Modified Korg Poly-61Synthesizer

YouTube via rolandsh1000

"Demo of my modified Korg Poly-61. I got it for cheap off local Craigslist because of some issues. The most problematic was the non-triggering keyboard. I swapped out the keyboard PCB from a dead Korg DW-6000 and now it works perfectly (I recommend if you can find a dead DW6k and you're trying to repair a Polysix or Poly-61, you'll be amazed how much better the DW6k keyboard works).

Anyway, the P-61 is a lot like a Juno-60 or -106, in that each voice has one real digitally-controlled sawtooth core oscillator (DCO), VCF, and VCF. So it's essentially an analog polysynth under digital control. What it has over the Junos: an extra true-digital oscillator (fairly lame, but useful for some things), real analog envelopes, two LFOs. What the Junos have over the P61: chorus and, most importantly, analog controls to tweak all parameters.

The P61 designers apparently wanted to save money and followed the lead of the Rhodes Chroma and Moog Source in the user interface, so the P61 used a digital button interface to adjust parameters settings. IMO, this sucked because 1) it inhibited sound exploration 2) the resolution on the voice and modulation parameters was limited.

So, I decided to bring out a lot of these parameters of the P61 out to the panel and convert them to true analog control. This meant that these parameters could not be stored in patches (though other parameters still would be), but I was willing to forgo that since I basically just play for fun, not on stage. The parameters I brought out were the global ones (changes made by the microprocessor to all voices at once), which made it easy to have one knob or switch control all voices - all my mods are either switches or resistors/pots, no active electronics were added. I think you could make ALL of the parameters under analog control, but to go beyond what I did, you'd have to modify each voice circuit, which is a lot more work. :)

Controls added:
DCO1 waveform switch (saw, pulse)
DCO1 PW/PWM switch
DCO1 PWM amount
DCO2 on/off 'harmonic' switches: 2', 4', 8', 16'
VCF cutoff
VCF resonance
VCF keyboard tracking switch
VCA EG/gate switch
MG frequency
MG waveform (tri, squ)
MG DCO amount
MG VCF amount
Joystick:
- LFO2 waveform (tri, squ)
- LFO2/cutoff switch
- Joystick/Knob select switch (vertical joystick disabled in favor of rotary knobs)
- LFO2 DCO amount
- LFO2 VCF amount

In sum, these synths seem quite inexpensive for what's inside and with this added analog control (now it's somewhere between a Juno-6 and -60 as far as patch storage and user control), it's a lot more fun to play!"