The Folk Driver is a low-medium gain overdrive developed by SoulSonic FX after being challenged by Björn Juhl (of BJFE) to create a DIY project inspired by sound of the BJFE Honey Bee. Here’s what Martin (soulsonic) had to say about it after designing the circuit back in ’09:
My goal was to keep the design as simple as possible, but still try to fit in some tricks. This uses both positive and negative feedback to get its sound. R8 [100k resistor between emitters] is something I learned from the big old red RCA book – it’s positive feedback to boost the gain of the first stage; it was suggested as an alternative to using cathode bypass capacitor in a tube stage, well, it works just as well with a transistor. The combination of R9+C4 [100k and 470p in series from Q1 emitter to Q2 collector] is negative feedback to reduce the high frequency gain and give the signature smooth sound. It also promotes stability in the circuit. I settled on the clipping diode combination after trying several different kinds, and the 1N4001+1N4148 combo had the best sound for this thing and reminded me most of the HB.
Should fit in a 1590a just fine. Here’s a demo:
