HD are based in Seattle, one of theworld’s guitar capitals, and AndyMarshall (THD’s CEO and

designer) is one of the top names inguitar amplification, with designcredits for many other companies, aswell as his own. Dubbed by no less aperson than Aspen Pittman (of GrooveTubes fame) as, “the boutique ampbuilder’s boutique amp builder”, Andy’samps have been coveted in the Statesfor a long time – the Type O having a massive reputation. But most of hisrecent work has been dedicated to thisnew head which debuted at this year’sNAMM to great acclaim.

Like most overnight success stories,the UniValve didn’t happen overnightat all. As Andy explains: “I always likedthe concept of a single-ended guitaramplifier, so in 1994 I built a prototypeof the UniValve with somewhat limitedfeatures, but the same basic design. Webuilt five prototypes and had them inconstant road and studio use in New

York, LA, Nashville and Seattle. We hadno problems at all; either major orminor, and power tubes lasted muchlonger than we thought they would.This is the first time I’ve designed a product to be 100 per cent what Iwanted in terms of look, sound andfunction, and the fact that it’s being sowell received is quite flattering.”

We’ve said it before, but no-one beatsthe Americans when it comes to stylingan amp, and the UniValve’s looks areexemplary. The intricate chemically-etched patterns on the front panel areAndy’s tribute to architect Frank LloydWright and Mackintosh, one of the all-time great valve hi-fi amps, and thescreen printing all over the chassis is ascrisp as can be. Metalwork execution isabsolutely immaculate too. Computer-aided tools, that hold tolerances of onethousandth of an inch, are used topress and fold the chassis and lid. As aresult the fit is perfect. There’s similarattention to detail inside the chassis,where the thickest circuit boards we’veever seen are bolted down on metalstand-offs inside separate hi-fi stylescreened compartments. Panelcomponents and valve bases are linkedto these boards with flying leads in aperfect mix of PCB and point-to-pointconstruction that has all the strengthsand none of the weaknesses of thesestyles. Components are absolutely top-notch too, with metal film resistors,precision polystyrene capacitors andNichicon filter caps the highlights.

The front panel looks deceptivelysimple with a pair of inputs labelledRock and Roll, followed by knobs forvolume, bass, treble and somethingAndy calls Attitude. On the other sideof the orange pilot light a chicken headknob controls the UniValve’s Hotplatecircuit – a built-in power attenuatorwhich lowers the volume after theoutput transformer. There’s also aswitch to take the Hotplate out of thecircuit, followed by rockers for hi/lovoltage, mains and standby. On theback there’s a single speaker outletwith switchable impedance, a variableoutput which can be switched frominstrument to line level, as well asproper mains and line fuse protection.

There are two preamp valves andjust one power valve. One of theUniValve’s primary features is you canfit any commonly available power valvewithout rebiasing. You can also swapvarious preamp valve types with aminimum of hassle, which opens up allkinds of possibilities for tailoring gain,volume and tone to your own taste.

SOUNDS: The UniValve’s single-ended design is pure Class A, unlikethe quasi-Class A of push-pull designslike the Vox AC30 which step outsidethis mode as the power stage isoverdriven.

At low volume levels, and using theRoll input, the clean sounds are sweetand bell-like, with a chiming qualitythat may have you checking for a non-

THD UNIVALVE HEADPRICE: £899ORIGIN: USATYPE: All valve single-ended amp head OUTPUT: Nominal 15watts RMSVALVES: Choice of singleEL34, 6L6, 5881, KT88,6550, 5881, 6V6 andEL84 (with adaptor)power valves; two ECC81,2 or 3 in preamp DIMENSIONS: 190 (h) x390 (w) x 230 mm (d)WEIGHT (kg/lb): 8/18CABINET: Powder coatedsteelCHANNELS: OneCONTROLS: Volume,bass, treble, attitude,Hotplate level, Hotplatein/out, hi/lo voltage, noisereduction in/out, line outlevel and instrument/lineswitchADDITIONALFEATURES: Multiplevalve choice with norebiasing, Hotplate powerattenuator, noisereduction circuit,transformer-isolated vari-level line outOPTIONS: NoneRANGE OPTIONS: Noneyet, but a range of headand combo cabinets moresuited to live use isplanned for early 2002.THD’s other hot productsinclude the YellowjacketEL84 adaptors for most50/100-watt circuits, andvarious standaloneHotplate attenuators foralmost all impedancetypes

www.thdelectronics.com

Reprinted with permission from Magazine, December 2001, Pages 60 and 61

THD UNIVALVE HEAD TEST RESULTSBuild qualityPlayabilitySoundValue for money

WE LIKED It’s one of the world’s bestsounding, best looking and best made amps.More versatile than manyWE DISLIKED The current case format isn’tbest suited to live gigging, otherwise nothingat all. This is THD’s masterpiece

