Korg X-911 Guitar Synth

via this auction
"This guitar synth from Korg – circa 1981 – is just that and more besides as it is also blessed with comprehensive analogue CV (control voltage) and Trig (trigger) interface inputs and outputs via standard ¼ inch jack sockets. The three CV inputs cover control of the X-911’s VCO pitch, filter cut off and the FM In socket allows a synth’s LFO or envelope output (for example) for control of vibrato and other pitching effects on the X-911 VCO.

In effect, these interfacing sockets make the X-911 a very useful and comprehensive synth expander for the Korg MS series of synths and sequencers... the MS20, MS10, MS50 synths and SQ10 analogue sequencer. Other Korg synths (the Sigma?) from that era are also compatible if they use the Hz/Volt CV and Ground trig conventions. Interfacing with an MS series synth in this way could involve, say, the X-911 output being fed back into an external signal input of the controlling synth so that it behaves as if it’s part of its internal architecture! Beyond these synths the unit could be made to interface with any other analogue synths/sequencers using the more standard Octave/Volt and positive triggering conventions via a suitable converter.

As a straight guitar synth this unit tracks surprisingly well and has comprehensive input sensitivity switching to deal with a wide range of synth, guitar, microphone (for voice, wind instruments etc) and other signal control levels. It’s also a great effects box for processing other external instruments like drum machines or vocals. The filter design is derived from the Korg MS series of synths.

Broadly speaking the X-911’s instrument and synth outputs can be rapidly combined, muted, mixed (with each other or the input signal), octave split etc using the illuminated switches and balance fader with the right hand ‘synthe’ selection offering additional filter enveloping curves with variation control. Interestingly, the first two synth waveforms (16’ footage) are square/pulse types that are pulse width modulated by their simple but variable envelope knobs which also modulate the main LP filter cut-off.

To my ears it sounds like a darker, heavier and denser (in a good way) version of say, an MS10, veering more, perhaps, toward the characteristic of the earlier Korg 700 and 700S. It can certainly do very weighty bass."