Roland GR-500 Paraphonic Guitar Synthesizer

Introduction to the Roland GR-500:

The Roland GR/GS-500 paraphonic guitar synthesizer system was introduced in 1977, and it laid the foundation for the very successful Roland vintage 24-pin guitar synthesizers, like the GR-300 and GR-700, that would follow a few years later.

The GR/GS-500 uses the same 24-pin cable as the later synths, and many of the control voltages, string outputs, etc. are the same across all the synths, with slight variations. The different systems are not 100% compatible, but can be engineered to work together with a few modifications.

The GR-500 has five sections: Guitar, Polyensemble, Bass, Solo Melody, and External synth. The GR-500 was ambitious in its scope. The Solo Melody section tackled nuanced pitch-to-voltage analog synthesis, with ramp and pulse waveforms and various means of filter modulation. The Bass section similarly offered different bass voicings. The Polyensemble is a pseudo-synthesizer section, using individual waveshaping of each string output to achieve a synthesizer sound without the complexities of pitch-to-voltage synthesis. Even the guitar, the GS-500, had an equalizer switch for different guitar tonalities, and a clever infinite sustain system.

This approach of incorporating different sound elements into one large system was not uncommon in the 1970s. At the same time the GR-500 Paraphonic Guitar Synthesizer was released, Roland was also making the RS-505, Paraphonic String Synthesizer, which combined strings, polysynth, and a bass section.The term "paraphonic" was invented by Roland, as a marketing shorthand for "parallel" plus "phonic."

Output Matrix:

The GR-500 has a useful output matrix. There are three separate outputs, plus one mix/combined output. Each section can be assigned to any one of these outputs. In addition, there is an external synthesizer input, so an external expansion synth can be combined with the internal sounds.

Polyensemble:

Custom "Trigger Pulse Generator" chips. Click to enlarge.

The first "synthesis" section of the GR-500 is the Polyensemble section. After some initial high-pass and low-pass filtering, each string is processed by a Roland "trigger pulse generator" chip. This is a custom chip, made for Roland by Mitsubishi, part #140-017. This is one of two custom Roland chips in the GR-500, with no detailed documentation regarding what exactly Roland put inside these chips. The tradition of the "mystery chip" continued with the IR3109 in the GR-100 and GR-300, and the 80017a in the GR-700.

The output from these "trigger pulse generator" chips goes to both the synthesizer section, and to the Polyensemble envelope generator, where each string passes through its own envelope generator before going through a chopper gate (similar to the GR-300), then to the filter/voicing section. The GR-500 has three identical envelope generators in different sections, with attack, decay, and sustain controls. It is my experience that once a signal falls below the input gate threshold, the envelope generator closes abruptly.

The four outputs of the Polyensemble, "F", "L", "M" and "H" are filtered/equalized outputs of the same source. The Polyensemble can be played directly, or can be processed through the low-pass filter in the Solo Melody section.

Bass:

Custom "Fundamental Generator" chips. Click to enlarge.

The Bass section represents the first real pitch-to-voltage conversion in the GR-500. The magic of the bass synthesizer section happens in the other proprietary, custom Roland chip, part #140-016, the "fundamental generator" chip. Like the trigger pulse generator chip, the contents of this chip remain a hidden Roland mystery. The output of the "fundamental generator" chip is a square wave, used to drive the analog synthesis in the Bass section.

A string select switch allows the player to choose from having bass on all six strings, strings 4, 5 and 6, or just strings 5 and 6. The is also a dedicated touch response switch. Like the Polyensemble section, there are different bass voices: "percussion" (long and short), "soft" and "hard." And again, like the Polyensemble section, these different voices represent the same output processed through different filters. The "percussion" setting calls to mind the percussion sound of the bass section in an aging Hammond organ. The "soft" sound calls to mind an electric bass played with fingers, and the "hard" sound is reminiscent of an electric bass played with a pick. In my studio, the bass section was impressive in its thunderous, room-shaking quality.

Solo Melody:

The Solo Melody is very much an expanded version of the Bass section. The Solo Melody section uses the same proprietary, custom Roland chip, part #140-016, the "fundamental generator" chip to convert the guitar output into a square wave used to drive the analog synthesis engine. But the Solo Melody section offers the choice of a 16' or 8' pulse wave, or a 8' reverse-ramp wave. There is also a pulse width control, and the width can either be set manually, or controlled by the envelope generator, or a triangle wave low-frequency oscillator.