T

�����

GOLDTHD UniValve head £899Just how much tone can you cram into an amp? The UniValve probably sets the record. It was oneof the hottest new products at this year’s NAMM and, finally, it’s here by Nick Guppy

GIT218.thd 8/11/01 5:44 pm Page 60

existent chorus pedal. Plug into thehigher sensitivity Rock jack, and thegain increases for some seriously goodlead tones. As the volume goes up, sodoes the distortion. This is acombination of pre and power stagecut-off, and the characteristic isheavily dependent on which powervalve is in use. For example, the buzz-saw grind of an EL34 can besubstituted for the focussed mid-rangepunch of a 6L6, the butter-sweet wailof a 6V6, or with a special Yellowjacketadaptor you can even switch to anEL84. The valve defines power outputtoo: a KT88/6550 gave almost 17Wwhile an EL84 delivers just 4W.

You also have infinite control overthe level using the Hotplate attenuator,so you can drive the amp intomeltdown at whisper-quiet levels. Asthe UniValve has its own built-indummy load you can even unplug thespeaker for total silence (don’t try thison any other amp!). This is perfect fordirect-recording or hooking the

UniValve up to another amp. Thealmost noiseless transformer-isolatedline-out is the best we’ve ever heard,and it works equally well in slave ordesk mode, delivering a dynamic soundthat closely matches speaker output.

The orange light in the middle is atypical ‘boutique’ feature. It’s part of a clever noise-reduction circuit thatkeeps hiss and hum at bay and glowsbrighter the harder you play. This isdead handy for recording, and if youfind the pulsating light off-puttingthere’s a useful off switch underneath.

With only a little practice, there’s anamazing range of tone available. TheAttitude control sweetens or hardens a note’s attack, while the simple tonecontrols always seem to have just theright sweep, no matter how the amp isset up. The hi/lo voltage switch also hasan effect on the tone, though its mainfunction is to stop smaller valves likethe EL84 and 6V6 from burning out.

The UniValve’s features are obviouslyideal for studio use, but can an amp

this small work live? Well, think aboutthis: how far do you turn up the masteron your 50 or 100-watt head? If theanswer is less than eight or nine, youshould hear just how loud a UniValve isat full tilt, even with just four wattsfrom an EL84. Using a modern 4 x 12”fitted with high sensitivity drivers, thisamp can easily cope with an un-mic’dgig, although clean headroom issomewhat at a premium, and thebigger output valves are more suitableif you want the amp to do anythingmore than full-bore distortion.

VerdictWe’re convinced that the UniValve isnothing less than a masterpiece. Withits ability to use a number of differentvalves without rebiasing, not tomention the recording-friendlyHotplate feature, the versatility andrange of tones is surprising. Almosteverything we plugged into after usingit sounded flat and one-dimensional bycomparison. One of these amps and ahandful of valves can deliver so muchtone, you might think twice about thatspace-age digital modeller after all.

Nothing good is ever cheap. If youmention the phrase American hand-built boutique amp most people startto think of implausibly high prices, soto find out this superlative tonemachine costs under £900 is almost toogood to be true. Under our new ratingssystem a five star verdict demandssomething very, very special indeed –and the UniValve delivers it all, andthen some. One of the best amps ever?You’d better believe it.

The rivalsOrange AD30R £829Cornford Hurricane

£1,199Torres single-endedamp kit £TBCCornford’s new Hurricaneis one of the UniValve’sfew real competitors,with an equally brilliantsound, but less flexibility.Orange’s AD30R is one ofthe few mass-producedamps that approachesthis kind of tone,although it can’t competefor build quality andversatility. Torres’ single-ended design is still indevelopment, but may bethe only other big single-ended design you canbuy in the UK

THD UniValve headRATING

All the tone in this five-staramplifier emanates from a

single valve. Clever eh?

GIT218.thd 8/11/01 5:44 pm Page 61