MXR Distortion +

The pedal uses a single op-amp and a pair of germanium diodes to ground (parallel-push) for clipping in a very simple configuration with only Output and Distortion controls, no tone control; the pedal uses no discrete transistors.

[1] The pedal's crunchy heavy metal sound was featured by Randy Rhoads in his work with Ozzy Osbourne.

[2] Jerry Garcia of the Grateful Dead used this pedal exclusively for distortion in the late 1970s.

Rowland S. Howard (The Birthday Party/These Immortal Souls/Crime & the City Solution/Solo albums) also used this pedal across his career.

Guitarist Slash has talked about using the Distortion + in his early guitar days to help define his tone.

An original MXR Innovations distortion plus pedal from 1979, block logo, without LED and battery-only operation (no AC Adapter).
MXR Distortion + on a guitar pedalboard . Distortion + is the yellow unit on front of the pedalboard.