NPN Fuzz with Sziklai Transistor compound

Inspired by Pete Moore's Darlington Pig

26/10/05 news: Fellow stomboxer MartyB has made a PCB layout for this circuit: Check it out!

Here is an adaptation of the classic Fuzz Face circuit.

The Sziklai connection (also called complementary Darlington) uses two complementary transistors to form a higer gain device (typically the product of the individual gains). This is a good way to put to use those PNP germaniums that are too low gain to fit on a fuzz pedal. The NPN counterparts should be low gain too, but can be silicon. The compund behaves as NPN, so this circuit is negative ground

So I replaced both transistors on the standard Fuzz Face with Sziklai compounds made of BC549B and AC128 transistors. The BC549s gain was around 250, and the AC128s close to 120 (but leaky).
Had to change some resistor values and adjust the bias pot until I got good sustain with minimum gating effect.
Click on the image to enlarge

Caution

The germanium transistors can get hot quickly in this configuration. Resistors R1 and R2 control a little the current into them so they don't burn out. They also control somehow the gain of the stage, so this can have an effect in the sound.

I made some samples with it: sound samples
I'm hopping to get some lower gain transistors for a more "traditional" sound. This one turned out to be pretty high gain for my taste.
Added 26/10/05: 2N2369A, 2N3055, MJ2955 had been suggested as low gain silicon NPN transistors.

This can be combined with all the other tricks you can do to Fuzz Faces: piggybacking, replacing germanium for silicon, using MOS transistors, etc.
Experiment, but keep your transistors cool!

More info

The technology of the Fuzz Face by R.G. Keen
Sziklai conection called "compound transistor" at Wikipedia
The Brit-face at Plate to plate

v1.0 21/10/2005

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