Roland Vintage Guitar Synth Gear for sale on eBay!
Roland GM-70 Pitch-to-MIDI Converter
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 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."
CV #3, the MIDI whammy bar found only on the Ibanez IMG2010, can be used "center" mode or "absolute" mode. In "center" mode, the whammy bar transmits values of 64 to 0 as the bar is pushed down, and values of 64 to 128 as the bar is pulled up. In "absolute" mode the whammy bar transmits values of 0 to 128, whether the bar is pushed down or pulled up. It still amazes me that the Roland GM-70 has such excellent support for the MIDI whammy bar found on the IMG-2010, but Roland never built its own guitar with a MIDI whammy bar.
One final observation: when carefully calibrating my rig, I noticed that both the GM-70 and MC1 have a pretty coarse control resolution. Rather than seeing numbers smoothly scroll from 0 to 64, or 0 to 128, I would only see even numbers. I would have to say this indicates a lack of resolution in the GM-70 and MC-1 circuitry.
Roland GM-70 Block Diagram (click to view on a new page).
Sound-On-Sound Magazine article detailed the history of Roland Corporation during the 1980s.
Version History:
 |
 |
 |
 |
 |
 |
Click on image to enlarge. |
|
There are minor differences in the GM-70 throughout the production run. There were a total of four versions of the GM-70, version 1.00 through version 1.03.
Early GM-70s have a large, cumbersome EMI (electromagnetic interference) filter attached to the 24-pin input, and a sticker attached to the top of the unit with the message, "Complies with the limits for a Class B computing device pursuant to Subpart J of Part 15 of FCC Rules." This same sticker can be found on the back of some GR-700s and GR-77B synthesizers.
Later GM-70s dispensed with the EMI filter, and removed some additional filtering components from the circuit board. Curious, Roland also added two additional screws on the top panel.
- Version 1.00: Initial GM-70 Operating system software.
- Version 1.01: Changed controller 94 text to CELLES DEPTH from SELLES DEPTH. Addresses error where foot volume (connected to GM-70) did not reach maximum value. This software revision also fixes MIDI choking in Poly Mode
- Version 1.02: Corrects problem with GM-70 following MONO mode or POLY mode reset.
- Version 1.03: Unexpected mode messages. This issue is not noted in the Roland GM-70 service manual, but is addressed in a July 7, 1987 service bulletin. See service bulletin below regarding the version 1.03 software.
Repairs - Service Bulletins:
Roland Service Bulletin No. 1000285 - GM-70 - Unexpected mode message - July 7, 1987:
Roland notes that there is a software bug with version 1.02 software. The GM-70 will send an unexpected Mode message when changing patches. The solution is to change the EPROM from version 1.02 to version 1.03.
Download the original GM-70 service bulletin.
Download the GM-70 Service Manual.
Repairs - Roland GM-70 Lithium Battery Replacement:
The original lithium batteries installed in the Roland GM-70 have a service life of 5 years, but they have lasted much, much longer. You may find your GM-70 does not retain its memory settings. If so, you may need to replace your lithium battery.
Why do the Roland GM-70 and Ibanez MC1 include synthesizer inputs?
 |
|---|
IMG2010/MC1 manual showing both MIDI and audio synthesizer connections. Click on image for larger view. |
You may have noticed that both the Roland GM-70 and Ibanez MC1 include analog 1/4" inputs for synthesizer, in addition to MIDI input and output, and a guitar output.
The Roland GM-70 has a stereo input and stereo output, plus one MIDI output, and the MC1 has two mono inputs that are summed to a mono output, and MIDI out "A" and "B".
Why? Keep in mind that both these units are some of the very first MIDI processors ever built. At the beginning of MIDI, it was not clear how manufacturers would actually implement the MIDI specification. If you buy a keyboard or MIDI module today, it is accepted that the unit will support MIDI controller #1 for modulation, #7 for volume, #64 for sustain, controller #71 for filter resonance, and #74 for filter cutoff.
But in 1985 it was not clear that MIDI controller #7 would be
universally implemented as volume control. So the inputs on the GM-70 and MC1 pass signal through voltage controlled amplifiers, with the control voltage supplied by the volume knob on the guitar controller. If a synthesizer did not support MIDI volume, the output of the synth could still be passed through the GM-70 or MC1 for volume control. This makes sense, if you check out the MIDI implementation for the Prophet 600, regarded as the first MIDI synthesizer, there is no support for MIDI volume, only note on/note off, program change, and modulation wheel.
