 and 2 type BFY 51electrolytic condensers, SCR ref. 2N 5062 25 Out 100v DC and100u1 25v DC and over 100 other parts Including variable,fixed and wire wound resistors, electrolytic and other con-densers. A real snip at L1.15.FRUIT MACHINE HEART, 4 wheels with all fruits.motorised and with solenoids for stopping the wheels with alittle Ingenuity you can defy your friends getting the "jackpot."E0.05 + £4 carriage.DESOLDERING PUMPIdeal for removing components from computer boards as wellas for service work generally. Price £6.35.4 -CORE FLEX CABLEWhite pvc for telephone extensions, disco lights, etc. 10metres E2, 100 metres £15. Other multicore cable In stock.MUGGER DETERRENTA high -note bleeper, push latching switch, plastic case andbattery connector. Will scare away any villain and bring help.E2.50 complete kit.HUMIDITY SWITCHAmerican made by Honeywell. The action of this devicedepends upon the dampness causing a membrane to stretchand trigger a sensitive microswitch. Very sensitive breathingon It for Instance will switch it on. Micro 3 amp at 250V cc.Only II -IS.

E&MM MARCH 1981 21

ELECTRONICS

Starting PointAs it is hoped this series will show, it is within the capabilitiesof practically anyone to gain a good basic understanding ofelectronics. For those whose main interest is electronics con-

struction, design, or servicing, it is probably best to concentratemainly on the characteristics of the various components and the wayin which they are employed in practical designs, rather than on thedetailed theory of their operation. This approach will be used in this

Current FlowA basic understanding of current flow is an essential piece of background

knowledge for anyone trying to get to grips with electronic components andcircuits. An electronic current consists of a flow of minute particles calledelectrons. All matter is made up of miniscule building blocks called atoms, andelectrons are one of the constituents of atoms. The electrons are very muchsmaller than the rest of the atom (the 'nucleus'), and they are in orbit around thenucleus. In the case of most substances all the electrons are held firmly in orbitand are not easily dislodged, but in others there is a 'free electron' in the outerorbit which is only loosely bound to the atom. In fact the free electrons tend tomove randomly from one atom to another.

By applying an electro-motive force (E.M.F.) to materials having freeelectrons, these electrons can be made to proceed in the samegeneral direction(although still in a rather haphazard fashion). This flow of electrons constitutesacurrent flow.

A common source of E.M.F. is a battery, and metals are the main materialswhich are plentiful in free electrons. Thus if a piece of wire is connected acrossthe terminals of a battery a heavy current flows through this 'circuit'. Substanceswhich readily permit a heavy currentflowarecalled 'conductors'. Most materials,such as plastics, are practically devoid of free electrons and strongly resist anycurrent flow. These are known as'insulators'.Thusvirtuallynocurrentflows if, forexample, a piece of PVC sleeving is connected across a battery.

The two terminals of a battery are identified by '+' (positive) and '-' (negative)signs. The electron flow is from the negative terminal to the positive one.Unfortunately, the pioneers of electricity assumed a positive to negative currentflow and based many laws of physics on this assumption. This has led to asituation today where we sometimes talk in terms of electron flow (negative topositive) and at other times in terms of 'conventional current flow' (positive tonegative). The behaviour of components and circuits can be explainedsatisfactorily using either, and it is really a matter of choosing whichever is themore convenient. However, to avoid confusion it is necessary to make it clearwhich convention is being used.

Ohm's LawThe amount of current flowing in a circuit is measured in units called

'amperes', but the abbreviated terms 'amps' and 'A' are more commonly used.The current flow in a circuit is governed by two factors: -1. The strength of the E.M.F. applied to it2. How readily it conducts or resists a current flow

The strength of an E.M.F. is measured in volts(V), and obviouslythe higherthevoltage, the larger the current it will force through a given circuit. In fact thecurrent flow is proportional to the applied voltage and a doubling in the voltageapplied to a circuit, for instance, doubles the current flow.

Rather than specify how readily a circuit conducts it is more usual to specifyits 'resistance' to a current flow, and resistance is measured in ohms. The higherthe resistance in ohms, the more difficult it is to force a given currentthrough thecircuit. The currentflow is inversely proportional tothe resistance of a circuit, andso halving the resistance of a circuit, for example, would double the current flow.

Resistance, current, and voltage are mathematically related toone another by'Ohm's Law', and if any two quantities are known, the third can be calculated.Ohm's Law is as follows: -Current = Voltage divided by Resistance, orResistance = Voltage divided by current, orVoltage = Current multiplied by Resistance

BATTERYBi

9V

T

RESISTORR1

1OR

Figure 1. Current flow through a resistor.

by Robert Penfold

series, and it should enable even absolute beginners to quickly andeasily grasp an understanding of electronic circuits. Each sub-sequent part of the series will be accompanied by a simpleconstructional project which will demonstrate the practical applica-tion of the theory that has been covered, as well as being a usefuland worthwhile piece of equipment in its own right.

The power rating of resistors tends to be reflected in their physical size, the greater surfacearea of larger types permitting more rapid dissipation of heat into the air. (a) "3W carbonfilm, (b) 1/2W metal oxide (close tolerance), (c) 1/2W carbon film, (d) 1W carbon film, and

Examples of potentiometers: (a) 0.1W horizontal preset, (b) 0.1W vertical preset,(c) 0.25W horizontal preset, (d) carbon potentiometer, and (e) dual gang carbonpotentiometer.

If we consider a simple example, the circuit diagram of Figure 1 showsa 9 voltbattery connected across a 10 ohm resistor. It should perhaps be pointed outthatin circuit diagrams the components are represented by a set of symbols; two ofwhich are shown here (others will be introduced when we come to consider thecomponent concerned). The lines joining them represent the connecting wires,and dots on the lines indicate connections. Where lines cross one anotherwithout a dot at the intersection there is no connection; this is just a point on thediagram where it is necessary for lines to cross over one another.

In our simple example of Figure 1 the current flow is 9 volts divided by10 ohms, or 0.9 amperes. If we knew the battery voltage and current flow but notthe resistance of R1, then this resistance could be calculated (9V + 0.9A = 10R).The word 'ohms' is often abbreviated to the Greek letter omega (a) or shown as acapital R, as it appears here. If the battery voltage was the unknown quantity thiscould be calculated as 1OR x 0.9A = 9V.

As Ohm's Law is not merely of academic importance and is much used whentackling practical problems in electronics it is well worth spending some timeand effort to ensure a proper understanding of it, working out a few contrivedexamples if this will help.

22 MARCH 1981 E&MM

ELECTRONICS

UnitsIn practical electronics it is often necessary to use very large or very small

quantities. It is quite common for circuits to employ resistors having values ofmany thousands or even millions of ohms. On the other hand, circuits oftenhandle signals having amplitudes of only a few thousandths or millionths of avolt. To avoid constantly using very large or very small numbers, quantities areoften given a prefix ahead of the letter denoting the units in use. The prefixindicates that the value is given in some multiple or subdivision of the basicunit. The prefixes commonly encountered are listed below: -

x 1,000 = k (kilo)x 1,000,000 = M (mega)x 1,000,000,000 = G (giga)x 1,000,000,000,000 = T (tera)1/1,000 = m (milli)1/1,000,000=µ (micro)1/1,000,000,000= n (nano)1/1,000,000,000,000 = p (pico)

A potential of 0.005V could therefore be given as 5mV or 5 millivolts, or aresistor value could be given as 3.9M or 3.9 megohms instead of 3,900,000 ohms.

Series and ParallelIt is possible to combine resistors (and other components) in series or in

parallel, or in a combination of the two. Series and parallel connection areillustrated in Figure 2a and Figure 2b respectively. In each case th ree devices a reshown, but obviously any number of components could be used with eithermethod of connection.

As one would expect, when several resistors are added in series the totalresistance through the combination is higher than the resistance of any onecomponent in the circuit. This is merely because the current hasto negotiate notjust one resistor, but all those in the chain. In fact the total resistance is simplyequal to the sum of all the resistances in the circuit. Thuswith the example va luesshown in Figure 2a there is a total resistance of 7.9k (1k + 2.2k + 4.7k = 7.9k).

R1

1k

7k9 R2

TOTAL 2k2 R1

tORR220R

R3100R 6 25R

R34k7

(a) (b)

Figure 2. a. Resistors in series. b. Resistors in parallel.

When resistors are connected in parallel the total resistance of the circuit isless than the value of any one resistor in the circuit. This is due to the additionalcurrent paths provided by the other resistors in the circuit, with the appliedvoltage causing the appropriate current to flow through each resistor. Therefore,for a given level of current flow a lower supply voltage will be needed for severalresistors in parallel than for justone of the resistors, and the parallel combinationobviously gives a lower resistance.

The equation for parallel resistance in a circuit containing two resistors is:-

R total - RI x R2R1 + R2

For example, a 10 ohm and a 30 ohm resistor in parallel exhibit a combinedresistance of:-

01 x 30 - 300 -7R total -10 + 30 40 5 ohms

For three or more resistors in parallel the equation is: -

R total =1 I 1

RI + R2+ R3

etc.

Thus (say) 10, 20, and 100 ohm resistors in parallel would have a combinedresistance of: -

R total =1

1 1 1

10+20+ 100

1 1

0.1 + 0.05 + 0.01 0.16

1 divided by 0.16 equals 6.25 ohms.Parallel resistance calculations are not as easy as series resistance

calculations, but are not really difficult when done with the aid of an electroniccalculator.

It must be stressed that these equations cannot be applied to components ofany type (e.g. capacitors). Different components behave in different ways whencombined in series or parallel. Batteries for example, produce the same voltagewhen connected in parallel (see Figure 3a), no matter how many are used. Thismethod of connection is not advisable in practice incidentally, since the actual(rather than nominal) voltage supplied by a battery varies according to theamount of 'charge' it contains. An ordinary 9 volt dry battery for instance, mighthave an actual voltage of 9.5 volts when new, and only about 7.5 volts when it is

819V

IN829V

1

9V

B1

9V

(a)

829V

9V

B29V

NO

839V

T

(c) (b)

27V

Figure 3. a. Batteries in parallel. b. Batteries in series. c. Batteries in reverse series.

nearly exhausted but still usable. Therefore, two practical batteries might wellhave slightly different voltages, causing the one having the higher voltage todrive a current through the other! The amount of current that would flowdepends upon the difference in the battery voltages and the internalresistances of the batteries. The internal resistance is that contained within theinternal structure of the battery. Although an innate property of a battery, theeffect is much the same as if an actual resistor was connected in series with thebattery, and in this case it limits the current that would flow.

Internal resistance also results in the battery voltage falling as the currentdrain is increased, the lost voltage effectively being dropped across the internalresistance. For example, a battery having an internal resistance of 10 ohmswould suffer a drop in output voltage of 2 volts if a current of 200mA (0.2A) wasdrawn from it (V = C x R = 0.2 x 10 = 2 volts). All practical power and signalsources possess internal resistance, and there is thus a limit to the amount ofcurrent they can provide.

When batteries are connected in series in the manner shown in Figure 3b,their total output voltage is equal to the sum of the individual battery voltages,giving an output of 27 volts in this case. The method of connection shown inFigure 3c is of no practical value since one battery tends to cancel out the other,giving zero output voltage if they have the same voltage!

E&MM MARCH 1981 23

ELECTRONICS

Voltage DividersWhen a voltage is fed to a series resistor circuit (as in Figure 4) part of the

input voltage will be present across each resistor. It would be possible tocalculate each voltage by first finding the total series resistance, then

B1

9V

4R1 I

3k 1 5V

6V

R29k 4-5V

R33V6k

7 5V

Figure 4. Kirchoff's Voltage Law.

calculating the current flowing in the circuit using Ohm's Law, and finally usingOhm's Law again to work out the three voltages.

A quicker method is to calculate the total resistance in the circuit, and thenwork out what fraction of this each resistor's value corresponds to. The voltageacross each resistor is then equal to the input voltage multiplied by theappropriate fraction. In our example of Figure 4 there is a total resistance of 18k,and R1 has a resistance equal to 3/18ths of this, or 1/6th in other words.Therefore one sixth of the input voltage appears across R1 and with a 9 voltsupply this obviously equals 1.5V (1/6 x 9/1 = 9/6 = 1.5V). If you calculate thevoltages for R2 and R3 you should find these are 4.5V and 3V respectively.

The voltage across two or more resistors is equal to the sum of theirindividual voltages. In our example this gives 4.5V (1.5V + 3V) from the bottomof R3 to the top of R2, and 6V (4.5V + 1.5V) from the bottom end of R2 to the topconnection of Rl. From the lower connection of R3 to the top of R1 there isobviously the input potential of 9 volts, and the sum of the voltages across theresistors must equal this value (1.5V + 4.5V + 6V = 9V). This is known asKirchoff's Voltage Law.

Voltage dividers are much used in practical circuits because they enable anyrequired voltage (less than the supply voltage) to be easily obtained. Sometimesa variable voltage is required, and then a component called a potentiometer isused. A potentiometer has a track which is usually made from carbon, but issometimes wound using a special wire (resistance wire) which, unlike ordinarywire, has a fairly high resistance even over quite a short length. A connection ismade to each end of the track and there is a fixed resistance between these twopoints. A third connection is made to a wiper which by means of a control shaftcan be moved from one end of the track to the other.

131

MN POTENTIOMETER

RV I

OUTPUT

RVI

Figure 5. Use of a potentiometer togive a variable voltage.

Figure 6. The circuit symbol fora preset potentiometer.

Figure 5 shows the circuit symbol for a potentiometer, and also shows how itcan be used to give a variable voltage. If the wiper is right at the top of the trackthe output potential must be ,equal to the full input voltage, since the wiperconnects direct to the upper track terminal. Similarly, taking the wiper down tothe bottom end of the track connects it direct to the lower terminal and giveszero output voltage. With the wiper at an intermediate setting there is anintermediate output voltage, with the sections of track above and below thewiper acting as voltage divider resistances. For example, half the input voltagewould be present at the wiper if the latter is set at the centre of the track. Thusthe wiper voltage can be varied from zero to the full input potential.

Potentiometers are commonly used as volume and tone controls, andsimilar applications where a panel mounted control is required. There is also apreset type which is normally of very simple construction, and intended formounting inside equipment on a component board. These are adjusted using ascrewdriver when initially setting up the equipment and may never need anyfurther adjustment. Figure 6 shows the circuit symbol for a preset poten-tiometer.

By ignoring one of the track connections of a potentiometer, or connecting itto the wiper, it can be used to provide a resistance that is variable from zero tothe full track resistance by using the other end terminal and the wiper. It is quitecommon for potentiometers to be used in this way.

Figure 7. Four resistors in a bridge circuit.

Bridge CircuitFigure 7 shows a simple example of a form of circuit known as a 'bridge'. In

this case the four elements of the bridge each consist of just one resistor, butother components are sometimes used in this configuration. The resistors arearranged as two voltage dividers, and with the values shown there is 6 volts atoutput A and 4.5 volts at output B. As the voltage across the two outputs is equalto the difference between the two potentials there is obviously 1.5 volts(6V - 4.5V = 1.5V) in this example. The voltage at output A is closer to thepositive input rail potential than the voltage at output B, and output A istherefore positive of output B.

A useful property of this circuit, and one that is often exploited in practice, isthat with identical voltages at the outputs there is zero output from the circuit.

PowerThe amount of power or energy applied to a component depends upon both

the voltage applied to it and the amount of current it passes, and the power levelis proportional to both. Power is expressed in units called watts, and power issimply equal to voltage multiplied by current. To take a simple example, if 10volts is applied to a resistor and a current of 300mA (0.3A) flows, the power inthe resistor is 3 watts (10 x 0.3 = 3 watts).

Most of this energy will be converted into heat, and a resistor will overheatand be destroyed if it is unable to lose the heat that is generated into thesurrounding air with adequate rapidity. Resistors are therefore given a powerrating which should not be exceeded, and in the interest of good reliability theyshould really be run well within this rating. In most modern circuits only very lowpowers are involved, and miniature resistors having a rating of around I/4watt aremore than adequate in the vast majority of cases.

ToleranceApart from a resistance value and power rating, resistors also have a

tolerance rating. This merely indicates that the actual value of the component iswithin a certain percentage of its marked value. Thus a 100 ohm resistor couldhave an actual resistance of anything from 90 to 110 ohms (ie 100 ohms ±10%). Ordinary 5 or 10% components are suitable for most circuits, but in someapplications close tolerance (1 or 2%) components are required.

Obviously it is not possible for resistors to be manufactured and sold in everypossible value, and so they are available in a series of standard values, or'preferred values' as they are known. Most circuits specify values from what hasbecome known as the E12 series of values, which is as follows:- 1, 1.2, 1.5, 1.8,2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2 ohms. Components having values higherthan these by a factor of 10, 100, 1,000, etc. are also available, up to a typicalmaximum of 10 megohms. Some ranges of resistors include values which arelower than these by a factor of 10, but such low values are only required veryinfrequently.

There is another series of values known as the E24 series and this includesall the E12 values plus the following:- 1.1, 1.3, 1.6, 2, 2.4, 3, 3.6, 4.3, 5.1, 6.2,7.5, and 9.1 ohms. These additional values are only available with a tolerance of5% or less, and are used much less often than the E12 series.

These sequences of values probably look rather illogical at first, but this isnot the case. The E12 series gives a range of values that steadily increase byroughly 20% per step, and the E24 series rises in increments of approximately10%. E&M M

24 MARCH 1981 E&MM

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f19.95 £32.50For around 30 functions

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PROGRAMMABLEFX-3500PStatistical regression and integrals.Non-volatile memories and stores.38 functional (non-volatile) steps, 2 pro-gramme storage capability. Unconditionaland conditional jumps. 7 (non-volatile)memories, one independent, 6 constantmemories. 18 pairs of parentheses, nest -able in 6 levels.61 built-in functions, including: Integrals(Simpson's rule). Linear regression, log-arithmic regression, exponential regres-sion and power regression.Hyperbolics, sexagesimal and co-ordi-nates conversions. 10 digit mantissa or10 +2 exponent. Two silver oxide batteriesgive approximately 1,000 hours continu-ous use with power -saving automatic cut-off, with data and memory protection.Dims: 9/32 x 21/2 x 51/4 inches. Suppliedwith leatherette wallet.

:n7/71 ef. Cijer"75.6e1S,

i,23456189Cj3

FX-8100 SUPER SCIENTIFICOur best selling scientific. 46 scientific functions, clock, calendar, alarm,countdown alarm, interval alarm timer, 1/100 second stopwatch with lap timing.1/4 x 234 x 51/2 inches. Leatherette wallet. RRP £27.95 - £24.95

To TEMPUS (Dept. E&MM), 164-167 East Road, Cambridge CB1 1DB

Please send me

Remittance enclosed £

Access or Barclaycard No.

Name

Address

Post Code

E&MM MARCH 1981 25

ELECTRONICS

CO\TNUITYTESTER by Robert Penfold

Acontinuity tester is a veryuseful gadget around thehome, workshop and

on stage - it is invaluable fortesting fuses, jack leads,speakers, semiconductor junc-tions, printed circuit boards,power transistor/heatsink insula-tion and a multitude of otherpotential sites of trouble. Likemost testers, this design gives anaudio indication of continuity,and has the advantage of twomodes of operation, giving in-creased versatility particularly forprinted circuit board checking.

A problem that is often en-countered when testing for shortcircuits on component boards isthat a semiconductor junction(which can be a diode or part of atransistor or integrated circuit)connected across tracks to betested could give a false alarm.When forward biased there is avoltage drop of about 0.6 voltsacross the junction, but this dropis not normally sufficient to pre-vent the tester from operating andindicating continuity. Thoughfalse alarms of this type can oftenbe checked by reversing the testprobes (ineffective in circuitswhere there are two junctionsconnected 'back to back') thistester can operate such that con-tinuity will only be indicated if thevoltage drop across the testprobes is less- than about 0.5volts, avoiding misleading resultsdue to forward biased semicon-ductor junctions.

The CircuitThe circuit diagram of the

continuity tester appears in Fig. 1;it is basically just an audio oscil-lator feeding a loudspeaker.

IC1 is an audio power amplifierdevice, and it is made to oscillateat a frequency of several hundredHertz by applying positive feed-back through R3, Cl and R1. R2 re-duces the amount of feedbacksomewhat, and prevents theoscillations from becoming un-stable. C2 couples the outputsignal to a high impedance loud-speaker.

With S1 in the 'off' (open)position the unit can be used as a

SK1

S1

fi

0

33k

R22k7

PROBES SK 2

TR1 0

C1 10nF

R1

14IC1

3,4.5,10.11,12

8

R35k6 sim

C3100uF

1=1

C21uF

4BOARD OUTLINE

0 0

LS164R

tk

R41k8

D1

BC 179TR1

b

PIN VIEW

LM 380IC1

14

TOPVIEW

tk

D1TIL 220

PIN VIEW

Figure 1. Circuit Diagramof the Continuity Tester

simple continuity tester for leads,fuses, semiconductors etc. andshorting the two test probes to-gether will connect the supply tothe circuit producing an audiotone. L.E.D. indicator D1 will alsoturn on giving a visual indicationof continuity. When using the unitfor checking semiconductors,connecting the junction one wayround will result in it blocking thesupply and preventing oscillation,while connecting it the other wayround produces conduction andan audio output tone from theunit. The device is open circuit ifoscillation cannot be obtained, orclosed circuit if both methods ofconnection produce oscillation.

If S1 is switched to the 'on'position, power will be applied tothe oscillator circuit via the base - Internal view of Continuity Tester.

26 MARCH 1981 E&MM

ELECTRONICS

emitter junction of Trl. However,the circuit will not oscillate as thecurrent flowing in the base -emitter circuit of Trl switchesthis device hard on. It thereforeobstructs the feedback, and alsofeeds a small D.C. potential to theinput of ICI so that it is not biasedcorrectly. DI now operates as anon/off indicator and helps toprevent the unit being inadver-tently left switched on.

If the test probes are shortcircuited, Trl becomes switchedoff by the short circuit across itsbase -emitter terminals, and theoscillator is able to function nor-mally. A certain amount of re-sistance across the test probes isalso sufficient to switch off Trland produce oscillation. A for-ward biased silicon junction willgive a voltage of between about0.5 volts and 0.7 volts (dependingupon the exact type) across thebase -emitter terminals of Trl. AsTrl is a high gain device, even thelower figure is sufficient to main-tain the device in a state ofconduction and block the oscil-lator. Thus the unit will not re-spond to forward biased siliconjunctions.

Germanium semiconductorjunctions have a lower forwardvoltage drop than silicon types, soa forward biased germaniumjunction connected across thetest probes will switch off Trl andgive an audio tone from the unit.This is not too mportant as mostgermanium devices are nowobsolete and little used, butTrl can be replaced by a ger-manium p.n.p. device (0072,0081, 0081D, AC128, etc.) if it islikely that the unit will be used totest equipment employing ger-manium devices.

The current consumption ofthe circuit is only about 10 to15mA, and this is provided by asmall (PP3 size 9 volt battery.

ConstructionA plastic box measuring about

114 x 76 x 38mm (type PB1)makes an ideal housing for theunit. A speaker grille must bemade in the left hand side of thefront panel, and this can merelyconsist of a pattern of holes about4mm. in diameter. D1, SK1, andSK2 are mounted in a vertical linedown the right hand side of thepanel, and S1 is fitted on the righthand side of the case. Thespeaker can then be fitted inplace, using epoxy -type glue asthere is no provision for screwfixing on miniature speakers. Fitthe loudspeaker in a positionleaving sufficient space for thePP3 battery to fit next to it.

The other components are fit-ted onto a small printed circuitboard which is detailed in Fig. 2,and construction of this is quite

S1off

on

B1

SK2

SK1

T RI

R4

E=1 -i

L

0-, -1-

TTR

0 R2 IC1

0 R3

E&MM

CONTINUITYTESTERGA 11M

V

jr°I 00 uNLs 1L L9WN MCA'2 3

LS1

Figure 2. Continuity Tester PCB & Wiring

PARTS LIST Semiconductors SK2 Black 4mm socket (HF69A)

Resistors - all 5% 16 W carbonRI 33k (M33K)R2 2k7 (M2K7)R3 5k6 (M5K6)R4 1k8 (M1K8)

IC1 LM380TR1 BC179DI TIL220 (0.2 in. red LED)

MiscellaneousSi Ultra -miniature SPST toggle

(QH40T)(QB54J)(WL27E)

BITest probe pairPP3 batteryPP3 connectorPrinted circuit boardLED CoverCase P81

(HF33L)

(HF28F)(GAI 1M)(YH54J)(LF01B)

Capacitors switch (FH97F) (or similar)CI lOnF mylar (WW1.8U) LS1 Loudspeaker 66mm diameter Insulated hookup wire (BLOOA)C2 luF 63V electrolytic (FB12N) 64R impedance (WF57M) 6 BA 1/2" bolts (BFO6G)C3 100uF 104 electrolytic (FB48C) SK1 Red 4mm socket (HF73Q) 6 BA nuts (BF18U)

straight forward. The completedboard is wired to the rest of theunit before being mounted in thecase, and Fig. 2 also shows thiswiring. 6BA or M3 fixings are usedto mount the board on the rearpanel of the case so that it fits inthe space to the right of thespeaker and battery. The printedcircuit board can be used as atemplate when marking the posi-tions of the two 3.3mm diametermounting holes in the rear panel.

After giving all the wiring acouple of thorough final checks,the unit is then ready for testingand use. E&MM

E&MM MARCH 1981 27

CA(

Super 6£162.00 plus VAT

Super 10£219.00 plus VAT

The professional scopeyou've always needed.

When it comes to oscilloscopes, you'llhave to go a long way to equal thereliability and performance of Calscope.

Calscope set new standards in theirproducts, as you'll discover when youcompare specification and price againstthe competition.

The Calscope Super 10, dual trace 10MHz has probably the highest standardanywhere for a low cost general purposeoscilloscope. A 3% accuracy is obtainedby the use of stabilised power supplieswhich cope with mains fluctuations.The price £219 plus VAT.

The Super 6 is a portable 6MHz singlebeam model with easy to use controls

and has a time base range of lus to100ms/cm with 1 0mV sensitivity. Price£162 plus VAT.

Calscopes are available from:Aitken Brothers Watford Electronics35 High Bridge 33/35 Cardiff RoadNewcastle upon Tyne WatfordNE1 13W HertsTel: (0632) 26729 Tel.: Watford 40588/9

Maplin Electronics Supplies LtdPO. Box 3Rayleigh, EssexTel.: 0702 715155(Mail Order) CALSCOPE

28 MARCH 1981 E&MM

TRANSCENDENT 2000 SINGLE BOARD SYNTHESISERDesigned by consultant Tim Orr (formerly synthesiser designer for EMS Ltd.) andfeatured as a constructional article in ETI, this live performance synthesiser is a 3octave instrument transposable 2 octaves up or down giving sweep control, a noisegenerator and an ADSR envelope shaper. There is also a slow oscillator, a new pitchdetector, ADSR repeat, sample and hold, and special circuitry with precisioncomponents to ensure tuning stability amongst its many features.The kit includes fully finished metalwork, fully assembled solid teak cabinet, filtersweep pedal, professional quality components (all resistors either 2% metal oxide ort/2% metal film), and it really is complete - right down to the last nut and bolt and lastpiece of wire! There is even a 13A plug in the kit - you need buy absolutely no moreparts before plugging in and making great music! Virtually all the components are onthe one professional quality fibreglass PCB printed with component locations. Allthe controls mount directly on the main board, all connections to the board are madewith connector plugs and construction is so simple it can be built in a few eveningsby almost anyone capable of neat soldering! When finished you will possess asynthesiser comparable in performance and quality with ready -built units selling formany times the price.Comprehensive handbook supplied with all complete kits! This fully describesconstruction and tells you how to set up your synthesiser with nothing moreelaborate than a multi -meter and a pair of ears!

COMPLETE KIT ONLY f168.50 + VAT!

TRANSCENDENT 2000 P1"1111

Cabinet size 24.6" x 15.7" x 4.8" (rear) 3.4" (front)

1024 NOTE SEQUENCER/COMPOSER - see our advert on Page 56

- _Ell VOCODERPONSTRA,

t x z

ETI VOCODERCOMPLETE KIT ONLY f195 + VAT!

Panel size 19.0" x 5.25". Depth 12.2"

Featured as a construction article in Electronics Today International this design enables a vocoder of great versatility and high intelligibility to be built for anamazingly low price. 14 channels are used to achieve its high intelligibility, each channel having its own level control. There are two input amplifiers, one forspeech either from microphone or a high level source e.g. mixer or cassette deck and one for external excitation (the substitution signal) from either high or lowlevel sources. Each amplifier has its own level control and a rather special type of tone control giving varying degrees of bass boost with treble cut or treble boostwith bass cut. The level of the speech and excitation signals are monitored by LED PPM meters with 10 lights -7 green and 3 red which indicate the level at 3dBsteps. There are three internal sources of excitation -a noise generator and two pulse generators of variable frequency and pulse width. Any of the internalsources and the external source can be mixed together. There is a voiced/unvoiced detector which substitutes noise for the excitation signal at the points inspeech where the vocal chord derived sounds of the speaker are substituted for by the unvoiced sounds of sibilants, etc. There is a slew rate control whichsmooths out the changes in spectral balance and amplitude enabling a change of the speech into singing or chanting and other special effects. A foot switch isprovided to permit a complete freeze in spectral balance and amplitude whenever required. An LED on this indicates when the freeze is in operation.An output mixer allows mixing of the speech, external excitation and vocoder output. The majority of the components fit into the large analysis/synthesis boardwith the rest on 8 much smaller boards with the controls and sockets mounted on them for ease of construction. Connectors are used for the small amount ofwiring between the boards.The kit includes fully finished metalwork, professional quality components (all resistors 2% metal oxide), nuts, bolts, etc. - even a 13A plug!

TRANSCENDENT DPX MULTI VOICE SYNTHESISER

Another superb design bysynthesiser expert Tim Orr

published inElectronics Today International

COMPLETE KITONLY

f299 + VAT!

Cabinet size 36.3" x 15.0" x 5.0" (rear) 3.3" (front)

The Transcendent DPX is a really versatile 5 octave keyboard instrument. These are two audio outputs which can be used simultaneously. On the first there is abeautiful harpsichord or reed sound - fully polyphonic, i.e. you can play chords with as many notes as you like. On the second output there is a wide range ofdifferent voices, still fully polyphonic. It can be a straightforward piano as a honky tonk piano or even a mixture of the two! Alternatively youcan play strings overthe whole range of the keyboard or brass over the whole range of the keyboard or should you prefer -strings on the top of the keyboard and brass as the lower end(the keyboard is electronically split after the first two octaves) or vice -versa or even a combination of strings and brass sounds simultaneously. And on all voicesyou can switch in circuitry to make the keyboard touch sensitive! The harder you press down a key the louder it sounds-just like an acoustic piano. The digitallycontrolled multiplexed system makes practical touch sensitivity with the complex dynamics law necessary for a high degree of realism. There is a master volumeand tone control, a separate control for the brass sounds and also a vibrato circuit with variable depth control together with a variable delay control so that thevibrator comes in only after waiting a short time after the note is struck for even more realistic string sounds.To add interest to the sounds and make them more natural there is a chorus/ensemble unit which is a complex phasing system using CCD (chargecoupled device)analogue delay lines. The overall effect of this is similar to that of several acoustic instruments playing the same piece of music. The ensemble circuitry can beswitched in with either strong or mid effects. As the system is based on digital circuitry digital data can be easily taken to and from a computer (for storing andplaying back accompaniments with or without pitch or key change, computer composing, etc., etc.).Although the DPX is an advanced design using a very large amount of circuitry, much of it very sophisticated, the kit is mechanically extremely simple withexcellent access to all the circuit boards which interconnect with multiway connectors, just four of which are removed to separate the keyboard circuitry and thepanel circuitry from the main circuitry in the cabinet.The kit includes fully finished metalwork, solid teak cabinet, professional quality components (all resistors 2% metal oxide), nuts, bolts, etc., even a 13A plug!

POWERTRAN MANY MORE KITS ON PAGE 56 - MORE KITS ANDORDERING INFORMATION ON PAGE 4

All projects on this page can be purchased as separate packs, e.g. PCBs, componentssets, hardware sets, etc. See our free catalogue for full details and prices.

E&MM MARCH 1981 29

ELECTRONICS

SUBIMSSWOOFERby Jeff Macaulay

Add full deep Hi-Fi bass down to27 Hertz to your stereo system

This woofer system is designed to be used in conjunction withexisting speakers to extend the bass response, but at the sametime is capable of being integrated into a full scale active speaker

system.For maximum flexibility the woofer is fed from the output terminals

of the power amplifier used in the existing system. A variable cut -oft2nd order Butterworth filter is employed so that the woofer can berolled on to complement the bass roll -off of the existing speakersystem.

Before discussing the woofer in more detail it is instructive toconsider the deficiencies of most speaker systems when it comes toreproducing deep bass, where an important constraint is themaximum perm issable size of the enclosure. It is well known that theinfinite baffle enclosure rolls off at 12dB/octave below the bass unit'sresonant frequency. This situation can be improved to some extent bymaking the enclosure more inefficient, but then a high power amplifieris required to reproduce good bass. Another problem facing designersis that the bass unit is usually intended to reproduce the midrange aswell. It is clearly advantageous to roll off the bass at some reasonablepoint to avoid intermodulation distortion which would occur due to thelarge cone excursions that are required. Interestingly the requiredoutput at 30Hz is some 8dB less than is required in the midrange. Thepeak power in music and speech signals occur at around 150 Hz.

Of all the possible forms that a woofer can take the most simple andeffective method is to employ a bass reflex system. By suitable choiceof drive unit a fairly compact, and hence domestically acceptableenclosure can be built that will respond down to 30Hz withoutproblems. I write from experience of two such systems, one of whichhas been working in my own lounge for over a year, where the bass isoften felt as well as heard. Even at high volume levels there is noapparent distortion and efficiency is also very high.

30Hz seems to be the optimum value at which to fix the lower -3dBpoint. Any lower and the cabinet begins to assume massiveproportions. Moreover the dimensions of the average domesticlistening room limits the lowest frequency that can be reproduced toaround 30Hz. Going this far down will usually add another octave to theresponse in any case. The output power at this low frequency dependson the available cone excursion. At 30Hz the port is radiating sound aswell as the speaker and this effectively doubles the area of the cone.When the relevant calculations have been made the output soundpressure level (SPL) is found to be 90dB at 1 metre. Put another way, ifthe main system is producing 96dB the bass unit will still have plenty ofheadroom. In fact these output figures are average - the bass speakeris capable of handling larger peaks.

The electronics required consist of an amplifier and a variableactive filter system, designed to roll off between 50-100Hz adjustableby means of a potentiometer. The filter and power amp are installedinside the speaker cabinet, with the controls externally accessable.

The size of the cabinet is closely related to the characteristics of thedrive unit employed. After some research the most suitable unit wasfound to be the Kef 8200, requiring an amplifier power of only 20 wattsRMS in this application. This unit has a free air resonance at 25Hz andwhen mounted in a sealed undamped enclosure of 2.4 cu.ft. this risesto 45Hz. From this information the acoustic volume (ie. the cabinetvolume which enables the response to extend to 25Hz at -3dB whenreflexed) can be calculated.

Vas = V

\

f\ 0 /

2

-1

Where f, = free air resonant frequency, fc = resonant frequency incabinet, V = volume of cabinet. This gives a value for Vas of 5.38 cu.ft.By rearranging the formula for V the cabinet volume can bedetermined for any chosen value of fc. In order to maintain a smoothresponse to 30Hz the resonant frequency must be 42Hz ( 2 x 30Hz).For the B200 the volume is 3.4 cu.ft. This is a little large to be accom-modated in the average lounge and so experiments were undertaken tolower the resonant frequency. The easiest way is to add a small amountof extra mass to the cone itself. This was conveniently done by addingtwo 34" sq. pieces of bitumised felt panels to the cone, spaced equallyon opposite sides of the centre. Suitable material is readily available asself adhesive car damping panels. This lowered f. from 25Hz to 21Hzand, more importantly, allows a 2.4cu.ft. cabinet to be used for a fc of40Hz. By the time damping has been added to the enclosure it can bereflexed down to 27Hz.

Having actually determined the required enclosure size attentioncan now be turned to its mechanical details. Because the highestfrequency to be handled is 100Hz the cabinet will be acousticallysmall. What this means is that air resonances inside the cabinet cannotoccur because the dimensions are small compared with wavelength ofthe sound being emanated. The wavelength of a given frequency canbe found simply by dividing the speed of sound, 344ms-1, by the

30 MARCH 1981 E&MM

ELECTRONICS

00

z

00cc

0

z

'ThEN-Y-V-Y1 °

0

CON

OD I- CC

CC >(.) I- CC

cc

CO CO

CC 1- F-

O 00

CO N.CC Cs,

N CC

CC

°D

0 1- 11--s=

00

r-+Tr °

cocc

cc

F-

10F -

0+UO

EllLL

r->CC '1

OOD

La=

TR1,3 BC 109TR2 BC 107B

TR 4, 5 BC 142TR6 BC 143

PARTS LISTResistors - all 5% carbon unless specifiedR1,2 820R 2 off (M820R)R3,4 100k 2off (M100K)R5,6,9 22k 3 off (M22K)R7 4k7 (M4k7)R8 27k (M27K)RIO 1M8 (MIM8)R11 120k (M120k)R12,131k8 2off (M1k8)RV1 4k7 log. pot. (FW21X)RV2 22k lin. dual gang pot. (FW86T)RV3 2k2 carbon preset (WR82D)

CapacitorsC1,5,6 10uF 25V electrolyticC2 100nF polyesterC3 47nF polyesterC4 100uF 25V electrolyticC7 2,200uF 63V electrolyticC8 4,700uF 63V electrolytic

SemiconductorsTR1,3 BC109TR2 BC107BTR4,5 BC142TR6 BC143TR7,8 2N3055REC1 S005

MiscellaneousT1 Transformer 240V prim.

0-28, 0-28 sec. 84VALS1 Kef B200 SP1014FS1 Fuse, 20mm IA Quick Blow

Chassis fuseholder, 20mmSI Toggle switch, DPDTPLI P429 3 -pin chassis plug

P646 3 -pin line socket4 -way push -type connectorT03 Mounting kitsHeatsink, 2.1° C/WControl knobsAcoustic waddingMains cable, 3AConnecting wireCapacitor clip to suit C7Capacitor clip to suit C8Printed Circuit Board

3 off (FB22Y)(BX76H)(BX74R)(FB49D)(FF22Y)(FF28F)

2 off (Q833L)(QB31J)

2 off (QB39N)(QB40T)

2 off (BL45Y)(Q109K)

(WB17T)

(WRO3D)(RX49D)(FH39N)(HL2OW)( IL44X)(BW71N)

2 off (WR24B)(FL54J)

2 off (RX08J)1 m (RY06G)3 m (XROOA)3 m (XR37S)

(FL33L)(FF35Q)(GA08J)

The KEF B200 SP1014 drive unit is available from:

Wilmslow Audio Ltd,35/39. Church Street,Wilmslow,Cheshire.

Price £13.50 inc. VAT + £1.00 p. & p.

E&MM MARCH 1981 31

ELECTRONICS

r

SIGNALINPUTS

R1 R2 [1111R4 R3

O R5 R60 C1

C2

TR1R80 +.1.0 4

C5

TC3

R7

00 000R9

E&MM

`rTR10 R6

R11

FROMT1

ccw

00

LL

RV1 RV2a

LS1

IC7 -1t16@- + C8

TR8 TR7

Figure 2. The Woofer PCB.

frequency. Thus the wavelength of a 100Hz tone is some 3.44m and a30Hz tone has a wavelength of 344/30 = 11.45 metres. Theresonances that plague normal speaker systems occur when one of theinternal dimensions is equal to or a multiple of the wavelength of areproduced signal. Since the largest internal dimension of our cabinetis 0.53m these resonances will be avoided. Another consequence ofthe smallness of the cabinet is that the polar diagram is totallysymmetrical across the working range. In other words the speaker isomnidirectional. However, the wavelength of the sounds emanatingfrom the enclosure have practical consequences for the positioning ofthe unit in the listening room.

The lowest note that can be sustained in a room is a function of itsmaximum dimension. The lowest note, in fact, that can be reproducedis found from the relationship, F = 344/2L where L is the longest roomdimension in metres. Different dimensions will cause peaks and dipsin the response, but of course this will happen whatever form thewoofer may take and occurs naturally even in large halls. It does have abearing on the siting of the enclosure which must be chosen for bestresults by empirical methods.

CircuitFigure 1 shows the complete circuit of the sub -bass woofer

electronics. For descriptive purposes it can be divided into threesections; mixer, filter and power amplifier.

R1, R2 and RV1 form a passive mixer and gain control. The signalsfrom the speaker sockets of the amplifier are fed into the 'top' of R1 andR2. The signal from the wiper of VR1 is fed via the DC blockingcapacitor Cl into the filter built around TR1. The values of thecomponents are such that a 2nd order Butterworth response isobtained with maximum slope and minimum ripple in the pass band.RV2 allows the cut-off frequency of the filter to be varied from

50-100Hz to suit the bass roll -off of the existing pair of speakers.The active element of the filter, TR1, is configured in the emitter

follower mode. This produces a low impedance drive for the poweramplifier, which is a little unusual in that the circuit is of the shuntfeedback type. The reason for its adoption here is that it is easyto buildand unconditionally stable. The 2N3055's on the output are more thancapable of delivering the 4mV/us slew rate required fora bandwidth of100Hz! The output power of the amplifier is 20W RMS and unlike themajority of current designs the output is capacitatively coupled to thespeaker. This has the advantage that if a breakdown were to occur inthe amp then the speaker will be protected from DC current. The valueof C7 is such that the response is 3dB down at 10Hz.

