I wasn’t very familiar with Korg Poly-61.  I’d had a DW-6000 and, having only seen the occasional picture of the P61 on the web, I thought it was another largely digital hybrid, encased in a plastic shell.  One appeared for super cheap on my local Craigslist ($25, I’ve paid more for Casios!) – the seller said on the phone that it had several issues, so I figured I’d collect it for parts which I’ve done with other synths (harvest the CEM or SSM chips, some keys, a chorus board, etc). 

 

But when I showed up to buy it, I was surprised that it was actually quite weighty, made of metal and wood, like a Juno or a Polysix.  Then I went back on the internet and downloaded the service manual and found out that my initial assumptions were _very_ wrong.  The P61 is nearly all analog, but for the DCO’s and the horrible, horrible digital parameter access/control.  What’s good:  the main DCO is of the Juno type (well-described elsewhere as a sawtooth core under digital timer control), not a sampled waveform; EG’s are analog from the SSM2056; the two LFO’s are simple but analog; VCFs are interesting 12dB/oct OTA based; VCA is serviceable Korg transistor+op amp.

 

The digital control of all that analog is awful though.  Not only is it a ‘one-at-a-time, punch in the parameter number’ design, but there’s not even a slider (Rhodes Chroma, DX7), encoder (Moog source), or rotary pot (AX-80) – you get to use only incremental up and down buttons.  In a word, it sucks.  I can only guess that Korg was trying to dramatically cut the price of the unit.

 

So, if you don’t absolutely need presets (the Juno-6 comes to mind), the P61 is a perfect mod candidate.  There’s a number of parameters that the microprocessor controls in a global (all voices) way, with a single CV.  The list of mods that I made is:

 

 

Now, the work here isn’t particularly beautiful, because I didn’t want the project to take more than a few days.  But it all seems to work pretty nicely.  Some of the controls could be made a little more linear or logarithmic, depending upon the function, but this P61 is now _fun_ to play.  Having voices instantly adjustable is really great for this synth because of the chord hold and arpeggiator functions.  You can tweak a drone, or filter sweep an arpeggio. 

 

How does the P61 sound?  It’s not as warm as the Juno-60, but the filter is more aggressive and the 2^nd oscillator can add weirdness or give you some detuning for a phasing effect, like the Juno chorus.  One nice thing is, with the mods being purely analog, there is no stepping at all, as you can sometimes hear on the Juno.