The GR-300 was considered the first "playable" guitar synthesizer. (It's predecessor, the GR-500, was plagued with tracking problems that rendered it virtually unplayable.) The GR-300 had no MIDI and could only be played through a GR-300 series guitar controller.

The actual synthesizer module sat on the floor and had the rugged appearance of a large guitar-type foot pedal (complete with carrying handles). It featured 6-voice polyphony, one voice per string and 2 oscillators per voice. Each pair of VCOs were harmonically locked to each string but could be tuned separately to play different pitches. The GR-300 also featured a VCF with variable lengthsweep up and down, and an LFO. Each string had an enable-disable switch as well as a string sensitivity switch (basically audio compression). Built-in footswitches controlled the VCO mode (single/dual), the VCO harmonize pitch (detuning of the VCO's), and the VCF mode (on, bypass, or inverted). There was also a pedal control input for the VCF. The GR-300 could output either the guitar, the synth, or a mix of the two.

 Body: Ash and Walnut
 Finish: Acrylic (natural)
 Neck: Maple and Mahogany, thru neck
 Fingerboard: Select Ebony
 Frets: 22
 Bridge: Fixed, adjustable
 Nut: Polycarbonate
 Tuning machines: Gotoh
 Pickups: Two Roland PU-114H Humbuckers
 Scale: 24 3/4"
 Truss Rod: Adjustable
 Neck Width: 1 11/16"
 Body Width: 13"
 Body Depth: 1 3/4"
 Overall Length: 38 3/4"
 Weight: 9 lbs 6 oz.