This circuit (Brown Sound in a Box 2) was by far my favourite distortion back in high school. The cool thing was, if you wanted one, you just have to build one or know somebody who could. The circuit was designed by Ed Guidry, similar to works by Jack Orman and Aron Nelson. Back in the day, it was one of the highest recommended builds on the forums. Many would suggest that his design was the original precursor to many of the "high gain amp" pedals that came out in the 2000's. It's basically a Marshall stack tone faker.
It has a tonne of gain, and a huge clean bottom end to fake a big amp. My build also has improved noise spec. This circuit also responds excellently to rolling back the instrument volume knob.
Distortion is achieved by overdriving Fairchild field effect transistors (FETs), being the closest solid-state relative to vacuum tubes. No diodes are involved for clipping. There are three stacked gain stages. The first two are μAmp stages, which is a classic valve topology developed to achieve high gain performance from tubes. The final is a class a stage.