Here’s Wampler’s Plexi-Drive, another Marshall-in-a-box pedal. The original unit uses a 470µ capacitor for power filtering, which seems like overkill to me. I’ve replaced that with a 100µ cap that should do the job just fine.
Some build reports on FSB say that the 15k resistors from 9V to the drains of the J201s might need to be tweaked to bias the JFETs correctly (4.5v), so either socket those positions or use trimpots. Also, if the tone control is too dark sounding for your taste, replace that A25k pot with an A500k to brighten things up.