ConstructionThe printed circuit board should be assembled following the

component overlay, in usual order of resistors first, then capacitors,followed by the semiconductors. The pins for the off -board wiring canbe soldered in at this stage, but the wiring should be left until after thecabinet is completed. Check the orientation of the electrolyticcapacitors and semiconductors, and make sure there are no tracksshorted by solder bridges. Drill holes in the cabinet back for the push -connector, volume and cut-off frequency pots, on -off switch, andmains chassis plug. Fit these components. Mount the transformer andfuseholder using woodscrews and then the two capacitors C7 and C8using clips and screws. Drill the heatsink to take the T03 powertransistors, and mount them using mica washers etc. Mark fixingpositions for the PCB and heatsink, and then wire up all the off -boardcomponents. This is best done by soldering wires of the right length tothe veropins on the PCB before mounting it, then connecting the mainsand output components. Finally mount the heatsink and PCB, andsolder the wires from the latter in place.

32 MARCH 1981 E&MM

ELECTRONICS

IleO0 0

LIO 41/4sa .

OUTSIDE 0

...-

Figure 3. Woofer cabinet construction.

Cabinet ConstructionThere are several possible materials that could be employed for the

cabinet. Domestic considerations, and the desire for a ready madefinish dictated the use of veneered chipboard. Melamine teak boardhas an added advantage of being denser material than either the whiteor wood veneered board. These facts led to its adoption for this project.The internal volume of 2.4 cu.ft. and the desire to keep thewoodworking simple determined the dimensions at 22'/2" x 15" x 15"external. This means that the cabinet, excluding battens, can befabricated entirely from 15" boards. If the wood is cut to size at thetimber yard the only tools required will be an electric drill and jigsawattachment.

Assembly is straightforward and should proceed as follows:

1) Label each panel with its respective part letter on the worst face.This saves any possible confusion as work proceeds.

2) Cut the battens H, J, K, M and N to size and mark as in 1).3) Mark out the positions of the battens on the panels with a felt tip

pen. This is about the only thing that will mark the surface of theboards without smudging.

4) Glue the battens into their respective positions. The best glue touse with this material is 'Thixofix'. This adhesive is often employedfor fixing table tops. It is a contact adhesive having the advantagethat the glued surfaces can be moved relative to one anotherbefore they are permanently joined. A permanent joint is made bysimply pressing the parts together.

5) Having fixed the battens with adhesive secure more permanentlywith 3/4" panel pins. Use four for each batten.

6) Using the B200 template mark out the position of the four fixingscrews on the front panel. Remove the central area of the templateand mark the inner circle. Remove the template and drill out themounting holes.

7) Mark out the 43/4" square cut-out for the port. At this point it isadvisable to drill four 3/8" holes near the corners of the port cut-outto facilitate the use of the jigsaw.

8) Take part C and glue it into position on the baffle.9) Cut out the front baffle apertures. The baffle can be painted matt

black at this stage. Blackboard paint is suitable.10) Take parts D and E and glue and pin togetherto form a square tube

as shown in detail two.11) Insert the port just constructed into the aperture on the front

front baffle. If there are any gaps between the port and front panelit should be filled from the rear of the baffle. The port must bemounted so that the end is flush with the front of the baffle.

12) Take the side, bottom and top panels (A and B) and the front baffle,apply adhesive to all surfaces that will butt together, and leave for15 minutes.

CUTTING LIST

Quantity

2

Dimensions(inches)

15 x 15 x 5/8

Material

Veneered Chip

Part

2 221/4 x 15 x % Veneered Chip B

1 15 x 7 x % Veneered Chip C

2 11x3x5/8 Veneered Chip D

2 11 x 41/4 x 5/8 Veneered Chip E

2 21 x 15 x 5/8 Veneered Chip G

2 20 x 2 x 1 Soft Pine H

4 10% x 7/8 x % Hardwood J

4 21 x 7/8 x % Hardwood K

2 13 x 2 x 1 Soft Pine L

1 13 x 2 x 1 Soft Pine M

4 15 x 7/8 x 3/8 Hardwood N

13) Assemble the cabinet except the back panel, using screws inaddition to the glue to fix the front panel to its supporting battens.Check that the back panel will fit tightly in position.

14) Glue and screw the battens (L) onto the back panel (G).15) Add the felt panels to the KEF B200's cone as previously

described, then attach the drive unit to the front baffle using thebolts and T nuts provided.

16) Install the electronics. Stretch a 12" square piece of acousticwadding across the back of the drive unit and fix it with a dab ofglue in each corner.

17) After the setting -up stage, roll up 2 metres of wadding and place itin the cabinet (the position is not critical) then screw the back on.

Setting Up and UseThe quiescent current of the

output pair must be set to elimi-nate crossover distortion. Beforeapplying power turn RV3 to itsmost clockwise end and cover themains terminals of the trans-former switch, and fuse withinsulating tape. Apply power andif all seems well measure thevoltage at the positive terminal ofthe output capacitor C7. Thisshould be 20V ± 2V. Switch off anddisconnect the wire to the collec-tor of TR7. Insert a multi meter toread current and switch on again.The current should be 10mA.Adjust RV3 until it reaches 30mA.Reconnect TR7. Remove the tapefrom the mains terminals andscrew on the back of the cabinet.

Play some programme mater-ial with a good bass content.Experimentally adjust the volumecontrol on the bass unit for whatyou judge to be the correct level.At this point it is as well to go andsit in the stereo seat and listencarefully. Often further adjust-ment will be required since thelevel of bass heard depends onone's listening position. The filteris best set with a voice signal.

Radio 4 is a good source ofassorted voice signals. Start ad-justing from the 100Hz (clock-wise) end downward. Speech willprobably sound a trite boomy butas you adjust a point will be foundwhere the voice sounds naturaland well balanced. Play somemusic, preferably a piece that youknow well with a reasonable basscontent. In all probability it willtake some time to find the opti-mum position for the controls.However, even before that youshould find that your enjoymentof all signals will be enhanced. Itshould go without saying thatthese adjustments should bemade with the tone controls in theflat position, or better switchedout.

It is most important that thewoofer be sited with care. Al-though no stereo information isbroadcast below 100Hz it is im-portant not to disturb the stereoimage. If you sit too near thewoofer the sound is likely to sufferbecause of the Haas effect (if twoindependent speakers are repro-ducing the same signal it willappear to come from the nearersource).

E&MM

33E&MM MARCH 1981

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34 MARCH 1981 E&MM

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AUTO SHUT OFF

RON ICA

off

1133 CI

to Dec 2009). Memory bank stores up to 11dates, displays 'MEMO' and flashes ondesignated dates. Display flashes as batterylife nears end. Back light. Water resistant.Adjustable stainless steel strap.

GENTS MULTI MELODY ALARMCHRONOGRAPH only £14.95 +85p p&p with free Slimline Credit CardCalculator (usual price £7.95).Just look at the points the above watch offers.Constant display of hours, minutes, seconds,weekday, date and month, with mode andchime indication display. Six independentworking modes:(1) Normal watch(2) Musical alarm playing "Oh Suzzana"

LC -333

In MI

11= 1131 113 11:11

11= 1131 1E1 MI

IN 1E1 OKI

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35

ELECTRONICS

Coactirr MAKEROne of the nice features about a magazine such as this is the way

readers can contribute, thus presenting their ideas to a large numberof people. Each contribution may be a full feature or constructionalarticle describing some piece of electronic, electro-musical

Circuit maker will be an informalarea of the magazine where the bestsubmissions each month will be pub-lished. No set theme is intended, andall ideas will be treated equally. Natu-rally, if the idea is good enough it mayform the basisof a full article written byyourself or one of our main contri-butors. The ideas submitted need notbe circuits -general tipstosave moneyor make life easier will also beconsidered.

It may often be hard for you todecide if your idea is worthy of possiblepublication. The simple answer is toread the notes that follow and try it. It isimportant to have a go since manygood ideas are missed, purely be-cause the designer th inksthatthe ideais of no interest. For those people whohave ideas and would li ke to contributehere are some notes to assist you inmaking up your submission.

The main problem with a 'new' ideais that it might not be new. If thecircu ithas been published before it is notoriginal, and generally cannot bepublished again, even by a differentmagazine. It is very hard to define themeaning of 'original' in this case, andmuch of the meaning depends on thecircumstances. In general, a circuittechnique is original if it has not beenpublished before, otherwise an ack-nowledgement should be made even ifit is only '... the standard 741 cir-cuit...' A good example of where thisoccurs is in the active filter. It uses theSallen and Key configuration of re-sistors and capacitors to give a But-terworth type of roll off. The quote 'Idesigned this active filter for a 12 dBroll off after 10kHz' is a bit much, but'I designed a Sallen and Key 2nd orderButterworth filter using a 741' is quiteall right.

Improvements to previously pub-lished circuits are useful, and very

equipment, or more probably, a short piece containing the circuitdiagram and a short piece of explanatory text. It is thus our intentionto set aside pages in each issue for 'Circuit Maker', a feature dedicatedto short ideas, mostly sent in by readers.

10kHz Filter: not wildly original!

1k

(a) Naughty! Gate will fail.

+5V

S.(b) Correct method

1k

relevant, but the source of the originalidea must be clearly stated.

So, the idea seems to be original.Obviously the prototype works, but is asecond version using a different batchof components certain to work as well?To be suitable for publication everycorrectly built version of the circuitshould work. Designs to be wary ofcontain transistors biased withoutfeedback, bipolar op -amps with veryhigh value resistors around them anddevices used near their rated maxi-

mum. Different manufacturers usedifferent specs, and so any designmust be based around the lowestspecifications available. Circuitbodges which work 'but we don't knowwhy' must be avoided at all costs, aswell as designs that work, but overloadthe device. For example, a TTL gatedriving an LED. In (a) the gate stands areal chance of failing since mostgateswill only source uAmps rather than themAmps required for the LED. It doeswork fora time but the gate will not like

it. The technique in (b) is fine becausethe gate will sink typically 10 mAmpswithout any trouble.

Having established that the designis original and practical it is worthsending in. How should it be pre-sented? Firstly, and most importantly,the presentation should be neat andlegible so that we can read it. Enve-lopes and cigarette packets are out!Text (typed and double spaced) anddiagrams should be on separatesheets, preferably A4 size and clippedtogether rather than stapled. Naturallyall the text and drawings should benumbered, the drawing numbers cor-responding to the text. The length ofthe text depends on the complexity ofthe idea, but 50-300 words shouldsuffice.

The drawings must be clear, pre-ferably done with black ink on whitepaper; a black ball pen is suitable andcheap. It is worth buying an elec-tronics stencil for drawing from a goodoffice supply shop, and with the aid ofthis and a ruler clear drawings areeasy to do. As a rule inputs should beon the left, outputs on the right, withthe drawing going from top to bottom.Number all IC pins, including thepower pins and check that all com-ponent types and values are indicatedwhere relevant.

Prepare a declaration sheet statingthe parts that are original and indi-cating those that are not. Also statethat the ci rcuit has not been submittedto any other magazine, and will not beso unless rejected by us. Sign thisdeclaration. Finally, photocopy all thesheets (it is not unknown for things toget lost in the post) and send itoff to oureditorial address, with the envelopeclearly marked 'Circuit Maker'. Youwill hear fairly quickly after the sub-mission reaches us.Chris Lare

Disco Cue LightTerry Barnaby, S. Glamorgan

Nearly all disco DJ's use head-phones to cue up the next record, but,for the majority of records, a simpleLED will suffice. The LED driver circuitis connected to the top of each deckfader, or to the original cue output,thus obtaining a signal irrespective ofthe fader position. Provided that theLED driver has the right attack time(sufficient to miss clicks andscratches) and a long delay time (tomake the indication clear) cueing be-comes very easy. Naturally this sys-tem will not work if the record startsvery quietly when headphones mustbe used.

The circuit is very simple. A high

gain op -amp charges the 10uF capa-citor via a diode and 330R resistor(which sets the attack time) when thesignal exceeds the 80 mV threshold.

INPUT 33nFFROM 0_11TOP OFFADER

220k

The voltage on the capacitor switcheson the transistor, and hence the LED,the decay time being determined bythe base current of the transistor.Under certain circumstances recordrumble may trigger the LED and so ahigh pass filter preceeds the circuit.

+15V

+15V

330R 1N4148 56k

1k

LED

BC184L

36 MARCH 1981 E&MM

ELECTRONICS

+15V

56k

18k

18k

16k

56k

+15V

SEIMENSK16410k

+15V

5

2k2

OV

+15V

INPUT 2k2TOAMP

REED SWITCHNORMALLY OPEN

REED RELAY 1k OR GREATERSHORTS INPUT SIGNALWHEN CLOSED

+15V

ti

+15V

1k

titi

+15V

1k

ti

IC IS LM 339

Over TemperatureIndicator and Cutout

Some items of equipment, parti-cularly amplifiers, are prone to over-heat if the heatsinks are covered orthe air flow is somehow obstructed.The temperature rise continues untilthe equipment fails, usually expen-sively. A method of automatic shut-down is desirable, but at the sametime warning of over temperature isneeded since a sudden uncontrolledshutdown in a disco is awkward to saythe least.

This simple circuit uses a ther-mistor to sense the temperature, and aquad comparator to drive three LEDsand a reed relay. The thermistor andresistor develop a temperature de-pendent voltage which is fed to eachstage of the comparator, where it iscompared with reference voltagesgenerated by the resistor chain. Thecomparator outputs are normallyhigh, thus the LEDs are off until therelevant threshold voltage is reached.The fourth comparator feeds a smallreed relay which is used to short outthe signal input to the amplifier whenfinally triggered. The sensitivity of thecircuit may be altered by adjustmentof the resistor chain (here set to 50°Crange), and the lower point set byaltering the 2k2 in series with thethermistor. A fourth LED could beadded to indicate operation at lowtemperatures, by connection with a1 k0 series resistor between the powerrails.

Cheap Third HandPhilip Watkins, Gwent

Soldering wires to plugs andsockets can be a real nuisance. Atthe rate of one hand for solderingiron, one hand for solder, one hand. ..Obviously it helps if the wire is fast-ened to the plug first by passing itthrough the terminal holes and bend-ing it back, but the plug and wire stillmove all over the place as soon as thesoldering iron is applied. A cheapanswer to this problem is a cablespring for a domestic iron, sold to liftthe iron cable up and stop it rubbingagainst the ironing board. These canbe purchased at any good hardwareshop. These springs come completewith a table clamp and a plastic clip -which just happens to fit jack plugsetc. The plug is put in the plastic clip,which holds the plug and wire veryfirmly.

PL44lle COP WIRE

CLAMP gCREW

Multiple SpeedOscillator

There are many non critical appli-cations where a logic -controlledmultiple speed clock oscillator is re-quired. The usual way of doing this isto provide a free running oscillator foreach desired clock speed and thengate them, or physically stop theoscillators not required. The alter-native here uses only one oscillatorblock; the speed is changed by switch-ing in extra capacitors.

OUT

1. BASIC OSCILLATOR.

The circuit is based around thestandard Schmitt triggeroscillator (1).The capacitor alternately charges anddischarges through the resistor, thusproducing a square wave output. Theaddition of two diodes does not nor-mally affect the operation, but if eitherone of these diodes is disconnectedthe oscillator stops, and this is the way

2. WITH DIODES.

the multiple speed version works (2).The capacitor corresponding to thefastest speed is permanently con-nected, but the other two are onlyconnected via one diode. The otherdiode is taken to the external controlsignal. When this signal is low thecapacitor will affect the oscillatorspeed (making it slower) but when it is

OUTSLOW

MEDIUM

high (or floating) the capacitor iseffectively disconnected. Using thevalues shown speeds of 11kHz, 4kHzand 1k Hz approx. were obtained (3).

10k

ALL DIODES1N 414 8

3. GATED SPEEDOSCILLATOR.

E&MM MARCH 1981 37

ELECTRONICS

BALANCED LINESYSTEMby Chris Lare

This interface system was ori-ginally designed to connecttwo high impedance micro-

phones to a tape recorder with ahigh impedance input, with a longcable run between them. Thesystem has been tried with up to25 metres of cable and littledegradation of the signal wasnoted, even in a very hostileenvironment next to a major thy-ristor lighting installation. Thesystem consists of two parts; astereo line driver and a stereoreceiver. They are connected by astandard 5 -pin DIN plug lead,which is very convenient. A slightpenalty is paid for this conven-ience since the interchannelcrosstalk is degraded, but notnoticeably so. In the ideal situa-tion separate line drivers andreceivers should be used for eachchannel, and with independentconnecting leads.

The UnbalancedLine

The unbalanced line is theusual method of connectingaudio equipment (Figure la). Theaudio signal is carried by thecentre core, contained within ascreen formed by the return pathwhich will always be the 'earthy'side of the transmission. Thescreen helps reduce inductiveCouplings of external noise (hum,RFI etc.) to the core, but it's effectis only limited, and over a longcable run the noise picked up willbe of a high level. The amount ofpick-up can be reduced by run-ning the core from a low im-pedance source into a fairly lowimpedance termination. A typicaltermination impedance would be600 ohms, although 200 ohmswill sometimes be found. Low im-pedance driving has a furtheradvantage in that treble loss dueto cable capacitance is muchreduced, as is shock noise whichoccurs as the cable is moved.

The Balanced LineThe balanced line overcomes

all of the problems mentionedabove, but the main disadvantageis that two signal cores are re-quired as well as the screen. Thisnaturally makes the cable andconnectors much more expen-

sive. Figure lb shows the generalidea of such a line. One corecarries the signal as in the un-balanced case, and the other corecarries an inverted version of thesignal. The screen is connected toground, but in this case does notact as a signal return path. At thetermination the difference of thetwo signals is taken as the finaloutput, thus the output is identi-cal to the inputs, although a gainof two will be noted. However, anynoise induced into the system willbe of the same phase on bothlines, and will cancel out at thedifferential point. The rejectionratio is very high indeed, limitedonly by the common mode rejec-tion of the differential point. Theonly problem that may occur isthenoise (particularly spikes) caus-ing intermodulation distortion atthe differential point. This can beavoided with suitable high fre-quency filtering ON BOTH IN-PUTS to the differential point. Thisproblem is very small when com-pared with the overall improve-ment obtained.

Early balanced lines usedtransformers, and lines of thehighest quality still do. Figure 2illustrates the operation of a bal-anced line with transformers. Theinput signal is split into twophases by the first transformer,and travels to the second trans-former which acts as a differentialpoint. Note that the screen servesonly to earth the source (if neces-sary) and screen the cores; it doesnot carry any part of the signal.Transformers of this quality arevery expensive, and are them-selves prone to pick up hum, sountil the introduction of op -ampsbalanced lines were limited tostudio applications.

The op -amp is an ideal build-ing block for balanced lines, asshown in Figure 3, since bothphase inverters and differentialamplifiers may be easily imple-mented.

Balanced lines are never runat high impedance, and 600ohms is the norm. In some equip-

* MA*16.10. * At* * t. - * * * ** It, *. * * * `...n * " * * \,,,\\*' Lust pacentill\.\ *.\\\\ UAW

SOURCE +

CORE -SIGNAL

SOURCE

DESTINATION

SCREEN RETURN PATH

SCREEN SERVES AS SCREEN ONLY

CORE A POSITIVE PHASE SIGNAL

8 -DESTINATION

CORE R- NEGATIVE PHASE SIGNAL

(a)

(b)

Figure 1. Unbalanced and balanced systems

SOURCE

SIGNAL

EARTHYENO OFSOURCE

LINE

I SIGNAL

DESTINATION

l../ i CORE A

1 SCREEN

n1

I SIGNAL -PHASE n ICORE B

SIGNAL 0TO AMP

0

LIMN TO ENSURE EARTH CONTINUITY

Figure 2. Implementation of balanced line using transformers

Figure 3. Implementation of balanced line using operational amplifiers

MARCH 1981 E&MM38

ELECTRONICS

ment (particularly continentalmicrophones) a 200 ohms sy-stem may be found, but as a rulethis can be plugged into a 600ohms system with little or noconsequence.

Line Driver CircuitA stereo pair of drivers was

built around a quad JFET op -amp(Figure 4) chosen mainly for itsvery low power consumption.Each pair of amplifiers forms aphase and antiphase generator.The first op -amp inverts the sig-nal and the second op -amp re -inverts the output from the firstsuch that the two outputs are ofthe same level but exactly out ofphase and can be used directly. A100R resistor is included in eachoutput as a protection againstshort circuits, and a capacitor isobviously required to block theD.C. level. The op -amps arebiased to half rail by R15 and R16which hold the non -inverting in-puts at 4.5 Volts.

A single 9 volt battery is usedto power the circuit. This isswitched by the right input jacksocket, which is stereo and has itsscreen and centre spring con-tacts connected together when amono jack is inserted.

Line ReceiverCircuit

The line receiver circuit(Figure 5) takes the out of phasesignals generated by the driverand produces a single outputfrom them. In this way the re-ceiver performs an identical func-tion to most mixer input stages.

The in phase and out of phasesignals are applied to the non -inverting and inverting inputs ofthe op -amps respectively. Theseop -amps are connected as stan-dard differential amplifiers, with again of 0.5. Thisgain losscountersthe natural effect of a balanced

I/PR

1K1

L

162

UPI

^ 0

CI

220,,F

6 C4

0 I

R2

56

1M0RI

R3

56

ICI b

Rd

566

2200E

R9

56

RBMO

RI

56

ICI c

ICI PIN4

R5

5640151006

/CI a

R6+"2 20

RIIO566

R12

566

=7.- 22 uFICI

PIN 11

100R 2267

R7 + C3II1006 226F

" 22uF

30

R13 + C5 5= I 0

R161001.

100R 22uF

614 + C622

100R 2267

4

80-

BOARD OUTLINE ICI 1.7347

SK1

( 1

( 2

3

( 4

5

SCREEN

0/P

Figure 4. Line driver circuit diagram

SKI

1

2

SCREEN .L

I/P

CI +22 uF

I C2 4.

2261

C4 +

R5I-1 I-330/7

2

5606

R2

560R

R41A10

I R6330R

ICI

IC IC;PING

&

R7

242

R151004

+ C33

luf

C5 +

122u,

RIOIMO

RB

5601/

CIS560R

RI1IMO

R133306

RI23306

ICI b

614

242

6161006

Cl +22,,F

IC2

+ C6 4

luF

PIN

ICI182

11,1

ri 0/P

Cy 61 L

61

9V

BOARD OUTLINEICI 1F353IC? L F351

Figure 5. Line receiver circuit diagram

Line Driver Line Receiver

E&MM MARCH 1981 39

ELECTRONICS

Figure 6. Line driver track layout and component overlay

line of this sort and ensures thatthe output is exactly the same asthe input (Note: the 100R outputimpedance of the driver and the560R input impedance give 660Rtotal, hence the 330R feedback isexactly correct). Due to thenature of this circuit a low impe-dance rail splitter is required, andso IC2 is connected as a voltagefollower to achieve this.

The input capacitors are notrequired if the receiver will alwaysbe connected to the driver sincethat has output capacitors, sothey may be replaced by links. Donot be tempted to miss out theoutput capacitors from the driveras well since the d.c. offsetsrequired are half the battery volt-age, and there is no guaranteethat the battery voltage will be thesame in both units, besides whichit is bad policy to leave equipmentwith a D.C. offset on its output.

ConstructionThe Line Driver and Receiver

are each constructed in a smallplastic box with the sockets fittedon the front and the printedcircuit board fixed to the remove -able back with 6BA bolts. Whenthe components have been sold-ered to the board (IC's last), wireup the sockets using screenedcable making sure that thescreens are connected at thesocket ends only, in order to avoidthe possibility of internal earthloops. Connect the earths of thesockets together and wire up thebattery connector, paying carefulattention to the stereo jack socketconnections. Note that Dinlatchsockets are specified in the partslist. Used with latching plugsthese are well suited to this appli-cation, but non -latching connec-tors could be used. As specifiedthe units can still be connected

rIOVI)

R32"I= Co'

R

R270

R4

R14

C4 aPR c"N 0

X 0C5Qcr,

R15 .11

0,

L

rFigure 7. Line receiver track layout and component overlay

LINE DRIVER PARTS LISTResistors - all 5% V3W carbonRI, 8 1MOR2-5,9-12 56kR6, 7, 13, 14 100RR15, 16 100k

CapacitorsCl, 4 220n polycarbonateC2, 3, 5-8 22uF tantalum 16V

SemiconductorsICI LF347

MiscellaneousJK1 Mono jack socketJK2 Stereo jack socket

5 -pin DIN socketCase P81(or alternative)Printed circuit boardPP3 connector

B1 PP3 batteryMiniature screenedcable6 BA' " bolts6 BA nuts1mm Veropins

by a non -latching 5 -pin DIN lead.Construction is completed byscrewing on the back of the case,with the battery held in place bya piece of foam or pneumaticpacking material. Each prototypewas finished off with rub -on let-tering followed by a coat ofvarnish and four stick -on rubberfeet.

2 off (M1M0)8 off (M56K)4 off (M100R)2 off (M100K)

LINE RECEIVER PARTS LISTResistors - all 5%'/, W carbonR1, 2, 8, 9 560RR3, 4, 10, 11 1MOR5, 6, 12, 13 330RR7, 14 2k2R15,16 100k

2 off (WW45Y) Capacitors6 off (WW72P) CI, 2, 4, 5

C3, 6(WQ29G) C7

(HF90X)(HF92A)(BW989)(LF01B)

(GAO1B)(HF28F)

(XR15R)

(BFO6G)(BF18U)(FL24B)

In Use

22uF tantalum 16V(see text)luF tantalum 35V22uF tantalum 16V

SemiconductorsIC1 LF353IC2 LF351

MiscellaneousSKI 5 -pin DIN socketJK1 Mono jack socketJK2 Stereo jack socket

Case PBI(or alternative)Printed circuit boardPP3 connector

81 PP3 batteryMiniature screenedcable6 BA 1/2" bolts6 BA nutslmm Veropins

Figure 8 indicates how theunits are used to connect a taperecorder and microphones. Sincethe system will easily manage770mV (0 dBm) it can be used toconnect pre -amps and poweramps for group or disco.

4 off4 off4 off2 off2 off

4 off

2 off

(M560R)(M IMO)(M330R)(M2K2)(M100K)

(WW72P)

(WVV60Q)(WW72P)

(WQ31J)(WQ30H)

(BW98G)(HF90X)(HF92A)(LFOIB)

(GAO2C)(HF28F)

(XRI5R)

(BFO6G)(BF18U)(FL24B)

ConclusionThis balanced line system

offers considerable advantagesover the more standard unbal-anced system. In most cases theextra cost of using balanced lineswill be more than justified.

E&M M

SHORTLEADS

0HIGH Z

MICROPHONES

IN

DRIVER

IN

RECEIVER

STANDARD SPIN DIN LEAD

ANY LENGTH

OUT

OUT

SHORTLEAD

MIC IN

TAPE DECK

MIC IN

Figure 8. Using the balanced line system for tape recording

40 MARCH 1981 E&MM

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2708 Ex Equip £2-25 TMS4030JL 300 NS 4KX1 DYNAll devices full spec. and guaranteed. Bulk enquiries welcome.

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Sound proof enclosure £25.00 + VAT

EQUIPMENT CASESGIVE

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Superb professional fully enclosed, made for theG.P.O. to the highest standard, offered at afraction of their original cost they featurealuminium sides, hinged removable front panel,which can be secured by 2 screws to preventprying fingers. All are finished in two tone G.P.O.grey and although believed brand new may haveminor scuff marks/scratches due to bad storage.Dimensions 16"D x 6'/,"H x 14 N"W

NATIONAL MA1012 LEDCLOCK MODULE

*12 HOUR* ALARM* 50/60 HZThe same module as used in most ALARM/CLOCKradios today, the only difference is our price! Allelectronics am mounted on a PCB measuring only3" x 11" and by addition of a few switches and 5/16volts AC you have a multi function alarm clock at afraction of cost. Other features include snoozetimer, am pm, alarm set, power fail indicator, flash-ing seconds cursor, modulated alarm output etc.Supplied brand new with full data onlySuitable transformer £1.75. £5.25

SEMICONDUCTOR'GRAB BAGS'

Amazing value mixed semiconductors, includetransistors, digital, linear I. C.'s, triacs. diodes, bridgemcs. etc. etc. All devices guaranteed brand new, fullspec. with manufacturers markings, fully guaranteed.

50 BAG E2.95 100 + BAGS E5.15

MUFFIN FANSKeep your equipment Cool and Reliable with our tested ex equipment"Mullin fans" almost silent running and easily mounted. Available intwo voltages. 110 V.A.C. E5.05+pp 90p OR 240v A.C. E5.15-i-pp90p DIMENSIONS 41' n 41 e 14 r.

ELECTRONICCOMPONE NTS8, EQUIPMENT 66%

DISCOUNTDue to our massive bulk purchasing programmewhich enables us to bring you the best possiblebargains, we have thousands of I. C.'s, Transistors,Relays, Cap's., P.C.B.'s, Sub -assemblies, Switches,etc. etc. surplus to our requirements. Because wedon't have sufficient stocks of any one item toinclude in our ads., we are packing all these itemsinto the "BARGAIN PARCEL OF A LIFETIME"Thousands of components at giveaway prices!Guaranteed to be worth at least 3 times what youpay plus we always include something from our ads.for unbeatable value!! Sold by weight

2.5kIs f 4.75+pp E1.25 Skis f 6.75+pp f1.8010kIs E11.75+pp f2.25 20Ids E19.99+ pp f4.75

£325 + CAR+ VAT

Made under licence from the world famous GE Co.The ICL Termiprinter is a small attractive unit withso many features it is impossible to list them in thespace available! Brief spec. as follows; RS232serial interface, switchable baud rates 110, 150,300, 130 cps), upper and lower case correspond-ence type face, standard paper, almost silent run-ning, form feed, electronic tab settings, suited forword processor applications plus many morefeatures. Supplied in good condition and in work-ing order. Limited quantity.

CONNECTDIRECT TOYOUR MICRO

Made by the "BALL MIRATEL" CORPORATION USAthe CD12 is a self contained, mains powered chassisprofessional monitor. All controls are inbuilt on asingle PCB with exception of the brightness controlwhich can be brought out for external use. Manyfeatures such as composite video, quoted bandwidthof 19 Mhz, superb linearity and definition make this amust for any MICRO/CCTV application.Brand new and boxed only E0750+ carriage E7.50 + VAT.

Input harness, brightness pot and connector £2.50+ VAT. Dimensions 9"H x 11"0 x 114'W

HURRY WHILE STOCKS LAST

OP PRESS -STOP PRESS -STOP PRESS -ST

STEP INTO THE 80'sWITH TOMORROW'S WORLD TECHNOLOGY

TODAYThe "TANTEL" Post Office approved

PRESTEL-VIEWDATAADAPTOR

At last this amazing piece of micro technology is available ata price you can afford. Just connect to the aerial socket ofany colour or black and white domestic TV receiver and toyour Post Office installed jack socket and you are into theexciting world of PRESTEL. Via simple push button use youare able to view a staggering 170,000 pages of up to theminute information on many services and utilities, ordergoods from companies, even play games!! All this andmore without ever leaving your armchair!

ONLY £170 + £1.75 carr+ VAT Send f197.50p

Note: When ordering please give the address and telephone number where theTantel adaptor is to be used, we will arrange all details with the Post Office for

installation of the jack socket (normally within 7 days).

WE'VE BOUGHT ANOTHER SHIPMENT!SAVE OVER £1300!!

DZM 180 CPS HIGH SPEED

MATRIX PRINTERSThis must be one of our greatest bulkdeals, this fabulous printer is listed atover £1800 and judging by theconstruction we are not surprised.Made under license from theLOGABAX Co. the DMZ180 is anexceptionally sturdy high speed 180 cpsmatrix printer, capable of printing up to132 characters per line on standard "Fan Fold" sprocket fed paper. Aprecision 7 x 7 matrix head using ruby bearings, gives a clearconcise type font. Many other features include internal buffer forhigh throughput, standard ink ribbon, software controllable formand tab functions, standard "CENTRONICS" ASCII parallel interfaceetc. etc.Optional extras Floor Stand £30.00 + VAT, Paper Stand £18.00 +VAT

NOW ONLY

f499 +%

S ELECTRONICSDept E.M. 64-66 Melfort Rd., Thornton Heath, MAIL ORDERCroydon, Surrey. Tel: 01-689 7702 or 01-689 6800 INFORMATIONUnless otherwise stated all prices inclusive of V.A.T. Cash with order. Minimumorder value £2.00. Prices and Postage quoted for UK only. Where post andpacking not indicated please add 50p per order. Bona Fida account ordersminimum £10.00. Export and trade enquiries welcome. Orders despatchedsame day where possible. Access and Barclaycard Visa welcome.

NOCK SOFTYEPROM BLOWER

Software development systeminvaluable tool for designers, hobby-ists, etc. Enables open heart surgeryon 2716, 2708 etc. Blows, copies,reads EPROMS or emulatesEPROM/ROM/RAM in situ whilstdisplaying contents on domestic TVreceiver. Many other features. £115+ carr. + VAT. Optional 2716, 2716Function Card £40 + VAT. PSU £20

+ £1.50 carr. + VAT.Write or phone for more details.

ICCARDS

BRAND NEW PCB organised as a 3K x8 page memory with 24 socketed 2102-1650ns Rams, 4 Epmm Sockets and 16TTL Chips for decoding. All IC's guaran-teed.

Complete with circuit only

£24.50 +11.75 P.P.Dimensions 264 x 195mm.

0.1" connector.

DIABLO S30 2.511

Limited quantity of these ultra high speed accesshard disk drives type Diablo 30. They accept inter-changeable 200 TP1 disk packs and require only a +and --15v DC supply. Fully DEC RK05 compatible,supplied second hand and in excellent condition.

Only £425 + can + VATDimensions 7"H x 174'W x nro

"THE MULTIVOLT SU"The PSU to end al/ your MPU/LAB requirements,made by "Weir" Electronics at over £200.00. Thesupply features full regulation, current limit, andovervoltage protection on all 7 outputs, just look atthe spec.+5v @12 amps, +5v @4.5 amps, +5v @4amps,+30v @2 amps, +12v @ 2.5 amps, -12% @2.5amps and -9v @lamp.A superb unit supplied in two grades, completewith data.Brand New, Fully Tested £59.99Used and Untested £39.99Carriage and Insurance £7.50

KEYBOAR* LOW PRICE CHASS

DSIS *

A special bulk purchase enables us to offer the above keyboardat a lowest ever price. 49 coded keys encoded into a direct TTLcompatible 7 bit output. Features such as delayed strobe, 5 voltDC single rail operation and rollover protection make this anabsolute must for the MPU constructor! Supplied completewith connection diagram and edge connector, at a secondh?4,"no time to test"price of only E20SUPER CASED VERSION Same as above spec but housed inattractive two tone moulded,free standing case. Unit also

11f2serial converter (no details) etc. 7.50includes an all TTL parallel to

5v D.C. POWER SUPPLIESFollowing the recent "SELL OUT" demand for our 5v3 amp P.S.U. we have managed to secure a large quan-tity of ex -computer systems P.S.U.'s with the followingspec.; 240 or 110v A.C. input. Outputs of 5v @ 3-4amps, 7.2v @ 3 amps and 6.5v @ 1 amp. The 5v and7.2v outputs are fully regulated and adjustable withvariable current limiting'on the 5v supply. Unit is selfcontained on a P.C.B. measuring only 12" x 5" x 3'.The 7.2v putput is ideal for feeding "on board" regu-lators or a further 3 amp LM323K regulator to give aneffective 5v @ 7 amp supply.Supplied complete with circuit at only E10.15 +CI .75pp.Believed working but untested, unguaranteed.

MARCH 1981 E&MM 41

ELECTRONICS

CIRCUITS &STA\DARDS

The concept of a 'standard' andthe modern electronics industrydo not seem to mix. Each day a

different manufacturer introduces adevice which may or may not conformwith previous simi lardevices, theterm'compatible' being used for thosewhich are similar and might workinstead. The list of examples of failureto comply with standards is endless,for example it might be thought thatthe 741 offers a standard pin out forallop -amps and comparators since it wasamong the first op -amps to be univer-sally manufactured. Instead we havedevices such as the 311 comparator,where not only are the power require-ments different, but the inverting andnon -inverting inputs are reversed!

The most notable non-compata-bility that has occurred was whenCMOS logic was first introduced. Thedesigners, for reasons best known tothemselves, ensured that none of thestandard CMOS chips followed wellestablished TTL patterns, either inpi nout or numbering. Although it mustbe accepted that CMOS ca nnot usuallybe plugged into a TTL circuit directlythe adoption of a standard numberingsystem would have saved manydesignproblems. Naturally CMOS has im-proved over the years, to such anextent where a CMOS gate will driveTTL, and pin compatability becameimportant. Thus a completely newCMOS family called the 74C series waslaunched, offering numerical and pincompatability with TTL.

The T092 transistor package de-serves a brief mention. This packagehas three leads, and at some timemanufacturers have assembled thispackage with most possible combi-nations of base, collector and emitter.Not content with these six alternativesother enterprising people designedthe T092z, which features the centrelead offset from the other two.

Nowhere, however, is this lack ofstandardisation less excusablethan inthe area of circuit diagrams. Up to afew years ago it was well-known thatcircuit diagrams might differ in thesymbols used, although in time atraditional set had slowly evolved. Inorder to try and improve the situationthe British Standards Institution pre-pared a specification of circuit sym-bols in the hope that everybody wouldfollow it. These new symbols tendedtowards the European style, obviouslydesirable with increasing communi-cation between countries. The onlyproblem with the new symbols wasthat very few people liked them at the

RESISTOR

I- POTENTIOMETER

PRESETPOTENTIOMETER

GENERALCAPACITOR

GENERALPOLARIZEDCAPACITOR

CAPACITORELECTROLYTIC

CAPACITORELECTROLYTICNON -POLARIZED

NGENERALDIODE

WIRESCROSSING

I WIRESJOINING

mlnMAINS ORCHASSISEARTH

01.11110111

=ONO,

SIGNALEARTH

Figure 1. Component Symbols

time and they were largely ignored,resulting in yet more hybrid diagrams.Understandably, in some ways, themost reluctance to adopt the symbolshas come from established com-panies and publications who havedeveloped their own 'standards' pre-viously, or even in some cases, since.However, we at Electronics & MusicMaker feel that as a new publicationwith a particular responsibility to allwho are interested in electronics atevery level from the classroom to theprofessional lab., and one which willsoon be considered an authority in itsfield, we should set out from the veryfirst issue to use a professionallyrecognised system for the represen-tation of electronic circuits and func-tions. To this end, all circuit diagramswill be drawn in accordance withBritish Standard 3939; GraphicalSymbols for Electrical Power, Tele-communications and Electronics Dia-grams.

Since this implies that circuits inE&MM will be presented in a slightlydifferent way to many of the estab-lished magazines it seemswell worth apage or so examining the waythey willbe drawn and documented.

Component SymbolsThe most obvious difference is the

rectangular symbol for the resistorwhich replaces the zig-zag. Poten-tiometers will be drawn as the box, towhich an is appended. When thepotentiometer is functioning as avariable resistance rather than a divi-der the relevant circuit connection willactually be drawn, rather than rely onan oblique arrow. The symbol for apreset resistor is somewhat obscure,in that it is the standard potentiometersymbol, through which an oblique 'T' isdrawn.

Fixed capacitors follow old estab-lished principles, and four main typesare specified, although only three arein common use. All non -electrolyticcapacitors are drawn as two solidrectangles perpendicular to the wireconnection. A tantalum capacitor, al-though non -electrolytic, is polarised,and as such a'+' sign will be appendedto the positive end. Electrolytic capa-citors will still have the '+' on thepositive end, the associated rectangleof which will be merely outlined toindicate the electrolytic type. Thefourth class, and the rare one, is thenon -polarised electrolytic, which nat-urally will be shown as two outlinedrectangles. Manually variable capa-

42 MARCH 1981 E&MM

ELECTRONICS

citors will appearas the standard non -polarised rectangles, through which isplaced an oblique arrow.

The use of a ring, or envelopearound a semiconductor is optional,except where connection is made to it.This will be turned to good effect in ourcircuits because a single discretetransistor will be surrounded by itsown envelope, where as those withinan array or integrated circuit will not.This will save much time on the part ofthe reader who is looking for 5 tran-sistors, only to find them all enclosedin a single chip. Diodes, on the otherhand will not be ringed.

Another item in circuit diagramsthat f requentlyca uses confusion is nota true symbol, but simply the methodof illustrating connections. If twowirescross on a diagram, usuallyat90° thenno connection between the two isintended. The traditional 'hoop' overthe second wire will not be used. Ajunction would be shown as a dot overthe intersection, butthiscan obviouslylead to mistakes if the dot is not clear,so to avoid this a junction will only beshown at a 'T' between two wires.

Finally, a brief mention of theground symbols to be used. It is veryimportant to distinguish betweenmains earth, chassis earth and circuitearth. Under normal circumstancesmains earth and chassis earth will bethe same, simply for safety reasons.Chassis earth is shown as a horizontalline, with several oblique lines be-neath it. Signal earth on the otherhandis very rarely mains earth, particularlyin audio work where earth loops must

be avoided. Such a signal earthappears as three horizontal lines,diminishing in size. Note that thisearth will be frequently connected tomains earth by a resistor, and shouldnotas a general rule be leftcompletelyfloating.

Figure 1 shows the component'symbols I have specifically men-tioned, and many of the rest are quitefamiliar or self explanatory. I n the nearfuture we shall be preparing a freewallchart/leaflet showing a completeset of standard symbols in use inE&MM, along with component refer-ence details, value representations,etc., to help you draw your own circuitdiagrams clearly and accurately.

Value ConventionsOne very good system that has

emerged in recent years is the methodof expressing a component valueusing the scaling factor to replace thedecimal point. This avoids many mis-takes of the sort that occur if the pointis not clear. In this notation 2.2k2 iswritten as 2k2, 100k12 as 100k, 2.212as 2R2 and 1k52 as the specific 1k0.Capacitors follow the same pattern, sothat 2.2AF becomes 2u2, and 12pFremains the same. As a rule 'c' (10-6)will be written as the letter 'u', whichwill simplify typing and typesettingconsiderably. The very nice pointabout this format is that it is notnecessary to specify 'Ohms' and 'Far-ads' because resistance or capaci-tance is implied by virtue of the

component symbol and the magnitudeinvolved. The one exception to this isthe way of writing a 0.001 Faradcapacitor, which is not, as one mayexpect, lmO (corresponding to milli -10-3), but simply 1000uF. All mean thesame, but the latter is much morecommon. To aid those people not sureabout the scaling factors, those com-monly used in electronicsare shown inTable 1.

