The 7120 is derived from the Vox UL 7-series amp circuit. These amps were a hybrid design with a transistor preamp which included a built in fuzz. The 7120 pedal is a simplified version of that preamp, combining the fuzz circuit with a notch filter tone control (originally the amp's Middle control).
I added a gain control, because it is pretty wild and compressed at maximum. At lower gain settings, it produces a nice raunchy distortion which responds to picking dynamics and it cleans up well from the guitar. With the Fuzz knob cranked, it gets hairier and more compresses, especially with hot pickups.
Individually hand built and hand wired on 0.15" Veroboard