These sound effects or samples were written on a large 24-pin ROM chip that was produced by MXR.
The ROM chip had to be inserted into the circuit in order for the sounds to register.
Most of the pedals had two outputs that provide two distinctly different versions of the same pedal. These original pedals in the series included the Dyna Comp, Distortion , Phaser, Stereo Chorus, Stereo Flanger and Time Delay.
These were higher quality pedals, with electronic FET switching and dual LED indicators.
Barr later left MXR and went on to found Alesis, Sherwood, and the top five managers/engineers of MXR co-founded Applied Research & Technology, and Laiacona (was long gone when inbred fighting between genius Keith Barr and others within the MXR family caused the death of MXR) and had founded Whirlwind USA.
Jim Dunlop acquired the MXR brand in 1987 and continues the traditional pedal line of original MXR classics that have come to define the brand, such as the Phase 90 and Dyna Comp, as well as modern pedals like the Carbon Copy and Fullbore Metal.
MXR continued to manufacture most of the Reference, Commande and 2000 Series pedals until they closed their doors in 1984. In 1983, MXR introduced one of the first multi-effect rack units for guitar and bass, the Omni.
The Omni had 6 different effects: sustain, distortion, delay, equalization, flanger and chorus.