Factor Value

p 10-12 F

n 10-9 F,

m(u) 10-6 F,A,V,S

m 10-3 A,V,S

k 103 st(R)

M 106 n(R)

CommonlyScaledUnits

Table 1. Scaling Factors

Componentsand Parts

Each electronic component in thecircuit will be identified byoneormoreletters and a number, for example R1,C3, TR6. Components for stereo usewill generally have a fixed numericaloffset added to the number for onechannel. In this way, componentR101, a resistor in the right channel,

will be matched in the left channel byR201, where an offset of 100 has beenadded. The low numbers (1-100) aregenerally used for components com-mon to neither channel, most ob-viously those associated with thepower supply. All potentiometers,fuses, sockets and transformers willbe included in the numbering systemwith appropriate identification letters,although obviously some items suchas the box will not be numbered.

These component numbers, andthe parts not numbered, will be col-lated into a single component list atsome stage in the article. This collationwill be in the form of a four columnlisting. These columns will containrespectively the component identifi-cations, component type, value and/or description, the number of eachcomponent required where it isgreater than one, and finally theMaplin Electronic Supplies stocknumber for the part, allowing theconstructor to obtain a full set ofcomponents with the minimum ofbother.

Further information about theBritish Standards can be found in theBritish Standards Institution Yearbook, available in most public libra-ries, and a full set of the standards,including BS3939, can be found inmany large reference libraries. Copies,of the B.S.I. Yearbook and standardsare available from:British Standards Institution,Newton House,101, Pentonville Road,London N1 9ND E&MM

AND NOW A DIMMERTHAT MAKES TOUCH DIMMERS OBSOLETE

CT4000 CLOCK/APPLIANCE TIMER KIT

Two years ago TK Electronics launched atouchdimmer kit, the TD300K. which made knobcontrolled dimmers obsolete. This was --...

such a great success that manymagazines and more retailers soonproduced similar designs. SO THATOTHERS MAY FOLLOW, TK have'designed a touch dimmer kit with an -

Infra Red Remote Control, enablingyou to switch and control thebrightness of your lights from thecomfon of your armchair etc las well as manually by touching the frontplateor by using the TDE/K extension kit).As with all our kits, these pens come complete with all components.including RF I suppression, frontplate, a neon to help you find the switch inthe dark and a neat box for the transmitter. The plastic frontplate has no metalpads to touch. ensuring complete safety and enabling the plate to becovered with a decorative finish to blendwith your room decor.

We have designed the light dimmerunit to fit a standard wall box, the

transmitter to fit your hand and theprice to fit your pocket.

01In two years' time everyone

will be selling remote controldimmers but you can have your

TDRK300K kit NOW for only£14.30 for the dimmer unit and

£4.20 for the transmitter. For themore athletic of you, the TD300K is stillavailable at £6.50 and the TDE/K at£2.00.

DON'T FORGET to add 40p P&P and15% VAT to your total purchase.

NEW REMOTE CONTROL KITS

MK6 - Simple Infra Red Transmitter - A pulsed infra red source which comes complete with a hand heldplastic box. Requires a 9V battery.

MK7 - Infra Red Receiver - Single channel, range approximately 20 ft. Mains powered with a triac outputto switch loads up to 500W at 240V as. can be modified for use with 5-15V dc supplies andtransistor or relay outputs.

'Spacial Price. MK6 and MK7 together. Order as RC500KMKB - Coded Infra Red Transmitter - Based on the SL490, the kit includes two IR LEDs. measures only

8 x 2 x 1.3 crns. Requires a 9V IPP3) battery.MK9 - 4 Way Keyboard - for use with the MKB kit, to make a 4 -channel remote control transmitter.MK 10 - 16 Way Keyboard - for use with the MK8 kit, to generate 16 different codes for decoding by the

ML926 or ML928 receiver (MK 12 kill.MK 12 - 16 Channel IR Receiver - for use with the MKB kit with 16 on/off outputs which with further in-

terface circuitry. such as relays or Via., will switch up to 16 items of equipment on or offremotely. Outputs may be latched or momentary depending on whether the ML926 or ML928 isspecified. Includes its own mains supply. Size 9 x 4 x2 crns, excluding transformer.

£4.20

£9.00£12.50

£5.901.90

£5.40

£11.95

The CT4000 has been designed to preset the state (on or off) of fouroutputs at four times per day for up to 7 days in advance, enablingthe unit to control tape recorders, appliances, central heating, lights,etc. The times are set on a 0.1" high red LED display by means of akeyboard and the output states are displayed on four LEDs. Eachoutput can switch up to 20mA at 9V. For mains loads use our SolidState Relay Kit (MK2). The kit includes a PCB, keyswitches, I.C. 4digit LED display, transformer. plus all other components and, ascreen printed and drilled box which can also accommodate up to 4Solid State Relay Kits.

£25.25 Size: 10 x12 x 4.5 cms.Colour: Black.

D.V.M. THERMOMETER KIT DISCO LIGHTING KITSBased on the ICL 7106. ThisKit contains a PCB, resistors,presets, capacitors, diodes, ICand 0.5" liquid crystal display.Components are also includedto enable the basic DVM kit tobe modified to a DigitalThermometer using a single

diode as the sensor. Requires a 3mA 9V supply.IPP3 battery) £19.50

ALL COMPONENTS ARE BRAND NEW AND TO SPECIFICATION.ADD VAT AT CURRENT RATE TO ABOVE PRICES. 50p P&P MAILORDER - CALLERS WELCOME BY APPOINTMENT

1* 11 Boston Road, LondonW7 3SJ. TEL. 01-579 9794

TK Electronics101.111111

VISA

INTEGRATED CIRCUITSWI" 555 Timer

741 Op. Amp.AY -5-1224 Clock

AY -5-1230/2 Clock/TimerAY -3-1270 ThermometerICL7106 DVM (LCD drive)LM377 Dual 2W Amp.LM379S Dual 6W Amp.LM380 2W Audio Amp.LM382 Dual low noise PreampLM386 25OrnW low voltage Amp.LM1830 Fluid Level DetectorLM2907 f -v Converter (8 pin)LM2917 f -v Converter (14. pin)LM3909 LED Flasher/OscillatorLM3911 ThermometerLM3914 Dot/Bar Driver LIN.LM3915 Dot/Bar Driver LOG.MM74C91 1 4 digit display controllerMM74C915 7 segment -BCD converter 96pMM74C926 4 digit counter with 7 seg. o/p £4.5055666 Touchdimmer E2.50S9263 Touchswitch 16 -way £4.85SN76477 Complex Sound Generator £2.52TBA800 5W Audio Amp. 68pTBA810AS 7W Audio Amp. £1.00TDA1024 Zero Voltage Switch £1.20TDA2020 20W Audio Amp. £2.85ZN1034E Timer £1.80All ICs supplied with data sheets.Data Sheets only. 10p each device.

21p19p

£2.60£4.50£8.20£7.00£1.45£3.50

80p1.0075p

£1.50£1.40£1.60

60p£1.20£2.10£2.20£6.50

Each unit has 4 channels (rated at 1KW at240V per channel) which switch lamps toprovide sequencing effects, controlled manuallyor by an optional opto-isolated audio input.

DL1000KThis kit features a bi-directional sequence, speed ofsequence and frequency ofdirection change beingvariable by means of poten-tiometers. Incorporatesmaster dimming con-trol £14.60

D L210008A lower cost version of theabove, featuring unidirectionalchannel sequence with speedvariable by means of a presetpot. Outputs switched only atmains zero crossing points toreduce radio interference tominimum. £8.00Optional Opto InputDLA1 60p

24 HOUR CLOCK; APPLIANCE

TIMER KIT

Switches any appliance up to1KW on and off at presettimes once per day. Kit con-

.

rains: AY -5-1230 IC, 0.5"LED display, mains supply,display drivers, switches,LEDs, triac, PCBs & full in-structions.

CT1000K Basic Kit £14.90CT1000KB with white box (56/131x 71 mm)

£17.40Ready Built £22.50

E&MM MARCH 1981 43

ELECTRONICS

CAR BATTERYMONITORby David Hough

Any number of things from afaulty alternator to left -on head-lights can result in a flat carbattery - and the first you arelikely to know about it is when youturn the key one morning and thecar won't start! This useful littleunit is designed to warn you inadvance by displaying the bat-tery's state of charge with a row often LED's. The Monitor costs lessthan a fiver to build, and since itconsumes a miserly 20mA, canbe left connected directly to thebattery.

The Car Battery Monitor willeven reveal faults like a slippingfan -belt, which prevent the bat-tery charging but leave the dash-board battery warning light off,and show how the battery ishandling the strenuous work ofstarting the car (it takes 20 min-utes of running to put back what afive -second start takes out).

CircuitThe National LM3914 bar -

graph IC is used to drive a row ofred, orange, and green LED's,indicating the battery charge volt-age in ten steps of approx. 1/2Veach from 9V to 14V. The ICcontains an input buffer, a poten-tial divider chain, comparators,and an accurate 1.2V referencesource. Logic is also includedwhich gives the choice of bar ordot -mode operation - the latter isused in this application. The com-parators cause the LED's to lightat 0.12V intervals of the inputvoltage.

TR1 acts as an amplified diodeand raises the lower end of thedivider chain and the negativeterminal of the reference source(pins 4 & 8) to 1.9V. The upperend of the chain (pin 6) is con-nected to the reference sourceoutput (pin 7) and therefore is atabout 3.1V. The potential dividerformed by R1 and RV1 attenuatesthe supply voltage and uses it asthe signal input to the compara-tors such that a supply range of 9-14V covers the span of the dividerchain and is indicated over thewhole of the ten -LED display. TheLED brightness is held constantby an internal constant currentsource.

ConstructionBend the leads of each LED

through 90° about 5mm from thebody, then solder them in positionon the PCB with all the othercomponents. Drill a line of 'A"holes in the front of the base forthe LED's, two in the bottom formounting the PCB, and one in theback for the supply leads. Mountthe PCB using 6BA bolts with 1/4"spacers, connect the supply, andafter setting up screw the lid on.

Setting UpAdjust RV2 until the voltage at

its wiper is 1.9V, and then adjustRV1 until the end green LED lightswith a fully charged battery (alter-natively use a variable voltagebench PSU).

PIN VIEW

TOP VIEW

TR1BC 10619

IVL3914

01-3 redD4-7 orangeD8-10 green

TIE 209

PIN VIEW

27k

'

111111'1.7 16 15 14 13 12,

1IC 1 10

5 2 6 7 8 4

+VE

al

- VE

Figure 1. Circuit diagram of the Car Battery Monitor.

kobbbbbbbbb r 792 DI D2 D3 D4 05 D6 07 08 D9 DIOa0 18

+ ICIVE OM E&

MM Agli

VE 0 1 R2

.-C=I'w.4=3-"2 VMI R3TRI ....1 IRV2tg

R1 "=} f

Figure 2. Car Battery Monitor PCB.

PARTS LISTResistors - all 5% '4W carbon unlessspecified.

R1

R2R3RV1RV2

27k1 k2

15k10k Hot 5 -min preset47k Hor. 5 -min preset

SemiconductorsD1-3 TIL209 redD4-7 TI L209 orangeD8-10 TIL209 greenTR1 8C108ICI LM391

MiscellaneousPrinted circuit boardVe robox 301

(M27K)(M1 K2)(M15K)(WR58N)(WR60Q)

3off (WL32K)4 off (WL34M)3off (WL33L)

(Q832K)(WQ41U)

(GAI 9V)(LL12N)

GA 19V

o ISS 1

cL0-4-d)

44 MARCH 1981 E&MM

LOUDSPEAKEThe complete fully re-viewed range of VideotoneSpeakers which dominatewithin their class. NOW ATLOWEST EVER PRICES.

D100Minimax 11GB3GB2GBSD 93

£38.00£44.00£50.00£60.00

£207.00£40.00

AMPS- TUNER -CA ETT30 watt amp MC input SA4 130 £75.00Stereo Tuner ST 4120 £68.00Cassette full features SC 4200 £95.0050 watt amplifier WA7700 £77.0020 watt amplifier LA2020 £58.00This new range of Electronics from Videotoneredefines the words quality and value for money to a new high.

MICROPHONESMU 105-22 £29.30MU 105-12 £22.25MU 25 C £17.39

HEADPHONES/Superbly made £9.69with top flightperformanceHP90 £12.65HP80 £9.69

Quality plus value alwaysVIDEOTONF

ALLPRICESINCLUDEVAT

ALL PRODUCTSON DISPLAY &CONTINUOUSDEMONSTRATIONS

98 CROFTONPARK ROAD

LONDON SE4TEL: 01-690 8511/2

1101 DIRECT IRON US 1INDGET THE SkilE HIGHWIN/TY 41 LOW PRICES!

IN CORALCARTRIDGES

Fast becoming one of the top namesMOVING COIL MOVINGUK's No. 1 CartridgeMC 81 £48.87777EX £35.00777E £25.00

HEADAMPH300 £51.75T100 £24.75

MAGNET555SX £7.28555E £14.22666E £32.48

HEADSHELLSS100 £6.00S101 £7.00S200 £4.00

TURNTABLESSansui SR222 Mk2 £69.00Sansui P5OS £69.00

* A MESSAGE FROM VIDEOTONE *Dear CustomerYou will find that the products advertised on this pageare the best possible value for money. They are onlylow in price because we have eliminated large amountsof selling costs that other brands have to suffer. Thesesavings are passed directly onto you. We have full bro-chures on any specific item you may be interested inand a competent realistic staff of engineers at ourLondon Showrooms to help you in your choice. Ourconsumer protection packages are comprehensive andwe offer every form of financing you may require. Wecarry out our own servicing and are dedicated to givingValue for Money. We are confident our products areunbeatable. You may purchase with confidence bec-ause our Engineers have specially selected them fromcompetitive sources throughout the world and weimport them directly ourselves. Remember, you have21 days trial period on all products. That is themeasure of our confidence.

Cliff Hardcastle, Managing Director.

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DETAILBROCHURE

LISTS O FTHE

KLOCALI SALES OUTLET1NAME 1ADDRESS I

1

E&MM MARCH 1981 45

WILMSLOW'The firm for Speakers

HI-FIDRIVEUNITS

AUDAX HD12.9D25 £8.75AUDAX HD11P25EBC £7.50AUDAX HD20B25H4 £14.95AUDAX HD13D34H £12.95AUDAX HD24S45C £21.95AUDAX WFR 15S £23.95

CHARTWELL CEA205 pair £61.25

COLES 4001 £7.65COLES 3000 £7.65COLES 3100 £7.95COLES CE2000 61/2" £14.95

CELESTION HF1300 II £12.50CELESTION HF2000 £12.50

DALESFORD 010 tweeter £8.45DALESFORD 010 ferrofluid £8.95DALESFORD D30/110 £11.25DALESFORD D50/153 £12.25DALESFORD 050/200 £12.25DALESFORD D100/250 £29.95DALESFORD 0300 £35.75

DECCA London Horn £79.95

ELAC 6NC204 61/2" £7.50ELAC 8NC298 8" £8.95

EMI type 350. 13" x 8", 4 ohm £9.45EMI 14A/770, 14" x 9". 8 ohm £19.50

ISOPHON KK8/8 £8.15ISOPHON KK10/8 £8.45

JORDAN WATTS Module £24.95JORDAN WATTS Module Mk III £28.50JORDAN WATTS HF kit £10.50

JORDAN 50mm unit £33.50JORDAN crossover pair £34.00

KEF T27 £9.45KEF B110 £12.25KEF 8200 £13.50KEF 8139 £27.75KEF DN12 £9.40KEF DN13 £6.75

LOWTHER PM6 £63.00LOWTHER PM6 Mk I £67.75LOWTHER PM7 £99.00

PEERLESS K010DT £10.95PEERLESS DT1OHFC £10.50PEERLESS K040MRF £13.60

RICHARD ALLAN CG8T £13.50RICHARD ALLAN CG12T Super £29.50RICHARD ALLAN HP8B £20.75RICHARDALLAN LP813 £14.50RICHARDALLAN HP128 £33.50RICHARD ALLAN DT20 £9.95RICHARDALLAN DT30 £10.75

SEAS H107 £9.95SEAS H211 ferrofluid £10.95

SHACKMAN ES units pair £136.00SHACKMAN ES units with cabs. pair ..f170

)'OF WILMSLOWThe firm for Hi-Fi5 Swan Street.Wilmslow. Cheshire.

SWIFT

PA GROUP &DISCO UNITS

CELESTION G12/50TC £19.50CELESTION G12/80CE £24.50CELESTION G12/80TC £23.75CELESTION G12/125CE £42.00CELESTION G15/100CE £37.95CELESTION G15/100TC £38.50CELESTION 018/200 £64.75CELESTION POWERCEL 12/150 £66.00CELESTION POWERCEL 15/250 £88.00

FANE CLASSIC 45 12"FANE CLASSIC 55 12"FANE CLASSIC 80 12"FANE CLASSIC 85 15"FANE CLASSIC 150 15"FANE CLASSIC 125 18"FANE CLASSIC 175 18"FANE GUITAR 80L 12"FANE GUITAR 80B/2 12"FANE DISCO 10012"FANE PA85 12"FANE BASS 100 15"FANE CRESCENDO 12E 12"FANE CRESCENDO 15E 15"FANE CRESCENDO 18E 18"FANE COLOSSUS 15E 15"FANE COLOSSUS 18E 18"FANE J44FANE J73FANE J104PANE J105

£13.95£15.50£19.75£26.00£37.95£43.95£47.95£26.25£27.25£28.75£26.75£39.00£57.50£74.50£94.75£99.95

£107.00£6.90

£10.90£15.95£23.95

GAUSS 3181A 10" 150 watts £115.00GAUSS 4281 12" 300 watts £146.00GAUSS 4581 15" 300 watts £162.00GAUSS 4583A 15" 400 watts £162.00GAUSS 4882 18" 400 watts £220.00

GOODMANS 8PA £5.05GOODMANS PP12 £22.50GOODMANS DI12 £25.50GOODMANS GR12 £24.95GOODMANS 18P £48.45GOODMANS HIFAX 50HX £21.85GOODMANS HIFAX 100HX £24.50

McKENZIE C12100GP £24.45McKENZIE C12100TC £24.45McKENZIE C12100 BASS £24.45McKENZIE C12125GP £39.95McKENZIE C1.2125TC £39.95McKENZIE GP15 £35.10McKENZIE TC15 £35.10McKENZIE C15 BASS £59.60

MOTOROLA PIEZO HORN 31/2" £8.50MOTOROLA PIEZO HORN 2" x 6" £12.25

RICHARD ALLAN HD8T £20.25RICHARD ALLAN HD1OT £21.75RICHARDALLAN HD12T £29.75RICHARD ALLAN HD15 £52.75RICHARDALLAN HD15P £52.75RICHARD ALLAN ATLAS 15" £77.00RICHARD ALLAN ATLAS 18" £96.00

WILMSLOWAUDIOKITS FOR MAGAZINE DESIGNS etc.

EVERYTHING IN STOCK FORTHE SPEAKER CONSTRUCTOR!BAF, LONG FIBRE WOOL,FOAM, CROSSOVERS, FELTPANELS, COMPONENTS, SPEAKERSTANDS & BRACKETS ETC.,LARGE SELECTION OF GRILLEFABRICS (send 22p in stamps forfabric samples).

Kits include drive units, crossovers,BAF/long fibre wool etc. for a pair ofspeakers

Carriage £3.95unless otherwise stated

Practical Hi-Fi & Audio PRO9-TLincluding felt panels andlevel controls £152.75

carriage £5.00

Hi-Fi Answers Monitor £146.00

Hi-Fi News State of the Art £189.00

Hi-Fi News Midiline £99.75

Hi-Fi News Miniline £49.00

Hi-Fi News Tabor with J4 bass units £66.00Hi-Fi News Tabor with H4 bass units £70.00

Hi-Fi for Pleasure Compact Monitor £116.00

Hi Fi for Pleasure E.C.M.including felt panels, foam etc. £77.50

carriage £5.00

Popular Hi-Fi Jordan System 1 £125.00

Popular Hi-Fi Mini Monitor £77.00

Popular Hi-Fi Round Soundincluding complete cabinet kit £74.00

Practical Hi Fi & Audio BSC3 £65.00

Practical Hi-Fi & Audio Monitor £180.00

Practical Hi-Fi & Audio Triangle £120.00

Practical Hi-Fi & Audio DBS4 £85.00carriage £5.00

Everyday Electronics EE20 £29.50

Everyday Electronics EE70 £150.00carriage £5.00

Wireless World T.L. KEF £125.00

Wireless World T.L. RADFORD £190.00

ALL PRICES INCLUDE VAT AT 15% AND ARE CORRECT AT 12/2/81

SEND 50P FOR 56 -PAGE CATALOGUE 'CHOOSINGA SPEAKER' (or price list only free of charge)

Export catalogue £1 or S3 U.S.

Tel: 0 6 2 5-5 2 9 5 9 9 for speaker drive units, kits, PA equipment, mail orderenquiries, and all export enquiries.Tel: 0625-526213 for Hi-Fi equipment and complete speaker enquiries.

1.72- Lightning service on telephoned credit card orders

SPEAKERK ITSSPEAKER KITS Prices Per Pair

Carriage £3.95unless otherwise stated

COLES NIMBUS KIT mounted on baffle £69.00

DALESFORD SYSTEM 1 £54.00DALESFORD SYSTEM 2 £57.00DALESFORD SYSTEM 3 £104.00DALESFORD SYSTEM 4 £110.00DALESFORD SYSTEM 5 £142.00DALESFORD SYSTEM 6 £95.00DALESFORD 'D' KIT including cabinet £79.95

KEF Reference 104aB kit (133.00plus £5 carriage

KEF Cantata kit ... £199.00 plus £5 carriageLS3 Micro Monitor kit £76.00

LOWTHER PM6 kit £132.75LOWTHER PM6 MK I kit £139.95LOWTHER PM7 kit £199.00RADFORD Studio 90 £181.00RADFORD Monitor 180 £243.00RADFORD Studio 270 £309.00RADFORD Studio 360 £450.00

RICHARD ALLAN Tango Twin £55.50RICHARD ALLAN Maramba £77.50RICHARD ALLAN Charisma £111.00RICHARD ALLAN Super Triple £102.50

RICHARDALLAN Super Saraband II £159.95RICHARDALLAN RA8 kit £62.75RICHARD ALLAN RA82 kit £98.75RICHARD ALLAN RA82L kit £108.00

SEAS 223 £42.50SEAS 253 £67.00SEAS 403 £79.95SEAS 603 £134.95WHARFEDALE DENTON XP2 kit ......£31.45WHARFEDALE SHELTON XP2 kit .....£40.40WHARFEDALE LINTON XP2 kit .......£56.20WHARFEDALE L60 kit £52.50WHARFEDALE L80 kit £72.00WHARFEDALE L100 kit £87.00WHARFEDALE E50 kit £129.00WHARFEDALE E70 kit £160.00WHARFEDALE E90 kit £249.50

WILMSLOW AUDIO BA1 sub bassamplifier/crossover kit £37.95

plus £1 carriage

CARRIAGE & INSURANCETweeters, Crossovers 70p eachSpeakers:4" to 61/2" 9 Op each8" to 10" £1.10 each1 2", 1 3" x 8", 14" x 9"£2.00 each15" £3.00 each18" £5.00 eachSpeaker Kits £3.95 pairMag. Design Kits £3.95 pairunless otherwise stated

WILMSLOWCE

The firm for Speakers

35/39 Church Street,Wilmslow. Cheshire.

46 MARCH 1981 E&MM

Alphanumeric Membrane KeyboardFEATURES:

107 Operations Touch or Tactile Feel Action Sealed, Wipe Clean Matt Polyester Surface Fully Encoded ASCII 8bit Parallel or Serial 2 key rollover Shift lock Indicator

Key activated 'CLICK', Data Ready pulse

' Layout to BS& European requirements 59 assigned keys 1. user designated

' Output TTL/DTL/MOS compatible

Numeric Pad option Size 12mm key 235 x 150mm

PRICES (cwo) £48.00 ex VAT (Parallel)

& Manufacture : Telephone For Details and Guide priLes

'L

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CONTROL

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LLAMINA

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We Specialise in Custom Keyboard Design

Manufactured in the UK by

LAMINA KEYBOARDS LTD42-45 NEW BROAD STREET LONDON EC2M 1GlY

Other Standard ProductsHEX KEYPADS 12mm key (0-F) Commoned array £8.25 Matrix 4x 4 £10.00 Gold SS Contacts

Mini alphanumeric 100 x 175mm Fully Encoded £29.50

Fully VANDAL & WEATHER PROOF HEX KEYPADS (STAINLESS STEEL KEYS) £35

Phone 01 628 0898

FREE

BURGLAR ALARM BOOKLETOur new FREE booklet entitled, 'Planning, Installing and MaintainingHome Intruder Alarm Systems', gives advice on how to do just that.

At Linton Electronics we do not assume that because you are concernedabout Home Security you are automatically a leading authority on thesubject of Intruder Detection Equipment and Systems.

Our new FREE booklet takes you step by step through the maze of allthe different equipments available, explains their various functions,advantages and disadvantages, and does it all in language you canunderstand.

Our new FREE booklet also gives pointers as to how an intruder in yourhome might operate, so indicating how your Intruder Alarm System cannot only be effective, but cost effective too.

In short, our new FREE booklet has been written to give you confidencein the system you install. As a mail order supplier of Intruder AlarmEquipment we feel that that is important.

Write, or telephone our answering service NOW for your free booklet.We will send your copy by return of post.

113ELECTRONICS

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DIFFERENT SECONDARY VOLTAGE TO THOSE STATED CAN BE MADEAVAILABLE PROVIDED V.A. RATING IS NOT EXCEEDED

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06FE06 6 a 2 0.5A ea 2.18 60p 12FE40 9-0-9 1.5A 2.65 90p

12FE06 6 x 2 IA ea 2.76 90p 12FE50 12-0-12 1.0A 2.65 90p

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50FE06 6 x 2 3A ea 4.20 1.30p 20FE50 9.0-9 2A 3.30 90p60FE06 6 x 2 4A ea 5.16 1.30p 20FE60 12-0-12 1.6A 3.30 90p

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12FE09 9 x 2 0.75A ea 2.76 90p 50FE40 6-0-6 6A 4.10 130p20FE09 9 x 2 IA ea 3.40 90p 50FE50 9-0-9 5A 4.10 130p50FE09 9 x 2 2.5A ea 4.20 1.30p 50FE60 12-0-12 3.5A 4.10 130p60F809 9 x 2 3A ea 5.16 1.30p 50FE70 15-0-15 3A 4.10 130p

06FE12 12 x 2 0.25A ea 2.18 60p 50FE60 20-0-20 2A 4.10 130p

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12FE12 12 x 2 0.5A ea 2.76 90p 60FE50 9-0-9 6A 5.00 130p20FE12 12 x 2 0.8A ea 3.40 90p 60FE60 12.0-12 5A 5.00 130p50FEI2 12 x 2 1.8A ea 4.20 1.30p 60FE70 15-0-15 4A 5.00 130p60FE12 12 x 2 2.5A ea 5.16 1.30p 60FE80 20-0-20 3A 5.00 130p80FE12 12 x 2 3A ea 6.50 1.60p 60FE100 28-0-28 2.2A 500 130p

06FE15 15 x 2 0.2A ea 2.18 60p 60FE110 30-0-30 2A 5.00 130p

08FE15 15 x 2 025A ea 2.40 60p 80FE40 12-0-12 6A 640 160p12FE15 15 x 2 0.4A ea 2.76 90p 80FE50 15-0-15 5A 6.40 160p20FE15 15 x 2 0.6A ea 3.40 90p 80FE60 20-0-20 4A 6.40 160p50FE15 15 x 2 1.5A ea 4.20 1.30p 80FE80 28.0-28 2.5A 6.40 160p60FE15 15 a 2 2A ea 5.16 1.30p 80FE90 30-0-30 2.3A 6.40 160p80FE15 15 x 2 2.5A ea 6.50 1.60p 90FE60 20-0-20 4.4A 7.00 160p06FE20 20 a 2 0.15A ea 2.18 60p 90FE90 30-0-30 2.8A 7.00 160p12FE20 20 x 2 0.25A ea 2.76 90p 90FE100 36-0-36 2A 7.00 160p20FE20 20 x 2 0.5A ea 3.40 90p 100FE26 26-0-26 4A 7.80 180p50FE20 20 x 2 IDA ea 4.20 90p 100F E30 30-0-30 3.3A 7.80 180p60FE20 20 x 2 1.5A ea 5.16 1.30P 100FE36 36-0-36 3A 7.80 180p80FE20 20 a 2 2.0A ea 6.50 1.60p

150FE26 26-0.26 5A 9.00 200p06FE30 6.0-6 IA 2.10 60p 150FE30 30-0-30 4.5A 9.00 200p06FE40 9-0.9 0.6A 2.10 60p 150FE36 36-0.36 4A 9.00 200p06FE50 12-0-12 0.5A 2.10 60p 150FE42 42-0-42 3A 9.00 200p06FE60 15.0-15 0.4A 2.10 60o

BATTERY CHARGERS08FE40 9.0-9 1A 2.25 60p 48FE12 0-6.12 4A 5.60 130p08FE50 12-0-12 0.6A 2.25 60p 66FE12 0-6-12 5A 6.00 160p08FE60 15-0-15 0.5A 2.25 60p 70FE12 0-6-12 6A 7.00 180p08FE70 20-0-20 0.4A 2.25 60p 90FE12 0-6-12 8A 9.00 200p

FLADAR ELECTRIC PAYMENT TERMSP.O. Box 19 TRADE ENQUIRIES C.W.O. Cheques,Brookside Engineering Indust. Units WELCOME Postal OrdersSpringfield Drive, Westcliff. Essex All Prices include 15% VATTel: (0702) 335791

E&MM MARCH 1981 47

J

COMPUTING

MICROPPrawcESSORSThe aim of this series of articles is to teach by example the basic principles of microprocessor hardware and software to the levelat which the reader will be able to understand, modify and even design microprocessor -based projects. The basic ideas will bepresented as clearly and as simply as possible, and by working through complete design exercises the details will be dealt with as

they arise. Whilst specific processors will be used for the examples, the reader should have enough knowledge at the end of the seriesto interpret data sheets and thus design working systems around any of the popular microprocessors.

Minis & MicrosFirst of all, let us discuss a few important terms. A microprocessor is a multi-

functional device which can perform simple, logical, arithmetic and controloperations during the execution of external programs (software). Note that themicroprocessor itself is useless without software (stored in memories) tocontrol it, and some connections to the outside world (keyboards, sensors,displays, etc.). Clearly, there is little point in a microprocessor carrying out acalculation if the result cannot be observed in any way. Connections to a nd fromthe microprocessor system are referred to as 'input' and 'output' (I/O) andcompatability between the processor and the sensor or indicator is ensured byuse of an interface. The sensors may detect switch closures or physicalquantities such as temperature or pressure; different types of interface will berequired accordingly.

So, a working microprocessor -based system must include memory devicesand I/O devices. A special case is the micro -computer, a typical example ofwhich is shown in Figure 1. The special features of a computer are that it isautomatic and reprogrammable. This system is automatic in that onceexecution of a program has started the processor will continue to carry outinstructions in a sequence determined by the results of simple, logicaldecisions. No operator intervention is required to make processing progressfrom one instruction to the next. The system is re programmable because thesoftware in the program memory may be modified; the number of possibleprograms is effectively unlimited. The only additional requirement for amicrocomputer is that the central processor unit (CPU) must be a micro-processor.

By contrast, the CPU in a mini -computer is composed of discrete logic gates,the job of the microprocessor being done by a large number of devices. Theminicomputers of 15 years ago were very similar to many of today'smicroprocessors. Many of these older machines are still used because verylarge amounts of software have been written for them and it is often moreexpensive to change to micro -based systems than to maintain the mini-computers. However, contemporary minicomputers are used where higherspeed and greater precision are required.

Somewhere between the microprocessor and the microcomputer is thededicated micro system. Here, the microprocessor software and hardware areconfigured to perform just one function. For example, an electronic chess gamemay use a dedicated micro. This approach is becoming more and morecommon as micro -electronic devices become cheaper. Some of the projects inthis magazine will feature dedicated micros.

A word of warning -there are many different microprocessors on the market,all with their advantages and disadvantages, as reflected in their usage andtheir price. Some are better for numerical work, some for process control andyet others for text manipulation. The one chosen for a project will depend uponthe application and upon the user's experience (better the devil you know?).Usually, neither the software nor the hardware are compatible between onemachine and another. But don't despair; with the knowledge gained from thisseries and a manufacturer's data sheet you should be able to handle virtuallyany of the more common microprocessor types.

. .

Limits of UseThere is nothing that can be done by microprocessors which could not have

been done before. However, it would nearly always have required circuits of fargreater size and cost and would very often not have been worthwhile in terms oftime and cost. Furthermore, the reprogrammable aspect of microprocessorsmeans that greater versatility can be built in.

However, there are some jobs for which microprocessors are simply notsuitable. For example, for direct processing of video signals a microprocessor ismany times too slow. Such limitations are often overcome by using severalprocessors or by using the processor to control other, faster circuitry. On otheroccasions, however, the objective is best met by the use of discrete analogue ordigital techniques or by special devices such as programmable logic arrays(PLA's). It pays the designer to be aware of the alternatives to microprocessorsso that he can choose the best solution to a problem.

PROGRAMMEMORY

DATAMEMORY

TAPE

0 0

INTERFACE

MICROPROCESSOR(CPU)

NTERFACE

000VISUALDISPLAY

INTERFACE

0INTERFACE

O

-11.1111111.MOM'

KEYBOARD

0INDICATORS

Figure 1. The elements of a basic microcomputer system

MemoriesIt is clear from the preceding discussion that memories form an essential

part of any microprocessor -based system; they are required to store programsand data.

The following terms will help us to distinguish between the many differenttypes of memory device:

Volatile - A volatile memory is one from which the data is lost if the powersupplies are disconnected. This is the case with many semiconductormemories (memory 'chips'). Magnetic discs and tapes, however, are non-volatile.

Read/Write - As the name implies, read/write memories may be written toand read from by the processor during the execution of a program. On the otherhand, read-only memories (ROM's) may only be read by the processor. They areprogrammed with permanent or semi -permanent data before connection to themicroprocessor system. For historical reasons, semiconductor read/writememories are generally referred to as RAM's (random access memories) eventhough ROM's may also have random access.

Random/Sequential Access - Data may be read from or written to anylocation within a random access memory, irrespective of the previous locationaccesses. Semiconductor memories are normally random access. Data mayonly be read from sequential devices in the order in which it is stored. Thus,magnetic tape is a sequential access medium. For program execution,random access is preferable. Therefore most microprocessor systems containsome random access memory in the form of semiconductor ROM's and RAM's.

Static/Dynamic - These terms are usually applied to semiconductor RAM's.A static RAM retains its data for as long as power supplies are maintained.Dynamic RAM's, however, need to be 'refreshed' some 500 times per second bythe application of a special sequence of signals. Some microprocessors providethese signals automatically; with others, special circuitry is required. However,dynamic memories are usually cheaper for comparable storage capacities, andmore data may be stored on one 'chip'.

48 MARCH 1981 E&MM

Specific memory devices will be introduced in the examples in later articlesso that readers can become familiar with their use.

Note that in the system illustrated in Figure 1 data memory and programmemory are shown separately. The microprocessor, however, cannot tell datafrom programs and the two are usually mixed together within memory. In somecases, some or all of this memory may be on the same 'chip' as the CPU. This isthe so-called 'single -chip microcomputer'. The memory is then usually maskprogrammed by the manufacturer and this is economical only for very largequantities.

Note also that all inputs and outputs must go via the microprocessor. This isusually, though not always, the case in small systems.

SignalsElectrical signals may be divided into two types; analogue and digital.

Analogue signals may take on any voltage. For example, audio signals areanalogue. Digital signals may only take on a limited number of voltages. Morespecifically, binary signals have only two possible values, on and off. For most ofthe devices which we will be dealing with the two voltage levels areapproximately zero and plus five volts. As the voltages do not have to settle toaccurately defined levels, switching can occur at very high speed.

The signals are also quantized in time. This means that changes in voltagelevel only occur at particular times. The timing is controlled by a high-speedreference signal (clock) so that all the various signals within the system aresynchronised.

Binary dataAs the signals with which we are dealing may have only one of two levels,

data is expressed using the binary number system.In the denary number system (the one which we normally use) there are ten

digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. The binary number system has only two digits:0 and 1. Consider a three -digit denary number, 295. The right -most columnshows five units (5 x 10°), the centre column nine tens (9 x 10') and the left-most column two hundreds (2 x 102); columns to the left of these would showincreasing powers of ten.

Similarly, the columns in binary numbers show increasing powers of two. Forexample, consider the binary digit 1001102 (the subscript indicates base 2 orbinary). The weights of the columns are shown below.

25 2° 2' 22 2' 2°Column value: =32 =16 =8 =4 =2 =1Binary number: 1 0 0 1 1 0

Thus, 1001102 =(1x32)+ (0x16)+ (0x8) + (1x4) + (1x2) + (Oxl)=32+4+2=38

The standard word length for the most common microprocessors is 8 bits(binary digits). An 8 -bit binary word is called a 'byte', and this may be used torepresent numbers between 0 and 255. To familiarise yourself with the use ofbinary numbers, try converting between decimal and 8 -bit binary.

Binary AdditionFirst, we will look at decimal addition. Take the following example:

16+ 27

43carry 1

Only the d igits 0-9are allowed, sowhen 9 is exceeded a carry must be added tothenext column. Similarly, in binary arithmetic only Oand 1 area llowed and when 1 isexceeded a carry must be added to the next column:

COMPUTING

Binary Decimal Binary Deci ma I Binary Decimal0000 0 0000 +0 1000 -80001 1 0001 +1 1001 -70010 2 0010 +2 1010 -60011 3 0011 +3 1011 -50100 4 0100 +4 1100 -40101 5 0101 +5 1101 -30110 6 0110 +6 1110 -20111 7 0111 +7 1111 -11000 8 1000 -0 0000 +01001 9 1001 -1 0001 +11010 10 1010 -2 0010 +21011 11 1011 -3 0011 +31100 12 1100 -4 0100 +41101 13 1101 -5 0101 +51110 14 1110 -6 0110 +61111 15 1111 -7 0111 +7

(a) (b)Unsigned Signed

binary binaryTable 1. Various binary number

(c)2's

complementrepresentations

The 'two's -complement' number system is illustrated in Table 1(c) and it isalmost universally used for the representation of signed binary numbers. Noticethat as the binary number is incremented the decimal number it represents isalso incremented for all values within the range -8 to +7. (If more digits wereavailable the range would be increased). This implies thattheadditionof anytwoof the numbers will result in the correct sign and magnitude. For example:

0100 +41110 + -6

(1)0010 =-2

Notice that there is a carry from the most significant bit. However, as the twonumbers added were of different signs, the result must be within the range, andthe carry may be ignored. Let us consider another example:

0100 4+0110 +6

1010 = -6

The answer is clearly wrong, as the two numbers added were positive but theanswer is negative. The correct answer lies outside the range of a 4 -bit 2's -complement number.

In order to determine the magnitude of a 2's -complement negative number itwould be useful to be able to negate, it (i.e. convert it to a positive numberwith thesame magnitude - its '2's -complement'). This is done by negating the individualbits of the number and adding 1. For example, take -5:

1011 -50100 Invert

1 Add 10101 +5

and conversely,

0101 +51010 Invert

1 Add 11011 -5

As subtraction may be accomplished by complementing and adding, an inverter0101 (5) 0111 (7) and adder may be used for 2's -complement subtraction. For example, let us0110 (6) 0011 (3) subtract 2 from 5:1011 (11) 1010 (10) 0010 +2

carry 1 carry 111 1101 Invert0001 Add 1

Signed Binary IntegersSo far, we have only looked at positive numbers represented in binary form.

For reference, these are shown in Table 1. However, we very frequently need torepresent negative numbers for mathematical purposes. One way in which thismight be done is by simply using one bit of the number as the sign and theremaining bits as the magnitude.In Table 1(b) the most significant bit (MSB) is the sign; 0 for positive, 1 for nega-tive. However, this representation is almost never used. Note that there are tworepresentations for zero (+0 and -0) and also that there is an discontinuitybetween 0111 and 1000. The simplest (and most common) form of binarycounter increments 0111, to give 1000 as in the unsigned case. But with thesystem shown in Table 1(b) this results in a change from +7 to -0. The system iscomputationally unwieldly and a far better one is available.

E&MM MARCH 1981

11100101

(1)0011

= -2+5

Total = 3

Again, the overflow may be disregarded as we are subtracting numbers of similarsign within the range.

With 8 -bit microprocessors, we are normallyconcerned with 8- bitor 16 -bit 2's -complement numbers, and although the range is greatly increased theprinciples involved are essentially the same. In general, the number range toran n -bit 2's -complement word is +(2 n-1-1) to -(2"-1). Thus an 8 -bit word mayrepresent numbers from -128 to +127 (2's -complement) or 0-255 (unsignedbinary).

Next month we will take a look at the structure and operation of a realmicroprocessor, and see how it communicates with memory and interfaces.

E&MM

49

JOIN UP WITH LITESOLDNew `1,' Series soldering irons, designed to latest safety

standards. Outstanding performance, lightweight andeasy maintenance. Heating elements enclosed instainless steel shafts and insulated with mica andceramic. Non -seize interchangeable bits, 'Copper'or 'Long -Life', fit over heating elementsfor high efficiency. Non -roll GRPhandles and screw -connected3 -core mains leads.

