The Boss SD-1 Super OverDrive is a pedal with a simple design, using only one dual operational amplifier (uPC4558C) and 6 transistors, with an asymmetric overdrive circuitry for a classic, natural tube amp growl. It generates the warm distortion of an overdriven tube amplifier while maintaining the subtle nuances of a guitar player's picking technique.
The schematic is nearly identical to the classic OD-1 OverDrive, the only major difference is the tone control circuit. The design is simple and easy to follow: the guitar signal is buffered with Q5 and enters the first half of the uPC4558C dual operational amplifier. There are 3 silicon diodes in the negative feedback path of the op-amp. Two diodes are in one direction and only one in the other. This arrangement produces asymmetrical soft clipping -- one side of the waveform is clipped more severely than the other. The tone corrector and level control circuits are next. The signal finally exits the circuit after the output buffer made with Q6. The bypass circuit uses a classic arrangement with 2 JFETs (Q1 and Q2) serving as solid-state switches and a symmetrical bistable multivibrator made with Q3 and Q4.
ICs, transistors and diodes used in the SD-1 Super OverDrive: