Clearly a Fuzz Face inspired circuit, but with two interesting features that totally change the nature of this pedal, a knob for Bias control that regulates how much voltage is fed into the second transistor, and a big muff tone stack just before the output that allows you to shape the tone according to your taste.
The circuit starts as two gain stages running into each other with an input gain control and a sag on the second stage (bias). Then you have the voltage feedback added, and it became similar to a fuzz face in topology, but it sounds nothing like one!. In this case, the sound is totally dependent on the transistors; the original version works with a couple of 2N1711 NPN silicon, replace them and it’s a whole different beast.
For further analysis on this circuit take a look at this thread on Free Stomp Boxes Forum.