Order direct at these specialprices or send 25p for 4 -pagecolour leaflet, or 60p for16 -page colour catalogue.

Model LC18 Generalpurpose 18 watt iron forvirtually all electronics assembly and servicing.Normally 240 volts but also available, in 12 and24 volt. Iron fitted with 3.2mm copper bit:£5.23. Iron with 3 spare bits 1.6, 2.4 and4.7mm: £7.11

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50 MARCH 1981 E&MM

COMPUTING

SHARP MZ 80Graham Knight

Many of the latest generationof microcomputers can beadapted to play electronic

music with the addition of a few com-ponents. Some micros have built-inspeakers and one, the Sharp MZ-80K,has particularly appealed to musi-cians interested in playing and com-posing melodies on a computer. Musi-cal notes can be programmed on theSharp using both Machine Code andBasic language, and the graphics canbe used to display a keyboard on thescreen.

Let us examine the musical com-mands available from the Sharp Basicin detail. Seven tempos can beassigned from very slow to fast usingTempos 1-7. Notes are assigned ac-cording to their pitch (octave andscale) and the duration can be selec-ted from a semibreve note to a demi-semi quaver. Similar durations canalso be assigned to rests when nosound is heard.

Playing a musical scale on the SharpMZ-80K is simplicity itself - enterMUSIC "CDEFGAB-C" to hear thescale of C Major. The length of note isassigned by acding a number to thepitch designation with the numbers 0to 9 giving a full range of durationsincluding dotted notes.

When a series of notes are to beplayed which have the same durationthe number only needs to be assignedafter the first note. Forexample MUSIC"C5DEFGAB-C" plays the C Majorscale in crotchets. The same scalecan be played at different speeds byselecting Tempos 1 to 7.

Any notes can be sharpened byprefixing with a # sign, thereby allow-ing music to be programmed in anykey. Thus the scale of D Majorwould be programmed as MUSIC"D3E#FGA13-#C-D" and whenplayed will be in quavers. With a littlepractice it is soon possible for anyonewith a little musical knowledge toadapt music to a Sharp program. Theexample listing the program to play'The Entertainer' showsjust howeasy itis to write music in Sharp Basic.

Many tunes have repeating or re-curring passages which would be.tedious to program. In the secondexample the program plays an Etudewhich changes in tempo and goesfrom a major to a minor key. Althoughthe program is quite short the tuneplays for a considerable time - pro-gram space is saved by assigning therepeating passages tostri ng variables.The music contained in lines 5, 6, and7, defined as strings J1$, J2$ and J3$,is the major section of the melody.Line 8 defines the Tempo and alsoselects the number of times the firstthree lines of music are to be played.Similarly lines 9, 10 and 11 aremusical strings which are called byline 12.

It is also possible to use the SharpBasic 'Poke' commands to writemachine code programs which canvary the pitch at high speed and over avery wide range. Examples aregiven ofprograms to reproduce various sound

<- the melody microl

effects which can be used to greatlyenhance games like Space Invadersand Startrek. The variety of soundsproduced are limited only by theingenuity of the programmer but theexamples of police sirens, trim -phones, wolf whistles etc show whatcan be achieved using POKE, STEPand USR instructions.

Many schools are already using theSharp MZ-80K in their physics andmathematics departments for a wholevariety of microcomputer applica-tions. Some of these schools are nowbeginning to,rea I ise the potential of theSharp in assisting with the teaching ofmusic. For music teaching the Sharpcan display a keyboard, with notesplayed from the computer keys. It is

also easy to program a stave withmusical notation on the screen withappropriate notes lighting up as a tuneis played.

Although the built-in VDU makes theSharp compact, it is often useful to beable to displaythe information on yourown television. The circuitry shownenables a standard TVtobe used via itsaerial input and is easy to constructand set up.

The UHF modulator add-on unitcontains very few components and itcan easily be constructed on a smallpiece of Vero board. The modulatoritself is of the type commonly used inTV games and these are relativelyinexpensive but reliable devices. theoutput is around Ch36 and can be

tuned in on an ordinary UHF TV set.Although the Sharp MZ-80K is a 525line unit with 60Hz vertical syncs thisdoes not present any problem on astandard British 625 line TV set. Thevertical hold will need to be reset andthe height (frame amplitude) controladjusted - no further adjustments willbe needed to the set. The levels of syncand video signals can be adjusted withthe two potentiometers to give a goodpicture on the external TV set.

The four leads going to the MZ-80Kmain circuit board are simply con-nected to pins 2 (sync), 3 (video), 5(ground) and 6 (+12v) on connectorCN2. There are six pins to this con-nector and pin 1 is marked clearlynearest the centre of the board. E&MM

CN2 PINNos.

TOMZ -80K

MAINCIRCUIT VIDEOBOARD

1N914

3

6CN2 +12V

CONNECTOR

SYNC

1N914

2k2

5 -411-

GROUND

MINIATUREHORIZONTALPRESETS

TO CHANNEL

INC::(

OUT

36

TV68R)

GAME+VL(.MODULATOR27013

ZENER I XXO5F)

4n7 7V5MYLAR 400

mV--T8k SOLDER

TO CASE

Circuit diagram for connecting external TV to MZ-80K

5 PRINT":1202BSE " THE ENTERTRINER "6 CLP: TEMPOS7 MUSIC"0341D3E3-E5E3-05E3-C3-C7-C3R0-C330-#03-E-C-D"8 MUSIC"-E583-05-C7R5D3#03E3-05E37C5E3-C-C8A36#F3P-C"9 MUSIC"-E5-03-C-A85-C-003403E3-05E3-1:5E3-C3-C7-C3RO-C3"

10 NUSIC"-I1.3#03-E-C-D-E-EB-G5-C8RO-C3-0-E-C-D-E-E-C-U-C-E"11 MUSIC"-C-3-0-E-E3-C-D-C-E-C-D-E-E8-05-C7R9"

5 JIWC1-17-E-C7G-E-C-Et=1-014-F-DA-D" 'ETUDE '

6 J2S="618-8-1-G-#F-F-DE-C-E-CBGFD"7 13$="C1-8C-GECIGE-05R"8 TEMP05:MUSICTIS:1284,111;1264,13t

NIS="01-F-ADFA-13-#ADGA#A-A#CEG#FAGF-F-DPF"10 N21="DIFA-D-F-REG#G-E-6-0P-R-F-D-E-#CA-D#GAEFMC"11 N3S="01-0-F-RDEF#CDFP-#C-D5R5"12 TEMP04.MUSICNIS;N21;NISM2t1N31

The Sh.rrm. MZ-OOK hasnr,c1 the following rotes

car, be Ocksic-

CDE PWO*RftS C*DS*E P*G*F1* C*D*E F-**o=e*

'"''' armT4 Cersia_

307 PRINT"E011The tone is continuously yardable. over.308 PRINT" 1a wide ranse.309 FOR1=11.01000:NEXT:CLR310 FOR1=11-0240311 FORK=11.0255STEPJ*2312 POKE4514,1:P0KE4513,1(015R<68)313 NEXTK:NEXTJWSR(71)314 FRINT"NSCA variety of effects can he produced for315 FRINT"use with games etc-.316 FCR.J=1T02000:NEXTJ317 PRINT"DePMERICAN POLICE SIREN313 FORI=17012:POKE4514,3:FORK.11-0255STEP7319 POKE4513,K:USR(68):NEXTK:NEXTJ:MUSICW"320 PRINT"SPHOTON TORPEDOES":FORT.11.04:FORK=1-10150321 POKE4514,KlUSR(68):NEXTIOMUSIC"RI":NEXTT:MUSIC"R7"322 PRINT"STRIMPHONE ";:TEMPO4323 POR1=11.03:FORK.11.02:POKE4514,1:FORL=1T015324 POKE4513,150:USR(68):FORM.1TOE4NEXTM325 POKE4513,255:USR(68):FORM.ITO6lNEXTM326 NEXTL:MUSIC"R3":NEXTK:MUSIC"F'.8":NEXTJ327 PPINT"ENGAGED328 MUSIC"84RGRGRGRGRGRGRGR6"336 MUSIC"RE."337 PRINT"SSEXY WHISTLE338 FORJ=11.02:FORA=-255TOOSTEP12339 8=ABS(A):POKE4514,1,POKE4513.8340 USR(68):NEXTRIMUSIC"RI"341 FORA.-25570255STEP8342 B=1:18S(R)lPOKE4514,1:POKE4513,8343 USR(68):NEXTA:MUSICW":NESTJ:MUSIC"R7.363 PRINT"OBBOAND NOW ....364 FORT=1701000:NEXT

E&MM MARCH 1981 51

'MICRON' may sound small - but we all know that it's much larger than an atom!

The un-beatable features of Microtan 65 and Tanex have been brought together to give you Micron,

a ready built and tested computer of outstanding value. Fully supported by comprehensive documentation,

Micron represents an ideal starting point in personal computing. We've taken a full O.E.M. licence

for Microsoft Basic, which means that you'll have the support of the most popular Basic available,

(as used on PET, APPLE, TANDY etc.). If you want to expand Micron there's no problem, just move into

the system rack and choose from the range of Microtan modules. Read the information, study what the

magazines have to say about us and compare what we have to offer with other systems, then we feel

sure that you'll be convinced that we've produced an excellent product.

CIFULLY BUILT, TESTED AND CASED.0 6502 BASED MICROCOMPUTER.CIVDU ALPHA NUMERIC DISPLAY.08K RAM.CI32 PARALLEL I/O LINES.02 TTL SERIAL I/O LINES.01 SERIAL I/O PORT WITH RS232/20mA LOOP,AND 16 PROGRAMMABLE BAUD RATES.

CI300 / 2400 BAUD FILENAMED CASS. INTERFACE.CIDATA BUS BUFFERING.COMEMORY MAPPING CONTROL.071 KEY ASCII KEYBOARD, INCLUDING NUMERICKEYPAD.

CIPOWER SUPPLY INCLUDED.

TANGERINECOMPUTER SYSTEMS LIMITED

Forehill WorksForehill Ely Cambs England

SOFTWAREO 10K EXTENDED MICROSOFT BASIC.O ALL THE USUAL BASIC COMMANDS.O INTEGER AND REAL NUMBERS.O INTEGER AND REAL ARRAYS.O INTRINSIC FUNCTIONS: ABS, INT, RND

SGN, SIN, SQR, TAB, USR, ATN, COS,EXP, LOG, TAN.

O USER DEFINED FUNCTIONS.O READ AND DATA STATEMENTS.O DUMP AND LOAD PROGRAMS.O PROGRAM EDITING COMMAND.O STRING FUNCTION FOR TEXT I/O.O BASIC CAN CALL MACHINE CODE SUB-

ROUTINE.O USER MACHINE CODE INTERRUPT HAND-

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CI DATA CASSETTE FILE HANDLING IN BASIC

Tel: (0353)3633

52 MARCH 1981 E&MM

microtan 65

The Microtan system is rapidly becoming accepted as the ultimate approach to personal computing. Start

with Microtan 65, a 6502 based single board computer, and expand to a powerful system in simple and

in -expensive stages. The Microtan system is a concept and not an afterthought, this means expansion

is easy and very efficient! Unlike many other systems, you'll find it difficult to outgrow Microtan,

and you won't be wasting your money on a product that will only last you a few months! When you are

ready to expand, Tanex is waiting. The features offered by Tanex are tremendous, and you _an start into

them for just £49.45! Cassette interface, 16 I/O lines, two 16 bit counter timers, data bus buffering,

memory mapping and a further 1K of RAM are standard. From thereon expansion is simple, just plug in

extra integrated circuits to get yourself 8K of RAM, a further 16 I/O lines and two more counter timers

a serial I/O line with RS232/20mA loop and full modem control, XBUG - a firmware package containing

cassette file handling routines, plus a line -by-line assembler (translator) and dis-assembler, PLUS

10K EXTENDED MICROSOFT BASIC, a suped-up version of the Basic as used by major manufacturers such as

Apple, Tandy and Nascom, NO OTHER LOW COST MICROCOMPUTER OFFERS YOU THIS SUPERB PACKAGE. O.K. so you

want more memory, try Tanram for size! Upto 40K bytes on one board starting for as little as £50.60.

RAM freaks will be pleased to hear that our system mother board offers page memory logic which will

support 277K Bytes, satisfied? To house these beautiful modules you can choose between our mini -rack

(as used on Micron), which accepts Microtan and Tanex, or our system rack pictured above. The system

rack will support 12 modules. What are these extra modules? Well for starters there's a couple of I/O

modules, parallel and serial offering upto 128 I/O lines organised as 16 8 bit ports and 8 serial I/O

ports respectively. Shortly we'll be introducing high definition (256x256) colour graphics, A to D

and D to A modules, IEEE 488 Bus interface, a PROM programmer, disc controller and TANDOS - a 6502 CPM

system. So there's plenty to keep you busy. Send for more details, and find out how you can get started

ALL PRICES QUOTED INCLUDE V.A.T.for just £79.35!

AIM 65, KIM 1, SIM 1 USERS- READ ON!

We have produced a T.V. interface module which simply

connects to the expansion socket of your computer and

produces a display of 16 rows by 40 characters! Of even

more interest will be our Buffer module, which allows

you to expand into our system rack, giving you access

to the full range of Microtan modules.

Please underline the information required.

AIM T.V. INTERFACE. MICROTAN SYSTEM.

NAME:

ADDRESS:

PLEASE ENCLOSE 12p STAMP. THANK YOU.

E&MM MARCH 198153

COMPUTING

3ASICALLY 3ASICThis regular series will attempt to teach BASIC to those who would like to use it for any home,business, scientific or musical application, but have no previous programming experience.

BASIC is a programming languagecurrently widely available and usedon most personal computer systems.It was devised at Dartmouth College inthe U.S.A. as a high-level languagethat would be easy to teach and learn.There are many versions of BASIC butthey are all based on a standard. Onceyou have learnt the fundamental con-cepts and how to think about writing acomputer program, you will find that itis relatively easy to write and modifyyour own programs to run on anycomputer (provided it has an inter-preter which translates the BASICstatements into a form which can beexecuted by the computer). Thisseries will describe the BASIClanguage by giving specific examplesof the fundamental statements andexamples of how they can be com-bined to achieve more intricate pro-grams.

What is aProgrammingLanguage?

A programming language is a verywell defined way of communicatingwith a computer. Imagine that you aregiving instructions to a friend to teachhim how to mend a puncture. Thesequence of instructions that you tellhim are the equivalent of a program.His brain can be thought of as a com-puter which recognises words and

translates them into actions enablinghim to carry out your instructions.Programming a computer is just asstraightforward. You tell the computerwhat you want it to do using state-ments from a strictly definedlanguage (such as BASIC). The com-puter recognises and converts yourinstructions into actions - there isalready a program in the computer'smemory which changes the BASICstatements that you type in, into thestrings of binary numbers which thecomputer can manipulate to performthe actions.

This analogy can be extended - ifyou tell your friend what to do usingnonsense words he would not be ableto interpret what you are trying to tellhim and would probably ask you torepeat your instructions using wordshe could understand. Similarly, if youtry to type into the computer words orstatements which are not defined inthe BASIC language, the interpreterprogram in the computer memory willnot understand and will tell you bydisplaying an error message on thescreen. Although the interpreter pro-gram may except your BASIC pro-gram the statements taken togethermay not do quite what you hadintended because of a small program-ming error. Then you will have to'debug' the program by analysingwhat it does and why. Once themistake has been located one or moreof the statements will have to be

Graham Hall

CTERMINAL )

OPERATION

INPUT

PRINT

(OR OUTPUT)

Used to start orfinish a program.

Used to include analgebraic computationor logical process.

The diamond contains aquestion. A decision ismade and the correctbranch taken to exit fromthe diamond.

Denotes input from aninput device to the computer.

Denotes output from thecomputer to an output device.

The program branches to (x)a smaller sub -program at thispoint and then returns to thispoint afterwards.

Arrows on linesindicate direction.

Figure 1. Common flow chart symbols.

54 MARCH 1981 E&MM

COMPUTING

changed. As you gain more program-ming experience you will find it be-comes much easier to write programsthat do exactly what you had intendedfirst time. Remember you are alwaysin control of the computer - it onlydoes what it is programmed to do. Youmay have heard the computer jargonword 'GIGO' which stands for GarbageIn Garbage Out - if you type a non-sensical program into the computeryou will not get meaningful results.

Algorithms andFlow Diagrams

The key to writing an efficientcomputer program which can beunderstood by other people is tospend quite a lot of time thinkingabout the problem to be solved beforewriting any code. Although this maybe time consuming, it will in the longterm save you considerable time andeffort. In computing terms the solu-tion to a problem is called an'algorithm'. An algorithm is a finitenumber of steps which have to becarried out one by one in order tosolve the problem. Each of the stepscan be translated into the relevantstatements of a programminglanguage to enable a computerto per-form the operations necessary to pro-vide you with a solution to theproblem.

A clear concise way of expressingan algorithm is in the form of a 'flowdiagram'.

A flow diagram enables you toquickly see the sequence of operationor flow of an algorithm. By studying aflow diagram it is often easy to seeomissions or errors in the algorithm. Itis then straightforward to change theflow diagram before any code iswritten. The program may still containerrors but they should be easy tocorrect without large scale alterationsto the program.

There are certain conventionsused by programmers when drawingflow charts. The symbols used mostfrequently are shown in figure 1.

Now lets see how a flow diagramhelps to give a clear representation ofa problem.

An airline operates a service toEdinburgh. The standard single fare is£40. However, at certain off-peaktimes the single fare is reduced to£25. The return fare is £10 cheaperthan the combined cost of two singlesbut this reduction does not apply tothe off-peak reduced fare.

At first glance the informationcontent makes things a little confus-ing. We can simplify the way theinformation is presented using a flowdiagram (see Figure 2). Note that analgorithm is not needed to solve thisparticular problem.

Suppose you want to know howmuch the off-peak return fare toEdinburgh will be. The information isquickly obtained by glancing at the

Figure 2. Flow diagram to represent airline fare information.

flow chart, answering the questions inthe decision boxes and reading thefare from the statement box.

Next month we will look at a morecomplicated problem and an

algorithm to solve it. Some of theBASIC language statements will beintroduced so that you can start towrite your own programs.

E&MM

LB ELECTRONICSSUPERSALE '81All full spec. 2114 (45Ons) £1.85, p&p 25p. 2708£2.00 p&p 25pTEXAS INSTRUMENTS 2716 single rail, fullspec. £5.95.CANNON D TYPE plugs & sockets & coversstocked.SHARP LCD talking clock. This superb clock withnormal time display, built-in stop watch and timer,chimes on the hour and half hour. Abrand new line£39.99 p&p (RD) L1 .00 .

BARGAIN 1PRICE SMASH FND 500 .5in. LED displays, fullspec. 50p each, 30p p&p, large quantities POA.BARGAIN 2Battery eliminator 6VDC 200MA 240V AC inputideal for calculators, radio, etc., give away price95p each. Large quantities POA p&p 45p.BARGAIN 35 digit 7 segment OIL LED .11" displays 4 for f1.50p&p 30p.

BARGAIN 474LS266 50p 74LS245 £2.40. 74LS240 £1.00745260 35p p&p on all above 30p.BARGAIN 55K multiturn Din -loots. PCB mounting, per box of 14£2.50, p&p 30pLED's (full spec.)TIL209, red 10p 0.2in. red 12p. 0.2in. green 28p.0.2in. yellow 28p.RL54 red Axial lead 15p.P&P on all above 30p.BURR OUG H S keyboard, 96 key station. Onboardcrystal and TTL. Brand new and boxed. 500mm x190rnm. At the time of advert no data. No keytops atall. Clare pender. Reed switches. Bargain £12.00each, p&p £2.00.

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out of business hours.New retail premises, now open Mon, Tues, Thurs,Fri and Sat, 9.30-6.00 Lunch 1-2.15 weekdays.Closed all day Wednesday. We are situated just offthe A40 opposite Master Brewer.

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DIGITAL VOLTMETERMODULE

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* Requires only single supply between 7 & 12 volts(220mA)

* High accuracy +0.1'/ +1 digit* Large bright 0.43" high efficiency displays* 4 readings per second sampling rate* Size only 41 x 95 x 10mm* Supplied with full data & applications information

This brand new, quality module manufactured by AutonaLimited (who are one of the U.K's largest module manufac-turers) means you can build accurate test equipment, multi -meters, thermometers, etc. easily and at a fraction of the costof ready-made equipment. Full details are provided showinghow to measure A.C. voltage, current, resistance andtemperature.Send your cheque or P.0 (f 11.95 + f1.79 V.A.T. + 50p p. & p.= £14.24) now to: -Dept. E.M.M.RISCOMP LIMITED21 Duke StreetPrinces RisboroughBucks HP17 OAT

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E&MM MARCH 1981 55

CHROMATHEQUE 5000 5 CHANNEL LIGHTING EFFECTS SYSTEM

Panel size 19.0" x 3.5"

Depth 7.3"

COMPLETE KITONLY

f49.50+ VAT!This versatile system featured as a constructional article in ELECTRONICS TODAY INTERNATIONAL has 5 frequency channels with individual level controls oneach channel. Control of the lights is comprehensive to say the least. You can run the unit as a straightforward sound -to -light or have it strobe all the lights at aspeed dependent upon music level or front panel control or use the internal digital circuitry which produces some superb random and sequencing effects. Eachchannel handles up to 500W and as the kit is a single board design wiring is minimal and construction very straightforward.

Kit includes fully finished metalwork, fibreglass PCB controls, wire, etc. - Complete right down to the last nut and bolt!

MPA 200 100 WATT (rms into 8 ohm) MIXER/AMPLIFIER

COMPLETE KITONLY

f49.90+ VAT!

MATCHES THECHROMATHEQUE 5000

PERFECTLY!Panel size 19.0" x 3.5"

Depth 7.3".

Featured as a constructional article in ETI, the MPA 200 is an exceptionally low priced - but professionally finished -general purpose highpower amplifier. It features an adaptable input mixer which accepts a wide range of sources such as a microphone, guitar, etc. There are widerange tone controls and a master volume control. Mechanically the MPA 200 is simplicity itself with minimal wiring needed makingconstruction very straightforward.

The kit includes fully finished metalwork, fibreglass PCBs, controls, wire, etc. - complete down to the last nut and bolt.

SP2-200 2 -CHANNEL 100 WATT AMPLIFIER

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f64.90+ VAT!The power amplifier section of the MPA 200 has proved not only very economical but very rugged and reliable too. This new design uses 2of these amplifiersections powered by separate power supplies fed from a common toroidal transformer. Input sensitivity is 775mV. Power output is 100 rms into 8 ohm from bothchannels simultaneously.

The kit includes fully finished metalwork, fibreglass PCBs, controls, wire, etc. - complete down to the last nut and bolt!

POWERTRAN Many more Kits on Page 29. More Kits and orderinginformationon Page 4

All kits also available as separate packs (e.g. PCB, component sets,hardware sets, etc.) Prices in our FREE CATALOGUE.

1024 COMPOSER COMPLETE KIT ONLYf89.50+ VAT!

READ ALL ABOUT IT! IN ELECTRONICS TODAY INTERNATIONALProgrammed from a synthesiser, our latest design to be featured in Electronics Today International, the1024 COMPOSER controls the synth. with a sequence of up to 1024 notes or a large number of shortersequences e.g. 64 of 16 notes all with programmable note length. In addition a rest or series of rests can beentered. It is mains powered but an automatically trickle charged Nickel -Cadmium battery, supplying thememory, preserves the program after switch off.The kit includes fully finished metalwork, fibreglass PCB, controls, wire etc. - complete down to the last nutand bolt!

BLACK HOLE CHORALIZERThe BLACK HOLE designed by Tim Orr, is a powerful new musical effects device for processingboth natural and electronic instruments, offering genuine VIBRATO (pitch modulation) and aCHORUS mode which gives a "spacey" feel to the sound achieved by delaying the input signaland mixing it back with the original. Notches (HOLES), introduced in the frequency response,move up and down as the time delay is modulated by the chorus sweep generator. An optionaldouble chorus mode allows exciting antiphase effects to be added. The device is floor standingwith foot switch controls, LED effect selection indicators, has variable sensitivity, has highsignal/noise ratio obtained by an audio compander and is mains powered - no batteries tochange! Like all our kits everything is provided including a highly superior, rugged steel,beautifully finished enclosure.

COMPLETE KIT ONLY (49.80 + VAT (singledelay line system)De Luxe version (dual delay line system) also available forf59.80 + VATCabinet size 10.0" x 8.5" x 2.5" (rear) 1.8" (front)

56 MARCH 1981 E&MM

ELECTRO-MUSIC

.111M11.

.111111.

..111..

mai

The idea is to take an active view ofvideo and describe some of the thingsyou can get up to without having toapply fora second cred it card. In other

6 words we will be taking a fairly saneand value for money approach to whatyou can do with video. From time totime we will review new machines andreport on accessories: we will tell you ifthey are worth buying and whetherthey really do represent the first majoradvance since the Philips 1500. Valuefor money will be discussed and nodoubt names will be named.

We will not adopt a pseudo -intel-lectual approach but neither will weinsult your intelligence by leaving outevery technical fact. Three of thenewest video magazines have averredthat they will not confuse their readerswith technical jargon, but half thereason why people buy technicalproducts is to feel that they areparticipating in "Tomorrow's World"!So we won't shy away from volts andmegahertz when necessary. And bythe way, we assume you are readingthis column to find out about video, sowe won't waste your time with write-ups about home computers, citizensband or programmable calculatorswhich are all very nice but nothing todo with video.

Right, having got that over with,what have we left to write about? Let'sstart with something contentious, likecheap tapes. Are they worth buying,will they damage your machine'shealth? If you have a VHS machine(and according to the ads, seventy percent of you do) you will probably havetaken more than a cursory glance at arecent statement issued by JVC Ltd. Itwarned buyers that there were 'pirate'VHS cassettes being imported fromcountries like Hong Kong, Korea andTaiwan which were not licenced byJVC(the originators of the VHS system)and that these unlicenced blank tapesmight damage your machine. What itfailed to say was they were consider-ably cheaper than 'legit' VHS tapes,even at discount prices, and mightdamage the profits on blank tapesmade by the 'proper' manufacturers.Fundamentally the statement is true.These 'non licenced' tapes may bediabolical, but I wouldn't say they allare. For instance, there is a brand onsale in some areas which has a nameending in "... rex" (no, not Memorex,but that's the brand of tape in them!).These blank tapes retail at £6 for anE-180 which is not bad when someprovincial monopolists are still charg-ing £14 for the same article (someonewill write in and say he knows a shopcharging £15). Are the 'pirate' tapesany good? Well, the distributor claimsthe tape in them is Memorex (a job lot,

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New readers start here! That includes you so welcome to "Workingwith Video". We've called it that because if you have taken thetrouble to buy this magazine you must have a fairly creative

interest in building, making and modifying things, not just connectingtogether black box systems bought straight off the shelf in the HighStreet. So if your interest in video extends beyond taping "TheProfessionals" so that you can watch "Shoestring" as well, or taping awhole week's "Coronation Street" while you take your winter sportsholiday this column should appeal to you.

of course) and the plastic shells,marked made in Japan, are the sameas you see on many other tapes.Results are just slightly poorer thanbest branded tapes, i.e. a few moredropouts (tiny spots of missing pic-ture) and a slightly noisier (grainier)picture. If you don't buy manytapes I'dleave them well alone; on the otherhand, if you usea lot of tape and wanttosave £3 or £4 a tape you can probablyput up with a slightly poorer picture.

Not to be confused with 'pirate'cassettes are the USA imports whichhave been around for several months.When the first VHS video recordersarrived inthiscountrythere were somelocal shortagesof blanktapeand someenterprising people imported tapesfrom the United States. Whether thetape now on sale is still the remnants ofthese imports I don't know- I doubt it -but several shops have them, includ-ing a large national discount storewhose name would appeal to astro-nomers. Most of the tapes carry theRCA trademark and they are of topquality. The only thing which mayconfuse you is the numbering, VK250and the like. I don't know what thesenumbers mean unless they relate tothe physical length of tape inside, but

the VK250 actually lasts for about 3hours and ten minutes. One shop inLondon's Tottenham Court Road sellsthem for £7.90 which is a very reasonable price, so look out for these.

While on the subject of tapes, it'spleasant to see the price of pre-recorded material coming down. It'sstill got a long way to go to reach asufficiently realistic level where youand I will go outand buy a filma month,but the latest IPC Video catalogueshows a welcome step in that direc-tion. They sell all sorts of tapes, notonly their own company's offerings,and they have knocked off severalpounds from the price of most. Theonly snag is that by the time you haveadded on a hefty post and packingcharge you're almost back to recom-mended selling price! Not quitethough, and it probably indicatesthereis a fair old margin in the price readytobe cut if sales start to take off orsomeone starts a price war. It istempting (but somewhat misleading)to look across the pond and makecomparisons with the United Stateswhere virtually all hit feature films areavailable on tape more or less im-mediately, and at sensible prices. Veryfew big -name films cost more than the

0

equivalent of £30, many are less, andmany shops will getyou the film of yourchoice within a couple of days,that is ifit is not already in stock. There areseveral mail order tape clubs (likebook and record clubs over here) butthe difference is that you are notcommitted to buying merchandiseyou don't want and the introductoryoffers really are a bargain. Such is life!

By the way, don't ask your friend inthe States to send you across one ofthese tapes unless you happen to havea multistandard TV set and videorecorder. It won't work, so save thedisappointment. I know people whohave been sent really 'exotic' materialwhich they couldn't play back. Whilethey seethed because they couldn'twatch their films somebody else wasprobably grinning, because a signifi-cant proportion of tapes are nowinspected by our customs, and, yes,they do have viewing equipment forforeign TV standards. You can tellwhen your tapes have been inspected:the parcels are resealed and to cap itall, they don't botherto rewind the tapeafterwards! Bit of a nerve isn't it? Afriend rang them up about this andalso complained he had been 'stung'quite heavily on some blank tapes hehad been sent as a gift. To have to payVAT and customs duty on four blanktapes sent as a gift didn't seem fair tohim. Well, it did to the customs, whowere just carrying out instructions, butthey did suggestthat if you were havingtapes sent regularly,they would be lesslikely to attract duty if they were sent inones or twos. I daresay not many of youare, but in fact a multistandard mach-ine need cost no more than £100 overthe price of a normal videorecorder ifyou go to the right place. Of course youwill need adual standard TVsetas well,but careful study of the small adver-tisements in 'Exchange & Mart' mightfind you a bargain. I myself got abeautiful six month old Sony 18" dualstandard set for £230 in this way,which is fa r chea per than the list price.In a future column we will discuss thepleasures and pitfalls of secondhandpurchases in greater detail.

Well, that's it forthe first issue. Lookforward to seeing you again in the nextissue, and if you have any comments,queries, or nasty video problems dropus a line at the magazine. We cannotanswer technical problems individual-ly (unless they are written on the backof a five pound note) or we'd never findtime to write the magazine, but if wefeel the problem will be of interest tomany readers we'll answer it on thispage. Meanwhile, if you have had anyfunny dealings with mail order tradersor good secondhand buys why notshare the news?Andy Emmerson.

E&MM MARCH 1981 57

MUSICALMICRO24 TUNEDOOR BELLBUILD THE WORLD FAMOUS

CHROMA-CHIMEGive your friends a warm welcome. Yes, think howdelighted and amazed they will be to hear themusical Chroma-Chime play when they press yourbutton!The Chroma-Chime uses a microcomputer to play24 well-known tunes. The kit is simplicity itself forease of construction. Absolutely everything neededis supplied, including:* Resistors, Capacitors,

Diodes, Transistors,I.C. Socket and all hardware

* Texas Instruments TMS1000 microcomputer

* Comprehensive kitmanual with fullcircuit details

* Ready drilled andlegended PCB included

Plays 24 well-known tunes including:

Star Spangled Banner, Tell Overture,Greensleeves, Rule Britannia,Colonel Bogey, Oh come all ye faithful,plus many other popular tunes.

* No previous microcomputer experiencenecessary

* All programming retained is on chip ROM* Fully guaranteed* Ideal present any time

r-MP0027A Micro -computer chip available separatelyif required. Full 24 tune spec device fully guaranteed.

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amps £ P&PVolts3-0-3 200 238 2.60 0.5 102 3.60 90.700.6,0.6 1A 1A 212 3.00 75 1.0 103 4.60 1.059-0-9 100 13 2.30 70 2.0 104 7.30 1.200.9, 0.9 330 330 235 2.15 .70 3.0 105 8.60 1.200-8-9, 0-8-9 500 500 207 2.75 75 4.0 106 10.85 1.300-8-9, 0-8-9 IA 1A 208 3.85 6.0 107 15.10 1.50.750-15, 0-15 200 200 236 2.15 70 . .. 118 20.20 1.700-20, 0-20 300 300 214 2.75 90 10 0 119 24.10 2.2020-12-0;12-20 700(DC) 221 3.50 90 60 VOLT (Pri: 220-240)0-15-20, 0-15-20 1A 1A 206 4.60 1.05 Sec 0-24-30-40-48-600-15-27. 0-15-27 500 500 203 4.05 85 Ref. Price

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Ps 220-240 Volts 0 126 5.60 1.052.0 127 7.55 1.20

Amps Price 3.0 125 11.10 1.3012v 24V Ref. £ P&P 4.0 123 12.35 1.500.5 0.25 111 2.30 75 5.0 40 14.15 1.601.0 0.5 213 2.75 .90 6.0 120 17.60 1.602 1 71 3.25 .90 AUTO TRANSFORMERS4 2 18 4.05 .85 Input /Output Tapped 0-115-210-240V6 3 70 5.60 .958 4 108 7.40 1.20 VA Ref. Price

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300 53 10.10 1.2030 VOLT (Pri; 220-240V) 500 67 10.85 1.50Sec 0-12-15-20-24-30V 1000 84 111.60 1.60

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58 MARCH 1981 E&MM

ELECTRO-MUSIC

he word techniques encom-passes a large variety of mean-ings, not only is it the way or

means to do something but also theskill, operation and approach to getthat something done. All techniquesare of a very personal nature, and canbe adapted to one's own style ofplaying, once you have achieved acertain basic level, these techniqueswill grow with you in termsof operationand creativeness.

The most fundamental technique isto understand the instrument you willbe using, not only in itscapabilities butin the way it is eventually heard bythelistener. We will be examining thesynthesiser and its associated equip-ment, not only in thei r workings butthebasic techniques involved in usingelectronic instruments especially invarious forms of music.

Understanding yoursynthesiser

When you sit down with your syn-thesiser, whether it be keyboard ope-rated or modular based the under-standing of what actually happenswhen you rotate a knob or depress aswitch is of the utmost importance.

A synthesiser completely and sim-ply reverses the processes by whichour brain discerns sound. Sound isbroken down by the human ear intothree basic elements and their pos-sible changes. These elements are:Pitch, Timbre and Volume. Let us takea closer look at how these can bethought of in synthesiser terms.

PitchThe frequency of 'cycles' per second

determines the pitch of a soundwave.Frequency is measured in Hertz (Hz)units, one Hz equals one cycle persecond. In musical references we usecommon relationships, i.e. A= 440 Hzor the tonic solfa, do-re-mi scale.

Changes in pitchWhen referring to changes in pitch weare relating to vibrato, tremolo andpitch bending. When you come tomake use of a change in pitch therearecertain questions to ask yourself:

ii (a) How many times do I want thepitch to go up and down each timeI playa note?

(b) How many times per second do Iwant the pitch to rise and fall(fluctuation speed)?

HIGH

1

BASICPITCH

LOW

VIBRATO(SEVERAL CYCLES

PER SECOND/

SECONDCYCLE

PITCH BEND(RISING I

Fig. 1

Figure 1 shows that in vibrato thepitch fluctuates regularly above andbelow the basic frequency of a note,but in pitch bend the pitch risesorfallsjust once.

You must be clear about this dif-ference because on the synthesiseryou will be using two completelydifferent modules to synthesise theseeffects.

Guide to Electronic Music TechniquesVince S. Hill

TimbreTimbre or tone colour depends on

the shape of the sound wave inoperation. Any regular waveform canbe broken down into its fundamentalfrequency and a finite number ofharmonic components which are odd

FUNDAMENTAL If /

.l',, 2nd. HARMONICS (21)3rd HARMONICS (31)

rA.'.`/ 4 th.HARMONICS (4 1)

AN,

Fig. 2

SUM OFf 4-211.3f +41

and even multiples of the funda-mental, these are otherwise known asovertones.

It is the ratio of each of theseharmonics in relation to others whichdetermines the waveform, thereforeany increase or decrease in theamount of harmonics will change thetimbre. When we talk of a sound beingbright, clear, heavy or dull we areresponding to its timbre.

Taking a sawtooth wave as anexample, Figure 2 offers visual con-firmation that any complex periodicwave consists of a number of sinewaves (the fundamental, which is ofgreatest intensity and lowest pitch,and harmonics or overtones which aresimple multiples of the fundamentaland of lesser intensity).

The waveforms andtheir uses

Waveforms can be broken down intotwo basic groups, periodic and aperio-dic. Periodic waveforms are those thathave pitch and are of a repeatingnature, i.e. in a chain of completecycles the cycle being produced lookslike the preceding cycle. Aperiodicwaveforms do not have any repeatingpatterns, sounds with aperiodic wave-forms have no pitch, e.g. those madeby wind, surf, snare drum, etc.

The most common waveformsfound on a synthesiser are as follows:Sine Wave:

The sinewave has noharmonics, it isa very pure tone, it is a very roundedsound akin to that of a tuning fork.

Triangle Wave:A very basic waveform having very

few harmonics, a triangular wave maybec ha nged into a sine wave by the useof the Low Pass Filter. The timbre issoft and rounded, excellent for fluteand vibe type effects.Sawtooth Wave: N

The sawtooth wave, sometimesknown as a 'ramp' waveshape is rich inall harmonics, and one of the most

useful to the synthesist. Used forstring, brass, voice and other har-monically rich sounds. Due to theplentiful supply of overtonesthe VCF ishighly effective.Rectangle Wave: Ill

The rectangle or square wave isvariable depending on the width at thetop, called the pulse width, when thetop and botton widths are of equaldistances it is a square wave, andpossesses the hollow qualities of thereed family. Like a clari netthere are noeven harmonics.Pulse Wave:

As the pulse width proportionatelydecreases, a strong shift intone colouroccurs, the sound becomes 'nasal' inquality, i.e. oboe or harpsichord.

Noise: ANNNoise signals are unique in thatthey

are irregular, have no clear pitch andcontain a mixture of all frequenciestogether. Noise can be used asa soundsignal source for special effects, andas a control signal for irregular modu-lations. There are two common formsthat noise usually takes, these are pinknoise and white noise.

Pink noise has a greater proportionof low frequencies than high, beingperfect for thunder, waves and deeppercussive effects.

White noise is noise which is musi-cally balanced; high and low frequen-cies sound equally loud, white noise isvery useful to synthesise wind, surf,gun shots and rim -shot percussivetype sounds, it is also very effectivewhen used as a modulation signal toobtain the sound of the musiciansbreath when playing a wind instru-ment - again the VCF is well appliedhere.

Changes in TimbreWe do not pay much attention to

changes in timbre in the everydaysounds we hear around us, eg. traffic,talking, telephone etc. Only whensomething dramatic happens, ie. carcrash, shouting, increase in telephonevolume does one pay any clear atten-tion.

If you hear a trumpet being playedsoftly, you hear a rounded and mellowtone, if played loudly the sound be-comes bright and sharp, a clearindication of how timbre changes inproportion to volume.Applyingvibratoto a brass instrument will also causesmall variations in timbre which in thiscase, are proportional to the regularfluctuations in pitch. You will see thesame type of cyclic pattern as inFigure 1.

Try to visualise changes and timbrein graph formation, this is an im-portant skill in playing and under-standing the synthesiser.

VolumeWhen we relate to a sound being too

soft or loud, we i nfact mean itsaveragevolume albeit that the amplitude isconstantly changing. With a synthe-siser it is much more important to

think about how the volume changesover time. For example how do youreally differentiate between a flute andpiano if they played the same note?The most obvious difference isthewaythe volume rises and falls. In this wayvolume does not have 'static' charac-teristics like pitch and timbre, theother two elements that determine'sound quality'.

Changes in VolumeIn Figure 3 you can see from the

graphs the characteristic patternsproduced as volume rises and fallsduring one note. The changes involume on a synthesiser are effectedby the envelope. Again, develop anunderstanding of what happens whenyou heara sound, howdoesthe volumerise?

DRUM

I E

Fig. 3

PIANO FLUTE

ME TIME

Does it remain constant? What is thedecay of the sound? All these factorsrelate to every sound made.

Let us now relate this to the synthe-siser, the pitch is effected from theVoltage Controlled Oscillator (VCO),the timbre is created from the wave -shaping circuitry on the VCO andfinally altered by the Voltage Con-trolled Filter (VCF) or resonance con-trols and the volume is processedthrough the Envelope Generator (EG)and Voltage Controlled Amp. (VCA).

Whether you switch link, patch linkor pin patch, to synthesise any soundyou should use the technique ofproducing the sound in the followingsteps.

AnalysisAnalyse the sound you have in mind,

break it down into its three elementsand look at them individually.(a) What is its pitch?(b) What kind of timbre does it have?(c) How does its volume change over

time?

SelectionSelect the modules you will need

accordingly to the results of youranalysis. Decide which modules willbe able to produce pitch, timbre, andvolume and their respective changes.You must have a clear concept ofexactly what each module is capableof.

ProgrammingProgramme your selected modules

by patching them together and ad-justing their control voltages. Pro-gramming is the end result fromselection and analysis, hooking up inthe correct order to obtain the effectrequired.

If you look at the synthesiser in thisway, a far more logical direction tosound and its characteristics is ob-tained and can be directed to any formof sound make up and synthesis.

In the next article we will be lookingat the modules and following thesound to its end. E&MM

E&MM MARCH 1981 59

ELECTRO-MUSIC

Each month we review the latest Electro-Music Equipment - from synthesisersto sound reproduction and effects!