The Solo Melody section has a great sounding 24 dB per octave low-pass filter with resonance. The filter cutoff can also be controller by the LFO, envelope generator, manual control, or external foot pedal. In my tests, I was able to use a Roland EV-5 pedal to get very musical sweeps from the filter. The low-pass filter can also be used to process external sounds, and to process the output of the Polyensemble section.

Polyensemble Waveform Click to enlarge.	Bass Waveform Click to enlarge.	Solo Melody Waveform Click to enlarge.

Versions: With and Without Solo Section Tuning Offset, serial numbers 671299 and below, and serial numbers 671300 and above.

Solo Section Tuning Offset. Click to enlarge.

There are two versions of the GR-500. The clearest distinction between the two units is a 6-pin DIN interface jack in the "External Synthesizer Control" section on the rear panel, found in the earlier version, or a pitch offset knob, found in the later version.

All GR-500s have 1/4" interface jacks for connecting the GR-500 to external control voltage synthesizers. The outputs include a pitch (voltage) output, plus positive and negative gate control voltages. The early GR-500s, with serial numbers 671299 and below, combined these outputs on a 6-pin DIN jack for easy connection to other Roland synthesizers with a similar 6-pin DIN connection. In these early GR-500s, the solo synthesizer voice is locked to the pitch of the guitar, but after the initial wave of GR-500s shipped, Roland responded to guitar players' requests for a way to offset the tuning of the solo section, to achieve a fatter, richer sound.

Second Oscillator Upgrade. Click to enlarge.

Adding A Second Oscillator

The later GR-500s, with serial numbers 671399 and above, have the 6-pin DIN jack removed and replaced it with a tuning offset knob, so the solo voice could be detuned slightly. This simple addition of an external knob to detune the solo voice section masked what is actually a fairly complicated modification to the GR-500.

Early 24-pin connector (top), later connector (bottom). Click to enlarge.

In order to offer the ability to detune the solo voice section, an entire new oscillator had to be added to the GR-500. This new oscillator had an internal control for tuning, and pulse-width adjust. Also, by adding in this second, independent oscillator, the GR-500 player was now able to also use the portamento feature. This was offered as a free upgrade by Roland to all GR-500 users. In the early GR-500s, the portamento feature only works on external synths.

Careful observers will notice that GR-500s in promotional photos have silver capped control knobs, but the actual GR-500s I have seen have the more familiar black topped knobs.

Finally, the early GR-500s are generally seen with the pin-type connectors, and they use the C-24B 24-pin cables with pin-type ends more commonly identified with the Ibanez 24-pin synths and the Korg Z3, though the Roland SCC-700 used the same connectors as well.

The later GR-500s switched to the locking ring connectors, the C-24D. These are the much more familiar locking ring cables sold with most of the GR-100, GR-300, and GR-700 systems.

GR-500 / GS-500 Televison Advertisement

Photos:

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GR-500 GS-500 Eight-Part Video Introduction:

GR-500 Performance Videos:

Audio:

Listen to "Artic Circles" a short GR-500 demo by Chuck Hammer using the sustain system.

Modifications:

Please see the section on adding a second oscillator to offset the pictch of the solo melody.

Schematics - Repairs - Service Bulletins:

There are two versions of the GR-500. The later versions introduced a tuning offset control for the solo voice section. The service manual covers both versions of the GR-500. The service manual addendum specifically address the modification to add the tuning offset to the solo section.

Like all vintage synthesizers, the controls in the GR-500 can become unreliable with age. Mouser Electronics stocks a 50K linear slider that is a close match for the 50K linear sliders used in the GR-500. The 30 mm travel matches the GR-500 components, but two of the four pins do not exactly line up. If you need a replacement slider, this is a possible option.

Accessories Roland PC-50 Remote:

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The Roland PC-50 is perhaps one of the all-time rarest accessories in the vintage Roland guitar synthesizer series. The PC-50 has the ability to store three presets for the Roland GR-500, plus a manual option. Each preset stores the settings of the levels for the Polyensemble, Bass, Solo Melody, and the External Synth. In the manual mode, control is returned to the settings on the guitar.

Filter Pedal:

In my tests with the Roland GR-500, I found the Roland EV-5 pedal to work great with the external filter pedal input. The EV-5 uses a linear 10K potentiometer, with the wiper (output) of the potentiometer connected to the "tip" and the "sleeve" (ground) and "ring" connector to the left and right terminals.

Magazine Advertising:

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1977 Japanese Brochure with Sample Patches:

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1977 Roland GR-500 Brochure - Paraphonic Guitar:

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