MOScato Fuzz

Well, I'm not sure if it's a fuzz or some kind of distortion. To my ears it sounds very much like the distortion used by The Beatles on their later days. It has good attack and "crunch", but also good compression and sustain (pretty tubey, what can I say?).
It uses the CMOS IC CD4007 (a Toshiba TC4007UBP is in my prototype), wired as three inverters, and also has a clipping section which uses two 2N7000 mosfet transistors. Too much MOS in there, so I labeled the effect MOScato, which is some kind of wine we drink here in Buenos Aires.

It has a resemblance with other circuits using inverters, such as the Red Llama. The MOScato has a different gain control (kinda subtle) and adds the mosfet diode clipping, besides using the 4007. I suppose it can be built with three CD4049 stages as well. Try it if you have that IC at hand.

About the mosfets: they are wired as diodes, with the drain and gate tied together. Beware, they are not wired "back to back", as that would defeat the mosfet action (because of the internal diode they have). I used two of the same batch, which happened to be well matched with a threshold around 1.6v. This provides a pretty symetric distortion. You can substitue other kinds of diodes, LEDs, etc, here, as you'll do in a regular opamp-diode-clipping-a-la-tubescreamer stage.

Checking on the scope, the distortion looks very symetric at lower amplitude signals, but seems to change to assymetric when hitting it with a higher amplitude. I'm not sure what could cause this, it needs some further investigation!

This circuit may have a high sensibility to what you connect before and after it (specially before). I would connect the guitar direct to it, and a high impedance effect (or a standard amp input) after it.

Listen for yourself:

Gibson SG to MOScato to Fender Blues Deluxe (bright switch off). Recorded with my brand new FOSTEX FR2-LE portable recorder (with its internal mic!)

Bridge 100% gain (again)

Here's the schematic: Click on the image to enlarge

As always, any suggestions or comments are welcomed. And if you build it, let me know how it goes!
Regards!
Miguel

v1.0 03/10/2008

Miguel Canel, Buenos Aires, Argentina bioroids.miguelNOSPAM@yahoo.com.ar (Quitar NOSPAM) http://www.bioroids.com.ar