"Our OLD SCHOOL tremolo pedal recalls the luxurious tremolo sounds of vintage tube amps. Derived from a rich sounding, but feature-limited tremolo circuit from the 1960s, we added extra range to both speed & depth controls. But we did not stop there! We added two unique circuits - one to starve the circuit to add grit & chop, and another that can adjust the speed or depth based on your playing dynamics."
You can find Madbean's PDF with schematic here.