A Very Groovy Steggo - Cloning the Uni-Vibe

The Shin-ei Uni-Vibe is a very early chorus / vibrato pedal first sold in the 1960's. It has been used by many legendary guitarists including Jimi Hendrix, Robin Trower, and David Gilmour. It was marketed as "Vibra-Chorus" the Uni-Vibe uses a series of phasing filters connected to light dependent resistors (LDRs). The LDRs themselves are modulated by a small light bulb whose intensity and rate of pulsation are controllable using the knobs on the effect itself. I'd wanted to do a Uni-Vibe clone for ages, and the PedalPCB board looked very approachable, so I took the plunge!

PedalPCB offers a couple of different varieties of the Univibe. It's essentially the same circuit, but I decided to go with the larger form factor Electrovibe board. The overall layout on this board is absolutely amazing. There are a huge number of resistors, transistors, and electrolytic capacitors, and they're all laid out in very neat rows. All of the transistors are aligned the same way, and all of the electrolytic capacitors are aligned the same way!

Even though this is a classic effect, I'm using all new components (generally from Mouser) for this build. The resistors are all 1% metal film (Yageo and KOA Speer). The few film capacitors are a mix of WIMA and KEMET and are all 5% tolerance. All of the electrolytic capacitors (and there's a small army of them) are Nichicon. There are also several transistors, and all of these are modern 2N5088s. The lamp is the recommended 7371 incandescent lamp. I used 9203 LDRs for the light dependent resistors. There are a couple of very modern components for such a vintage design, but both of the IC's are part of the charge pump so the pedal runs at 12V using a normal 9V power supply.

Because of how I decided to wire the chorus / vibrato toggle switch and how I placed the DC jack, the top center of the enclosure is a little tight. That being said, everything does fit - snugly if not comfortably. I'd placed the input and output jacks a little higher in the enclosure than I do on a normal 125B since I was using a 1590BB2, but any future builds I'll give myself a little more room as my preferred Switchcraft jacks are just a little tight! As always the audio and power jack connections are insulated with heat shrink tubing.

Given the groovy nature of the pedal, I figured that it needed an equally groovy enclosure. I found a really cool looking stegosaurus online, and got the license to use it, but it was just black and white like a coloring book. So I hand colored it in illustrator to create the Groovy Steggo mascot for this pedal. I then put him on a concrete wall along with some suitable graffiti to create the rest of the labels for the controls.

The pedal has to be dialed in a bit with the gain and bias trimmers. I just did it by ear based on several online demos, and the sound is really cool. The chorus is fairly organic and isn't nearly as shimmery as the 70's choruses. It's pretty cool on its own, but the vibrato is where the pedal really shines. The volume generally has to be turned fairly high to achieve unity, but that's a feature of this design, not a bug. The intensity and speed controls give you everything from light modulation to a very pulsing vibrato depending on what you need at the time.