Durham Sex Drive

The Durham Sex Drive is a pretty versatile Tube Screamer variation. It can go from clean boost to medium overdrive. The traditional input and output buffers have been removed and there's a toggle switch (SPDT on/off/on) to select between different clipping options–hard, off, and soft.  Pots are board mounted and it'll fit snuggly in a 1590B.

Durham Crazy Horse

For Fuzz Friday here's an really interesting circuit from Durham that's both an overdrive and a fuzz. As the name implies helps you get some Neil Young tones, but does a lot more than that. The input stage features soft clipping in the feedback loop of an opamp,  much like a Tube Screamer. The 2nd half of the opamp acts like a buffer, pushing a Fuzz Face-style stage. This then pushes another Fuzz Face-style stage that feeds into a Big Muff tone stack. The addition of the Volts control to starve the opamp of voltage makes this a really versatile pedal. I've laid this out with on board pots that will ideally fit in a 125B with top mounted jacks. Here's the schematic for reference.