Pigtronix Fat Drive

Original info:
"Pigtronix FAT Drive takes a futuristic analog approach to create complex crunch tones using CMOS clipping and a variable low pass filter for tone shaping. Bringing the tone control all the way clockwise takes this filter completely out of the circuit for total transparency and robust low end. Rolling the tone control back smooths out the highs, leaving ample mid-range bloom and bottom end punch.

A Hi / Lo toggle switch brings additional versatility to the FAT Drive’s wide-ranging palette of overdrive tones, altering the gain structure for enhanced crunch and soaring leads. The FAT Drive features true bypass switching and runs fine on standard 9-volt power but ships with an 18-volt adapter for superior headroom, clarity and overall output"
Schematic available here.

Durham Sex Drive

Original info:
"I designed the SEX DRIVE pedal to fulfill the very particular needs of good friend Charlie Sexton.
 The goal was to build a “clean-boost” pedal that would supply additional bottom end and sustain when needed. The pedal would have to provide a boost that would not alter the original quality of the amplifiers natural tone. Most important, was to not add a “nasal” tone like the other pedals in his effects graveyard.
The result was the SEX DRIVE pedal"
You can find the original FSB thread here.