E&MM's special in-depth reviews look at what's new in the world of commercialmusic -a vital updating for both electronics designers and musicians.

aUV* ". MOO

11111111 IM1111.111

With polyphonic synthesisersappearing in the shops morefrequently now, it must be

natural for a manufacturer's designteam to want to make their instrumenthave more 'orchestra' groups andeffects than their competitors.Yamaha, however, in their SK20 haveproduced a synthesiser that takes thethree most important polyphonicsounds and utilises their uniquecustom chips to give an advancedtechnology machine for its price. TheSK20 functions as a polyphonic syn-thesiser and a string synthesiser (withthe POLYSYNTH section), as well as aharmonic drawbar ORGAN. The key-board plays up to seven notes over its5 octave range or fourteen notes ineither of the split keyboard modes. Inaddition, string chorus effects, Leslie -type tremolo, delayed vibrato and de -tuning are featured.

The ConstructionYamaha's instruments always have

a high class finish in terms of physicalmaterials, and the SK20 is certainlyno exception. Styled like the CS40/20M and 15D it has rosewood grainend panels, semi -matt black metalpanels and wooden base. The weightof the whole package is only 33lbwhich must make it one of the lightestpolyphonic instruments for its size(10(W) x 15.8(H) x 40.6(D) cms). Nocase is provided and the footswitch(FC-4) and footcontroller (FC-3) areoptional extras at £13 and £19 respec-tively. Servicing couldn't be easierwith all of the main panel opening upas in Figure 4 and a removablekeyboard (see Figure 3).

Yamaha Symphonic Ensemble SK20

The CircuitryThe SK20 essentially comprises

three separate sound sources -organ, string and polysynth driven bya common keyboard. The machine isbuilt around 4 Yamaha custom largescale chips. The 61 note keyboardspeaks to the digital tone generatorsvia a 40 -pin chip called the 'KeyAssigner YM62100'. There are 13note lines, 5 upper and 5 lower octavelines on the input, interfacing with thekey switches through a diode matrix.Octave and note identities are sent bythe Key Assigner and output as 12 -bitcodes indicating octave, note, key-board and keying state. These 12 -bitcodes or parties are put on 4 -bitdata lines KC1 to KC4. They are

organised as 4 -bits wide by 3 -bitslong. Each bit is 1 microsecond dura-tion. The Key Assigner is the samedevice used in Yamaha's more up-market organ range and for thisreason has the output capability ofinstructing up to 18 sound channels:7 upper, 7 lower, 1 pedal and 3 autoarpeggio sounds. In this particularapplication, only the 7 upper and 7lower instructions are used.

Tone GenerationTwo tone generator LSIs are used

for production of the basic waveformsand their associated sound amplitudeenvelopes. The 2 ICs share the same4 -bit input data lines KC1 to KC4 fromthe Key Assigner.

The organ wave generator IC

Fig. 2. This board contains Yamaha's own LSI chips employing their PASS technology.

YM70200 receives 13 master inputfrequency instructions CI -C from anLSI daughter chip, YM62200, whichcombines with the keyboard data onits KC1 to KC4 terminals. This pro-duces a set of sine wave outputs 16'through to 1' by Yamaha's PulseAnalogue Synthesis System(Pass).These sine signals are low passfiltered and sent through to thevolume slider controls of the panel. 4'and 2' pitches are also connectedthrough two VCA envelope controlgates for the percussive attack voices.Three preset flute combinations arederived from mixing resistors andtheir associated FET resistor gates.Normal flute voices are collectivelypassed through a 'brilliance' filtercircuit and on to a 'level' control and

60 MARCH 1981 E&MM

ELECTRO-MUSIC

'tremolo/ensemble' selector gating.The polysynth and string basic

sound sources are produced fromanother (Pass) wave generator LSIchip, YM70400 - this device pro.duces 8' and 16' square waves and 4'sawtooth waves which pass throughmixing amplifiers into selector gatingwhich directs these sources to theappropriate treatment (sawtooth 16'and 8' are derived from the squarewave mixing with the 4' sawtooth).

Polysynth and sources are routedthrough a voltage controlled filter;TG00156, giving gate selectable highpass or low pass outputs. The filterprovides voltage control for attacktime, decay time, sustain level andrelease time.

Three diode resistors matricesprovide preset control for the variousparameter voltages (e.g. initial level,attack) required to set the particularpresets on the panel.

Two string voice sound sources,16' and 8' sawtooth, are passedthrough their selector gates and acommon LDR to the string level con-trol (which can be the optional FootController FC-3).

Polysynth and string level outputsare mixed and passed through acommon 'brilliance' filter and out tothe tremolo/ensemble selector gates.

EffectsTremolo/Ensemble effects are ob-

tained from a common board employ-ing 3 delay paths (BBDs). AnotherYamaha custom LSI, YM63300 clockgenerator, provides 3 outputs of0.64Hz with 120° phase differencebetween them and 3 outputs of 6.4Hz,also with 120° phase difference.These 0.64Hz and 6.4Hz outputgroups are mixed and provide 3 com-posite control lines for the VCO drivesto the BBDs which then have a 120°phase difference. This produceseither a complex ensemble effect orby modulating the VCA at its outputachieves a rotating speaker/tremoloeffect.

A slightly unexpected method ofinterfacing some of the parametercontrols is employed, e.g. organ sus-tain lengths. Here the sustain sliderselects diodes via internal switchconnections and outputs a 3 -bit codeto a parallel to series converter (multi-plexer) through to a serial data inputon the wave generator instructing it toproduce the appropriate sustainlengths.

The two tone generator ICs (organand poly) are driven from the two key-board code groups - upper andlower. The polysynth IC is driven byupper key codes and the organ gen-erator IC is driven by lower key codes.By dividing the connections of theupper and lower octave input lineswith the common note lines, the tonegenerator groups are similarlydivided, giving the keyboard split.

The two tone generator ICs haveseparate master clocks which can befrequency modulated by the vibratodrive circuit. Modulation may beapplied to either one or both inseparate degrees. Pitch control isapplied in a similar fashion to the twoclock circuit inputs giving individualpitch control on both tone generatorgroups.

Fig. 3. Keyboard is removable and links via a ribbon cable.

The Controls and theirMusical Effects

The controls are well placed on theangled main control panel with micro -touch switches (that have LED indi-cators) in a row conveniently abovethe keyboard. There are 5 control'blocks above the switches from left toright: Output, Pitch, Vibrato, Organand Polysynth. Sliders make settingup much easier although it takes awhile to get used to the organ section- maximum volume on each drawbaris in its lowest position - as if youwere pulling a Hammond drawbar

Fig. 4. The SK20 opened up.

towards you.A connection panel on the rear

links a 'sustain' footswitch (for organand polysynth sections - either orboth can be selected from the panel)and a foot controller for 'string' or'mixed' output volume. There arethree standard jack outputs available- polysynth/string, organ and mixedpolysynth / string / organ. A low im-pedance stereo phone socket givesthe mixed output and a standard 11pin connector is provided for use witha Leslie Speaker System (2 channelinput type). An adjacent switch allowsthe speed of the rotating speaker to be

switched from the panel to fast/slowand on/off.

The 'Output' block has indepen-dent sliders for setting the volume oforgan, string and polysynth with arotary master volume control that canhave its output signal (the mixedoutput) switched on or off. Since thebackground noise of the instrument isvery quiet it's not really needed as astandby switch or noise reducer for amulti -keyboard set-up, but can proveuseful when the other two outputs goto effects boxes or different spatialpositions. If you get our demonstra-tion tape for this issue you'll hear a

E&MM MARCH 1981 61

ELECTRO-MUSIC

Fig. 5. Front panel (left) circuitry with sections clearly labelled.

very broad stereo image from theSK20 which is due to the mixed outputfeeding to the centre with slight echoadded. The separate organ and poly-synth/string outputs are then pannedleft and right respectively with a

phase box and flanger linked in thepolysynth signal line for furthereffects. Incidentally, the Roland CR-78gives the drum sounds (adapted forstereo with split instrument outputs),and the CS -30, operating from aYamaha pedal board and drum triggerpulse, gives a bass line to the openingpiece (see page 96 for details of demotape).

There are two rotary controls in the'Pitch' block for tuning adjustment tothe organ and polysynth sections.Since the string sound is derived fromthe polyphonic synthesiser section,

the polysynth tuning also affects thepitch of the strings. Interesting de -tuning effects can be obtained by firsttuning the organ to your playing'standard pitch' (e.g. 440Hz=A) andthen very slightly moving the poly -synth pitch sharper so that slow beat-ing occurs. A small amount of de -tuning will enrich the overall soundand a large amount will give, forexample, organ and strings (withouttremolo/ensemble) a fairgroundorgan effect. Pitch is variable fromA=435-450Hz.

Vibrato can be applied to organand polysynth in separate amountsusing 'depth' and 'speed' sliders andhas an initial delay of up to 3 secs. It'suseful on organ for improving the fasttremolo effect and with delay willallow playing with or without vibrato

depending on your use of slow orquick notes.Organ

The organ block contains the mainfeatures of a good harmonic drawbarorgan with separate sliders for select-ing 16', 8', 5'/3', 4', 22/3', 2' and 1'pitches in varying degrees. Despitethe lack of the two top mixtures, it hasa full-bodied tone that is particularlyclean in the bass. There's a 'brilliance'control to boost the top as well. Twoswitches select 'sustain' (which givesa decay after release of the keys) or'decay' (which replaces the normalorgan on/off key action), both adjust-ing from one slider. To completethe section there are 2 percussionsliders that give 4' and 22/3' punch tothe sound using 'decay' on minimum.Increasing the decay time gives glock-

car et

Fig. 6. Rear connection panel.

enspiel or vibraphone (with vibrato)tones. There is a certain amount ofkey click present, especially withincreased brilliance, for jazz/poporgan sound. A slight drawback is thatwith 'sustain' on this bright click effectis removed. Four panel switches give3 presets: 16'8'5%'; 16'8'4'2' and full,plus 'manual' selection.

Trigger action is worth noting -the polysynth only triggers when allnotes are released and a new note orchord is played. The strings alwaysplay and the organ plays according todecay/sustain settings. The note limi-tation is only evident with long 'sus-tain' set, playing runs up the keyboardwhen it only sounds 7 notes at anytime.

Tremolo/EnsembleTremolo is a very realistic rotating

speaker effect that is produced elec-tronically. It can be applied to bothmain synth sections and has two -speed switch selection that speeds upor slows down during changeover forjazz chorus and church organ sounds.Ensemble is best suited to applyingphase to the strings although it can beused with organ and polysynth. Un-less you are buying an external tonecabinet then you have a compromisehere - when ensemble is selected forpolysynth/strings, then tremolo iscancelled on organ and also reverts toensemble! Nevertheless, these twotreatments make a big contribution tothe final sound.Polysynth

Within this section are two controlsthat also affect strings. They areswitches for adding 'slow attack' and'sustain'. Once again the latter isreally the release control for the VCA.Two string pitches can be selected,either 16' or 8'.

The Polysynth section can have itsoscillator and wave source to be either16', 8' or 4' sawtooth, 16' or 8' sq uare-wave, or 8' sawtooth in bandpassmode - the others go through a lowpass filter. All the useful synthesiserfilter controls are provided - cut-offfrequency, resonance, EG depth andADSR - and if you've played any ofthe CS50, 60, 80 range you'll know thekind of sounds you can get fromthese. It's a powerful synth sound byany standard with very smooth filtercontrol using resonance that reallypicks out the harmonics. Three pre-sets for Polysynth give brass sounds- so now perhaps you're realising thisinstruments potential!

Finally, the keyboard can be splitwith the organ on the left and thepolysynth on the right and vice versa.You can get a walking percussive bassfrom the organ in your left hand withthe right making rich strings swell infrom the foot controller whilst poly -synth sounds shoot through the har-monics using added 'brilliance'! Allvery exciting and there's an SK50 twomanual on the way shortly so obvious-ly Yamaha have a lot of hopes for thistype of instrument which has bene-fited from their research and develop-ment in the lucrative home organistmarket - this machine would havebeen quite impractical for manu-facturers who use conventional off -the -shelf devices. If you can't afford itsprice of £870 including VAT, then takea look at the smaller SK10.Mike Beecher and Martin Christie

62 MARCH 1981 E&MM

ELECTRO-MUSIC

cciEwEn@Kmal@ 27rMao:o

Chris Jordan

If you are already thinking in terms beyond unison ramp waves through adecaying cutoff LP filter with a backdrop of sweeping filtered noise, thenyou've probably realized that a fully variable system with comprehensive

patching facilities, or at least a versatile switch -linked instrument with FM,Sync, PWM etc., is essential for original and creative synthesis, even if used inconjunction with simpler pre -patched and/or polyphonic instruments. If so,these articles will tell you about advanced techniques of synthesis to help youmake your own music, however humble it is, rather than infinitely less satisfy -

Voltage ControlWhat makes a synthesiser differ-

ent from any other electronic musicalinstrument, and also what makes asynthesiser player different from, inparticular a keyboard player, is theextensive use of voltage control. Itallows the parameters of signal gen-erators and processors to be deter-mined by the outputs of othergenerators and processors, in a waythat is fundamentally independent ofthe method of producing the controlsignal or the nature of the parametercontrolled. So, for example, a key-board can control the cutoff frequencyof a filter in the same way as an oscil-lator can control the pitch of anotheroscillator.

The most important differencethat can exist between one piece ofsynthesiser equipment and another isthe way the voltage controlled para-meters respond to their controlvoltages. This is the much talkedabout subject of 'linear' and 'exponen-tial' (sometimes called 'logarithmic')control voltage laws. The problemsarise from the fact that it is mostuseful for the pitch of an oscillator torise by one octave for each unit rise incontrol voltage wherever this may bein the overall range, but conventionalanalogue oscillators are based aroundintegrators which give a doubling ofrate of change of voltage, and there-fore a doubling of frequency, for adoubling of input current. Since pitchis related to frequency in an expo-nential fashion, an exponential con-verter is required to process thecontrol voltage (CV) in order to pro-duce the correct response. Additionalcircuitry, and sometimes trimming, isneeded to reduce the effects of temp-erature variation on the law and thetuning of each oscillator, so somesystems do without precision con-verters, directly generating a key-board voltage with increasing CVintervals for the same musical inter-val as it moves up the range. Theselatter are the so-called 'linear' sys-tems, which are potentially morestable and cheaper to make. It was theinsufficiently compensated exponen-tial synthesisers of the early seventiesthat gave the synthesiser a reputationfor perpetual bad tuning, and later onprompted one linear system manu-facturer to advertise with the lineAvoid the embarrassment of an out-

ing collections of well-worn synthesiser clichés. If not, don't be put off -perhaps we can simply stimulate your imagination. And remember, if you areusing equipment you've made yourself, then you have an advantage over theperson who has bought something equivalent - not only do you have an insightinto the way it works which can only help you in using it to the full, but you're ina position to make your own modifications and expansions when you reach itslimits of capability. After all, no-one is more suited to designing thespecification of a piece of equipment than its eventual user.

0 1 2 3 4 5CONTROL VOLTAGE (VOLTS)

600

500

NI- I- 400w

300

z200

Uu- 100

0 1 2 3 4 5

CONTROL VOLTAGE (VOLTS)

6

6

Figure 1 Linear and Exponential control voltage laws.

of -tune performance"!Generation of a 'pre -converted' key-

board control voltage gets over one ofthe problems of a linear system, butsince a control voltage change mustbe greater at higher frequencies forthe same effect on the pitch, a simpleeffect such as vibrato requires thesecondary CV to be multiplied by thekeyboard voltage before it is used,and where the precision of this mustbe as good as that of the keyboarditself (for example when using ananalogue sequencer), the multiplyingoperation must be very accurate.This is usually only available withthe keyboard as the primary source -when two low frequency oscillatorwaveforms or sample and hold out-puts are used to control pitch theywill appear to interact to condensethe higher pitches, and the provi-

sion of a cheap uncompensatedlinear - to - exponential converter ishardly a satisfactory answer. Glide('portamento') is usually produced byprocessing the keyboard CV, andwhere this is so it will suffer from thesame effect. Glide that has been gen-erated by a resistor/capacitor (RC)network will have the extent of thecurve increased on the way up anddecreased on the way down, whereasthe linear type will be equally con-densed towards the higher pitch ineither direction. Because linear glidefeatures a constant slew rate for eachsetting of the control, it will also takeproportionately longer to cover thesame musical interval the higher up itis played.

A more fundamental feature oflinear control is the fact that totranspose the pitch of a keyboard -

controlled oscillator up or down re-quires the keyboard CV to be multi-plied or divided - adding or subtract-ing a DC voltage as one would totranspose in an exponential systemcauses disruption of the scale inter-vals. Hence tuning of linear oscillatorsis often achieved by a 'Range' switchwhich changes the integrator timeconstant giving three or more foot -ages, in conjunction with a 'Tune' potwhich varies the gain of an input CVamplifier from around 0.6 to 1.6.Using an oscillator without a key-board -type controller then becomes abit awkward, since in the absence ofan input CV it will not run. So an extrapot is required to provide this CV; thisis called 'Sweep' or 'Free Run' andallows the whole range to be coveredwith a single control, though it suffersfrom the same old problem when asecondary CV is patched in for addi-tional control and this time multipli-cation is not practical. Of course, theFree Run control must be returnedcompletely to zero for equal tempera-ment from the keyboard, sequencer,quantiser or whatever. Unfortunately,not doing so does not provide equalmacro or micro -tones - alternativetunings of this type cannot be prac-tically produced in a linear system,though with an exponential keyboardthis is just a matter of amplifying theCV by the required scaling factor. Infact this is what happens when oneexponential system is interfaced withanother that employs a differentpitch -to -voltage ratio.

Most exponential synthesisers use1V/Octave as standard, but may re-quire trimming to match the scales ofphysically separate units. Connectinglinear synthesisers together also re-quires attention to the CV range,though since all oscillators must juststop with no input, and gain errorsappear as transpositions, the Tunecontrol can correct for any minormismatches.

For those of you who like sums, allthis can be represented quite simplyby:

f=2kwhere k represents the note requiredand corresponds to a depressed key,and f is the frequency that will sound.In an exponential system we can varythe scale and transposition easily:

f=2(ak +

E&MM MARCH 1981 63

ELECTRO-MUSIC

where a is the scaling factor and b isthe interval. In a linear system, 2k isgenerated directly so transpositionrequires multiplication:

f=2(k=2k x 2b

and for scaling:f=2ak x 2b

=(2k)a x 2b

Now we see why variable scale controlfrom a quantized CV generator suchas a keyboard is impractical. It re-quires the value of CV to be raised to avariable power!

Figure 1 shows the relationshipsbetween linear and exponential con-trol voltages and the pitch andfrequency of a VCO.

The fact that one cannot neces-sarily cause an important parameterto vary in accordance with the sum oftwo control voltages by adding theCV's and patching the result to theparameter control input is a severelimitation of the linear control system,and makes it only really useful forsmall, pre -patched synthesisers,where the VCO's are always underkeyboard control and simultaneousmodulation of a single parameter bymany signals is not required. The useof constant temperature ovens andmore advanced compensation cir-cuitry, plus the availability of inter-nally compensated monolithic expo-nential VCO's means that exponentialsynthesiser designs have the temp-erature dependance of exponentiat-ing semiconductor junctions wellunder control, with stability approach-ing that of linear instruments, andcertainly good enough even for liveperformance.

Since voltage controlled filters areoften required to track keyboard -controlled oscillators maintainingconstant harmonic content for dif-ferent pitches, they must exhibit thesame law as the VCO's. Accuracy andtemperature stability are not as im-portant, though these will necessarilylimit the usefulness of resonatingfilters as sine wave oscillators. It isinteresting to note that the CV law ofVCF's seems to impose particulardesign restrictions which affect thefilter's audio characteristics, causinglinear VCF's to sound weedy and lack-ing in character when compared withexponential VCF's: this is more than amatter of 2 -pole verses 4 -pole thoughdiscrete exponential VCF's often showsteeper cutoff's than linear ones. We'lltalk more about filter characteristicsin future articles.

Since signal amplitude is rarelyrequired to track another controlledparameter, voltage controlled ampli-fiers do not necessarily exhibit thesame law as other modules in thesame system. The choice is oftendictated by the envelope/transientgenerators since the most usefulenvelope shapes have exponentialattack and decay portions, like acous-tic instruments where decays proceedwith a constant percentage loss ofenergy from a vibrating body in eachunit of time. This shape of envelope isachieved with an exponentialenvelope generator and linear VCA, orvice versa, and since exponentialenvelopes are more useful for con -

t

0

(a)

500 000 1500 2000

FREQUENCY (HERTZ)

PROGRAM 100HzDEVIATION 100Hz 1.0%INDEX 1

. 11 I I II.1

500 1000 500 2000

FREQUENCY (HERTZ)

PROGRAM(b) DEVIATION

INDEX

100Hz400Hz 40%4

IIIII

0 500 1000 1500 2000

FREQUENCY (HERTZ)

(c) PROGRAM 100HzDEVIATION 600Hz 60%INDEX 6

500 10001

500 2000

FREQUENCY (HERTZ)

PROGRAM(d) DEVIATION

INDEX

200Hz400Hz 40%2

0 500 1000 1500 2000

FREQUENCY (HERTZ)

PROGRAM 50Hz(e) DEVIATION 400Hz 40%

INDEX 8

Figure 2. Spectra of frequency modulated sine waves.

trolling other modules, and like VCO'san exponential VCA is often just alinear VCA plus a (non -precision)exponential converter, the formeralternative is the most common. Thisis almost always the case in small pre -patched synthesisers, and often so inpatchable envelope shapers, eachbeing a combination envelope gen-erator and VCA. The choice of linear orexponential control on a VCA is useful,especially where it is controlled by anon -keyboard initiated envelope or aperiodic or complex low frequencywaveform, possibly controlling theamplitude of another control signal.Where an envelope generator is of theAD or ADSR type it is usually exponen-tal, linear slopes being reserved formultiple -stage or patch -program-mable generators.

Linear control of most exponentialVCO's is possible, though the inputmay not be provided. Where it is, anumber of techniques can be used toextend the capabilities of the VCO,such as stopping the oscillator with alow input voltage (only useful wherethe linear control input is DCcoupled), waveform shape modula-tion, and by far the most powerfulapplication: audio frequency FM.

FrequencyModulation (FM)

Frequency modulation is the dyna-mic control of the frequency of aperiodic waveform, and as such in-cludes most techniques of voltagecontrol of oscillator frequency such askeyboard control and vibrato. How-ever the term is usually reserved forthe technique of producing newtimbres by modulation of thefrequency of one audio frequencytone by another, especially where itappears abbreviated to FM. This tech-nique has the ability to produce suchcomplex spectra using simple sinewaves as the modulating ('program')and modulated ('carrier') signals thatbright waveforms such as pulse andramp are not often used, except fordense, noise -like sounds.

The effect of FM is to produce agroup of frequency componentsabove and below each harmonic ofthe carrier signal, each new partialbeing referred to as a sideband. With asine wave as carrier, two groups ofsidebands are produced, and if theprogram is a sine wave as well, thedistribution of the sidebands is simplydetermined by the program frequencyand the depth of modulation. This isillustrated in Figure 2, which showsspectra of a 1000Hz sine tone modu-lated with another sine tone at vari-ous frequencies and depths. Thespacing between the resultant com-ponents is equal to the modulatingfrequency.

The depth of modulation is ex-pressed as a deviation from the car-rier frequency in Hz or as a per-centage, and determines the spreadof the sidebands with 90% of theenergy contained with the range ofdeviation (indicated by the double -headed arrows on Figure 2).

The Modulation Index is the devia-tion in Hz divided by the modulatingfrequency, and determines the rela-tive amplitude of each sideband, sothat for each value of the index there

64 MARCH 1981 E&MM

ELECTRO-MUSIC

is a characteristic distribution, exceptwhere the deviation exceeds about50% and the symmetry becomescorrupted by lower sidebands which'reflect' through 0 Hz, adding to orinterleaving with components withinthe deviation range. Since the numberof sidebands within each half of therange of deviation is equal to themodulation index, the index tells howmany significant sidebands there arein an FM spectrum. For example, inFigure 2c the modulation index is sixand there are six significant com-ponents each side of the carrier.

The modulation index is an ideaborrowed from the field of FM radiowhere the modulating frequency andthe frequency deviation are small incomparison with the carrier fre-quency, and the relationship betweenthe sideband spacing and the carrierfrequency is unimportant. More use-

. ful to the synthesist are the deviationand the ratio of the two frequencies -if one frequency is an integralmultiple of the other then the side -bands will form a harmonic serieswith the fundamental at the frequencyof the lower, though it may be of zeroamplitude. If not, a non -harmonicovertone series of the sort that is socharacteristic of frequency or ampli-tude modulation is produced. It isinteresting to note that the results ofFM with simple fractional ratios suchas 2/3, 3/4 are ambiguous sounds withperceived pitches dependant onacoustic or musical context.

Going back to Figure 2, it can beseen that the total spread of (b), (d)and (e), non-reflecting spectra withthe same deviation, is largely inde-pendent of the carrier and modulatingfrequencies. Note that within thedeviation the sideband pairs are ofsuperficially irregular amplitude, andoutside they decay rapidly to zero. Inall illustrated spectra except (a) thecarrier frequency has a lower ampli-tude than the strongest new com-ponent - at some values of the modu-lation index, the lowest of which isaround 2.7, the carrier disappearsaltogether and the amplitudes of indi-vidual sideband pairs canalsobecomezero at certain index values.

To make practical use of FM, weideally need independent control ofthe pitch of the oscillators, the intervalbetween the modulating and modu-lated oscillators, and the percentagedeviation. The first two are simpleenough - they are basic requirementsof a system limited to simpler syn-thesis techniques - but the deviationis dependant on the amplitude of themodulating waveform which willnormally give a constant frequencydeviation in Hz, requiring multiplica-tion to retain a constant percentagedeviation with changing pitch. Theresulting decrease in the number ofpartials and their spread as the pitchrises is a disadvantage but is usuallytolerable, and sometimes quite use-ful, when FM is being used for simula-tion of natural instruments forexample. The percentage deviationcan be held constant over a limitedrange by passing the program throughan exponential VCA controlled by thesum of the carrier oscillator inputCV's. If you're thinking that this wasthe point of the exponential converter

E&MM MARCH 1981

AUDIO- - -CV- - --- GATE

KBD

LFO

r- VCO

SYNC.

-I

I

LIN.

VCA

EG

VCO VCA

EG

Figure 3. FM evaluation patch.

in the first place you are right, but thelinear control input should be used fortwo reasons:1. The exponentiation would distort amodulating sine wave, introducingextra sidebands into the result.2. More importantly, the distortionwould shift the mean level of themodulating waveform, causing thecarrier frequency to rise with increas-ing modulation depth.

This latter effect occurs even if theprogram is AC coupled where it leavesthe oscillator, as it must be for properlinear FM, due to the different effectexponentiation has on the upper andlower portions of the waveform. Thepitch shift effect can be demonstratedquite simply on a Minimoog: with onlyoscillator 1 switched into the mixer,oscillator 3 is set to independentcontrol and the oscillator modulationis turned on with the modulation mixcontrol completely on osc. 3. Holdinga note and then pushing up themodulation wheel introduces fre-quency modulation and the pitchrises accordingly. If this doesn't soundlike too much of a disadvantageremember that a small change ofoscillator frequency has a great effecton the relationship of the overtones inresultant sound. This means that re-tuning is needed every time themodulation depth is changed, but FMremains quite useful in a exponentialsystem where the VCO's don't havelinear CV inputs.

Linear CV systems are bettersuited to FM than exponential onessince the provision of a keyboard CVmultiplier makes constant percentagedeviation FM trivial, though not if thepatchable keyboard CV modulationinput is equipped with a simple linear -to -exponential converter as is oftenthe case, when it will have to bebypassed to obtain the full benefits.These include the ability to dyna-mically change the deviation, which isalso available with linear -inputequipped exponential VCO's.

The sound of a FM tone with themodulation depth decaying after thebeginning of each note is rapidlybecoming something of a cliché ofcomputer music and in particularmusic using modern digital synthe-sisers, though it would probably bedescribed as a decaying index soundby the composers who use it, sincethe modulation index is still con-sidered a useful measure of FM depthby computer synthesists. Frequencymodulation is very widely used indigital synthesis systems since inaddition to providing a large selectionof harmonic waveforms, it savesenormous amounts of computationtime over comparable methods ofproducing sounds with non -integrallyrelated overtones. In fact one mightalmost say that FM is to digital syn-thesisers what resonant low-passfiltration is to simple keyboard -basedanalogue synthesisers.

One disadvantage with FM, whichis particularly important in imitativesynthesis and computer synthesiswhere the result of an alteration isonly heard after a delay, is that to allbut the most experienced synthesistfinding a particular sound is a matterof trial and error, unlike subtractivesynthesis where one soon learns howa filter cutoff frequency or Q must bealtered to get the right timbre. Thiscan be alleviated to some extent byusing degenerate forms of techniquewhich limit the number or values ofthe variables and hence the range ofpossible sounds, making FM easier touse.

Groups of degenerate FM spectrawhere the carrier and program arefixed in simple musical intervalsresult from the use of oscillator syn-chronisation and this also allows theelimination of beating effects fromsounds produced by straight FM.Using Linear FM with the type of syncthat unconditionally resets thesecond oscillator at the same point ineach cycle of the first yields a whole

range of waveforms which retain aharmonic overtone series whateverthe settings of the VCO's. This isparticularly effective where one oscil-lator is the source of the waveformsfor both functions and the other is setat a higher footage, whereupon thesecond one becomes a waveformgenerator locked to the pitch of thefirst, with the timbre controlled by theFM depth and slave VCO 'pitch'. Sincethe latter is potentially voltage con-trolled, startling timbre sweep effectscan be obtained, and because onlytrue harmonic series are generated,this provides a versatile source of'safe' sounds for melodic keyboardplaying.

Figure 3 shows a patch for com-prehensive evaluation of frequencymodulation using sine waves with orwithout synchronisation. Modulationdepth is under control of an envelopegenerator and either or both of thecarrier and program can be modu-lated by the LFO in addition to thekeyboard.

A simple single VCO synthesisercan be used for basic experimenta-tion with FM if the filter is able to self -oscillate. The oscillator output mustbe re-routed to the filter CV input sothe VCO generates the program andthe filter becomes the modulated sinewave oscillator. An unused position onthe waveform selector switch can beconnected to bring in the FM if a sparepole is also available to connect thetriangle output to the filter CV input,using a series capacitor to remove DCfrom the waveform. If the oscillatorhas its own output level control, takingthe program from its wiper will givecontrol of modulation depth withoutthe need to reassign an existing filtermodulation control or to add anotherpot. The level control should be ACcoupled to the waveform switch orVCO output so that the level will not re-adjust itself each time the depth isaltered, though if the filter is exponen-tial a pitch shift will occur anyway.

E & MM

65

See and hear better with- Ak trAntiference

Aerials)1111 for TV, FM Stereo, Caravan

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lectronics Pocket Book Fourth EditionA Parr

Semiconductor technology has progressedat a startling rate and microprocessor chipshave caused an information revolution thatwill be as significant as the IndustrialRevolution proved to be. This fourth editionof Electronics Pocket Book is completelynew and covers the latest developments aswell as the basic principles. A usefulreference manual for both the professionalengineer and the enthusiast completely

))scilloscopes - How to use them,Explains, from first principles, what theoscilloscope does and how it works. Thecapabilities of both basic and advancedscopes and related instruments areexamined. Essential reading for all

rewritten to take account of the latestdevelopments in electronics includingmicroprocessors. The book provides a non -mathematical presentation of the varioustopics comprising electronics.

186 x 120mm 360pp Illustrated0 408 00481 9 £5.60 Paperback

how they work Ian Hickmanusers and potential users of these vitalelectronic tools.

216 x 138mm 128pp Illustrated0 408 00472 X £3.45 Paperback

RDER NOW. Cut out this coupon and return itPatricia Davies at the address below:

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Please sendcopy/ies of Electronics Pocket Book4th Edition(Parr) 0 408 00481 9 @ £5.60copy/ies of Oscilloscopes(Hickman) 0 408 00472 X @ £3.45copy/ies of Practical ElectronicsHandbook(Sinclair) 0 408 00447 9 @ £3.95copy/ies of Master Electronics in Music(Towers) 0 408 00262 X @ £3.25copy/ies of Electronic Projects in Music(Flind) 0 408 00391 X @ £2.50(EMM 3/81)

Also of interest

Practical Electronics HandbookIan R SinclairPresents a compact collection ofcircuits and applications for both theprofessional engineer and the homeconstructor. It covers passive andactive components, discretecomponent circuits and linear anddigital ICs. The operation andfunctions of typical circuits aredescribed using a minimumof mathematics.216 x 138mm 192pp Illustrated0 408 00447 9 £3.95 Paperback

Master Electronics in MusicT D Towers

Electronic 'special effects' andkeyboard instruments such as theeleCtronic organ are dealt with, aswell as magnetic tape music, musicsynthesisers and computer music.The book concludes with a survey ofthe history of electronic music.216 x 135mm 128pp Illustrated0 408 00262 X £3.25 Paperback

Electronic Projects in MusicA I Flind

Has been written for the electronicsenthusiast and the musician. Awide selection of projects from asimple metronome to a mini organis described.216 x 135mm 88pp Illustrated0 408 00391 X £2.50 Paperback

66 MARCH 1981 E&MM

ELECTRO-MUSIC

The electric guitar is a simplebeast, indeed in terms of to-day's micro -chip technology,

downright primitive. I don't propose tochange that, I like it, butwhat I will do inthis series of articles is show you howyou can exploit an existing wiringsystem more fully in order to makeyour guitar capable of coping with avariety of tonal demands. A couple ofhumbuckers can give a wide range ofsounds, and can be persuaded todo sowithout going active, although ulti-mately, dropping output impedancewill help the treble you achieve on theguitar to make it to the amplifier.

Firstly, it'll all make a bitmore senseif we understand a few pick-up basics.

A single coil pick-up consists of acoil wound around a bobbin, and in thecentre of the bobbin are either sixmagnets, one bar magnet, or six polesthat conduct the magnetic field frommagnets underneath the unit. Thewires from each end of the coil areconnected to two stronger wires, or asingle conductor and shield.

The vibration of the string (whichcontains nickel) over the pick-upexcites the magnetic field, and gene-rates a minute alternating current, thefrequency of alternation of which isexactly the same as the frequency ofalternation of the strings. That is,simply if you twang A 110, the string isvibrating 110 times per second, so thecurrent from the pick-up will alternatepositive to negative 110 times persecond. This current, when suitablymagnified by the amplifier, will pushthe speaker cone back and forth 110times persecond, and a beautiful, loudA will sound as the air between thespeaker and your ear is vibrated 110times per second. Do not believe theoccasional expert whotells you a pick-up gives D.C. - guitar mythology has tostop here.

The variation in the number ofwindings, choice of wire, type ofmagnet and so on give the pick-up itspower and tone characteristics, andsingle coil pick-ups are available thatgive you the option of earthing out partof the.coil to vary said characteristicsaccordingly.

Many single coil pick-ups cancause problems with intonation, andFender Strat- or Telecaster ownersknow them well. Where a pick-up hasmagnetic pole pieces, the magneticfield is closer to the string and inter-feres with its free vibration, causing adouble note effect particularly on 6thand 5th strings in higherfret positions.The only cure for this is to lower the

i pick-up and sacrifice a little power. Apick-up which has magnets under-neath and conducting poles will notgive this effect to all practical pur-poses, but for the purist this type maynot be tonally desirable. This problemcrops up less on humbuckers as fewmanufacturers use magnetic poles inthis situation. You may notice a slightpull on some power pick-ups, forexample the Dimarzio X2N, whichuses a very strong magnetic field. Onthis pick-up, the extra magnets underthe pick-up are cut away under sixthand fifth strings, so installing the unitthe right way round is important. Infact, there is such a healthy outputfrom pick-ups like this that droppingthem a little further from the stringsgives a negligible power loss - I run

E&MM MARCH 1981

three X2Ns in one guitar with noproblems.

A humbucker consists of two coilswired in series and over a magneticfield that varies from maker to maker.Here, I'm merely concerned with thealteration of the wiring up to getdifferent sounds, so suffice it to saythat various arrangements of polepieces conduct the field to the area ofthe vibrating string.

The out of phase bit can be confus-ing, because as experienced players,we tend to associate 'out of phase' withthe honky type of sound given by twopick-ups operating together in a mix,but with the output of one taken fromthe opposite end of the coil(s) to theother - that is, the phase of one iscompletely reversed in relation to theother. An apparently similar tonequality can be had from a singlehumbucker (with a correspondingdrop in volume) by running the twocoils in series, and in phase. Thissound most of us would instinctivelycall 'out of phase', and the smooth fatsound of a normally wired humbucker,coils actually out of phase, we wouldregard as sounding 'in phase'. Wherewe gettowi ring upforth is in th i s series,I shall therefore refer to normal andreverse coil phase, and hope that thatavoids confusion. If you should findthat you have a coil phase problem,remember you solve it simply byswapping around the two wires fromone of the coils.

The actual hum -cancelling effect

Adrian Legg

is achieved because the coils are inopposite phases, and when one 'hears'electrical interference, the other'hears' exactly the opposite and can-cels it out. The system does not cancelout string vibration, mainly becausethe strings are doing a much morethorough job of agitating the magneticfield. In fact, a similar hum -cancellingeffect can be had on a Fender Strato-caster. I found that on my test-bedStrat, which has phase reverseswitches fitted to all three pick-ups fortest purposes, reversing the phase of aback and centre pick-up mix can-celled out hum. Unfortunately, it alsosounded vile. This brings up anotherold chestnut, the straight mix betweenthese two pick-ups has been referredto for a long time as an 'out of phaseStrat sound'. To get that sound, thepick-ups have to be wired in phase.Wire them actually out of phase, andyour Mark Knopfler lickswil I sound notthe slightest bit like Mark Knopfler.

If you are goingto rewirean existinghumbucker from single conductorand shield cable to three or fourconductor, the phase of the coils willneed checking carefully. In somehumbuckers, the phase reversal of thecoils is done by winding the coils inopposite directions, and in others,simply by running the output from oneinto the equivalent wire end on a same -way -wound second coil. Diagramsthroughout this series will assume thelatter, as in Figure 1.

For humbucker wirings, I shall

stick to these colour codings as theyalso apply to most four conductorpick-ups already on the market.

Figure 2 shows the standardarrangement of volume and tonecontrols for a single pickup (in thiscase a humbucker) guitar. Thevolume pot acts as a potential dividerwith the pickup connected betweenthe most clockwise end of the trackand earth, the anti -clockwise endearthed, and the output taken fromthe wiper. In the full on position thewiper is connected directly to thepickup and the full signal is fed to thejack socket. As the control is rotatedanti -clockwise the wiper moves to-wards the earthed end, tapping off aprogressively smaller proportion ofthe pickup signal, until the live of thejack socket becomes directly con-nected to earth in the off position.

The tone control is connected as avariable resistance in a simple low-pass filter circuit, giving a variableamount of treble cut. The capacitorbypasses high frequencies from thepickup to ground, so that when thetone pot wiper is at the pickup end ofthe track, the amount of treble isreduced. At the other end, the fulltrack resistance is in series with thecapacitor, and so most of the treble isallowed to reach the volume control:The capacitor is usually of discceramic type, with a value of 50 or 22nanofarads (0.05 or 0.022 micro -farads). The treble cut effect willextend to lower frequencies withlarger capacitor values, and this willalso depend on the pot resistance, sothat at maximum treble the highestfrequencies will be cut slightly leav-ing the lower treble unaffected, andwith the tone control at minimum thehighest frequencies will be cut a lot,with the lower ones cut slightly.

Two alternative wirings of the tonepot, which give exactly the sameresult, are shown in Figure 3. Some-times the unused end of the tone pottrack is connected to the wiper: thisreduces the effect of dirt on the trackand causes the pot to act as if it was inits clockwise position (max. treble)should the wiper become totally dis-connected.

Next month we'll start with a des-cription of how to rewire two pickupguitars for independent operation ofthe volume controls. E&MM

SINGLE COIL HUMBUCKINGPICK-UP PICK-UP

ILIVEI

IEARTHI

RED

BLACK

ILIVEI

ICONNECTEDI

WHITE

GREEN IEARTHI

Figure 1. Pickup connections

TONE

TCW

2_T

CW

VOLUME

OUTPUT

FROM PICKUP

TONE VOLUME

EARTH CONNECTIONSSOLDERED TOPOT. CASE TO JACK SOCKET

Figure 2. Standard volume and tone circuit

TONE

CW

(a) lb)

Figure 3. Alternative tone control wirings

67

ELECTRO-MUSIC

In which Ben Duncan takes abreak from mixing discs andinstead, mixes electronics,

philosophy and pragmatic adviceto show that discotheque systemscan be much more than a pile ofindifferent gear plus mandatoryRosko-esque geezer at the mic.

At the ControlsThe control desk isthe nerve centre

of the DJ's operations, and regardlessof technical merits, the overridingrequirement is to be on intimate andunderstanding terms with your con-sole. Like a 48 channel concert desk,a

Gibson or a Bonneville, it's an exten-sion of your body and operating it mustbecome instinctive. Another point thatis rarely appreciated is that the desk isjust another link (kink??) in the chain;later on we'll look atthe discothequeasa whole, seek out the weak links in thesystem and look at ergonomics, butfirst a survey of the constituent parts.

