the Technology of the Univibe

7/5/2015 < The Technology of the Univibe http://www.geofex.com/article_folders/univibe/univtech.htm 1/12 The Technology of the Univibe Copyright (c) 19982010 R.G. Keen All rights reserved. Updated with mods March 2010 "Univibe" is a registered trademark which was purchased by and is now owned by Dunlop. "MXR" and "Phase 90" are registered trademarks purchased and owned by Dunlop. If you're an electric guitarist, you have to have been living under a rock to not know what a Univibe is. This is one of the fabled "Jimi" pedals, as Hendrix used it on a number of songs. Robin Trower's "Bridge of Sighs" is practically a Univibe anthem. These things have passed into legend and original ones now command prices of $300 to $800. The Univibe, for all the hype, is a phaser or phase shifter. It's one of the earliest of the footpedal phasers, and was implemented in discrete transistors, instead of the opamps that most later phasers like the MXR Phase 90 would use. The phase shifting stages used in the 'vibe have a heritage reaching even further back into electronic history; only with the 'vibe did this approach get mixed in the right proportions, however. It is probably the imperfections of the discrete, nonopamp implementation and the residual distortion of the transistor stages that give it its unique sound. The Univibe doesn't sound just like other phase shifters, and it's got a control marked "chorus", which may account for it's being considered something unique. Basic Blocks Inside the Univibe Preamp The preamp takes the signal from the two inputs, amplifies it a bit, and provides complementary outputs to driver the first phase inverter stage and a buffered "dry" signal to the output mixer. First three phase stages The first three phase stages are identical and do only the sweeping phase shift and preparation of the signal for the next phase shift stage. Last phase stage The last phase stage receives and buffers the phase shifted signal for sending to the "wet" side of the output mixer and vibrato output. Output Mixer The output mixer takes the shifted and nonshifted dry signals and does the mixing to get the moving frequencynotches "chorus" signal and adjusts the level of the phase delayed "wet" signal for output as the "vibrato" signal. LFO and Lamp Driver This provides the slow speed sweep of the effect. Power Supply Provides conditioned power to run things. Preamp Section The preamp section accepts two signals from the two input jacks. These are mixed in the two 22K resistors and 47K resistor to ground, and applied to the input of the preamp. While there is a relatively high input impedance at the preamp input, the 22K/47K resistor chain that the input jacks loads each input signal with a

the Technology of the Univibe

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