It uses a pair of dual opamps (5532 and a TL072) to so some things. Not an ungodly amount of gain is available as I care less for that these days and wanted something that would suit a variety of styles and guitars from your cover of Glycerine to Bad to the bone to Run to the hills. It goes:
input filtering -> switchable soft clipping -> fixed gain stage -> hard clipping -> tone stack -> recovery gain stage -> then either out, or to a boost option which is another op amp stage with a variable gain of 1.2 - 12x if you want a fattener or some fire.
I've kept the bass response pretty tame, if i recall, the filters between opamp stages are generally starting to roll off below 300hz which keeps the sound pretty tight and also fast to react so it's a lot of fun.
There's a hard clipping stage of 2x red LEDs to gnd before the tone stack, in parallel with a 4n7 cap. This isn't to make gain per se, but is to limit the volume as without these diodes it's just ear splittingly loud and unity is somewhere around 11 o'clock. The LEDs keep it loud but stop things getting too crazy for the circuitry downstream and the 4n7 cap rolls off some of the blatty sizzle you can get with shunted diodes. The LEDs with a vf of around 1.8-2v compress just a little when the gain is high but when the gain is low they're not doing much.
Overall, I'm 100% stoked with this design. It's hard to do anything original with drive pedals but this thing just sounds great and took a lot of tinkering, simulation and general BS, it has a bunch of options to add a lot of usability and there's nothing in there that's redundant.
There's a on/off/on switch in the first feedback loop for a selection of 2 x asymmetrical soft clipping options, or no clipping at all for the full experience, including my favourite combo of a red LED and 1n34 in parallel
pics:
![Image](https://i.imgur.com/pbVZoNk.jpg)
![Image](https://i.imgur.com/MQDKBvk.jpg)
![Image](https://i.imgur.com/zMD3Cjq.jpg)
I wish I could paint better.