Three parallel JFET fuzz circuits driven by a voltage controlled state variable filter with resonance control, mu-amp input stage and quite possibly, a wedgie.
In other words, this is one versatile fuzz box. The wide operating range of the frequency control, switchable resonance and the three drive pots allows this dweeb to go places you never thought possible. From extreme to relatively subtle; from super thin to ridiculously fat.
The Four Eyes Fuzz wasn't designed to sound like your favourite vintage fuzz. You might be able to tweak it to sound close, but it truly does its own thing.