This is a classic opamp distortion with some extras. First there is a JFET gain stage, that is like putting a boost pedal in front of an overdrive pedal. Then it is the opamp gain stage that has LEDs in the feedback loop to get a nice overdrive tone. After that there is a combination of silikon and germanium diodes to do some more clipping. Last there is an extra, low gain, JFET stage to make sure that it can be as loud as you like.
Three controls, distortion (opamp gain), tone (treble cut), and volume. The one in the pictures above also have two extra switches, one to give some extra boost to the first JFET gain stage, and the other to let some more lower frequencies in to the gain circuit.
The opamp can be any single JFET opamp, for example TL071, or as above, a vintage LM307. It can run on 9-18V DC.
Above is an early prototype.