Harmonics sets gain at the input. Bias moves the gain stage from a smoother drive, through a pseudo-octave fuzz, to a gated fuzz at the top of the travel. Balance sets the output level. The Drive/Fuzz switch puts the clipping diodes in circuit for the fuzz voice, or lifts them so the pedal behaves more like a transistor drive.

An internal trim, set to noon at the factory, changes overall gain and how strong the lower octave is. Fully clockwise is the closest match to a vintage Percolator. The footswitch is a relay true bypass. A click latches the effect. A hold longer than half a second makes the change momentary, and that hold can be disabled.