GramophonologyThe ideal discotheque turntables

are American broadcast models fromRusco, Gates and QRK, or the UKbroadcast standard - the JapaneseTechnics SP10. Regrettably, a pair ofthese with matching arms will costover£1,000 and most of us will have to

make do with something a little lessexpensive. A good discotheque turn-table is, of course, a single player, withtwo speeds (though 78 rpm can haveits abuses!) and a cueing arm. Lessobvious is the need for mechanicalsimplicity (which usually impliesrobustness and reliability), readilyavailable spares and an arm that willcomfortably track at 3-5 grams. Only ahandful of turntables meet thesecriteria, and perhaps the best knownand best loved is that exceptionalbudget Hi-Fi model - the Garrard SP25in its Mk. Ill and Mk. IV guises.Although obsolete, second hand oneswill be around for some years afterstocks of spares have been exhausted.The only essential modification is to

remove the superfluous bitsthat makeup the autochanger mechanism.Rather than attempt to describe thisoperation, it's much easier for you tosimply examine the deck and removeall the cogs and levers that appearinessential. Other useful modifica-tions apply equally to otherturntables:

(1) A piece of foam glued below thestylus will prevent damage should youdrop the arm as it swings from therubber mat to the arm rest.

(2) Wiring the mains and audiofeeds via reliableconnectors will makelife much easier if you have to removethe deck in a hurry for repairs.

The SP25 III/IV has only a fewfaults. Sometimes the 45 rpm settingprovides a very embarrassing 361/2

68 MARCH 1981 E&MM

ELECTRO-MUSIC

rpm! The problem could be a badlyworn pinch wheel (these should bechecked monthly), grease or oil on thepinch wheel, the motor drive shaft orthe turntable rim, orlessoften, a motordrive shaft that has .slipped downslightly, causing the pinch wheel tostraddle the 33 and 45 rpm stepssimultaneously. Another heartache isthe ease with which the headshellsnaps off, usually five minutes beforethe show! For this eventuality, a supplyof cocktail sticks and PVC tape willbandage the damage until you havefive minutes to replace the arm.Superglue could be used, but with themind boggling possibility of beingliterally glued to your turntable for theremainder of the gig! Finally, thecontacts under the headshell canmake bad contact with the cartridgecarrier, resulting in the sudden loss ofone channel. Cleaning and re -spring-ing the contacts may help, but oftenthe best course is to replace thecartridge carrier.

Other low cost turntables for yourevaluation include the old BSRmodels, the ubiquitous Technicsmodels and the now obsolete Con-noisseur BD2, although the latterturntable is unsuited to switch start-ing.

Many DJ's like to use slip mats, andwhilst the SP25 can be used for slip -cueing, a far better turntable with ahigh torque motor is another obsoleteGarrard model - the 401 (the fact thatall of Britain's best discoturntablesa reobsolete reinforces the feeling thatBritish industry is intent on selfdestruction). For many years, the 401,and its predecessor, the 301, were thebasis of the standard BBC turntable,and their tank -like constructionmakes them perfect for discothequeapplications. And because the 401 isout of fashion, it's readily availablesecond hand at low cost - witness theclassified advertisements in hi-fi jour-nals. Since the 401 is just a turntable,you will have to find a suitably robust12" arm. Most ex-Hi-Fi 401's will haveSME arms; ideally, these should beexchanged for a broadcast arm (e.g.QRK).

Mobile DJ's will often meet floorswhich are slightly uneven, and tiltingthe turntables only a few degrees canhave amazingly nasty effects on soundquality. A spirit level allows you tocheck the tilt of the floor and beer-mats/cigarette packets can be used tocancel out any unevenness. Mobilework also involves the turntables in alot of shaking around, and it's always agood idea to check the tracking weightis set correctly immediately aftersetting up, and if thestage is wooden, agoose stepping colleague can seek outany potential record bounce problemsat the same time.

Cartridges are much simpler. Cera-mic cartridges are robust, cheap tobuy and cheap to keep in stylii, andwhilst the bestceramicsare capable ofreasonable reproduction, the equali-sation required can be horrendouslydifficult to design. Contrary to popularbelief, getting the best out of a ceramiccartridge requires much more than ahigh input impedance stage; rather,that is an excellent way of killing all thetreble at the expenseof thudding bass.In any case, a medium cost magneticcartridge will always give better top

end and the only drawback is the costof replacing worn stylii. Domesticmagnetic cartridges, especially themore esoteric types are exceedinglyfragile, and will obediently self destruct(so decreasing profit margins) whensubjected to back -cueing and exces-sive tracking weight, let alone beingdropped on a record! Broadcastmodels are a must - these heavy dutycartridges are built to be thrownaround, to withstand the rigours ofback -cueing and the 3-5 grams oftracking weight necessary for bouncefree discotheque work. Inaddition, thestylii are designed for good visibility(invaluable when you have 5 secondsto cue up track 7 - or is ittrack 8??- on aK -Tel album!). The almost legendarybroadcast/disco cartridge is the Stan-ton 500AL, but the Stanton 680EL, theShure SC35 and SC39ED are alsoused. All of these cartridges come asnear to audio perfection as is neces-sary in a discotheque, but they eachhave a characteristic 'sound' or col-ouration, and apart from cost, thechoice is basically which sounds bestto you.

Die Vinyl SolutionConsidering the cost of replacing

stylii, and that of replacing 2,000ruined records, knowing when to re-place the stylus is a natural headache.A good test is to compare the soundquality of a suspect stylus with a spare(virgin) stylus by crossfading quicklybetween two identical recordings -preferably good 12" pressings whichare kept purely for test purposes.However, the virgin stylus shouldinitially 'run in' on a well worn disc forafew minutes to polish the tip. Alter-natively, a small self adhesive label,bearing the date of the last replace-ment on the side of the cartridge canbe invaluable if you don't have time tocheck your stylii regularlyand can onlybe bothered to change stylii at, say,quarterly intervals. Lastly, broadcastcartridges are invariably supplied inexotic boxes with hinges lids, reminis-cent of jewel cases. These can beglued onto the space between theturntables and used to store recordcentres, stylus cleaning brushes andstylii covers.

Disc amplificationTwo conflicting requirements a rise

here - good headroom and low noise.They conflict because to keep thenoise low, it's necessary to bring thedisc signal up to line level as soon aspossible. Once at line level (775 mV)we can start to process the signalwithout undue worry about addinghum and extra noise to it. However, lownoise also demands boosted highfrequencies when recordsare cut (andsimultaneously bass frequencies areattenuated to achieve a sensible play-ing time). The resulting constant am-plitude recording characteristic re-sults in a very inconstant input to thedisc amplifier, the treble being up to20 dB higher in level than the mid-range and the lowest bass being 20 dBdown. Clearly, if we raise the midrangeto line level in one jump to achieve lownoise, an additional 20 dB of head-room or input overload margin isnecessary to handle the high treble. Inaddition, 8 dB's of extra headroom are

Part of the author's 3kW rig.

required to handle heavily modulated,well pressed 12" singles with toppysynthesiser riffs, and another 10 dB'sor so are required as leeway, becausemany amplifier stages show signifi-cant distortion just before the onset ofoverloading. Thus we need at least 38dB of headroom and if for the sake oflow noise, we decide to amplify to linelevel in one jump, the output of the discinput amplifier will require a 110 voltpeak output capability! A more practi-cal alternative isto send the disc signalthrough a unity gain amplifier withtreble cut - once the high amplitudetreble is tamed, the headroom re-quirement falls to a more reasonable20 dB and the next stage can happilyamplify to line level. Unfortunately,this can be a noisy solution and a goodcompromise is to provide the inputstage with a mild (15-20 dB) gain andtreble cut, followed by a preset atten-uator to allow for variations in theoutput levels of different species ofcartridge, and finally another stage tobring the disc signal up to line level;this stage can also handle tape inputs.

Bass boost also has to beappliedtoone of the stages, and the choice isessentially a question of which stagewill handle the burden of an additionalfeedback network without incurringexcessive distortion. With this ar-rangement, an overload margin of40dB can be readily achieved and thesignal to noise ratio is only marginally(2 or 3 dB) lower than the theoreticalmaximum for bipolardisc input stages(around -70 dB, depending on thereference level). Fortunately, this de-gree of residual hiss isjustadequate inthe disco, for whilst ambient soundlevels of 110-120 dB make the resi-dual noise rather louder than it mightbe at home, hiss ridden momentsbetween vocals and music will in-variably be masked by your audience.

The need for good headroom is muchmore important and the commonlyencountered 20-25 dB of headroom isinadequate unless you roll off all thetreble above about 8 kHz; otherwisethe sound will be 'gritty', distorted andvery obnoxious at high levels. Fineraspects of disc input stages are dis-cussed at length in theserious hi-fi andelectronic journals, and rememberingthat your discotheque system is but achain with links, expensive improve-ments, to (for example) the speakersmight well go hand in hand with animproved disc input stage, becausethese are two particula rlyf ussy I i nks inany record playing system.

Tape SourcesApart from discs, some DJ's use

taped material in their shows, and toallow almost any tape machine, fromRevoxes to nondescript cassettes ofdubious oriental origin to be patchedin successfully, regardless of outputlevel or impedance, a high sensitivity(typically 50 mV), high impedance(50-100 K) stage is required, togetherwith a fader to match the level to thatofthe disc output. A headroom of 20 dBwill normally be quite adequate, pro-vided the fader/attenuator lies beforeany amplification stages; often thetape input stage is designed for unitygain and is merely a buffer.

Patching in external mains pow-ered tape machines can bring hum aswell as Sister Sledge, and whilstripping out mains earth leads maysolve the problem at home, it's simplytoo risky in a public place rife withinquisitive fingers and spilt Guinness;Disco -electrocution may be spectacu-lar, but the court damages can besomewhat sobering. Later, we'll look atsafe ways of avoiding niggling buzzes.

In the next issue - console struc-ture, crossfading and voice-overs.

E&MM

E&MM MARCH 1981 69

ELECTRO-MUSIC

A Glimpse of Current ActivitiesFour a.m. and sounds of a robot

tripping over emerge from a room atMaida Vale. But it's not really a robot,just a young man who is beginning tofeel rather mad as he walks aroundwith one foot in a bucket whilst rattlinga waste paper bin! His determinationto get the right sound has taken himmany hours into the night and despitethe array of electronic sound makingequipment he finally resorts to any-thing else at hand. It doesn't reallymatter what time you call in on theWorkshop - there's always someonehard at work.

Such is the life style of the com-posers at the BBC Radiophonic Work-shop studios, who spend a great dealof time preparing incidental music,theme tunes and sound effects forover three hundred radio and tele-vision programmes each year. Withschedules fully booked three monthsin advance, the team of six musiciansunder the enthusiastic directorship ofDesmond Briscoe make a very impor-tant contribution to the programmeswe watch and listen to.

I met Brian Hodgson at the studiosone afternoon before Christmas.Brian is responsible for the generalworking of the studios, besides con-tributing a great deal himself to thesuccess and future development ofthe workshop. After a quick cup ofBeeb tea we took a look in Studio H.

`Lord of the Rings'Seated next to a large mixing desk

was Elizabeth Parker, now working on'Lord of the Rings' and also respon-sible for the last set of sounds for'Blakes 7' and many radio pro --grammes. She will also be doing nextyear's 'Blakes 7' and probably 'TheDay of the Triffids' as well. We con-centrated on the 'Lord of the Rings' forour discussion. This was commis-sioned last June although Elizabethhad only just started working on itready for first studio takes, withfurther recording sessions plannedbefore the programme goes out inFebruary in 26 episodes. It's a fulltime job for Elizabeth with lots ofovertime thrown in as well, eventhough she is only concerned with theeffects. Whereas the 'Hobbitt' wasmade previously with the help ofRadiophonic sounds, this time theapproach is to more 'natural' sounds.In fact, natural sounds are used as thebasic material. For example, 'Shadow -

Elizabeth Parker in Studio H.

fax' the horse is represented by anactual horse neigh which is sloweddown and treated by an EventideHarmoniser which returns it to itsoriginal pitch giving a slightly out-of-this-world_feel to it.

To get a thunder effect, Elizabethstarted off with tin foil, tearing it apartslowly to make a cracking sound. Shelikes this much better than usingsound effects records or even a syn-thesiser, because it retains such asharp edge which can be spliced andedited together using the live record-ing for multi -tracking at differentspeeds. Add to that two white noisetracks and various degrees of echoand you've got the final effect.

Here in a nutshell is the art of theRadiophonic Workshop - combiningMusic Concrete with pure electronicsynthesis to make sonorous land-scapes and effects for radio and tele-vision programmes. Brian refers toMusic Concrete as a 'big bouncy baby- its been the starting point for somany sound effects!' and points outthat electronic synthesis very oftenemasculates the final result. The pro-gramme producer Jane Morgan also

prefers these more naturalistic effectsrather than electronics. Elizabeth'smain task is to integrate the soundswith the accompanying_string musicfor the series. It is also important thatshe establishes a good working rela-tionship from the outset with theproducer, who is obviously initiallyvery busy with casting and rehearsals.

Each episode lasts half an hour andthe effects, some specific, others onlybroadly outlined are indicated in theactor's scripts, e.g. a rippling andsucking tentacle noise of a nasty lakemonster! Whilst the sound for the Ringrequired liaison with the producer,most of the time Elizabeth works inde-pendently. Very often the script simplyindicates 'high vibrating' or 'low puls-ing' when the author really has nodefinite idea what he wants. Gandolf's'staff' was created by recording astriking match which was then sloweddown on playback and sent through aphase box with other treatmentsadded on top. Another sound wasbubbling water, done by Elizabethgurgling, wet towels slapping togetherand a river played back at low speed.Despite recent popularity of the voco-

der, it was only used for one sequence(it's the Roland rack Vocoder that'sused) for a sustained 'Aah' tonethrough it as a background to magicspells. You can't quite tell whether itshuman or electronic and like most oftheir effects it takes a lot of time andexperiment to find the right combina-tion of natural sound and electronictreatment.

Turning to the other equipment inthe studio, Elizabeth prefers to useRoland's 100M modular synthesisersystem, especially for 'Blakes 7',rather than start off on a keyboard.The Jupiter 4 was also sitting promi-nently in Studio H, although this andother instruments - synthesisers inparticular - are in fact shared by allthe team using the studios. If Eliza-beth wants a particular sound fromthe Yamaha CS80, for example, thenshe books Studio B instead. Yamaha'sCS4OM is used to play to storedsounds in addition to the Jupiter 4.

Recording equipment in the studioincludes a Revox A700, two StuderA80 machines and a Scully 8 -track.The mixing desk is a Soundcraft 16into 8 and Chartwell speakers areused for monitors. The other studiosare very familiar with a Studer 862 in.Studio G and a Glennsound 24 into 8.custom designed desk. Two othermixing desks are used, the Neve 806624 into 16 and a special desk fromTechnical Services which is 24 into 8.

Elizabeth emphasises that her aimin composing the sounds for 'Lord ofthe Rings' is to integrate them suc-cessfully with the acting and StephenOliver's music.

70 MARCH 1981 E&M M

ELECTRO-MUSIC

Dick Mills. Inset shows Time Code on Video picture.

Paddy Kingsland.

When all the sounds have beenassembled on tape they are taken toanother studio where they are in-serted in the script so that the actorscan react to them. Safety copies of themaster recordings are kept and moreobvious sound effects such as closingdoors and footsteps are left to theStudio Managers. Picking up the tech-

nical know-how is something thatElizabeth is doing all the time - in theend it's the ideas that count.

'Dr. Who'We then moved on, passing a train-

ing room and an interesting old mixerthat had pan -pots actually fitted ontoits faders, until we reached Studio G,

The Wavemaker Polyphonic System.

where Dick Mills was putting togetheranother 'Doctor Who' set of soundeffects. He's responsible for all theprogramme's weird and wonderfulsounds that emerge every week fromour TVs, especially voice treatmentsthat can't be done in studio. PeterHowell and Paddy Kingsland sharethe incidental music, alternatingthree programmes each usually, withRoger Limb popping in to fill in theoccasional episode. Incidentally, laterthis year Peter Davidson (from 'AllCreatures Great and Small') takesover Dr. Who's part. The 'Dr. Who'incidental music is now almost allelectronic although sometimes it maynot seem so. For example, 'WarriorsGate' used a time flip to a medievalbanquet and the authentic early in-struments were programmed on theYamaha CS80. Roger Limb is cur-rently doing the series 'Keeper ofTra ken'.

Collaboration between the musiccomposer and Dick's sound effects isessential to avoid clashes of soundand music bt any one time. Dickchooses his frequencies for soundeffects carefully so that they don'tappear as wrong notes in the music!Before video recorders and electronicsynthesisers were standard equip-ment for 'Dr Who', the composercould often lose track of the story lineby the time he had got togethermusicians using conventional instru-ments to play the music. Now, the.video recorder picture has a 'timingcode' inserted during recording toenable each sequence of music orsound effect to be synchronised with-in a hundredth of a second.

Dick prefers to use natural soundsas his starting point whenever pos-sible - after all, he was one of the firstcomposers at the Radiophonic Work-shop - and then uses a StereoFlanger, Phase Shifter, Double Reverband Pitch to Voltage converter fortreatment. For example, in 'WarriorsGate' a mirror was the gateway to timetravel. In the script the aural sensa-tion required was described to Dick asthe audio equivalent of what you feelwhen you touch the front of a TVscreen - static charge. To get thetingling effect he decided to use alarge sheet of oven foil. Even gruntingof pigs was recorded and treated forone Programme! Dick finds that hegets better ambience using naturalsounds. In the early days he recallsusing BBC's large Studio 1 to get along reverb time. He likes the StereoFlanger for robot voices and talkingweighing machines! The PhaseShifter gives him a constantly chang-ing background ambience that makessounds like spaceship hum muchmore interesting. He uses an En-velope Follower to deaden speech bycutting off a VCA sharply at the end ofwords. An old BBC PA stabilisingdevice provides an unusual way to get

phasing and since it could be voltagecontrolled, a high frequency input canring -modulate a voice for bell sounds.He's even tried a long tape loop rounda ribbon microphone that gives a verylong fade because each time it passesthe mic a little more gets wiped! Dickremembers when effects like Flang-ing didn't come in small black boxes,but were made by pressing yourthumb on the flange of a tape reel,thus altering the tape speed slightly.

All the 'Dr. Who' effects are re-corded in full track mono and simi-larly the music produced is alsomixed down to mono.

'Hitch -Hiker's Guide'If you've been watching the new, TV

version of 'The Hitch -Hiker's Guide tothe Galaxy' then you should be inter-ested in the work of Paddy Kingslandwho I found in Studio E. Paddy hasbeen composing the incidental musicfor this series (on BBC 2) since lastJune, when a pilot version of episode1 was first approved and six episodesplanned. Besides providing the inci-dental music, Paddy has to 'orches-trate' all the computer animationwhich appears as letters or graphicson the screen - they all have to havesounds that fit with the music. Othereffects that are required are explo-sions, spaceships taking off, monsternoises and, of course, alien voicesthat usually need special treatment.For the latter, an actor speaks thealien's lines and Paddy uses varioustreatments on the taped voice. Thestory had an interesting start for him,with a spaceship arriving and theearth being destroyed. Unlike theradio programme, where the timing ofan event is not absolutely critical forperhaps an explosion, the TV versionrequires precise sounds for the pic-tures so that a 'spaceship close-up'which immediately cuts away to'people panicking in the middle ofLondon' proved to need a complexseries of sounds, although the distinctsounds required were defined by thepicture action. Paddy's sound tapesare made in short sections, e.g. aspaceship has its sound fitting theexact number of frames. On the dubwhich is done at BBC TV centre withthe sound engineers, they play in theeffects tape at the right time onto amulti -track machine that eventuallyrecords the whole sound score (in-cluding actors' parts and possibly async track to ensure the mix stayswith the picture).

The Narrator in the story has twofunctions - as a story teller and as thevoice of a futuristic book that playslike a cassette tape recorder. Youpunch in a code and it comes out withsome information and that's what the'Hitch -Hiker's Guide to the Galaxy' is!Behind this narrator is music whichmust not swamp out the words - it

E&MM MARCH 1981 71

ELECTRO-MUSIC

must create the right mood for thescene. Nearly all of the music is elec-tronic, although one exception is thecommercials - there's a 'Pan Galac-tic Gargle Blaster' drink advert. This istreated like a real commercial usinglive music on keyboards, guitars anddrums. Paddy's work load is so heavythat he often has to switch every fewdays to a different programme to keepup with scheduled series. In addition,each adventure of four episodes has adifferent director, so that severalgroups of episodes can be overlappedto save time. Some directors simplydo the first and last episodes of anadventure.

Instruments in the studio includedthe Oberheim OB-X8 polyphonic syn-thesiser, often used for sustainedsounds. The Roland Jupiter 4 wasused a lot - the spaceship soaringaway was done with white noise andfour -note chords near peak reson-ance just before oscillation of thefilter. For the animation, computerblips and bleeps came from this alsoand occasionally during a 'wipe down',where a graphic style face is printedout, a single chord was played on theJ4 with its special arpeggio effectadded during a long decay. TheRoland CR78 rhythm machine is usedby Paddy all the time for guide tracksand occasionally for his own specialrhythms. He also employs a StereoFlanger, Voltage Controlled StereoPanner and likes to use the oldYamaha SY-2 preset mono synthe-siser.

The main areas of Paddy's workare sound effects, music backgroundand voice treatments and for the latterhe uses a clean voice recordingtreated by Harmoniser, Vocoder,Flanger, as well as echo plates (loopedround the flanger so that echo isphased as well as the voice). When thevocoder is used on a voice, a 'dirty'noise input is used as the carrier e.g.for the alien voice, and a slow fre-quency modulated echo is added tomake the 'depressed alien' voice.

Other AreasWe paid a brief visit to another vital

room within the complex that con-tains all the film and video facilities. Inthis room producers can check filmagainst sound tracks, measuring timein frames at TV speed (25 per sec.) orcinema (24 per sec.). The film track issimply inserted with the sound track(see photo) and run through so thatframes can be located and checkedfor synchronisation. Sync 'pips' aresometimes inserted on one track of a16 -track recorder as reference pointsfor intended music cues. There is auseful device designed by their owntechnical lab that stores the totalnumber of frames edited andsearches for this amount at the startof a new editing session. Also kept inthis room are copies of all the BBC'ssound effects records and these areoften used for specific items in a

script e.g. a steam train, bird sounds,animal noises and natural sounds.

In rounding up my enjoyable visitwe spent a few minutes with Peter

Peter Howell.

Film editing equipment.

Howell, who has devoted a lot of histime in the past to the 'Dr. Who' series.He likes the present 'all electronic'style of music which he composesmostly on the CS80. Listen for anautoharp in the programme too - itwas recorded via piezo pick-upsunder each string. (We plan to reviewRoland's electronic autoharp costingaround £160.) One day's work on 'Dr.Who' for Peter produces only a fewminutes of music, taking about 8 daysper episode, although that is often cutto four or five days to meet deadlines.We talked about his frequent use ofaugmented 5ths to create a sense ofanticipation - suspended minor 9thsare a favourite too. He uses plenty ofchromatic harmony, often startingfrom the key of C then modulating tosome remote key such as F# minor!The timing for his music writing has tobe accurate to 6 frames a second andfinal juggling can be done at thedubbing stage. He revealed thatkettle -drums in the 'Dr. Who' musicare really made by using a singletuned tom-tom with bottom skin re-moved through a harmoniser. Whilstsomeone hit the drum, Peter was play -

Desmond Briscoe, Mike Beecher and Brian Hodgson.

ing the harmoniser keyboard to getthe different pitches!

Peter came to the Workshop con-vinced he was a pop musician butover the last five years has realised hismusic is much more classical in style.'You don't have to dislike electronicsounds here but it helps! - it makesyou try and round them into some-thing more interesting!

Looking to the future, RadiophonicWorkshop have had the 'Wavemaker'Polyphonic System designed for themby Ken Gale (he was responsible for alot of the EMS Synthi 100 final de-velopment from David Cockerell'sdesigns). It has a 10 -note digitalkeyboard which is touch sensitive.With the keyboard is a digital con-trol voltage recorder that stores yourperformance on one track of a '4"tape. You can also lay one track at atime, then play it back whilst accom-panying it on the keyboard and it willre-record automatically. Thus pre-vious tracks can be edited or added towithout any noise degradation. Nextto the recorder is the 16,384 events,10 layer sequencer with micro -memory and the ability to actually

I Mr

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loop within a specific sequence. Thememory contents can be dumpedin serial form onto tape for storage.Although the sequencer might beconsidered primarily for storingvoltages to drive VCO's, the 10 out-put control voltages can also beused for filter control, sound en-velopes or spatial control. Thesequencer itself can receive up to 256'instructions' which in turn can beloaded on tape for use again at anytime. A new modular synthesisersystem is also under developmentand should prove ideal for the work-shop as it will always be expandable.

To the aspiring musician, theWorkshop composers task is anenviable one, but motivation is noteasy - getting down to composing,deciding on the right sound whenworking alone, and then finishing theprogramme on time. Despite the longhours and dedication to the sole taskof getting music produced, DesmondBriscoe has formed a team that bringsus a vast amount of electronic musicthrough the medium of broadcasting.

E&MM

72 MARCH 1981 E&MM

ELECTRO-MUSIC

For several years now Hi-Fi en-thusiasts have been experiment-ing with their turntables in the

hope of getting a better sound. Turn-table mats, record clamps and specialheadshells have appeared on themarket in profusion, each claimingsubstantial improvements.

I must admit to being highly scep-tical of these claims although somerecent experimentation with my ownequipment has justified some ofthem.

Before going on to describe theseexperiments in detail it would be aswell to describe my own deck. Back inthe heady days of '74, when the Hi-Fiboom was at its peak, most turntableswere made by Garrard.

The only viable alternative to theubiquitious SP25 was the 401 turn-table fitted with a SME arm and V151:11cartridge.

Around this time I swopped mySP25 for a BD1 turntable kit and anAcos Lustre arm fitted with a ShureM75ED. The arm is still available,albeit in a modified form, as the Regaarm for round £40. Since then onlythe cartridge has been changed foranOrtofon VMS20ELI. This cartridge isone of the most neutral soundingmoving magnet designs available atany price. The rest of the systemconsists of a home brew pre -amp andbi-amped speakers, the deep bassend being taken care of by an activewoofer system. It is, by now, a wellknown fact that any record deck canbe made to act as a microphone.

This can be easily demonstratedby placing the stylus on the stationaryturntable and monitoring the outputon a 'scope. Providing the 'scope isreasonably sensitive signals will beseen whenever sound is present in theroom.

Turntable mats have a dual pur-pose. One of these is to support thedisc. This may sound obvious but withthe standard of flatness of modernrecords, this is no easy task. The othermain purpose is to damp out platterresonances and acoustic pickup ofthe type described above. All turn-table mats do both these jobs to agreater or lesser extent. The recentwave of accessory mats claim to dobetter and positively improve thesound.

The first of these mats of which Ihave personal experience is made by

4 Griffin and retails for about £6. Whentried it certainly improved the trebleand to a lesser extent, the mid -range,but at the expense of the bass. Thelatter disappearing below 100Hz orso. Several other mats have sincebeen tried with varying degrees ofsuccess. Although they all provide animprovement on certain aspects ofthe performance they all seem to doso at the expense of others.

Naturally the differences are insome ways extremely subtle. Thisapplies especially to those whichaffect the stereo image. It is onlypossible to judge this properly onthose recordings which have not beenmulti-miked. These albums tend to besomething of a rarity these days!Record clamps as well seem to besomewhat problematical. Againseveral types are available. Most ofthem have a collet type fitting which is

HI-FIJeff Macaulay

Metrosound clamp.

ousm.0

SECTION A -A

Fig. 1. The turntable mat fabricatedfrom four 'Bostic' car sound -dampingpanels.

Completed turntable mat.

pushed over the spindle on top of therecord. A disc of material in turn fitsover this and is pressed onto therecord and secured by a nut whichtightens the collet.

A typical example is the metro -sound clamp which costs around£4.50. Like the mats this is claimed toimprove the separation between in-struments, improve the bass andgenerally reduce coloration. In fact I

found this device did fulfil some of theclaims made for it. It seemed to makethe instruments better defined andmade low level information moreintellegible.

However I found that the devicetended to lift the record away from theturntable mat rather than bind it moreclosely.

On the Rega turntable, however,with its more compliant mat theclamp operated as intended. Surpris-ingly though the difference was not somarked as with the BD1. An improve.ment none the less.

Most turntables, if struck with ascrewdriver blade across the rim, willring like a bell. My BD1 was a particu-larly bad offender in this respect. If anote of the same frequency were to bepicked up by the turntable it will reactlike a mechanical tuned circuit caus-ing a peak in the response. My firstexperiment was to remove thisresonance.

The obvious way to damp out aresonance of this kind is to add massto the turntable. The most convenientmaterial to use are Bostic car damp-ing panels. These are basically bitu-

mised felt pads and are self adhesive.They can be cut to size and shapedwith scissors and are thus convenientto use. Taking the turntable out I stucka strip of this material around theinternal rim of the platter. This treat-ment lowered the frequency of thenote produced and the decay timewas reduced. Some squdes ofmaterial were then added to theunderside of the platter and this againreduced the decay time to a fewmilliseconds. It sounded dead whenstruck. After refitting the platter andreplacing the existing mat somelistening tests were tried. The mainsubjective result was that the musicsounded much cleaner at high levels.Tapping the deck with the stylus rest-ing on the turntable showed that thewhole assembly was less prone topickup problems.

All this leads on to this month's doit yourself project. The 'Macaulay'turntable mat! This is fabricated fromfour 'Bostic' car sound dampingpanels. As already mentioned theseare self adhesive. The sticky sidebeing protected by a paper sheet.Figure 1 shows the completed mat inplan and cross section view.

This material's self dampingproperties absorbs vibrations in thedisc whilst damping platterresonances.

Construction starts by laying a pairof sheets side by side, paper sidedown. Take an LP record, preferablyan old one, and lay it on the panelswith the central hole over the join.Mark round the LP with a Stanley

knife. Remove the album and cut outthe semi -circles with a pair of scis-sors. Repeat this exercise with anothertwo panels.

At this stage you should have foursemi -circular cutouts. Take two ofthese and butt them together toproduce a circle. Now find a circularobject of about 41/2" diameter. Placethis on the centre of the disks, markround it and cut out the circle. Thecutout is required so that the recordcan lay flat and clears the raisedportion in the centre.

Peel the backing paper from thetwo panels with the 41/2" cutouts andpress these into place on the other twopanels as shown in Figure 1. Don't atthis stage remove the backing paperfrom the other two panels until youhave tried the mat out. The prototypeimproves the bass response andstereo imagery of my BD1 and im-parts a dry quality to the sound:Preferably the mat should be used inconjunction with a record clamp toprovide intimate contact between thedisc and turntable.

As with all things audio the onlysensible way to judge the difference isto hear it. If you like it the bottompanels can have their backing paperremoved and the mat stuck to theturntable, further improving thedamping.

One thing to watch when experi-menting with different mats is to re-adjust the arm height for parallelismin order to keep the vertical trackingangle correct.

Other less obvious factors canaffect the performance of recorddecks. The most common of these isthe build-up of oxide on the pickupplugs and the cartridge pins. Even ifthese are clean they can still givetrouble if they are loose fitting. Thecure for these ailments are selfevident and it does no harm to checkand clean all connections periodically.

The sound of a cartridge can bemodified by adjusting the input im-pedance and, or, the capacitive load-ing. Most pre -amps offer an inputimpedance of 47k. A couple of metresof connecting lead between the cart-ridge and pre -amp will also produce acapacitive load in parallel with theresistance. Some cartridges, notablyShure and Ortofon models, require aload capacitance of 200-400pF. Oftenthe capacitance of the cable is notsufficient to produce the optimumload. If your connections allow it500pf trimmers can be soldered be-tween the hot sides of the inputs andground.

If a record is then played it is

possible to adjust the sound to acertain extent to suit one's tastesimply by adjusting the trimmers.

These comments only apply tomoving magnet designs. Moving coilsare low inductance and capacitiveloading will have no effect.

The reason that capacitanceactually alters the response may notbe immediately obvious but it has todo with the internal inductance ofmoving magnet cartridges. The im-pedance of the inductance becomeslarger with increasing frequency. Inthe extreme hf the response may godown by several dB. The capacitanceforms a tuned circuit lifting theresponse. E&MM

E&MM MARCH 1981 73

ELECTRO-MUSIC

by Chris Lare

Amicrophone converts soundenergy into an electrical signal,and as such is the first device in

the audio reproduction chain. Unlikethe other parts of the reproductionchain (tape recorders, amplifiers,speakers) microphones are not often,seen in the High Street shops, thusleaving a large number of peopleunaware of their importance. Indeed,a microphone will probably placemore characteristics on the finalsound than anyother item in the chain.This implies that the choice of microphone is critical and that it i s well wortl-while taking some trouble to establishwhich microphone(s) is best for thejob in hand, particularly as one or twomicrophones will really stand out inany one application.

The arrayof microphonesavailableis considerable, and while the pro-ducts of three manufacturers (AKG,Beyer Dynamic and Shure) dominatethe scene, several other manufac-turers contribute on a smaller scale.As a rule the characteristic of themicrophone is dependent on the 'cart-ridge' employed and so little is gainedby putting a cartridge in anothermounting; unlike the domestic loud-speaker market where small com-panies all over the place are designingtheir own boxes around standardproducts.

A microphone consists of severalparts (Figure 1). The actual work isdone by the cartridge which is gen-erally mounted on shock absorbingrubber supports. The cartridge isprotected by the grille and case, thecable usually leaving the rear end ofthe case. Additional parts may beincluded depending on the end pro-duct such as switches and trans-formers. The cartridge will be one ofthree types, ignoring carbon typeswhich ceased to be seriously usedmany years ago.

These types are dynamic, ribbonand capacitor, each offering differentcharacteristics, although some over-lap does occur.

DynamicMicrophones

The dynamic microphone (some-times called moving coil) is the con-verse of a normal loudspeaker. Adiaphragm is fixed to a set of coilssuspended between the poles of amagnet, and as the sound causes thediaphragm to move current is inducedin the coils by the magnet (Figure 2).The coil and diaphragm must be verylight to allow the microphone to re-spond quickly to sound (ensuring awide frequency response) and yet bestrong enough to withstand jolts dur-ing its life. This is why high quality

74

dynamics are expensive, the costpurely related to the difficulty ofmanufacture of the diaphragm/coilassembly. A sma II transformer is oftenused to adjust the output voltage andimpedance to make the microphoneeasier to interface to otherequipment.

One problem with dynamic micro-phones is thattheyare prone to pick uphum in the coil, and in viewof the verylow signal levels present this can bequite serious. Many microphonesovercome this problem by mountinganother coil next to the moving coil,but wound in the opposite direction.The outputs of the two coils are added,

RUBBERGRILLE MOCK MOUNT.5CARTRI064-

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Figure 2. Dynamic Microphone Cartridge

either directly or by means of atransformer, and any hum inducedinto both coils cancels out since theinduced hum will be of opposingphase. The fixed coil is often called a'humbucker' (Figure 3).

Ribbon MicrophonesA ribbon microphone still employs

a magnet to induce an electric field,but this time into a single fine metalstrip. The strip is very light andcarefully shaped, making ribbonmicrophones expensive and delicate.They do offer tremendous clarity ofsound because of the lightness of theribbon and are thus very popularprofessional microphones.

CapacitorMicrophones

It is important to distinguish be-tween true capacitor (previouslycalled condenser) microphones andthe cheap electret capacitor micro-phones (see Figure 4). Thetrue capaci-tor microphones work on a totally dif-ferent principle to the magnetic micro-phones, and depend on the chargestored on a capacitor. The amount ofcharge that can be stored on a twoplate capacitor is related to the area of

Figure 3. Humbucking coil connection

INSULATOR MOUNTPLA6TIG ALUMINIUMCOATED DIAPHRAGM

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Figure 4. Capacitor microphone cartridge

the plates, and the distance betweenthem, implying that if the distance isaltered the charge stored mustchangeresulting in current flow.

In a capacitor microphone the baseof the cartridge forms one plate, andthe diaphragm forms the other. Assound impinges on the diaphragm itmoves closer to the base, resulting in acapacitance change (Figure 4), caus-ing a flow of current. However, theplates must be charged for this tooccur, resulting in the major problems

with capacitor microphones becausean external power supply is required,capable giving up to 50 Voltsorso. Thissupply can be arranged to use themicrophone signal cables, a tech-nique called phantom powering(Figure 5). A D.C. path is maintained tothe microphone via the coil whichprevent any A.C. interfering with thepower supply. The A.C. signal issuperimposed on the D.C. and thenretrieved by means of the capacitorwhich removes the D.C. component at

MARCH 1981 E&MM

ELECTRO-MUSIC

the receiver end. This sort of capacitormicrophone is in great demand inspite of the power supply, becausethey are very versatile and tough.

The electret capacitor microphonewas developed a few years ago in anattempt to gain the advantages ofcapacitor techniques withoutthe needto provide an external powersupply. Inan electret, one ofthe plates is chargedat the time of manufacture (a processinvolving heating and cooling - ana-logous to magnetisation) and so thepolarizing voltage is not required. Theoutput of these cartridges is very low,and a small field effect transistor isusually used to amplify it. This ampli-fier is usually mounted in thecartridgeitself and is powered by a 1.5 Voltbattery held in the handle of themicrophone.

The major problem with thesemicrophones is that the charged plateis necessarily the diaphragm andneeds to be slightly thicker than anormal diaphragm to hold sufficientcharge. As a result these electretmicrophones generally exhibit poorfrequency response and dynamicrange, and should be avoided at allcosts, although there are a few notable

Figure 5. Phantom powering

co

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Figure 6. Polar patterns

exceptions, by Sennheiser in parti-cular.

TechnicalSpecifications

The most important specificationsof any microphone are the polarresponse pattern and the frequencyresponse. It is essential that thesecharacteristics be decided upon be-fore any microphones are actuallyconsidered for purchase. Other fac-tors such as sensitivity and impe-dance can often be considered laterbecause many microphones areoffered in different configurations.

Polar PatternThe polar pattern defines where

the sound source has to be placed withrespect to the microphone. Threemain patterns exist (Figure 6), al-though a development of the cardioidgives steeper sides to the pattern, andis not surprisingly called 'hyper-car-dioid'. In a meeting or open interviewan omni-directional type is desirablebecause it does not matter where the

person speaking is with respect to themicrophone. The bidirectional ('figureof eighntypeisgenerallyused ina pairat 90° to each other to cover the entirearea, but in stereo. By far the mostcommon is the cardioid, since soundin front of it is picked up, but soundfrom behind (audience noise, etc.) issuppressed. This pattern is also muchused by the PA industry becausesound emerging from the PA, and thenreflecting from walls causing feed-back is largely rejected. It is interest-ing to note that the polar pattern islikely to change with frequency, andaccount of this should be taken.

One very important property of thetrue capacitor microphone is that itspolar pattern may be varied byalteri ngthe supply voltage. This is because theplates tend to pull further together inthe presence of high voltages, result-ing in different stress points, hence adifferent polar pattern. Some capa-citor manufacturers supply remotecontrol boxes for this purpose. Anadditional trick which is very popular isto design the microphone as a stan-dard body, upon which is screwed acapsule offeringthe desired response.This means that an entire rangecan beobtained more cheaply than buyingseveral different microphones.

Frequency ResponseThe table in Figure 7 shows the

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Figure 7. Frequency ranges of various instruments and responses of two microphones

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Figure 8. Construction of high quality cable

ranges of typical instruments andvoices. Obviously the microphoneshould be capable of picking up allthese frequencies if a natural sound isrequired. The response of a typicalvocal microphone, the Shure SM58, isalso shown. It can be seen that therespose is flat for the most part, risingabove 2 kHz. The rise will give the voice'presence' and generally make)t morepleasant to listen to, although it wouldbe disasterous for orchestral record-ing.

This peak leads on to feedback,which occurs when sound emergingthrough a PA travels back into themicrophone and is pream plified caus-ing the characteristic 'ringi ng' or 'howl -round' so often heard from poor PAsystems. Many people believe that awide frequency response will give riseto more feedback problems, but it is infact the peaks in the response whichcause the trouble. For example theSM58 peaks at 5kHz and 9kHz, andthus feedback at these frequencies ismuch more likely due to the increased'gain' of the system. In spite of this theSM58 is one of the most popular vocalmicrophones ever made because itnot only soundsgood, but iseasy to useand very robust. As a rule capacitormicrophones exhibit very flat re-sponses, and for comparison pur-poses the response of the AKG C414 isshown next to the SM58.

Sensitivity andImpedance

Microphones are also specified interms of sensitivity, which simplydescribes how much output voltage agiven sound level will produce. As arule the sensitivity is not all thatrelevant, but regard should be paid tooverload, either electrical or physicalwhen dealing with loud sound. Elec-trical overload is more I ikely to occuratthe tape recorder or mixer than in themicrophone, and happens when a veryloud sound is picked up, resulting in avery large electrical signal which isclipped at the following electricalstage. Some microphones, particular-ly capacitor ones with built-in ampli-fiers, overcome this by providing abuilt-in attenuator to reduce the out-put signal level. Physical overloadoccurs when the diaphragm cannotmove far enough and hits the endstops. This can quite often damage themicrophone, and must be avoided. Abass drum is a very severe test of amicrophone's capabilities, and onlyone microphone is universally accep-ted as being tolerant enough for this,the AKG D12, which was designed in1954, and generates only 0.5% t.h.d.for a sound level of 128 dBA (Com-parison -a bout thethreshold of pain).

Impedance ratings define the load(usually a resistance) that the micro-

E&MM MARCH 1981 75

ELECTRO-MUSIC

1

1

A Beyer Dynamic Ribbon unit (M500).

2 & 7Two extremes of dynamic microphones, theShure Unidyne B and the AKG D222. TheD222 uses two separate pickups for bassand treble giving a very extended response.

3

AKG D190 - all is not what it seems. Good forsnare drums and roto-toms in spite of whatAKG say.

A

6

4Shure SM58. Often used vocal microphonealthough frequency response is hardly flat.

5AKG D12. Bass drummers idol.

6Top range capacitor - the fairly recentlyintroduced Shure SM81, but at £150 it hadbetter be good.

7

A selection of microphones discussed in the text.

phone is designed to operate into. Thisis important because a wrong im-pedance load will not only alter thelevels, but also affect the frequencyresponse. Most professional micro-phones have quoted impedances of200 ohms or 600 ohms. This meansthat they should be plugged intoataperecorder or mixer with an imput'resistance' of about 600 ohms, thedifference between 600 and 200 notbeing critical. Most tape recorders arenot satisfactory as they stand havinginput impedances of about 50k ohmand a matching transformer shouldreally be purchased, although thetrickof connecting a 680 ohm resistoracross each input jack often works.

