This is a fuzz pedal I built, based on the Foxx Tone Machine.
Some notes about the original design: The first stage of the Foxx Tone Machine is similar to the Fuzz Face, a two transistor amplifier with a negative feedback from the emitter of the second transistor to the base of the first transistor. In a negative feedback circuit the gain is reduced. But unlike the Fuzz Face, there is a filter providing less negative feedback (=higher gain) on mid-frequencies. The signal is phase-split at the second transistor (one signal from the emitter, one from the collector) and rectified by two germanium diodes. This provides the octave-up effect. A switch can disable half of the phase-splitter to cancel out the octave effect. Then follows a gain control and a one-transistor recovery stage. Next follows a tone control circuit similar to a Big Muff tone control, cutting bass one way, cutting treble one way, and some scooped mids in the middle. Then comes a one-transistor recovery stage followed by the volume control.
My contribution to this design is to add a transistor input buffer to raise the input impedance (which otherwise is low and to make it sound completely different if not fed with a passive guitar signal). It may not sound like the original pedal, but close enough (compared to YouTube clips). It was not my intention to build a replica, only a cool fuzz pedal. I also added an output buffer, maybe not as necessary but always nice to have low output impedance. I used my goto-transistor 2N3904, and also use 100k pots instead of the 50k in the original.
Controls, from left to right, are sustain, tone and output level. The octave switch to the right and standby switch to the left.