Univox Uni Fuzz

The Univox/Unichord Uni Fuzz is a Superfuzz variant. Today we might call this the "desktop" version... maybe back then it was either the "amp top" or "studio" version. Note there is no footswitch, but instead a third 1/4" jack to plug in a remote footswitch like you might have for turning the tremolo on and off on your amp. (The stompswitch in the above photo is a mod.) No battery option here. The Uni Fuzz plugs directly into the wall.

The power supply gives the circuit a slightly higher +12V than the regular Superfuzz's +9V. This really has little effect on the end result. One modification option is to ditch the internal power supply and install a dc power jack for +9V from a pedal board supply. Considering I've done this at least twice, and seen another with this mod, it seems to be popular. Replacing the 1/4" cancel jack with a stomp is another obvious mod.

How does the Uni Fuzz achieve remote bypass operation? There is a rather large relay inside. The switch just activates or deactivates the relay coil.

Inside there are at least two different circuit board arrangements, but no major differences I've seen between circuits.

Uni Fuzzes and Superfuzzes have a very distinctive sound that you can't mistake once you're familiar with them. With the EXPANDER (gain) turned up, you should be able to play a quick, loud sound (hit strings hard then mute) and hear a slight gate effect on the noise of the circuit. Almost like a little gasp of air.

To troubleshoot a Superfuzz, start by printing out the schematic and writing down the voltages of each terminal of every transistor. Since there are 6 transistors, and about just as many "stages" (active and passive) the signal passes through, this is about as complex as a fuzztone gets.

The first 2 transistors form a x10 preamp. Using whatever test equipment you have, you should verify that you are getting the full x10 voltage gain before leaving this stage. For instance, a 0.1V input signal should emerge at least 1V strong. Troubleshoot the preamp until that's solved.

Next is a splitter. You get an inverted signal at the collector, and a non-inverted signal at the emitter. These signals should both be roughly equal.

Next we hit a "push push" amplifier/full wave rectifier. Notice that one base has our inverted signal and the other base has our non-inverted signal. Next thing to notice is that the emitters are tied together. The net effect is that is that we will only get our positive going half waves as signal at the collector (inverted). The tied emitters will ensure that the negative going base will be cutoff while the other base is positive going. Each signal gets "pushed" while we ignore the "pulls."

The trim pot shown on the official superfuzz schematic is often omitted on actual superfuzz circuit boards. If you do have one, it really shouldn't have much of an effect on a properly working superfuzz. If you have a low gain preamp (check that preamp stage) or are simply using a low level input signal, then the trim pot can adjust the quality of the octave up effect. However, if you boost the gain further you quickly leave the "nice" octave up region and enter the "Superfuzz" gnarly octave up region. At this point, the trim becomes much less effective, and its probably why they didn't even bother installing it after awhile.

Next we diode clip. This should just squash your signal from full power supply clip (0 to +12 in the Uni Fuzz's case) down to +/- the diode's forward voltage drop. Expect 0.1-0.3V for germanium devices and 0.6V for silicon. Superfuzz builders seem to like to toggle between the two. I personally like the even more crazy mod of lifting the clipping diodes all together for an amp killing over the top booster option.

Next the path branches. There's the ultra cool notch filter path or the 5:1 attenuator path. A switch selects which path your signal will take.

Since we just crushed our signal twice (diode clipper followed by filter or attenuator) there is a makeup gain amplifier, with gain roughly x10 again.

Uni Fuzz/Superfuzz repairs do have some common issues. There is usually at least one bad 10µF coupling cap. If you get a funny voltage or strange signal behavior, check for drifted resistor values. Noisy and broken transistors are common too.

If the fuzz sounds like a farty fuzz, like a poorly biased Fuzz Face, or just weak, then it is not right. If you don't get that "gulp" of air I described earlier, then it is not right. If you're getting a very pronounced, very "octavia" like octave up, then it is not right. (You definitely should get an octave up effect, but it should be a very, very dirty octave fuzz - not a clean octave at all... this indicates low gain somewhere before the clip stage.) I've heard a Superfuzz make all of these sounds. On one really messed up one, it actually when through a whole series of tones as I fixed it until it came back to regular Superfuzz sound.