This project is not currently active, since it turns out that most of the clipping is actually from the opamps and not the diodes. Perhaps this repo will come back sometime in the future. If you're looking for similar DSP nonlinear effects, please take a look at SOUL-VA.
Ultimate-Overdrive is a solid-state guitar pedal with touch-sensitive Plexi-like tones. Two parameters (drive and volume) control the single gain stage; high-quality opamp drives carefully placed diodes, resistors, and capacitors to produce a dynamic overdrive.
Ultimate-Overdrive.asc - LTSpice schematic
APPENDIX.md - Extra discussions and effect comparisons. Read this if you like to know more about this project's motivation.
SOUL-VA implements a similar effect with clipping, bias shifting, and compression (work in progress).