JFET gain stages stand in for the valves of a Marshall preamp, and the tone stack follows them as on the amps. Treble, Middle and Bass reproduce the original tone circuits part for part, so the knobs interact strongly.

An internal slide switch selects Super Lead or Super Bass voicing. Super Lead cuts low end early and adds gain, which suits humbuckers. Super Bass passes full bass with less gain and pairs well with fuzz pedals in front.

Pre-Amp sets gain and Master sets output. Rolling back the guitar volume cleans the sound up. An internal presence trimpot, reached by removing the base plate, adjusts final brightness and is factory set to halfway.