The GM-70 is a mid-1980's guitar synthesizer that uses the older GK-1 divided pickup with a 24-pin connector. It is known for its ability to control a wide array of MIDI parameters and despite the fact that it is one of the slowest MIDI converters ever produced (with a 40 millisecond response time being typical), it is sought after for its control options.
For a long time I used the GM-70 along with the pedal to control my rack of midi devices. It worked great.
Note: The GM-70 is a controller and does not have any built-in sounds of its own.
I also have an FC-100 foot controller that works great with this. Here it is.
(bottom) Roland GM 70 Guitar synth and midi controller
It has a built-in tuner, supports monophonic or polyphonic modes, and has connections for a FC-100 foot controller, EV-5 expression pedal, and DP-2 pedal switch.
Year Released: 1986
Patch Memories: 128
MIDI Connections: In, Out (No Thru)
Power Consumption: 22 watts
Weight: 4 Kg
Price: $200 (This is the pickup price).
NOTE: The GM 70 is activated by the FC100 Foot Controller. The two items should be used together. I am selling one, here it is. I could work out a deal for both units, as I've decided they are a matched pair and should go together.
Here's the blurb on the GM 70:
Roland GM-70 GR MIDI Converter Module
The Owners Manual is available as pdf
Features and Specifications:
128 Patches, each with four "Branches" (A to D)
Two editing methods to create a branch: General Edit and Individual Edit.
MIDI Poly and Mono Modes
Supports assignable MIDI control numbers from 0 to 95
CV #3 (Whammy Bar) supports "Absolute" or "Center" modes of operation
Up to 4 continuous controllers from guitar, plus 3 position mode switch
2 - Assignable foot switches (Roland FS-5L, FS-5U or similar)
1 - Assignable foot pedal (Roland EV-5)
Guitar volume control simultaneously transmits MIDI volume (controller 7)
Stereo input for one synthesizer
Optional use of Roland FC-100 foot pedal controller to change patches, plus adds one more MIDI switch and controller
Dimensions: 19" (W) 10.875" (D) 1.75" (H)
Power Requirements: 22 watts
Roland GM-70 Brochure
Roland 1987 NAMM Show brochure photo
Introduction to the Roland GM-70:
The Roland GM-70 was the first stand alone Guitar-to-MIDI converter built by Roland. Many longtime GM-70 users insist that the GM-70 is still the best Guitar-to-MIDI converter ever built. Like other modules produced by Roland during this time, the GM-70 sports a fluorescent blue display, calling to mind high-end Lexicon units of the same period. The GM-70 is flexible and easy to use as well. This much can be said about the GM-70: no other Guitar-to-MIDI converter ever built offers as many features as the GM-70, but no other converter is as slow as the GM-70!
Combined with a vintage Roland guitar synthesizer controller, no MIDI converter ever built offers as many control options as the GM-70. With the GM-70 you can control up to eleven possible MIDI parameters! That is four destinations for the four continuous controllers on the guitar, plus two possible destinations for the mode switch. In addition, the GM-70 has inputs for two more foot switches plus a Roland EV-5 foot pedal input. Then plug in the optional Roland FC-100, and you add an additional foot switch and EV-5 pedal input, for a total of eleven! The Roland GM-70: it goes up to "11."