Univox Super Fuzz

Univox Super Fuzz

Super Fuzz is a circuit that has many variations. It’s one of the popular building blocks that has been used for decades. It’s built around a full wave rectifier that produces an octave fuzz sound.

similar circuits that use the full wave rectifier:

Who played the super fuzz:

The Circuit

The circuit is built around standard parts. One of the great things about this circuit is that nothing is hard to get and many of the parts can be swapped with other common parts easily.

This circuit uses 6 NPN transistors. I used 2N3904 types. I’ve read lower gain types sound a little better. I suspect there’s a lot of opinion involved. Matching Q3 and 4 might help bring out the octave sound. I think that matching is not required for good fuzz tones. Having unmatched transistors might also remove some of the intermodulation (ring mod sounds) that the octave circuit produces, which might be a bonus for some.


This build has a couple mods suggested by derringer over at Freestompboxes.org.

The first mod adds a balancing trimmer POT2 in my schematic. This evens the gain between each half of the rectifier made up of Q4 and Q5. You can also use this to detune the octave which can bring up a better fuzz tone especially with chords. Or balance the two sides of the rectifier to bring out more octave. Use your ears!

A second mod is a trimmer on the ground side of the clipping diodes D1 and D2. This brings the volume up and allows you to “tune” the clipping section. Again use your ears. Lowering the resistance here starts the clipping earlier and adds compression. Turning the resistance up starts clipping later or can remove the diode clipping.

The original had a tone switch, which gave two options, here this has been converted to a pot that allows you to dial in the amount of mid scoop.

Here’s my build

I designed the PCBs with Eagle and had them manufactured through PCBWay.com. The boards came out really nice!

Sadly I made a mistake on this PCB. Luckily it was easy to fix by mounting C6 on the back of the board and using one leg as a jumper to the emitter of Q2. I’ll need to do an update of this before publishing.

The Enclosure

Keeping in the theme of making errors I had a hard engraving this enclosure. The finished work looks pretty rough. I used the 1/8″ flat end mill. It took me a couple tried to get the depth and speed right so there was a couple gouges. I had to stop the machine once and the mill dragged the bit across top of the box. Looks good enough for rock and roll.

The flat end mill was a lot faster than the engraving bit but the end results were not as smooth.


Definitely worth the build. I like these mods. I would recommend anyone into fuzz tones try this out. If you’re into overdrive and “amp tone” this might not be for you.

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