“The vintage 70s Schaller fuzz. Really nice, full fuzz sound, but
cleans up with the volume knob, just like a fuzz-face. The Schaller sounds good even on
higher-note leads; the fuzz doesn’t crap out past the 12th fret like a
Maestro Fuzz Tone or Sam Ash Fuzzz Boxx. Very cool pedal, not too many
around and uses BC109 transistors.”
Technical discussion on this effect can be found here.