Electro Harmonix built the MEL9-U Tape Replay Machine as a polyphonic effects pedal within the same product family as the B9, C9, and KEY9, applying shared signal-processing technology to the specific task of recreating the sounds of vintage tape-based keyboards. The unit was designed to sit in a signal chain without requiring instrument modifications, special pickups, or MIDI implementation.

The MEL9-U offered nine voices drawn from the Mellotron catalogue: Orchestra, Cello, Strings, Flute, Clarinet, Saxophone, Brass, Low Choir, and High Choir. It accepted guitar signal and tracked bends, slides, and whammy dive bombs. Bass guitar was also supported down to the open A string, and keyboards could be used within the pedal's polyphony limit of five notes and a range of A1 to A5. The Effects output carried a blend of wet and dry signal controlled by independent Effect and Dry volume knobs. A dedicated Dry Output jack delivered the input signal at unity gain. An Attack control governed the volume swell speed — turned clockwise, notes faded in more gradually. A Sustain control set the release time after a note stopped — turned clockwise, the fade-out time increased. The unit drew 100 mA at 9 VDC and measured 4.0" wide by 4.75" long by 2.25" high.

Owners requiring service, replacement footswitches, knobs, or power supply substitutions compatible with the 9.6 VDC, 200 mA specification should consult a qualified guitar technician or electronics repair specialist experienced with effects pedals.