Updates: July 2016
Roland GR-100

Roland GR-100 Electronic Guitar Synthesizer

Features and Specifications:

Complex hexaphonic distortion circuit
Additional sustain overdrive (mode 3)
6 individual -12 dB low-pass Voltage Controlled Filters, one per string
Frequency peak and sensitivity controls for VCFs
Built-in footswitch controls the VCF mode (on, bypass, or inverted)
Low Frequency Oscillator with rate control, for vibrato effects
Lush analog bucket-brigade chorus/vibrato
Pedal control input for the VCF
3 outputs: guitar, mix/e.q. and chorus
Synchronized, flashing LED status indicators
Dimensions: 11.75" (W) 9.8" (D) 3.75" (H)
Power Requirements: 9 watts
Response Time: 1.00 ms

Roland GR-100
"Little, yellow, different" - the GR-100

Introduction to the Roland GR-100:

The Roland GR-100 is the least known of all the vintage Roland guitar synthesizers. Not to undersell it, but the GR-100 is basically a one-trick pony, a super hex-fuzz machine. If six fuzz pedals with six -12 dB low-pass filters can make a guitar synthesizer, then this is a guitar synthesizer. But Roland wisely decided to call the GR-100 an "electronic guitar unit," whatever that means! I would have to say it is a very cool polyphonic fuzz box with a smooth low-pass -12 dB analog filter and a very nice chorus and vibrato circuit.

The GR-100 has its own internal hex-fuzz circuit. The GR-300 generates its hex-fuzz component by processing the hex-fuzz signal generated by the guitar controller. For example, the G-202 has a different hex-fuzz circuit than the G-808. And the G-707 has no hex-fuzz circuit at all. But none of that matters with the GR-100, as it has a slightly more sophisticated version of the G-303/G-505/G-808 hex-fuzz design.

The hex-fuzz in the GR-100 is smoother than what you hear with a GR-300, and it also has an additional sustain feature. With the mode switch in the down position (mode 1), you hear guitar only. In the middle position (mode 2) you hear the basic GR-100 hex-fuzz sound, and with the switch in the up position (mode 3) you hear the GR-100 hex-fuzz sound with an additional sustain/compression circuit

Roland IR3109 Low-Pass Analog Filter Design:

Roland GR-100
Roland IR3109 VCF Chip - (GR-300)

The other addition to the GR-100 is six -12 dB low-pass filters, one for each string. The GR-300 uses one custom Roland IR3109 VCF chip for its -24 dB filter, but the IR3109 has two identical, independent sections. The two sections are cascaded in the GR-300 to create the -24 dB per octave slope. In the GR-33B bass synthesizer, the filter section is also cascaded for -24 dB response, but the GR-33B adds a simple SPDT switch to access the cascaded IR3109 mid-point to provide the -12 dB output option. In the GR-100, three IR3109 chips are used, with each IR3109 chip processing two strings with -12 dB response. And the IR3109 is used in the GR-700 as well, as part of the dreaded 80017a assembly.

Roland GR-100
3 Roland IR3109 VCF Chips (GR-100)

If you have listened to filter sweeps using the GR-300, you may be a little disappointed with the GR-100. The GR-300 filter is a -24 dB low-pass design, meaning you can get fairly dramatic sweeps. The GR-100 only has half of the slope of the GR-300, so the effect is not as dark or strong. Using the envelope triggering, the GR-100 calls to mind a really cool auto-wah pedal, but with the advantage that each string is processing independently for greater clarity. The GR-100 also includes an adjustable frequency (resonance) peak as well.

One note on the Roland IR3109 chip: Roland seems to have a company policy of including at least one irreplaceable component made from "unobtainium" in every major product they build. The IR3109, the heart of the VCF/VCA in the Roland GR-100, GR-300 GR-33B and GR-700, is such a component. While it is possible to build almost an entire GR-100, GR-300 or GR-33B from scratch by following the schematics, you will still be missing the IR3109 and its mate the Roland BA662, which gives Roland analog synths much of their character.

Bucket-Brigade Analog Chorus/Vibrato

Ones of the nicest features of the GR-100 is the chorus/vibrato circuit. What can I say? This is vintage Roland analog sound. The circuit is quite similar to the old Roland CE-1 chorus pedal. The chorus/vibrato are two flavors of the same circuit. When in Chorus mode, the GR-100 offers a sensitivity control, which is like the chorus intensity control on the CE-1. Like the Roland CE-1, the "vibrato" mode offers full control over rate and depth, and represents the "wet" or effect only output of the chorus/vibrato circuit.

Owning a GR-100 just for the chorus and vibrato sound may be a bit extreme, but like so much of the analog world, there is nothing else quite as sweet and unique as the GR-100’s chorus and vibrato. And, in a nice touch, the Vibrato LED does not glow until the Vibrato circuit is actually engaged with the touch pads. Cool.

Roland GR-100 Block Diagram (click to view on a new page)

Links to more information:

Mix Magazine article detailed recording "Every Breath You Take" and Andy Summers' vintage Roland GR-100, GR-300 and US-2 rig.

Sound-On-Sound Magazine article detailed the history of Roland Corporation during the 1980s.

1982 Roland Product Brochure - Japanese - Featuring the G-303 and G-808.

Download the GR-100 Owner's Manual

Photos:

Roland GR-100
Roland GR-100
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Click on any image for larger view.

Videos:

WATCH NOW! YouTube Video Playlist

Schematics - Repairs - Service Bulletins:

There are no known service bulletins from Roland addressing any GR-100 problems. As a safety precaution, I strongly recommend replacing the original blue tantalum capacitors. These capacitors, while very popular in the late seventies, are known to fail.

GR-100 Failed Switch or Broken Pin Mechanism.

Download the GR-100 Service Manual Schematics.

Details on replacing the GR-100/GR-300/GR-33B 10 uF blue tantalum capacitors.

Accessories:

CB-300 Carrying Case

Page six of the 1984 Roland GR series brochure lists several options and accessories for the GR-100.

FV-200 volume pedal: The FV-200 volume pedal could be used to control the filter cutoff on all the vintage Roland synths, GR-100, GR-300, GR-33B and the GR-700. The FV-200 could also be used as a pitch pedal with the Roland GR-700. The both the Roland GR-100 and GR-300 owner's manual list the FV-20 volume pedal for use with the GR-300.

CB-300 case: The rarest of all vintage accessories, Roland made a leatherette case for the Roland GR-100, GR-300 and GR-33B.

And page five lists the Roland US-2 Unit Selector and the C-24D connecting cable.

Most of these accessories are impossible to find now, but there are modern equivalents that you can use to expand the playing experience with the vintage Roland GR-100.





Filter Pedal Input:

Details on the Roland GR-100/GR-300/GR-33B/GR-700 filter pedal options.