Originally produced in the early 80s, the SD9 was the distortion brother of the classic TS9 Tube Screamer. It ranges from mild overdrive to fuzz territory without losing articulation. The easiest way to describe the SD9 circuit is to say it’s half of a Tube Screamer, with a Big Muff tone stack. Original units only used half of the JRC4558 opamp (the other half was used to buffer the non-distorted stage to output). However, General Guitar Gadgets published a schematic with the 2nd half of the opamp used as a volume recovery stage right after the tone stack. (And the BMP tone stack is notorious for volume loss) Who doesn’t want louder distortion, right? So instead of the stock circuit, the layout below reflects the mods from GGG. I’ve added polarity protection and power filtering. Pots can be board mounted from the solder-side using right angle PCB pots.