Wiring UpSome care is necessary in order to

obtain the best results. Most pro-fessional microphones employ bal-anced line outputs (a full descriptionof which appears elsewhere in thisissue) and use cannon connectors,although 1/4 inch jacks are sometimesseen. It is essential that all micro-phones are connected up in the samephase so that a positive sound pres-sure produces a positive voltage on thesame input connector pins irrespec-tive of the microphone used. If this isnot observed the final sound will be

very hollow, and lack bass, due tophase cancellation of signals fromoppositely wired mics. If all the micro-phones are from one manufacturer noproblem will exist, but it is worth thetime tocheck if a mixture of makesareused.

The cable used to connect themicrophones up should be of a highquality, preferably with a properbraided screen, and of the low noisetype designed specially for micro-phones. This sort of cable employs asemi -conducting screen between thebraid and the core insulator (Figure 8)this must be stripped well back out ofthe way since it exhibits a fairly lowresistance and will affectthe operationof the microphone. It is fa Ise economyto use plastic jack plugs since they arevery unreliable - buy decent metalones, preferably the sort with integralcable clamp.

One from theHundreds?

It can be very hard to choose thecorrect microphone, much advicegiven is misleading, and some of itsimply wrong. In general it is best to goto a good dealer, who will let you testthe microphone in the envi ronmentforwhich it is intended. Under no circum-

stances buy a microphone withoutlistening to it tirst.

Firstly it is necessary to decide onthe polar pattern required, followed bythe decision about the frequencyresponse. For example, recording achamber orchestra needs an ex-tended top with a flat response, anobvious candidate for capacitor types,as would be a hi -hat cymbal. Howevervocal work through such a micro-phone would probably sound ratherflat, indicating a 'presence' peak maybe required.

Other problems emerge as themicrophone is tested, most particu-larly susceptability to stray noise suchas wind, pops and handling bangs.Pops are caused by close mikingvocals when like letters 'P' or 'B' startthe word. The rush of aircausesa nastypopping sound to occur. Wind noise isonly a problem outside (or near big airconditioners?) and simply resultsfromthe noise created by the airflow aroundthe microphone. Both these may bereduced by fitting a pop shield - asleeve of foam over the top of themicrophone. Handling noise is onlyrelevant if the microphone will notremain in its stand all night. A solid'clunk' as the artist removes or re-places the microphone in its stand isnot a very desirable effect. All thesefactors should be taken into account,

and most of them can only be exploredby using the microphone in question.

Most manufacturers quote appli-cations for much of their range. Inevit-ably these applications are a littlestretched since the manufacturerwants to convince the buyer that hismicrophones are more universal thanthose made by other people. Excep-tions do exist - AKG modestly refer tothe D190 as for 'General semi-profes-sional use, movie sound and announ-cer studios'. In fact, the 190 is not aparticularly good vocal microphonebeing very susceptible to popping, butit is blessed with a considerabletransient response and is used inseveral rigs and studios for snaredrums and roto-toms, and sometimeson cymbals, although it has a tendencyto sound a bit 'splashy' at times.

This section can be simply sum-marised however with two words, 'tryit', but you may need to find anunderstanding dealer first.

One final note: It is notworth buyingcheap microphones and an expensivetape recorder, better results will beobtained by putting half the availablefunds on a tape machine and splittingthe rest between two microphones. Onno account buy several cheaper ones,since in general two good micro-phones will last a lifetime, as well assounding a great deal better. E&M M

76 MARCH 1981 E&MM

ELECTRO-MUSIC

GET ORGANISED!Readers of this new magazine arebound to be constructors bynature. The field of electronics

is vast and there are myriads of ideasto whet the appetite in its application.Where music is concerned, more thanthe usual care is demanded if theresult is to be acceptable, even to thelayman. Electro-music has to be verymuch more than a simple go/no-gosituation and a great deal of thoughtshould go into the planning of majorprojects such as synthesiser or organ.

The idea of building a musicalinstrument will stem either from aninterest in electronics or because thepotential constructor already hasgood musical knowledge and wishesto have his own instrument. Bothcategories will have a lotto learn in theprocess as very few people possessboth high musical and electronicabilities. Possibly learning to play wellis more difficult than putting thecomponents together correctly!

The first essential part of theplanning is to know exactly what isrequired, and this is not as simple as itmay sound. Many gadgets that canproduce music are loosely called'organs' - indeed, you can buy one inWoolworths these days. Commercialorgans often bristle with so manyfacilities and frills that it is difficult toknow whether they are orchestras,synthesisers or organs. The use towhich the completed instrument willbe put will shape the plan to a largedegree, taking into account theamount of cash the constructor isprepared to spend.

Unless well endowed musically, itis a good idea to enlist the help of afriend experienced in music andtogether look at and listen to com-mercial instruments that appear to fillthe bill. There are excellent organ kitson the market today - Maplin, Wersiand several others - where a numberof the basic decisions have alreadybeen made by the designers but thecustomer still has options as to thescale and cost of the instrument. Withboth these and commercial instru-ments generally, it is a little difficult toknow exactly what you do require untilexperienced in playing that particularmodel.

COMPASSWhether the organ is to be built

from a kit or self designed, one of thefirst decisions to be made will involvethe size of the instrument.

The single manual version canhardly be termed an organ as, al-though the keyboard may be 'split' toallow playing of both solo and accom-paniment simultaneously, thearrangement has many limitations.The players usually appear to preferto stand (at least saving the cost of abench!) as part of a group of instru-mentalists and are mainly involved inproviding harmonic and rhythmicbacking to the lead instruments. If'pop group' orientated, the single

manual instrument is probably suf-ficient and does at least have theadvantage of portability. The outputmay well be pre -amplified only, withits signal feeding one of the channelsof a common amplifier system.

The 'spinet' organ is in the midwaycategory and is possibly the mostpopular size of organ for use at home.This type of small entertainmentorgan will have two keyboards andprobably 13 stub pedals. Contrastingtone -colours can be used between thesolo (upper manual) and accompani-ment (lower) and all of the normalorgan departments are represented.The staggered keyboards are shorterthan usual - about 3'/2 octaves - butthis limitation can be overcome tosome extent by careful choice ofpitches.

If classical music is the aim, theshort keyboards of the 'spinet' are aserious disadvantage, as is also theshort compass of the pedal clavier.Those aspiring to serious organ musicmust settle for no less than two full 5 -octave manuals and a 25 or 32 notepedal clavier as otherwise it will beimpossible to play works scored forthe King of Instruments. It is perfectlyfeasible to design a light music organon this scale but naturally the largermanuals and pedalboard willinfluence the size of the console in thehome.

CONSOLEOrgan kits take the console into

account but if the instrument is to beself -designed and used in the home,remember to consult the HouseholdManagement! The organ will be apiece of furniture - possibly thecentrepiece - and should be builtaccordingly. Take a tape measurewhen visiting an organ studio orchurch. There is no real standard forconsole measurements but it is worthremembering that one of the joys ofhaving completed an instrument is tohear it played skilfully by someoneelse.

If you wish to retain that friend-ship, make sure that the controls arerecognisable and accessible. Touchswitches and postage stamp sizedbuttons may look smart but are noteasy to cope with when concentrating

on music at speed. A reasonable sizedtab or rocker is a much better proposi-tion. Study the tab layout of severalorgans, noting any colour codingused. The final plan can then incor-porate the best of these, though I

would advise against a rainbow dis-play of tabs if possible. Normal prac-tice is to use white for flutes, red forreeds, yellow for strings and black fornon -speaking controls.

Some standardisation is neces-sary if you expect anyone to sit downand play the beast! Imagine gettinginto a car where the brake and clutchpedals had been transposed. While inthis vein, the relative positions ofmanuals and pedals are important:the top C of a 13 note pedalboard isusually below middle Eon the bottommanual. The height of the benchabove the pedals should be some 21"for comfortable playing.

PITCHESIn this particular article we are,

ignoring the electronic aspects as thegeneral plan must first be laid:Another consideration, which maydepend on the method of tone genera-tion in mind, is the number of pitchesto employ.

The electronic organ still copiespipe counterpart in many ways, in-cluding the matter of pitch. The abilityto bring in a number of these togetherhas always given the organ that fulland regal sound. Although a rank of61 organ pipes (covering one stopover the 5 -octave manual) may bedisplayed out of chromatic order fordecorative plirposes above the con-sole, the longest pipe produces thelowest note and the shortest thehighest. If the longest pipe is 8' long,that particular stop is known as 8'pitch (the exception being closedpipes, such as Tibia Clausa andStopped Diapason). A 4' pipe willproduce a note one octave above an 8'pipe and a 16' pipe will be one octavelower.

'Footage' is an organ term that hascrept into our terminology but pitch isthe better word. The pipeless organwe are considering will be capable ofproducing various pitches, includingmutation stops: these are dissonanttones based on odd harmonics of the

Ken Lenton-Smith

fundamental or 8' pitch and areextremely useful in building up brassytones. The original Hammond systememployed nine pitches (and is stillused by Hammond and imitators of itsdrawbar system) and all of these areuseful though the limitation in build-ing is often financial.

The upper (solo) manual shouldbe provided with as many pitches asthe pocket will stand. The table showsnine pitches and the notes that wouldbe heard on playing middle 'C' withgiven pitches switched in.

In all probability, the number willbe much less than this. A suitable butcomprehensive set of pitches wouldbe 16', 8', 4', 2-2/3' and 2' for the uppermanual. The lower (accompaniment)manual will not require 16' pitch andprobably 8' and 4' stops will be quitesufficient. At the same time, the self -designed instrument should becapable of expansion and modifica-tion at a later date in this respect. Thepedal section is normally equippedwith 16' and 8' pitches.

I should perhaps emphasise thatpitch only refers to the frequency ofthe note heard and has nothing to dowith tone -colour. An organ may wellhave several 8' or 16' stops, forexample, but each will sound dif-ferent because the tabs control filtersthat impart tonal variation. Mixingdifferent voices at various pitches is,of course, one of the pleasures ofplaying organ.

Summarising our prior thoughtson the instrument in mind, the musi-cal destination will predetermine bothsize and compass of the instrument.The console must accord with theroom concerned and its controls beinstantly recognisable. The choice ofthe number of pitches envisaged canonly be verified by experimenting withinstruments in the organ showroom.Commercial organ kits will cater for anumber of options and will no doubtinclude the suggestions made here.

Building an instrument is a fairlylong process, so there is no point inrushing these important preliminar-ies. Take plenty of time and makeplenty of notes before laying down thekeel. It is only too easy to find that youhave ended up with something notideal! E&MM

PITCH: Middle 'C' keyed at various pitches. 8ve

Pipe Pitch 16' 8' 51/2 4' 22A 2' 1% 11/2 1

Scale Pitch - Fundamental 5th 8th 12th 15th 17th 19th 22nd

TypicalStop Bass Principal Quint Octave Nazard Flute Tierce Larigot Piccolo

C* C* D* C* D* C* D* D* C*

(C* Consonant pitches) (D* Dissonant pitches)

E&MM MARCH 1981 77

NEWS

1

MINI -RELAYS

A new range of miniature printedcircuit board relays are being intro-duced by Ambit. They are availablefrom stock with 10-12V DC, 320Rcoils and to special order with operat-ing voltages from 3 to 24V. The lifeexpectancy for the mechanics isquoted at 107, with a contact life of 105at maximum ratings. Two types areavailable; the RBU is flux resistantand has two -pole changeover con-tacts with a 2A at 24V DC rating, andthe smaller RCU type has single -polechangeover contacts rated 2A at 100VAC or 24V DC. Price for the RBU is£1.85 and for the RCU is £1.65, insingle quantities. Available fromAMBIT INTERNATIONAL, 200 NorthService Road, Brentwood, EssexCM14 4SG.

HI-FI DISTRIBUTION BOXES

A very neat way of tidying up allthose cables behind the hi-fi gear. Thebox screws onto the back of the shelfand is unobtrusive and slim enough tofit into a small space. Units areavailable with four or six Europeanstyle 6A sockets.

There is a neon indicator for mainson indication and the units are sup-plied with over 2m of 6A mains lead. Aneat and relatively inexpensive solu-tion if you are using separate hi-fiunits.Maplin Electronic Supplies Ltd., P.O.Box 3, Rayleigh, Essex.

CHEAP BOXESWest Hyde Developments Ltd have

announced price cuts by more than25 per cent on their Bocon caseswhich are manufactured in WesternGermany. They are claimed to besuperbly engineered and precisionmoulded in the widest range ofcolours and sizes available from anytop quality supplier.

This scale of price reduction,together with very generous quantitydiscounts on all orders forten items ormore allows significant savings. Forfurther information contact ChrisLong, West Hyde Developments Ltd,Unit 9, Park Street Industrial Estate,Aylesbury, Bucks.

McKENZIE SPEAKERSMcKenzie Acoustic Ltd now haveavailable a new 'STUDIO SERIES' ofinstrument and disco loudspeakers.The technical data quotes 'High speci-fications coupled with a superb stan-dard of presentation makes themhighly desirable pieces of equipmentwhich competes and even betters allthe best types currently available'.

These firsttwomodelsareCl2-125GP and C12-125 TC, both 12 inch andrated at 125 watts. Model C12-125 GPis a general purpose unit suitable forguitar, keyboard etc. Model C12-125TC is a dual cone extended responseversion, which is useful for P.A. use orindeed for any application where aresponse extending up to around14kHz and high power handling isdesired.

Typical sensitivity has beenmeasured, with an input of 1 watt at1kHz sine from one metre on axis, at101dB. With broad band noise input 1watt at one metre, 104dB is presentand at their rated power, in excess of120dB is quoted.

These units which are built onpressure diecast aluminium chassisincorporate a finned heatsink over theanisotropic magnet assembly. Theyare claimed by the manufacturers tobe capable of superb sound andexcellent sensitivity operating for longperiods in the toughest conditions,with a high standard of finish attainedby using a durable gold colouredstoved epoxy for the chassis and satinblack for the finned magnet cover.

They are to retail ataround £49 and£52 respectively, including VAT.

FLAT SWITCH

A bank of 16 or more switches in athin flexible sheet with an adhesiveback that simply sticks on to a metalor plastic front panel has been de-veloped by Molex Electronics Ltd. Athin layer of silver is deposited as apolymer ink onto two sections of aflexible polyester sheet and a thininsulating layer with openings tocreate a contact gap is sandwichedbetween them. The connecting wireswhich can be two for each switch orX -Y matrix etc are brought out as a flat

SPACER SHEET

flexible strip. After passing the cablethrough a slot cut in the front panel,the flat cable is simply pushed into aspecial connector and plugged onto apcb. Although at present only avail-able in large quantities to customers'own designs, Molex are planning toproduce standard designs which willprobably be available through com-ponent retailers. Selling at around £3for a 16 -switch bank, they offer a low-cost easy -to -use alternative toordinary switches.Molex Electronics Ltd, Holder Road,Aldershot, Hampshire.

MULTICOLOUR LED

A new idea in light emitting diodeshave a green and a red chip encapsu-lated in a clear epoxy package. Unlikeother red/green LED's, this devicehas three leads enabling both the redand the green to be driven simultane-ously. It is therefore very easy tocontrol the drive current to each, togive different levels of brightness ofthe red and green, and this enablesthe effective output to be any colour inthe spectrum between green (565nm)and red (700nm).

The output light beam, althoughbright is very narrow and the device isconsiderably enhanced by using aclear "Cliplite" LED cover also avail-able from this supplier.Maplin Electronic Supplies Ltd, P0.Box 3, Rayleigh, Essex.

THYRISTOR WITHGATE TURN-OFF

BTW58's awaiting encapsulation.

A new device to be known as a GTO(gate turn-off switch) is available fromMullard. Like a thyristor, the GTO canbe turned on by positive gate drive,but unlike a thyristor if the gate istaken negative the device will switchoff. To be known as the BTW58, theywill be available with repetitive peakoff -state voltages of 1000V, 1300V or1500V, and an on -state DC current of5A.

Prices range from about £3 eachfor the 1000V version and at this pricethe device should prove very popular,because it combines the high over -current capability and high blockingvoltage of the thyristor with the ease ofgate drive and fast switching asso-ciated with bipolar transistors anddarlingtons.Mullard Ltd, Torrington Place, London.

78 MARCH 1981 E&MM

NEWS

There is a vast array of equipmenton the market at present, and1981 should bring major inno-

vations at affordable prices. On thekeyboard side we are seeing manydigital/analogue hybrids, the Prophet10 from Sequential Circuits featurestwo 61 -note keyboards, with 10 com-plete voices, each keyboard having itsown programmer so two completelydifferent sounds can be played atonce.

The Roland Jupiter 8 is an 8 voicedprogrammable unit with a 64 patchstorage capability, with one of itsspecial features being an arpeggiator.Oberheim also have some new

_ models in this field, these are theOB-SX, available in 4 or 6 voice con-figurations. The OB-SX is a presetversion of their very popular OB-X.

Going down market slightly, theMoog Opus 3 is worth checking out,with full polyphonic capabilities in-cluding Strings/Organ and Brass. It isstill able to produce strong polyphonicor lead synth tones.

Introduced into the UK are twonew models from Korg, the LP -10 is anelectric piano with six way EQ, 3preset tones which can be mixed andalso an inbuilt speaker system. Korghave also introduced the BX3 which isthe big brother of the CX3 singlemanual organ. The BX3 has two 61note keyboards, full drawbar prin-ciples and features an electronicrotary speaker effect.

MUSK IMAKIE2DMIEN7 SCENE

A very useful unit around atpresent is the Sescom CT -1A. This is acable tester in a small pedal type unitallowing you to pinpoint faults in XLR,phono or jack cables.

The guitar manufacturers keep onmaintaining the huge quantities ofmodels that we see in our musicstores.

Several companies are usingfamous names, pickups and hard-ware to expand their ranges. You cannow buy "Handbuilt Guitars" fromMighty Mite, there are two models, alead and bass variation with a onepiece mahogany body, solid mapleneck with brass bridges/nuts andfittings.

Westbury also feature Di Marziopickups on their ever increasing rangeof guitars. Pignose, once known onlyfor their small practice amp haveadded the 150R Crossmix to theirrange, the 150R has two completechannels which can be preset to dif-ferent tones and volumes, allowingthe player to switch from channel 1 tochannel 2 or being able to crossmixboth channels together.

Since Vox amplification wasbought over a year ago by Rose -Morrisit has been given a new lease of lifeparticularly with a very widely ac-cepted range of FX pedals. Thepedals, of which there are seven,come in a newly designed V shapeand are very competitive in price.

Morley have increased their pedalscope, a very interesting unit is theElectro-Pik percussion pedal, thisallows control of both decay andtimbre, the attack can also be mani-pulated allowing drawn bow effectssuch as violin, cello and even fluteand synthetic sounds are available.The Morley pedals will all act asvolume pedals too.

Finally this month, if you are in-terested in sound and communica-tions equipment encompassingAmps / Mics / Speakers / PA / StudioEquipment and much more, then takea trip to the Sound 81 InternationalExhibition at the Cunard InternationalHotel from the 17th -19th February1981. E&MM

LOOK TOTHE FUTUREby wearing a T-shirt with the specialElectronics & Music Maker symbol.

These superior quality T-shirts have oursymbol printed in silver on the front, andcome in red or black and S, M, L or XL sizes,price £2.75 inc. VAT & p&p. Sweatshirtsare also available in the same colours andsizes, price £5.99 inc. VAT & p&p.

E&MM T-shirts Dept., Maplin Publications,282 London Road, Westcliff-on-Sea,Essex SSO 7JG.

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E&MM MARCH 1981 79

3 CHANNEL SOUND/LIGHTCHASER

LB31000SLC f32.70

STEREO DISCOMIXER/PREAMP

LBPA3M - MagneticC - Ceramic

A high performance£33.70

sound to light system which Magnetic or ceramic deckautomatically switches to a chase when the versions - please statemusic ceases. Super sensitive with an anti- All the requirements of a stereo disco preamp oninterference circuit. The unit will operate from one board, left and right deck mixers/tonepractically any amp and control up to 1,000W/ controls/mic. mixer/tones/mic. auto fade overchannel, 5Hz to 70K. Controls: bass / mid decks/and P.F.L. The unit can be used withtreble / master sensitivity / chase speed. either LB100/150/250.

Full set of pots - £8.63

3 CHANNEL SOUND/LIGHT LBPA2 LBPA1LB31000SL £17.20 f19.50

A four channel mixer A stereo hi-fi preampand tone stage for and tone storage formics, guitars, etc. Can mag. p.a. / tape /be used with any LB tuner, etc. Set of pots

£22.70amps. Set of pots £3.27.£2.74.

All the advantagesof the SLC without chase. 3 -WAY ACTIVE CROSSOVER

Controls: bass/mid/treble/master sensitivity. LBACO1

f17.902/4/8 CHANNEL CHASER

LB81000LC LBPSU1

£7.20,i,e cr Bass/mid/treble

$ active crossover withstage booster! Available with crossover points of200 or 300Hz, and 2K or 3KHz (please specify)

£28.00 LBPSU1 supply for LBACO1 (1 or 2).

An all logic chaser system POWER AMPLIFIERSfor use with up to 8 channelsat 1,000 watts each. Facilities include foot- Tough dealing power amps for use in soundswitch trigger and module cascading (16, 24, 32 systems. Open/short circuit protection andchannel, etc.), chase speed and re -cycle delay. fused. Heavy gauge heatsinks and rugged o/p

devices (all operate down to 4 ohms

25W RMS 100W RMS 150W RMS 250W RMS4 CHANNEL SEQUENCER 20Hz to 60K 5Hz to 25K 5Hz to 25K 5Hz to 25K

0.07% THD 0.1% THD 0.1% THD 0.1% THDLB41000LS 96DB S/N 110DB S/N 110DB S/N 110DB S/N

LB25 LB100 LB150 LB250£11.20 £19.70 £29.20 £43.50

''.- Note all models are avai able with either 500mV

ip

or 775mV sensitivity Please state whenordering.

£19.20A 4 channel sequence generator for

I4. r LBRLD1banks of lamps up to 1,000W per channel. Two £6.20speed controls, cross effect to provide settingsbetween seconds and rapid burst. A de -thump unit for use with any LB power amps

1 AND 3CHANNEL DIMMERS POWER AMPPOWER SUPPLIES

LB31000LD LB25PS LB100PS LB150PS LB25OPS£11.20 £16.20 £19.00 £26.50

P/P £1.20 P/P 11.40 P/P /1.70

LB31000LD FOR GUITARS

f16.20 P.A. & DISCO PIEZOHORNS

Single channel version £5.75P/P 50p

LB11000LD £7.20

Power dimmer units for the theatre/stage appli-cations up to 1,000W per channel, with on boardsuppressing. The unit is also available withoutrotary pots for use with sliders - ,,,--:LB31000LD (no pots) £15.00 Sliders 75p each CELESTION LOUDSPEAKERS

(ALL STANDARD CONE 8 OHMS)

ROPE LIGHTS/DRIVER G12-65 G12-100 010-50LB41000LC-S (12in. 65W) (12in. 100W) (10in. 50W)

£24.20 £20.70 f1.70 £26.45 £1.P70 £14.70 £1.P70

24 feet ropes NEW - MINI MODULES - NEWRed/YellowBlue/Green Ingeniously designed mini pre amplifier build-

ing blocks for use in music and PA applications.You choose the type and number of units yourequire for your particular system and mount51 each module via its control direct onto yourpanel.

ROPE LIGHTS LBMM1 Pre -amp for mics, guitars etc.LBMM2 Mixer for up to 6 LBMM1 /2/3/4/5

£45.40 LBMM3 Bass/boost/cut for either LBMM1/2/3/4/5. LBMM4 Mid-boost/cut for eitherLBMM1 /2/3/4/5. LBMM5 Treble boost/cut for

A four channel chaser up to 1,000W per either LBMM1/2/3/4/5. LBPSU1 -, 15V supplychannel, with a sound trigger facility. The music for up to 12 modules. LBPSU +- 15V regulatedinput signal modulates the speed of the chase for up to 50 modules.giving an excellent sound/light effect. The unit MM1 £4.50; MM2 £5.20; MM3 15.70; MM4will control up to 10 ropes with chase speed and £5.70; MMS £5.70; PSU1 £7.20; RPSU £14.50.trigger level control. Discount on MM1/2/3/4/5 10 to 24 - 20%.

25 * -30%.

module is manufactured from the highest

Lquality components, fully tested, supplied with a

"r"""'4"'" NICEachconnection and circuit diagram and guaranteedELECTRONIC MODULES for twelve months.

All prices shown are VAT inclusive. PleasePROFESSIONAL ENGINEERING BY include 50p post/packing except where indi-

vidually stated. To mail order send cheque/P.0./PROFESSIONALS registered cash or Access number. C.O.D. ser-vice 11 extra. For the new Autumn catalogue

45 Wortley Road, Croydon, Surrey send 50p (full spec. shown).CRO 3EB. Tel: 01-689 4138 Please note this company has no connection

with LB Electronics of Hillingdon

TheProfessions/s.. .

Often heardrarely seenThis is more true than ever, simply because the abovephotograph shows the new "Studio Series".

Designed and built in the U.K. nothing has been spared toproduce the best, capable of meeting the demandingrequirements of the most discerning musician or D.J.

The first two models of this superbly engineered series,built on rigid pressure diecast aluminium chassis, are a125 watt general purpose unit plus an extended responsedual cone version. Both these powerful loudspeakerspossess excellent sensitivity capable of delivering inexcess of 120dB at their rated power, and that's a lot ofsound pressure in anybody's language.

And, take note, these loudspeakers which compete withthe best, won't break the bank at around £49 each.

The well established and successful "Professional Series"which are specified by leading equipment manufacturerscontinues as before.

If you're building a system - build it with.. .

Acoustics Limited

ROCKLEY AVENUEBIRDWELL, BARNSLEY, YORKSHIRE S70 5QY"lephone (0226) 43894

80 MARCH 1981 E&MM

NEWS

This is a monthly column spot-lighting the electro-music deve-lopments taking place in

America, where a lot of majorresearchinto electronics and music was pio-neered. In spite of ever-increasingadvances in this field being made byother countries, America can still offera few surprises to the electronic musicmaker. All specifications are based onmanufacturers information andshould not be constituted as a review.

Probably the most significant de-velopment since the 'chip' is theapplication of digital technology tomusical instruments and althoughsuch applications have been aroundsince the mid -sixties we are only nowseeing such developments in com-mercial units.

Just to belie the title of this column(and who wants to be pigeon -holedanyway?) one of the most compre-hensive designs in the application ofdigital technology comes from anAustralian company called FairlightInstruments. Their unit is called theFairlight C.M.I. (Computer MusicalInstrument) and the design concept isthat any sound can be played in amusical fashion.

Eight waveform memories canhold waveforms of sounds inputted viaa microphone or originally defined interms of harmonics and their enve-lopes by the synthesist, using a lightpen and VDU screen. These can beplayed independently, or eachmemory can be given the same soundfor 8 -note homogenous polyphonickeyboard playing. Since these wave-forms can be stored on disc, thenmodified or blended with others, thesystem allows a fascinating insightinto the nature of sound to be ga ined bythe synthesist and theoretically anysound forms or characteristics can beachieved by a combination of directand reproductive synthesis.

MARCH 19814111111V

: Ct.

Ian WaughThe keyboard is velocity sensitive

and this parameter, along with thepositions of various pedal and switchtype performance controls, can beassigned to control aspects of thesound such as volume, attack, vibratoetc.

A built-in sequencer facility allowsreal time recording of music played infrom the keyboard, including velocityinformation, and up to seven trackscan play along with the one beingrecorded, allowing complex multi -voice compositions to be assembled.

Also included in the system is 'TheComposer', a programming languageallowing music to be entered via analphanumeric keyboard and thenmanipulated in score form using the'Screen Based Editor'. The languagecan also compose music directly, inaccordance with general rulesdefinedby the programmer/musician.

Capabilities are determined by theprograms which are loaded via twofloppy diskettes. These can be up-dated as new programs become avail-able or as the user writes his own.

Con Brio have produced their ADS100 digital synthesiser with a view tointeresting the 'live' musician. It hascapabilities for 64 digital oscillatorseach with independentamplitude andfrequency control, and also 128 en-velope generators. Information isstored on an 8 -inch floppy disc whichprovides immediate recall of pre-viously determined patches and thedisc will also store any previously -played keyboard sequence or alter-native tunings. Each oscillator can beindividually modulated by envelopegenerators which consist of 16 sepa-rate segments. A video display of theenvelopes is provided. Additiona I voic-ings for the ADS 100 a re availa ble fromCon Brio.

Rocky Mount Instruments havelaunched their DK-20 which is des -

cribed as a digital combo keyboarddesigned to meet the demands of theclub musician. Factory presets in-clude guitar, piano, flute and clavinetand the sounds can be altered withdigital envelope and filter controls.The DK-20 uses digital tone gene-ration in order to produce an extraclean sound. A special feature ispolyphonic timbre modulation whichputs each note played through com-plex timbre changes during its enve-lope. A 'transient' button gives a bitingedge to the initial timbre -changingstages to make each note stand outeven during heavy chords. It would,perhaps, help prevent the keyboardsgetting lost behind mountains of guitaramps and speakers. Also included is abuilt-in mixer for sound blending andstereo output mixing.

New England Digital are now busypromoting their Synclavier II inAmerica and abroad with the phrase'Synclavier II - its the last synthesiseryou'll ever need'. Certainly it appearsnearer the musicians concept of asynthesiser than some of the othercomputer based systems available,since all synthesis functions, andthose of the integral 16 -track digitalrecorder, can be controlled directlyfrom the front panel. A button ispushed for the control to be changed,and a single 4 -digit numerical dis-play shows the value of the function

-

selected while a large knob is used toincrease or decrease it.

A new method of synthesis calledpartial timbres, along with frequencymodulation, immediate recall ofstored sounds (including 64 factorypresets), and a host of special effectsmake it an exceptionally powerful live -performance instrument. The Syn-clavier II is also very compact - thekeyboard unit, which holds all thecontrols, is lighter than a Minimoogand can be carried under one arm. Thecomputer unit is less than 19 inchessquare and can be sited away from themain console along with the disc drive.

Next month: what you can buy foraround $69,000,00 (whoever said,'Another day, another dollar' musthave been a musician), plus what'snew in some other areas of musicaland electronic development inAmerica.

Companies and manufacturersmentioned:

Con Brio, 975 San Pasqual St.,Suite 313, Pasadena, CA 91106;

Rocky Mount Instruments, Macun-gie, PA 18062;

New England Digital, Main St,Norwich, VT 05055.

Fairlight and Synclavier II dis-tributed by Syco Systems (UK) Ltd,20 Conduit Place, London W2. E&MM

81

NEWS

X00 Multipliesby the Yellow Magic OrchestraA & M AMLH 68518

The latest 'technopop' to in -vade England from Japan.Since Japan is so busy ex-

porting the latest in electronictechnology it is not surprising thatits musical exports should also bestate of the art. Unlike previouselectronic music from Japan, forexample Isao Tomita, the YellowMagic Orchestra's material is ori-ginal and not just interpretationsof well established classicalworks. Haruomi ('Harry') Hosono,bass and synthesiser player withthe Y.M.O., describes their musicas a kaleidoscope involvingdanceable rhythms, heart -pierc-ing melodies and 'a metallic con-cept meant to massage the frontallobes'. What the album lacks inmusical imagination is compen-sated by technical production.The Yellow Magic Orchestra pro-duce a clean powerful sound withpolyphonic synthesisers andsome interesting vocal treat-ments with vocoders and echounits. Short repeating sequencescombined with heavy pulsatingdrums are often used.

The Yellow Magic Orchestrahave fallen into the trap of label-ling their compositions with sug-gestive futuristic titles such as'Solid State Survivor' (could thisbe about a transistor which sur-vived a soldering iron placed onits can?) 'Citizens of Science' and'Technopolis'.

Side One begins with a "FozzyBear" voice introducing track 2with "YMO are ready to lay on ya -'Nice Age'," which turns outtobearepetitive track featuring vocalsreminiscent of M's Pop Music overa very western d iscorock beat, andwith interesting use of time -axis -modulated echo on the harmonyvocals. In England the album isreleased by A&M and is accom-panied by a free single butwhetherit becomes as successful as thework of Isao Tomita is doubtful.

414

Nevertheless it is well worth alisten, if only to find out whatelectronic two tone is like and togive your frontal lobes a massage!Graham Hall.

Short Storiesby Jon and VangelisPolydor Deluxe POLD 5030

NOT many people who havefollowed the developmentof Jon Anderson and Van-

gelis could have imagined thatthe uniting of two talented musi-cians could produce such ima-ginative and individual music;both retain their identities yetcomplement each other so suc-

JON AND \ ANGEL'S5101SIEfe-

cessfully.Short stories is an incomplete

overture, stretching sound andtempo in every conceivable direc-tion, leaving one in anticipation ofwhat is to come.

Vangelis seems to have re-turned to earth, using suggestivemelodies, he is able to createextraordinary emotion within hisplaying, the precise use of thesynthesiser and an in depthknowledge of the capabilities ofhis instrument give him a totallyproductive nuance, which untilnow I did not believe he had. Van -gel is' importance of exact timingin respect to falling filters, noisemodulation and the like makesthis a well produced and en-gineered record with dynamicprecision.

All tracks have their own storyto tell, the use of sequencing isquite apparent but laid knowinglyto produce heaven or hell; verysubtle modulations and thesometimes extravagant usage ofpercussion leads one to listen forthe technique involved. I foundthis difficult due to losing oneselfin the images produced.

The music complements thelyrics and vice -versa, Jon Ander-son sings with his heart, a distinctempathy and etheral quality

emits, he is able to add complexharmonics and rhythm wherethey should not exist.

Each piece is beyond analysis,it will mean something differentto all, the synthesiser has mademusic here, gone are the long,monotonous free form soundeffects that we thought electronicmusic consisted of, we have herethe complete spectrum of soundin pure musical notation. I'mwaiting for the next one!Vince S. Hill.

Travelogueby The Human LeagueVirgin V2160

The Human League's secondL.P. on Virgin records is anexciting collection of ten

tracks characterised by decayingfiltered timbres of synthesisersand the strict rhythm created bysynthesised drums and cymbals.Philip Oakey's expressive voicestands out from the backgroundof synthesisers putting the em-phasis as much on the lyrics asthe melodies. Only two of thetracks are strictly instrumental -they are 'Toyota City' and 'Gor-dons Gin'. Toyota City uses gentlesynthesised chimes to invoke anoriental flavour and Gordons Gin

is an electronic version of thecatchy theme used to advertiseglistening green bottles of a wellknown spirit!

There is a part of The HumanLeague's performance that can-not be gleaned from listening totheir albums- theirstage act usesslides and video films to enhancethe music. Adrian Wright, thevisual director, is considered as amember of the band rather than astage crew tehnician which illu-strates the importance of thevisual side of their act. An originaloutfit amongst a new generationof groups producing electronicmusic - if you cannot get to seethem live listening to this album isthe next best thing.Graham Hall.

82 MARCH 1981

NEWS

Music and the Synthesiserby Bruce GrahamPublished by Argus Books Ltd.Price £4.25

The unfortunate thing foranybodywriting a book concerning syn-thesisers is, that by the time the

research is completed, the manu-script edited and then published,

. some parts of the book become out ofdate. This is what has happened toMusic And The Synthesiser, not onlyhas the author taken his base -linefrom synthesisers that are not readilyavailable and purchased on the openmarket but he has neglected theJapanese syndrome which was quiteapparent and increasing when heresearched this project.

If, as Mr Graham implies the book is'written with the beginner in mind' thetransition of relating his ideas to thoseinstruments that a virgin synthesistcould understand yet afford would be avery tedious process.

11115113

SLIT ES SIN

hum Antiral

That is not to say however, that thismanual is without its merits. Theauthor glides through the history andthe explanations of the synthesiserwith comparativeease. Hethen beginsto develop further the basic elementsof synthesis and their physical rela-tionships. When advancing to thechapter regarding Patching, Signals,Voltage Control and Notation, we areattaining a much higher level thanproposed, mainly because there areno synthesisers commercially avail-able which use this type of pin patch-ing, unless second hand. In additiontothis, the synthesiser notation used isnot seen in today's owners manualsand setting charts, though the expla-nation of modules in the next chapterseems useful.

Mr Graham writesalsoon peripheralunits, the use of tape recorders with asynthesiser, this being an extremelyimportant and viable concept todayand a helping hand tothe newcomer insynthesis. The remainingchaptersareall useful in guiding the beginner andintermediate in relating electronics tomusical form.

Music And The Synthesiser isa goodguide but not mentor, theexplanationsare valid, healthy and correct, yet theauthor lets himself down terriblyin his glossary, which should be one ofthe most important parts of a booksuch as this, when he states that aflanger is 'an electronic phaser'.Vince S. Hill.

Adventures with Microelectronicsby Tom DuncanPublished by John Murray Ltd.Price £3.25

It has often been said that bookcritics only draw attention to anauthor's shortcomings, totally fail-

ing to point out the attributes and un-precedented parts of the text, but withthis book that is impossible. TomDuncan has made a perfect job in boththe layout and description of eachproject represented. The book is aimedat the non -technical but again theauthor has not been frightened to useup-to-date devices (in particular CMOSIC's) which, as the title suggests, arethe theme of the book. A good start ismade by giving a brief resume of all thecomponents necessary to constructthe circuits given as examples in eachchapter. All the circuits are construc-ted on Bimboard Building Blocks, adescription of which is given in the

ADMVM5VOTA

AOCVD-R1gCNOA00

MINCAN

second chapter. This is followed by achapter analysing in laymans termsthe anatomy and uses of the siliconchip. Each of the ensuing chaptersrevolves around a different electronicproject all of which are cheap andsimple to construct.

The format which Tom Duncan usesto represent each project is parti-cularly good. A list of the componentsrequired follows a short description ofthe circuit. This is succeeded by thecircuit diagram which is quite graphicin its representation. Next comes astep by step guide to constructionleaving no room for error. Notablyexplicit is the overlay of the circuit onthe Bimboard again ruling out thepossibility of making a mistake.

The book's only real 'letdown' can befound in the section of text entitled'How It Works'. This tends to be acommon misgiving in books designedfor the uninitiated - perhaps thebeginner would grasp the subjectfaster and progress to a more tech-nical level if more attention to detailwas paid in describing how the circuitreally operates. It is only fair to saythough that this section does improveprogressively throughout the book.Each chapter ends with a few ideas totry out and some suggested alterationsto the original designs. These are notfully defined leaving enough detectivework for the readers appetite to bewhetted but not satiated.Nigel Fawcett.

Element of ElectronicsA set of four books by F. A. WilsonPublished by B. Babani LtdBooks 1, 2, 3 Price £2.25 eachBook 4 Price £2.95

Having read these books, one'simmediati impression is thatthey are out of the paperback

class. They really constitute the sort ofinvaluable textbook that can be reliedupon in every situation and containmuch of the information necessary togenerate a deeper understanding of allthat crops up in the electronics field.

Individually the four books describethe simple electronic circuit and com-ponents, alternating current theory,semiconductor technology, andmicroprocessing systems and cir-cuits.

My initial complaint, having read thebooks, was that the author has over-rated the powers of the microproces-sor, and underrated the powers of the

human brain. However, although thisis still my indictment, in retrospecttheseries as a whole will certainly find ahome in my bookcase. The abundanceof correct formulae and notationthroughout the text provides usefulreference information.

In brief, the books progress throughfrom; an explanation of the electronand electric current, the sources ofelectricity, how this applies to thesimple electronic circuit, the forces atwork within this circuit, the relation-ships between the components in thecircuit, what happens to the circuit ifany part of it is altered, waveforms andtheir effects, time consta nts, the atom,diodes, transistors and the uses there-of, computers, computer systems,and what makes the computer tick.

Each book is well equipped withappendices, all delving deeply intothemathematics required to elucidate thepreceding chapters. All the books areadequately cross-referenced, whichby scanning the index, is infinitelyhelpful for those with a poor memoryfor theorems.

As previously mentioned, everychapter is armed with enough trigo-nometry or calculus to dissuade thecasual observer from making a pur-chase. However, my advice is addthese books to your collection, for theywill undoubtedly provide you with agreater insight into the complex andoften difficult subject of electronics.Nigel Fawcett.

Introduction to MicrocomputerProgrammingby Peter C. SandersonPublished by NewnesPrice £4.05

This book is aimed at the com-plete beginner and starts off withan introduction alongthose lines

including one of the best flow chartingexplanations I have seen.

After basics, the book proceeds to'Choosing a Computing ProgrammingLanguage'. This area could have beendealt with a little better, but thedetermined reader should gain someidea of a suitable language for hisprograms: Machine code, Assemblylanguage, COBOL, FORTRAN, Pascal,ALGOL, PL/1, APL, and of courseBASIC are all covered, although thehigher level ones only briefly.

The next fourchaptersaretaken upwith a 'crash course' in BASIC. Theconstruction of programs is describedin a clear and concise manner and adescription of possible differences in

system commands from machine tomachine is included. At various stagesexercises (with solutions) areprovided.

Chapter 7 is a quick guide totypesofBASIC, under headings such as:Integer Only, Matrix Instructions,Graphics Facilities etc. Included hereis a worthwhile comparison chartcovering the BASIC instruction sets ofvarious machines.

The next two chapters deal withAssembly Language and MachineCode programming. Obviously themost difficult area to convey to begin-ners - this is a brave attempt butwithout some other publication toexplain in greater depth the use of hex,octal and binary, the beginnerwi II startto flounder. On the plus side allexamples are shown using the fourmost popular processors (8080, 6800,6502, Z80).

The final section deals with pro-gram development and testing, ex-plaining how to avoid making errorsand find any that do occur.

