MATRIXSYNTH: Korg EX-800 Polyphonic Synth in Excellent Condition w/ Circuitbenders Polybeast Mod

Tuesday, April 25, 2017

Korg EX-800 Polyphonic Synth in Excellent Condition w/ Circuitbenders Polybeast Mod

via this auction

Details on the mods via Circuitbenders:

"Cutoff & Resonance Knobs: This mod can be found around the net under several different names and versions but essentially it adds knob controls for the filter cutoff and resonance parameters for realtime control. The resonance knob can take the resonance well into self oscillation and far beyond what is programmable from the front panel. This can produce the kind of screaming top end and subsonic bass that gives these machines a whole new range of sonic possibilities. The filter cutoff knob allows you to perform long filter sweeps for those squidgy burbling analogue lines that you knew your Korg was capable of but could never actually program. Both parameters are still also controlled by the normal programming methods which can set the range of the knobs control.

12dB / 24dB Filter Response Switch: Somewhat mysteriously the filter chip used in these machines has both 12dB/Oct and 24dB/Oct outputs but only the 24dB one is actually used. This mod adds a switch to select either a 24dB or less drastic 12dB filter response

VCF CV input: This socket round the back of the machine adds an external 0-5v control voltage input that controls the filter cutoff. The new filter cutoff control knob is disabled when a jack is plugged into the socket.


External Audio Input: This accepts a line level audio signal and inserts it before the filter and chorus effect so you can use it to process external signals. The input is set up so that a loud signal will slightly overdrive the filter for a dirty sound.

External Audio Path Switch: This switch sends the audio from the external input either via the DCO1 or DCO2 signal path or turns it off completely. The input doesn't respond to the DEG audio level envelopes but instead is gated on and off by the noise gate that korg implemented to silence the synth when all the envelopes are completely closed. i.e. when the DEG envelope for the chosen path closes completely at the end of the release phase, the noise gate is activated and the external audio input is cut. The audio input is still effected by the filter envelope.
An external input can easily be filtered without having to hold down a note by setting up a patch with all the oscillator tones turned off, but the DCO 'level' parameter set to full. If you use the note 'Hold' function and press a key the audio input will be audible and can be processed with the filter etc.

Input Level Knob: Its a knob that controls the level of the audio input. What more can we say?


These consist of a source selection knob and an FM amount knob. Essentially VCF FM allows you to modulate the filter cutoff at audio frequencies to create all kinds of clanging cross modulation and bizarre alien splatters & sweeps. This effect works best with the resonance cranked up into self oscillation which is where the new resonance knob mod comes into its own. The source selection knob allows you to select one of four sources for the FM signal. These are DCO1, DCO2, Noise and audio input. The audio input takes its signal from before the input level knob so you can use the audio to modulate the filter cutoff but remove the actual audio signal from the mix. The source knob also has an off setting."

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