Roland GR-500

The Roland GR-500 was a guitar synthesizer. Manufactured by the Roland Corporation and FujiGen in 1977, it was one of the first guitar synthesizers.

The synthesizer module included Polyensemble, Bass, Solo Synth, and External synthesizer control. Much of the voltage-controller filter and voltage controlled amplifier sections were based on previous analog mono-synths from Roland. Sliders adjust the VCO, VCF, VCA, and LFO sections; there is no memory to store settings.

The synth module is controlled by a highly modified guitar: the GS-500 guitar controller was built in a partnership between Roland and the large Japanese guitar builder FujiGen. The result was the Fuji Roland Corporation, established in 1977 through a joint capital investment.

The GS-500 controller used a special pickup system that connected to the synth module via Roland's own 24-pin interface. Controls on the guitar primarily were for adjusting the relative volume of the different sections: guitar, polyensemble, bass, solo section, and external synth. The GS-500 guitar does not have a standard 1/4" guitar output and cannot be used without the GR-500 synthesizer module. It has a particular infinite sustain system: the frets in the GR-500 are connected to its electrical ground, and when a player frets a string, an electric current passed through the string. The electric signal passing through the string is a greatly amplified version of the string signal detected by the divided hexaphonic pickup. Large magnets replaced the traditional "neck" pickup. As a result of Fleming's Law, the alternating electric current in the string passing through the strong magnetic field caused the string to vibrate and create a feedback loop and infinite sustain. The GS-500 used a bridge with plastic saddles to electrically isolate each string.

Here is a brief description of each section:

Guitar: this is the output from a humbucking pickup. A three position EQ switch, plus tone control, provided variation to the guitar signal. There is also an optional mild peaking filter, somewhat similar to a wah-wah pedal, on the GR-500 module.

Polyensemble: this is not a true synthesizer section, but rather a unique distortion circuit using custom Roland "trigger pulse generator" chips. These chips are covered in epoxy so the actual circuit is unknown. The output of the Polyensemble is sent to an Attack/Decay/Sustain (ADS) Envelope Generator, one of three identical ADS Envelope Generators in the GR-500.

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