In summary I would recommendthis book to anybody who is consider-ing buying a machine but is not surewhether he is going to be able tocompile and write hisown programs. Ifyou do purchase a machine it willprove a useful reference book, unlikemany others which you may grow outof. In fact the machine code sectionsyou may well grow into.Graham Daubney.

ER.EMM MARCH 1981 83

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Chorosynth (80060) f57.90This is an inexpensive 'touch' keyboard synthesiserthat anyone can play. The range covers 21/2 Octaves andhas 10 register effects. In addition 4 Chorus effects arepossible together with vibrato and glissando. The rangecan be switched to cover 6 Octaves. Single PCBconstruction.

Mini Mixer (81068) f37.50Small package, high performance mixer with 5 stereoinputs, treble and bass controls. Power supplyincluded. Slider controls for inputs. Frequencyresponse 20Hz-25kHz.

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Analcgue Reverberation Unit(9973) f38.45Uses a 1024 'bucket brigade' memory type SAD1024 todelay up to 100mS. Reverberation varied by changingthe speed of the clock pulse from 5kHz-500kHz.Signal/Noise ratio 60dB.

Our Project Packs include the electronic components, the PCB, sockets and solder together with assembly instructions. Cases, knobsetc can be supplied as extra items if required. This is only part of our wide range of projects. See our catalogue for details of otherprojects that we can supply. You can also ring our number between 12.30 p.m. and 1.30 p.m. any weekday for a recordedannouncement of any new items we have available.

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ELECTRONIC PROJECTS 1COST-EFFECTIVE PROJECTS AROUNDTHE HOME John WatsonIncludes a complete 7 -channel proportional radiocontrol system with CMOS coding and IC receiver;stereo synthesiser, tape/slide synchroniser, infra-red burglar alarm, temperature alarm, plus manyother circuits including regulators, oscillators etc.,all with the emphasis on performance for theminimum cost. 136 pages, £3.95

ELECTRONIC PROJECTS 2PROJECTS FOR THE CAR AND GARAGEGraham BishopEverything for the car electronics enthusiast, froma complete electronic ignition system to simpleaccessory circuits. Ignition circuits, anti -theftsystems, lighting controls, ice warning, brakemeter, strobe, even a sophisticated batterycharger, all are included with construction notes.118 pages, £3.50

BEGINNING BASICCONTINUING BASIC Peter GoslingAt last, here is a really easy -to -understand coursein BASIC. These two books form a completeintroduction to the language used by almost allhome computers, and many business ones. Thefirst book deals with the common BASIC instruc-tions, while the second delves more deeply intoalgorithms, strings, matrix manipulation, filehandling and subroutines. These books are usedin many colleges and schools. Beginning BASIC,104 pages, £2.95; Continuing BASIC, 112 pages,£4.25

All the above books are 9" x 6" format

ELECTRONIC PROJECTS 3AUDIO CIRCUITS AND PROJECTSGraham BishopPacked full with circuits for every aspect of Hi-Fiand electronics for pop musicians! Circuits foramplifiers and pre -amplifiers, from a 5 -com-ponent 2 watt IC power amp, to 70 watts perchannel. Also noise, rhythm and signal process-ing, sound -to -light, and electronic music.Complete with component lists, suppliers, etc.186 pages, f4.95

ELECTRONIC PROJECTS 4TEST GEAR PROJECTSTerry DixonTells you how to build quality test -gear for afraction of shop prices. Designs include powersupplies, generators and signal injectors, testmeters, component checkers and oscilloscopeaccessories - including a trace doubler. Fullcircuit layouts and construction notes. Build your-self a really well-equipped workshop. 104 pages,f3.95

MICROPROCESSORS & MICROCOMPUTERS- THEIR USE AND PROGRAMMINGEric HugginsFor the reader with no previous knowledge of thesubject, this book covers just about all you willneed to know about micros, their design, organi-sation, and programming at Assembly Languagelevel. Everything from simple descriptions toroutines for floating-point arithmetic! 224 pages,£4.95

paperbacks

84 MARCH 1981 E&MM

NEWS

PEQ nVP 1R)1Many attempts have been made to

duplicate the sound of rotatingspeaker systems for organs usingsolid-state circuitry to mimic theamplitude and phase modulationeffects produced by rotating direc-tional sound sources. Most take theform of signal processors that drive asingle amplifier and speaker system,but the invention described by theRoland Corporation in patent specifi-cation 1522850 uses a multiplespeaker arrangement and modulatesthe apparent location of the soundsource in order to produce a morecomplete simulation of the rotatingspeaker sound.

Three speakers are used, equallyspaced along a straight line facing thelistener. Each speaker has its ownpower amplifier and voltage con-trolled amplifier so that the signallevel of each can be separately modu-lated. The centre channel is fed withthe input signal directly, while theother two receive a frequency modu-lated version from a voltage con-trolled delay element (3 in Figure 1).The VCA's and delay are controlled bysignals from the modulation section,which consists of a 0.2 to 10Hz sinewave oscillator (2) and two phase shiftnetworks (P1 & P2). Since the modulat-ing signals for the outer channels are

Figure 1.

Patent Place is a regular feature that will describe patents of particularinterest to the electronics or electro-music enthusiast, especiallywhere they relate to or offer improvements over existing devices ordesign techniques, present some totally new idea, or offer scope forfurther experimentation by the hobbyist.

180° apart, and the signal for thecentre channel is 90° from each, themodulated signals from the threespeakers give the effect of a rotatingsound source (Figure 2) with anoverall tremolo effect. The delayelement is modulated by the samesignal as the centre channel VCA,causing the pitch of the tone to beincreased as the sound moves to-wards the listener and decreased as itmoves away, simulating Doppler shiftand producing vibrato.

A simplified system where thecentre signal is mixed with the outersignals for reproduction via twospeakers is also described. Bothsystems were used in the Roland Revotone cabinets where in three modelsthe speakers were arranged in a

single 'Leslie' - type enclosure.In patent specifications 1510416,

the Sansui Electric Company Ltddescribe a mechanical reverberationsystem using a number of tunable

vibration elements rather than aspring or plate -type delay device.

The vibration chords are made ofmagnetic material and are held undertension over two moving iron trans-ducers. A driver amplifier takes theinput signal and feeds it to the inputtransducer (see Figure 3). The chordsare simultaneously driven accordingto the input signal, and the outputtransducer picks up the vibrations foramplification. The resultant signal ismixed with the original to yield whatSansui call a "chordally emphatic,musically rich reverberation effect".Only the chords having resonant fre-quencies which correspond to com-ponents of the input signal continueto vibrate after the input stops: theother chords stop immediately.

As Figure 4 shows, the chords areheld at one end by pegs which canbe rotated to tune the vibration fre-quencies. They are also dependentupon the material of the chords so

Figure 3.

the resonances can be separated togive a more even reverb effect.

An arrangement is also proposedwhich uses a similar arrangement oftransducers and piano wires fixedat one end only as the vibrationelements. In addition alternativesusing piezoelectric or electrostaticmethods to achieve the same effectare also covered by the patent.

The sounds produced by suchdevices would be similar to that of a12/6 -string double -neck electricguitar with the volume of one neckturned up while the other is played, orthe sympathetic vibration effect of apiano played with the sustain pedalheld down. Whether such an effectwould be useful for a compoundmusical signal is doubtful, but it couldfind application in portable and homeorgans. E&MM

Copies of Patent specificationscan be obtained from:

Patent Office,(Sales Branch),St. Mary Cray,Orpington,Kent,BRS 3RD

Price £1.45 each

Figure 2.

E&MM MARCH 1981

Figure 4.

85

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ELECTROMUSICSPECIALISED INTEGRATEDCIRCUITSPurpose designed IC's for electronic musicand other audio applications. Wide range ofvoltage controlled oscillators, filters, amplifiersand envelope generators available in standardDIL packages and with versatile and easy to useconfigurations.

DIGISOUND 80MODULAR SYNTHESISERA system for the 1980's. Thirteen modulesplus power supply and keyboard controllercurrently available - more to follow.Advanced features yet simple to construct.A modular system offers great advantages forboth advanced user and the beginner. You candecide how the synthesiser is patched andit may be expanded to any size to suit yourpocket or specific needs. The beginner can makesure that each module is functioning properlybefore starting construction of the next.System is compatible with most commercialsynthesisers. High quality components, glassfibre and tinned PCB's plus full range of panelsand other hardware.

MICROPROCESSOR CONTROLThe DIGISOUND 80 keyboard controller isaccurate and completely free from voltage droopwhich bugs many designs. It is simple toconstruct and yet may be readily connected toa microprocessor to provide control facilitieswhich are only limited to ones imagination.Those with experience of programming cando their own thing but we will also be providingan expandable system with programmes whichwill run at the touch of a button. No knowledgeof computers required for the latter. The firstprogrammes include polyphonic control plussome keyboard routines which you probablyhave not dreamed of. Once a microprocessoris installed then it is the cheapest route tosequencing, composing and so on.

All the above is coupled with a fast andpersonal service which includes technicalback-up. Send now for further details and prices.

DIGISOUND LIMITED,13 THE BROOKLANDS, WREA GREEN,PRESTON, LANDS. PR4 2NQTel 0772 683138 (MAIL ORDER ONLY)

86 MARCH 1981 E&MM

NEWS

To begin with we are devoting aspecific page to education eachmonth so that a 'forum' for teachersand possibly pupils may be estab-lished. It is in the teaching of elec-tronics, computing and music that weare most interested to have yourviews.

From our overwhelming pre -pub-lication correspondence, we havefound that many readers have offered

Electronics & Music Maker looks to the future by choosing projects that useup-to-date technology and features that inform its readers of the latestdevelopments in electronics and electro-music.

Education in its broadest sense is therefore one of the key aspects of thismagazine.

It is also exciting that it will be read by teachers and pupils alike through itswide circulation in this country and many subscriptions abroad.

to write on subjects that coula be ofgreat potential value in secondary andfurther education.

With the increasing use of elec-tronics in music, the music teacherneeds to be aware of developmentsand ideas that will keep him or her up-to-date. Traditional methods and con-cepts are not to be ignored, simplyexpanded to bring the subject in linewith the enormous changes occurring

- especially in the use of computersto make music and the VDU as amusic notation 'blackboard'. Presen-tation of music appreciation can beenhanced by aural and visual im-provements as well.

Similarly, the science classroomcan only benefit from staff and pupilswilling to provide electronics projectsof low cost and yet incorporating thelatest circuit devices. Although the

teaching of computing does notnecessitate knowing how a micro-computer works internally, it isobviously valuable to have practicalknowledge for adding peripherals andmaking improvements.

We shall be interested to hear fromanyone who has a short article forpublication related to music, com-puting or electronics.

EDUCATIO\You have a problem?Computers are used in the real worldto help solve problems. The trouble isthat usually it is a big problem in itselfto get a computer set on the right roadin this task! In the classroom it is alsoa problem to know how to start off inthe right direction (for both pupil andteacher) in tackling problem solving.

The computer studies teacher hasfaced this situation for some time.Now more teachers ought to be in-volved. This is so because informa-tion (or knowledge) is becoming moreand more available, so much so that itseems nonsense to cram facts intopeople's heads all the time when theycan get hold of those facts at the touchof a few buttons (as is increasingly thecase). If you are shocked at this idea,just think. What use is it just to re-gurgitate facts, rules, and so on inisolation? All too often we hear of

people learning something under theheading of, say, 'mathematics' but areunable to apply what they havelearned in a closely related subjectsuch as 'physics'. We need to startdeveloping the skills of problem solv-ing across the whole curriculum sothat we all may cope with a danger-ously complex world somewhat better.than we appear to be doing now.Perhaps computing may be used tothat end.

Let us think, then, 'how can welearn to solve problems?' Let us startwith the computer and ask, 'how do Istart programming a computer tohelp to solve problems?' Oneapproach is to use the idea of 'suc-cessive refinement' - or 'top -downdevelopment'. With this approach westart with the idea of the problem itselfand begin to chop it up into smallerunits - or modules - tackling eachmodule as we can by further breaking

it down into yet more modules until wecome to the bare bones of the prob-lem. These bare bones we can thenimplement on the computer. Flowcharting is an essential aid in programdevelopment - and problem solving.

Figure la states that 'we have aproblem', and is a form of breakingthe ice. Then, for every problem wehave associated data - or 'input'; andfor every problem we require results -or 'output' (Figure 1b).Can we identifythe data? Can we talk of the requiredresults? If we can begin to answer bothor just one of these then we may begetting closer to solving the problem.

Every problem has one or more'keys'; these are principal parts of theproblem to solve - and therefore toidentify! Can we split 'the problem'into one or more keys? Can we splitthese keys into smaller units (see

Figure 2). If we can split up a probleminto these keys and smaller units thenwe may begin to link them togetherwith a flow chart.

These keys may be regarded asproblem modules in their own right.The idea of feedback is often incor-porated into the problem solvingscheme: this is where the variousstages of problem solution may beevaluated - it is a little like repeatedlyasking a question 'how am I doingnow?' (see Figure 3).

In future notes I hope to illustratethis in practice, but not only in tradi-tional computing areas. Control tech-nology and real time processing ofinformation is becoming increasinglyimportant. These, and other notes forguidance, I hope will be of potentialuse to both teachers and pupils alike.Steve Leverett. E&MM

PROBLEM

KEY.' KEY2 KEYS KEY4

Figure 2

FEEDBACK

INPUT

PROBLEM

OUTPUT

Figure la

E&MM MARCH 1981

Figure lb Figure 3

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88 MARCH 1981 E&MM

NEWS

Breadboard ExhibitionArecord number of people visitedthe Breadboard 1980 exhibitionat the Royal Horticultural Halls,

Westminster, with an increase inattendance of over 50% on last year.

A good time was had by all andeveryone we spoke to commented onhow smoothly the show ran and howpleased they were with the responseto their exhibits. Many of the largersuppliers elected not to sell com-ponents on their stands this year,giving their space over to some veryimpressive projects; ranging from anorgan at £23,000 down to an elec-tronic timer for a few pounds. How-ever, components were still exten-sively supplied by the smaller com-panies, some of whom reported goodsales of scrap PCBs, "dead boards"and bargain packs.

What follows is a brief look aroundsome of the stands.

AURA SOUNDSMany of the 'Wersi' organs were on

show on the main stand, and in thedemonstration room Mick Leary putthe Wersi 'Helios' through its paces.

CHROMASONICELECTRONICS

Although components were onsale, this company was very com-puter orientated. On show were theU.K. 101, the Video Genie and, ofcourse, Pets.

VERO ELECTRONICSEver popular as usual, all Vero

products were on show and for sale.Indeed judging by the crowds sellingwell. A competition was on each day atthis stand, with of course Vero pro-ducts as prizes. Of particular notewere a number of small beginnersprojects, a new area for this company.

BERNARD BABANI(PUBLISHING) LTD

Babani had their extensive rangeof books on show, which were also onsale. Michael Babani commented: "Itwas good to get out and meet readers!'Throughout the week a number oftheir authors called in at the stand.

ELECTROVALUE LTDComputers were much in evi-

dence on this stand with both Nascomand the new Gemini systems beingdemonstrated. A brisk sale of com-ponents was reported and it wasinteresting to note an on-line com-.puter terminal, allowing customers toplace orders direct from the stand.

N.I.C. MODELSN.I.C. displayed the TRS 80 model

3 computer. The first time this mach-ine has been seen in the U.K. Theyreported good sales of computergames and games books. At times allyou could see of their stand wasbobbing heads and flashing lights!

CLEF PRODUCTSMr Bootham was on hand to

answer any constructors' questionsand demonstrate his latest program-mable rhythm unit, which was verycompact and impressive. The usualrange of electronic pianos were alsoon demonstration, as was an elec-tronic rotor for use with organs orpiano.

A. MARSHALL(LONDON) LTDThis was one of the larger compan-

ies who elected not to sell com-ponents from their stand this year, butthey were still present in force featur-ing among other things a miniaturemetal detector, the 'Leader' range oftest gear and many printed circuitboard accessories. Catalogues wereavailable at half price. E&MM's stand attracted a lot of attention, too!.

MAPLIN ELECTRONICSUPPLIES LTD

Maplin had a commanding view ofthe show, with the majority of theirexhibits on the stage area of the hall.Atari were in the limelight with theirsystem 800 computer and its amaz-ing 'Star Raiders' plug-in ROM. Thiswas the first time this computer hadbeen on general exhibit in the U.K.Many of the musical projects werebeing demonstrated, including thenew Matinee organ. Books and leafletswere on sale, as was the new 1981catalogue.

J. P.S.Featured on the J.P.S. stand were

Nascom and Sinclair products. Salesof accessories and componentsflourished and special discounts wereoffered on a number of items.

ELEKTOR PUBLISHERS LTDOne of the main attractions on this

stand was a programmable TV game.Also, of course, back issues of themagazine, along with a plentifulsupply of boards for the projectscontained within them. For those whohaven't seen Elektor boards, they arethe best we've seen.

Just a few of the thousands who attended Breadboard.

BOSS INDUSTRIALMOULDINGS LTD

This company launched a newmicroprocessor breadboard whichwill be backed up by instruction onhow to build a micro on one board.Their normal range of boxes etc werealso on show.

WATFORD ELECTRONICSMicroprocessors were in evidence

on the Watford stand, and they alsooffered a laser kit for under £200.Superboard II was there as was theVideo Genie, and there was a specialoffer on the Base 2 Printer. They werepleased to note people coming fromlong distances to visit the show.

PRACTICAL WIRELESSThe main feature of this stand was

an amateur radio station, which gen-erated an enormous amount ofinterest. Practical Wireless T-shirtscould also be purchased. On oneparticular day an appearance wasmade by Mr Brian Rix, who contrarytopopular rumour was in fact a guest ofPractical Wireless.

T. J. BRINE ASSOCIATESOn demonstration was the new

Road -Runner wiring system for use inlogic circuit board wiring. This is theirown development and features ex-tremely low profile connections thatcan be made up to five times fasterthan with conventional wire wraptechniques.

CONTINENTAL SPECIALISTCORPORATION (UK) LTD

This company made a colourfulappearance with a range of their well-known breadboards, both on sale andbeing demonstrated. Also featuredwere many items of test equipment.To cater for the many younger peopleat this exhibition several games andcompetitions were held on the stand.Mrs Knight told us that their onlycriticism of the show was the noiselevel created by the multitude ofmusical instruments and electronicgames. Many other exhibitors alsoconsidered this a problem.

AMBIT INTERNATIONALEmphasised on this stand were

radio components and tuners, with ademonstration of some very up-to-the-minute VHF equipment, whichhas been described in various magaz-ine articles. DVMs and frequencymeter modules could also be seen.

It was particularly nice to see someclubs getting involved. The Associa-tion of London Computer Clubs had astand, as did the British AmateurElectronics Club, and many ElectronicOrgan Constructors' Society memberswere present looking for bargains.

It is, of course, not possible toreview every stand individually but wehope the above cross-section will giveour readers some idea of just whatwent on. This was the third Bread-board exhibition and without a doubtthe best to date. E&MM

E&MM MARCH 1981 89

Ingots of aluminium are 'forced' into pre -shaped lengths called 'extrusions' and are usedfor pillars, box edges etc.

Part of the large factory area for preparing One of the huge presses that cut the sheetmetalwork. aluminium.

Chemical preparation (anodising) of the aluminium to give its high quality finish.

Veroboard holes are machine punched one This rotating drum automatically insertsrow at at time. pins into a dual -in -line package (DIP).

A complex panel of sockets with numberingadded as well. Here's the same panel after wire -wrapping!

NDUSTRYPROFILEVero Electronics Limited

To the electronics constructor,the name of Vero must be a veryfamiliar one. It was in 1961 that

Vero Electronics was first formed byMr G. Verdon-Roe (son of the famousaviation pioneer, Sir Alliott Verdon) tomanufacture Veroboard, the firstcommercially available breadboardfor use with transistors. With very littlecompetition at the time the demandfor Veroboard was high, as it enableddesigns to be quickly prototyped andtested.

During the 60's, Vero establishedits main factories in the UK nearSouthampton and opened three over-seas companies in Long Island,America, in Paris, France andBremen, Germany.

Since then many different bread-boarding sizes and types that havebeen introduced for industrial usehave been made available to thehobbyist.

In 1979 the company was takenover by B.I.C.C. and today its main UKplant has over 500 employees and isdivided into 3 product divisions - CardFrames, Circuit Boards, and En-closures.

At the Card Frame Division are awide range of facilities for manu-facturing card and module frameassemblies and in 1977 a large,automated anodising plant was in-stalled. The Circuit Board Divisionproduces Veroboard, DIP boards,pins, DIP sockets and other acces-sories. Production tools are alsodesigned and made in the engineer-ing section.

Both metal and plastic cases aremanufactured at the Enclosure Divi-

sion and their output includes numer-ous boxes for housing constructors'projects.

Some of the more recent casesinclude sloping fronts, moulded -inbattery compartments, flip -tops, key-board enclosures, tilt legs, two-tonefinish, front panel displays, VDU's and19" card frames for computer boards.

For the microprocessor designer,special prototyping boards withseparate multiway connectors, rackpower supplies and heatsinks areproduced.

If you preferto etch a PCB yourself,you can use Vero's etch -resisttransfers.

Vero Systems is a sister companyin the group that prOduces recharg-able wire -wrap guns. This wire -wrapmethod of connection was developedto cope with the complex wiring ofmicro -circuit boards. It requires nosoldering and uses insulated wire thatcan be simply routed straight acrossthe board from one point to the next. Ifyou make a wrong connection, theVerowrap gun will also 'unwrap' it foryou.

The photographs give you a

glimpse of my days visit to thefactories based near Southampton.What they don't show is the warmhospitality I received and the en-thusiasm which Vero's managementhave for their products. BecauseVero's standards are aimed at in-dustrial level, they pay a lot ofattention to the finish and generalcare of materials at each point ofproduction. Eg. etching takes place ina dust -free room, the powder paintingprocess eliminates unpainted areas

90 MARCH 1981 E&MM

NEWS

on panels and items are oftenwrapped and unwrapped severaltimes during the assembly of a case.

Some of their most recent de-velopments include 'through -plating'of circuit boards, VDU cases (suchas the Research Machines 380Z),cloth textured panels, small pillarsmade from a single sheet and silkscreened panels.

Despite all the technology avail-able, I was surprised to find thatVeroboard is mechanically made.Holes are punched out in rows of clearcopper coated board. The grooves arethen cut to make the track run in onedirection.

Most of the metal is anodised. Thisin fact can insulate, unless a self -tapscrew is inserted - so don't alwaysassume a whole metal chassis isearthed from one point! Another pro-cess - alochroming - ensures elec-trical contact between panels.

Vero have a strong interest in thehobby market and have a. range ofHobbykits for you to build. Their'Products for the Electronics Hobby-ist' book at 40p is a useful referenceguide, and their sales staff provides apersonal service to retail shops andindividual customers to ensure thatwe get suitable high quality productsfor our building projects.

If you've never used Veroboard (oralready like using it), then make sureyou order your copy of Electronics &Music Maker, May Issue when weoffer a free board on which you canbuild any of the specially designedelectro-music circuits included.Mike Beecher. E&MM

A special painting process where powder isdeposited on panels by electrostaticattraction.

A 19" card frame being assembled.

Fitting together the 'G' range cases.

Through -plating of industrial circuit boardsis one of Vero's new developments.

Finished 'G' range cases that have all round accessibility and sloping visor.

Some of the larger boxes including VDUcases.

Mike Humphrey (I) Retail Sales Managerand John Burns (r) Commercial SalesManager.

A 'Verorak' kit assembled in 30 minutes, yetas strong and rigid as a welded structure.

E&MM MARCH 1981 91

Tune in to Korg technology

We've noticed increasing sensitivity over the price oftuners so we've increased the sensitivity of theWT 12 and dropped the price!

The Korg WTI 2 tuner, developed from thesuccessful Korg.WT 10A and with many newfeatures, all at a lower price, is vital equipmentfor musicians, roadies and sound engineers onthe road or in the studio. Every facility you'llever need - packed into a light weight pocket

sized unit. World beating quartz technology forperfect accuracy. Output socket for tuning viaexternal amp. Illuminated VU meter. Off pitchtuning facility. Batteries or AC operated, ACadaptor, batteries and carrying case included.Earphone socket - earphone supplied.

Rose Morris & Company Ltd, 32 - 34 Gordon House Road, London NW5 Telephone 01-267 5151

Tuning range ofseven octaves.

Built in mic fortuning all acousticinstruments.

Input socket forelectric instruments.

Only £85 inc. VAT.

ORGCENTRE

Korg products are available at all goodmusic stores. Korg key centres maintaincomprehensive stocks, providedemonstration facilities and givespecialist advice.

Rose -MorrisKOBE

THE SHARPMZ-80 COMPUTER SYSTEM

The Sharp MZ-80 System is a new approach to computerapplications and their efficient use. Our aim is to make computers

relatively simple and therefore better understood and better used bythose they are designed to serve. Take a look at the Sharp range- it will

change the way you think about computers.

SHARP COMPUTERAPPLICATIONS

Sharp Electronics (UK) Ltd., Sharp House, Thorp Road, Newton Heath, Manchester M10 98E.

92 MARCH 1981 E&MM

NEWS

This column willbe given to newsand views on CBand other shortrange two-waycommunications,including newsof amateur radio.

Let's start this month by intro-ducing CB. This stands forCitizens Band radio which is

a radio system for everybody,except in Britain. It started in1947 in U.S.A. when people hadhand held ex-U.S.A.F. walkie-talk-ies. They were made during thewar for intelligence agents whocarried them and conveyed infor-mation through a special aircraftsystem called The Joan -EleanorProject. It consisted of a verysmall transceiver (transistorswere not invented then, so it wasvalves all the way) on the groundand in the aircraft. The messagewas transmitted and recorded,then flown back and decoded,and proved to be a successfultechnique. 260MHz was occas-ionally used, thus allowing smallaerials to be used on the groundbased transceiver.

After the war people carriedthese sets everywhere - thencame the guy with the car! Thiswas no problem for he simplyfitted a transceiver onto the dash-board. This was the first mobileCB system. After 10 years therewere hundreds of thousands oflicenced users in the U.S.A.

In 1958 the American F.C.C.brought in the Class D CitizensSystem. This was on 27MHz andthat is where CB as we know itstarted. It is at present illegal inthe U.K. to import, manufactureor use 27MHz for speech modu-lated transmission. In otherwords, to make it easy, if you ownand use a CB transceiver you areliable to get a £400 fine and/orthree months in prison.

At this point, I must say thatneither the K.E.B.A. Club (Kentand Essex Breakers' Association)

nor Electronics & Music Makercondone the illegal use of 27MHztransmitters at all. We hope in thenear future to be able to say "seeyou on channel!" but at themoment nobody knows if andwhen this will become possible inthis country.

Next month we will bring somenews and views of other clubsaround Britain and give you moreinformation on the K.E.B.A.'s acti-vities. Let people in your areaknow about CB (not with T.V.I.)by sending your club's nameand phone number where youcan be contacted, and we will doour best to help you to help CB.

Till next month stay clean andgreen.

10-10The ElfK.E.B.A.

EVENTSFeb 17th -19th 'SOUND' 81 INTERNATIONAL EXHIBITION. Cunard Hotel, London

(See Music Maker Equipment Scene page)

Mar 2nd -5th AUTOQUIP EXHIBITION, Wembley Conference Centre, LondonCar equipment and accessories including in -car -entertainment.

Mar 8th -15th INTERNATIONAL AUDIO EXHIBITION CIT, Porta-Maillott, Paris

Mar 11th, 13th

Mar 12th -16th

Mar 17th -19th

Mar 24th -26th

Mar 31st

Mar 31st -Apr 2nd

Apr 1st -2nd

Apr 7th -9th

MICROSYSTEMS '81 EXHIBITION, Wembley Conference Centre,Exhibition covers all aspects of microprocessor systems,i.e., Hardware, Software & Peripherals.

'HOME VIDEO SHOW', Cunard International Hotel, London

London

COMPUTERMARKET, Albany Hotel, Glasgow.Aimed at senior management, executives and directors of organisationsusing or considering the use of computers.

COMPUTERMARKET, New Centry Hotel, Manchester

ELECTRONIC TEST & MEASURING INSTITUTE EXHIBITION,Wythenshaw Forum, Manchester

COMPUTERMARKET, Albany Hotel, Birmingham

NATIONAL ELECTRONIC CIRCUITS & MICRO ELECTRONICS EXHIBITION,Dallas, U.S.A.

COMPUTERMARKET, West Centre Hotel, London

We shall be pleased to publish news of forthcoming electronic and electro-music exhibitions, clubs- also special electronic music concerts.

E&MM MARCH 1981 93

S-2020TA STEREOTUNER/AMPLIFIERKIT 0

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FM Varicap Stereo Tuner with pilot .- 0 4,cancel decoder combinedwith a 24W r.m.s. per channel StereoAmplifier, using Bifet op. amps.Brief Spec. Amplifier Low field Toroidal transformer, Mag. input. Tape In /Out facility (for noise reduction unit, etc.) THD less than 0-1% at 20W into 8 ohms. High Slew Rate. Low noise op. ampsused throughout. Power on/off FET transient protection. All sockets, fuses, etc., are PC mounted for ease of assembly. Tuner section uses UM 1181 FET module requiring no RF alignment, ceramicIF INTERSTATION MUTE, and phase -locked IC pilot cancel, stereo decoder, LED tuning and stereo indicators. Tuning range 88-108MHz 30d8 mono S /N (Fc 0.70V. THD 0 3%

PRICE: £69.95 -,- VAT

NELSON-JONESMk. 2 STEREO FMTUNER KITA very high performance tuner with dualgate MOSFET RF and Mixer ready builtfront end, triple gang varicap tuning, ADA)linear phase I.F. and 3 state MPX de-coder. ,.....;

PRICE: £74.95 -,',AT ''

NRDC-AMBISONICUHJ

SURROUND SOUNDDECODER

a, t4R6C-ANISISONIC&Armand &rood Decode.. ,....,: . .

The first ever kit specially produced by Integre', for this British NRDC backed surround sound system which is the result of 7 years- research by the Arnblsonic team W W July. Aug.. '77The unit is designed to decode not only UHJ but virtually all other 'quadrophonic" systems (Not CD4), including the new BBC HJ. 10 input selections.The decoder is linear throughout and does not rely on listener fatiguing logic enhancement techniques. Both 2 or 2 input signals and 4 or 6 output ...i, are provided in this most versatile unitComplete with mains power supply, wooden cabinet, panel, knobs, etc.

Complete kit. including licence fee £57.70 -i- VAT or ready built and tested £76.95 + VAT

55050A STEREO AMP Very highperformance kit50 watts rms-channel 0 015% THD. S / N 90 dB. Mags/n 80 dB. Output devicerating 360w per channel. x

Tone cancel switch 2 tape monitor switches Metal case- comprehensiveheatsinks . ._ - -

Complete kit only £69.95 + VAT(Also available our 20w/ch BIFET S2020 Amp)

INTRUDER 1 Mk. 2 RADAR ALARMWith Home Office Type approval

The original ""Wireless World- published Intruder 1 has been re -designed by Integrex to incorporate several new features, along with improvedperformance. The kit is even easier to build. The internal audible alarm turns off after approximately 40 seconds and the unit re -arms. 240V ac mainsor 1 2V battery operated. Disguised as a hard -backed book. Detection range up to 45 feet. Internal mains rated voltage free contacts for external bellsetc.

Complete kit £52.50 plus VAT, or ready built and tested £68.50 plus VAT.

Wireless World Dolby noise reducerTrademark of Dolby Laboratories Inc. Typical performance

Noise reduction better than 9dB weightedClipping level 16.5dES above Dolby level (measured at 1"/, thud

rx.xxxxharmonic content)

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at

Harmonic distortion 0 1% at Dolby level typically 0 05% overmost of band. rising to a maximum of 0 12%Signal.to.noise ratio 75dB (20Hz to 20kHz. signal at Dolby level)

Monitor output

Dynamic range --,-90dB

Complete Kit PRICE: £49.95 -.- VAT (3 head model available) 30rnV sensitivity

Also available ready built and tested I Price £67.60 -- VAT

Calibration tapes are available for open -reel use and for cassette (specify which) . . Price E2.75 -.- VATSingle channel plug-in Dolby (3) PROCESSOR BOARDS (92 x 87mm( with gold plated contacts and all components Price £10.50 -t- VAT

We guarantee full after -sales technical and servicing facilities on all our kits, have you checked that BAKL AVICAnD__

these services are available from other suppliers? ,t !wt., VISA

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LIMITEDPlease send SAE for complete lists and specificationsPortwood Industrial Estate, Church Gresley,Burton -on -Trent, Staffs DE11 9PTBurton -on -Trent (0283) 215432 Telex 377106

94 MARCH 1981 E&MM

NEWS

NEXT MONTH - April Issueon sale at your newsagent from March 12th

THE SYNTOMA build -it -yourself drum synthesiser for less than you'd think possible!

DIRECT INJECT BOXIdeal for Musicians to record directly from the speaker terminals of theirinstrument amplifiers.

WORKSHOP POWER SUPPLY UNITSuperb, rugged design featuring 0-25 Volts at 0-21/2 Amps, metered voltage/current, and indicators for current limit and thermal shutdown.

CAR IGNITION TIMING STROBEAn ideal accessory for the car workshop.

POWER CONTROLLERA versatile unit with applications in the home or workshop.

MATINEE ORGANSPECTRUM SYNTHESISERContinuing these exciting electro-music projects.

STARTING POINTPart 2 of this informative practical series shows the beginner how tobuild an invaluable high impedance voltmeter.

ULTRAVOXA special look at the electronics and music of Ultravox's drummer, Warren Cann,with one of next month's offers including the group's latest LP 'Vienna'.

Plus all our regular articles covering Electronics, Computing and Electro-Music.

FIRST ISSUESPECIAL OFFERS

Each month, Electronics & Music Maker will be giving specialoffers to its readers that represent a substantial saving on normalretail prices. Items will be selected that are useful in ourspecialist area - electro-music.

The LP record BBC Radiophonic Workshop 21 (REC 354) isa real collectors item that introduces the sounds of the BBCRadiophonic Workshop.

T

Price £2.85Normally £3.99!

The record selects someinteresting music andeffects used on radio andtelevision productions,from the Workshop's firstelectronic music creationsto experiments usingsynthesisers and multi-track recording at thepresent time.

Here are two essential toolsfor the Electro-Musicians Workshop!!

1 pr. Insulated Long -Nose Pliers (length130mm). Perfect forbending and formingfine wire.

1 pr. Insulated Side -Cutters (length 130mm).Ideal for close cutting ofcomponent wires.

Price for both £2.95Worth over £8.00!Complete this Order Form for either or both of our first Special Offers.

Send this coupon and cheque/P.O. to:ELECTRONICS & MUSIC MAKER (Sales Department),282 London Road, Westcliff-on-Sea, Essex SSO 7JG.

Please send me:

Quantity Item Item Price£

Total£

1 pr. Insulated Side -Cutters1 pr. Insulated Long -Nose Pliers 2.95

BBC Radiophonic WorkshopLP record 2.85

TOTAL

I enclose a cheque/P.O. payable to: Electronics & Music Maker for £

PLEASE PRINT

Name: Mr/Mrs/Miss

£

Address

All prices shown include VAT, postage and packing.E&MM 3/81

JE&MM MARCH 1981 95

NEWS

QUO ZOG?

by STICHOS

The pattering primordial rainMade Zog the Caveman think againThat Life was brutish, short and dull,

So, with defiant rebel shout,Two bones he seized and then beat outBold rhythms on an unfleshed skull.

Now Zog the Minstrel tunes his stringsAnd with his harp a Saga singsIn vaulted, firelit Viking Hall

Telling of Heroes' feats of armsOpposing Gods with magic CharmsWhilst holding Cowardice in thrall.

Tending his flocks in Greece, Zog knewCloven imprints where willows grewThat marked the passing tread of Pan;

But, with syrinx -aided travel,Sought, by piping, to unravelThe God-given Destiny of Man.

The choleric clang of sword on shieldTo Legionary Zog appealed,And Cohorts thought him worth his salt

Because his need for rhythmic beatWas satisfied by marching feet,With contrapuntal cries of 'Halt'.

The world of Zog the Brit seemed goodSo he - as true-blue chappie wouldTakes God as Partner without qualms,

Takes rosin -tortured gut and playsBland tunes, (near swamped by clatt'ring trays),Beneath the shade of indoor Palms.

Zog - as a slave - laden with gyves -In a strange land - 'mid stranger lives -Blew soft on reed with poignant art

And made the golden surface -glossO'er ride the silver pain of Loss,As Music can - played from the heart.

Compuphonic Zog the EuroScreams defiance in crescendoUnfearful of a Wrath Divine,

While the searing Laser's flicker,And drum -beats made forever quicker,Means the skull that's pounded now - is mine!

Thus we skim the mellifluous pagesOf Mankind's music through the ages;But, as we end the present text -We wonder what will happen next?

r

L

Electronics & Music Maker is the first monthlypublication to produce its own cassettesthat will provide an unique auralcomplement to the magazine.Produced in our ownrecording studio, thecassettes will allow you tohear the sound of instrumentsand electro-musical effects in ourprojects and reviews.Demonstration Cassette No. 1 contains:1. The sounds of the Matinee Organ. 2. Musicalextracts played on the Yamaha SK20 synthesiserreviewed this month. 3. Examples of the basic wave-form and effects discussed in 'Guide to Electronic MusicTechniques'. 4. Music and sound effects played on the Sharp MZ-80K.Cassette Price: £2.45 inc. VAT and p&p.

- -tE&MM Cassettes Dept., Maplin Publications, 282 London Road, Westcliff-on-Sea, Essex SSO 7JG

Please send me copies of Demonstration Cassette No. 1 at £2.45 each. I enclose a

cheque/postal order for £ made payable to Electronics & Music Maker.

PLEASE PRINT

Name

Address

E&MM 3/81

J

ADVERTISERS INDEX

Antiference Ltd.Aura Sounds Ltd.

66 Linton Electronics 4711 Light Soldering

Developments Ltd. 50Bayd is 58Bi-Pak 14,15J. Bull (Electrical) Ltd 21

Ca lscope 28Chromasonic Electronics 88Chromatronics 58Clef Products

(Electronics) Ltd. 58Comp -Shop Ltd. 2,3Crimson Electrik 50

Digisound Ltd. 86Display Electronics 41Doram Electronics Ltd. 84

Fladar Electric

ICS 86lntegrex Ltd. 94

Lamina Keyboards Ltd. 47LB Electronics 55L & B Electronic Modules 80

Macmillan Press Ltd. 84McKenzie Acoustics Ltd. 80Mitrad 34,35The Modern Book Co. 55

Newnes Technical Books .66

Powertran Electronics 4,29,56

Riscomp Ltd. 55Rose Morris & Co. Ltd. 92

Sharp Electronics(UK) Ltd. 92

47 Tangerine ComputerSystems 52,53

Tempus 25TK Electronics 43

Videotone 45

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The symbol above will rep-resent Electronics & MusicMaker and portrays our aim

to bring together electronics andmusic - through its bold 'E' on anoscilloscope grid and its double'M' sound waveform that beginswith a suggestion of traditionalnotation.

It is your assurance that pro-jects and circuit boards have beencarefully prepared, tested andapproved and is your guaranteethat our magazine provides infor-mative and accurate editorial forthe electronics and music maker.

96 MARCH 1981 E&MM

A sad fact, proved to be true nightafter night, is that without properamplification, good guitarists withexpensive instruments will soundbad. The worse the sound, theworse the playing and everyone suffers. It's a waste ofgood money and talent.

Since Yamaha makeexcellent musical instru-ments they naturallyneeded amplifiers ofcompatible quality to do

Kemblel Yamaha, Mount Avenue, Bletchley, Milton KeynesTelephone 0908 71771

them justice, and since only the bestis good enough for Yamaha, theybuilt their own.

Like the rest of their instruments,Yamaha amplification is a satisfyingblend of sophistication and reliability;characteristics not shared by a lot of

their rivals.But then Yamaha

is a breed of its own.

YAMAHACraftsmen to the world'smusicians since 1887.

Make it for a Song!MI

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The NewNew Maplin MatineeAmazing Value

For Only £299 95 + £99.50 for cabinet if required.

Easy to build. Latest technology - means lesscost, less components and 80% lesswiring. Comparable with organs selling for upto £1,000.00. Two 49 -note manuals. 13 -notepedalboard. All organ voices ondrawbars. Preset voices: Banjo, Accordion,Harpsichord, Piano, Percussion. Piano sustainSustain on both manuals, and pedalboard.Electronic rotor, fast and slow. Vibratoand Delayed vibrato. Reverb.Manual and Auto-Wah. Glide(Hawaiian Guitar . Sound). Singlefinger chording plus memory. 30Rhythms! 8 -instrument voicing.Major, . Minor and Seventh chords.Unique walking bass lines with each rhythm.Unique countermelody line with each rhythm.Truly amazing value for money.Full construction details start in this issueof Electronics & Music Maker.

The complete buyers' guide to electroniccomponents. With over 300 pages, it's acomprehensive guide to electroniccomponents with thousands ofphotographs and illustrations and pageafter page of invaluable data. Get a copynow - it's the one catalogue you can'tafford to be without.

so in in NB In la In In OM SIMI NOM MI niPost this coupon now for your copy of our 1981catalogue price £1.Please send me a copy of your 320 page catalogue. I Ienclose (Plus 25p p&p). If I am not completelysatisfied I may return the catalogue to you and have mymoney refunded. If you live outside the UK send £1.68 Ior 12 International Reply Coupons.I enclose £1.25.

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rryorpionMaplin Electronic Supplies Ltd. -

All mail to: P.O. Box 3, Rayleigh, Essex SS6 8LRTelephone: Southend (0702) 554155. Sales (0702) 552911.Shops:159-161 King Street, Hammersmith, London W6. Telephone: (01) 7480926.284 London Road, Westcliff -on-Sea, Essex, Telephone: Southend (0702) 554000.Both shops closed Mondays.

Catalogue now on sale in all branches of WIISMITH wy Price £1.00