Korg Poly-61, with extensive modifications and MIDI

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via this auction

Sold for $675

"One-of-a-kind Poly-61 that has knobs installed for almost every parameter and also MIDI.

The knobs provide much greater control over the parameters than you could achive on a stock unit, both in terms of range and resolution. There are effectively two separate LFOs now (instead of the one + joystick/performance LFO)--the second one can be switched on directly or controlled by the joystick (as on the stock model). A triangle and square wave LFO are now also available. The programmable LFO has an extremely wide speed range (not sure how much greater than stock, but seems capable of being slower/faster).

Lastly, the second oddball digital oscillator now has individual octave switches broken out, so you have a basic additive square wave oscillator here that resembles a sawtooth wave when all switches are engaged. Oscillator 1 (a DCO) retains the original waveshapes, but now has better control over PW/PWM).

The caveat with these knobs is that the knobs override the internal parameters, so saving as before is not before. Non-knob parameters are saved; broken out parameters are not (think of it as being permanently in "manual" mode).

The Poly-61 in general has been pretty overlooked in favor of the Junos/Poly-6, but is a very unique instrument in its own right. The filter is a discrete 2-pole/12dB filter that is much closer to the Korg MS-20 series filter than than the Polysix SSM or DW-8000 Korg 4-pole filter. The envelopes are also extremely snappy, and the knob controls allow much better control over envelope shape. There are schematics out there to also add a separate release control to the VCA, which would make this even more powerful.

The side panels suffer from the usual edge and corner dings, but overall both the unit and front panel are in very good condition."