Building a Univox Square Wave Clone

[beastmaster]

I realize this is a rather ambitious project, seeing as the main parts have been out of circulation for quite some time. I was wondering if I could get some pointers from anyone who has tried to recreate this pedal. For instance, if you couldn't find the 2SC1212G and 2SK34C transistors, which did you use to replace them? What did you substitute the MD234 diodes with? Also, The schematic I have is pretty fuzzy, so I'm having trouble determining if I'm seeing 4.7uF caps, or 47uF caps; a 3.3uf cap, or a 33uf cap.

I've been doing some googling, and I keep coming across dead links for pcb layouts for this project. If someone has these files laying around, it would be amazing of you to post them.

As of right now, these are the subsitiutions I'm going to do:
Q1: 2SC1321G - 2N5088
Q2: 2SK34C - 2N5458
D1,D2: MD234 - ???

Here's a link to the schematics I'm working from: Univox Square Wave

[Mark Hammer]

I built one, using what I believe was a 2N5457 for the FET, 2N5088 for the bipolar and 1N914 for the diodes. Not a particularly inspiring pedal IMHO. The topography is a little bit like a Fuzz Face, actually, with clipping diodes on the output, followed by a tone/volume control pair.

Despite what it says, there is no gain/drive control to set the fuzz intensity. Given the structure of the circuit, I imagine that a suitable fuzz intensity control could be provided by replacing the 3.9k resistor to ground for the FET with a 4.7k pot, or perhaps a 2k pot and 1.8k fixed resistor in series. The pot would be connected such that one outside lug goes to the FET and the other goes to ground (or a fixed resistor then ground). The 560k resistor linking the FET and bipolar transistor remains connected the same way. The 33uf cap gets connected to the wiper of the pot.

This scheme would maintain a constant resistance to ground from the FET's source, but the cap would tap off different points and the path to ground through the cap would be preceded by selectable amounts of resistance. This would vary the gain of that transistor stage, and the distortion amount. The cap applies that gain across pretty much the entire spectrum. Smaller cap values apply it across the mids and highs but not the bottom. Historically, the cap to ground on the Fuzz Face varied over different issues, and some folks prefer smaller or larger values. Applying the boost to the entire spectrum will provide the fuzziest sound.

Personally, I found there was a surprising amount of clipping even without the diodes, so I installed a diode lift switch on mine that simply breaks/makes the connection between the two diodes and ground. You don't get quite as much clipping without the diodes in circuit, but you get a bit of volume boost, which can push your amp into distortion more easily. Six of one, half dozen of the other. If the diodes are germanium (1N34, 1N60, 1N270), you'll get stronger clipping and what seems like longer sustain, but at a cost of less output volume.

The control misleadingly labelled Distortion is nothing to write home about and simply varies the amount of bass signal that gets through. All treble passes through the .001uf cap unimpeded. Decreasing the resistance setting of the 250k pot makes it easier for mids and lows to make it through to the volume control. It's an interesting way of achieving a kind of mosquito-like buzz, I suppose, but personally I think that you might be better off installing the suggested distortion amount pot and replacing the 250kpot, .001uf cap, and 27k fixed resistor with a 10k-22k fixed resistor. If you're building it because you like the buzz, then straddle that suggested fixed resistor with a .01uf cap. If you prefer a woolier distortion tone, then stick a .001-.01uf cap to ground in parallel with the diodes. If you use germanium rather than silicon (1N914, 1N4148, 1N4001) diodes, then I suggest using a 4.7k-10k resistor just ahead of the volume pot, or maybe even opting for a 100k volume pot (log taper) to conserve signal level.

[beastmaster]

Having a gain control on this pedal would be ideal since there isn't one. I ordered enough parts for two of these, so I'll have one unmodified and one I can tinker with. I ended up going for 1N34s for the diodes, and I found a cleaner schematic somewhere. I downloaded it to my work PC, but for got to bookmark it. I'll upload it later.

Thanks for the input, Mark.

[beastmaster]

Univox Square Wave Schematics

[David Schwab]

I always thought the idea behind this is it was a square wave generator. That would explain why there's so much clipping and lack of a gain control. You can't get much fuzzier than square waves! Some of the old fuzz pedals are just all out fuzz, like the old Maestro unit.

[Mark Hammer]

Don't set your expectations too high. This is one of the pedals from what was a pretty barebones hey-WE-make-pedals-too seies of products from Univox. I owned the compressor from that series in the late 70's and while it was okay, it was nothing special, and neither is this pedal. As near as I can tell, the entire series had two knobs per pedal, one on each side. Not unlike MXR's commitment to two knobs per pedal, or E-H's commitment to one knob and a slide switch for many of their products. The pot they labelled Distortion was a cheap and simple way of radically changing the tone to get a buzzier sound. Keep in mind that this was a contemporary of the MXR Distortion+ which got thinner-sounding the more you cranked the gain, and the Big Muff that gave you wooly OR reedy. Here, the variable lo-cut control let you dial in thinner or fuller tones, without losing the sizzle and without requiring a third knob. Given the structure, it is probably capable of being somewhere in the neighbourhood of a Jordan Bosstone which, while seriously fuzzy, is no square wave.

[David Schwab]

Not unlike MXR's commitment to two knobs per pedal

One, if you count the Phase 90!

Keep in mind that this was a contemporary of the MXR Distortion+ which got thinner-sounding the more you cranked the gain...

Boy, those really do get thin! I never cared for them.

...and the Big Muff that gave you wooly OR reedy.

I modded my Big Muff back in the day, I added a stereo jack for power switching, and then used the power switch to bridge the two ends (I think.. been a long time) of the tone pot, so you would get the full range of the pedal. Lots of highs and lows!

But otherwise that wooly tone is the Big Muff sound, for me anyway. Maybe just back it off a bit. I had a Sovtec Muff, and it never got quite the same tone.