Distortion +

The MXR Distortion+ (M104) is a classic op-amp distortion pedal first introduced in 1974, making it one of the earliest commercially available op-amp-based distortion designs. Its simple two-control layout—Output and Distortion—covers a wide range of gain, from light crunch to classic late-'70s Marshall-style distortion and even fuzz-like tones with a tight low end. The Distortion+ became highly influential, inspiring later circuits such as the DOD 250 Preamp, Boss SD-1, ProCo RAT, and, more indirectly, the Klon Centaur. Despite decades in production, its core circuit has remained essentially unchanged, preserving the raw, gritty character that made it a favorite of players including Randy Rhoads, Jerry Garcia, Thom Yorke, Dave Murray, and Bob Mould.