[sdiy] polyphonic synthesis

[Ingo Debus]

deega wrote:
> I'm with ya.  I'd love to do a poly synth myself.

I've built one. I used Doepfer's voice cards from the 80s. This is a
synth voice (2 VCOs, 1 VCF, 2 VCAs, 2 ADSRs, all CEM ICs) on a 100mm *
160mm PCB. The CV generation is done by an ancient 6502.

> Regardless, I still give it thought.  Here's what I think is needed for a ten
> (hell, I gots ten fingers) voice polyphonic analog:

Mine is 5 voice, with two VCOs per voice.

> I really wouldn't want to skimp and pass the sum of all VCO's to a single
> filter and VCA set.  All modules would need to be built 10 times, with a single
> control panel.  I believe this would be tough.  I need to learn how to make one
> pot/switch control ten devices.  Relays come to mind for switches, but pots...
> oh boy.

Make everything voltage-controllable.

> I can see tuning each voice to sound exactly the same becoming the biggest
> issue.  With all the talk on this list stressing the need to match components,
> I'd imagine matching components across 10 identical modules would be a
> nightmare (understatement?).  And what of thermal stability?  Even if matched
> well, the boards will still behave differently due to temperature difference on
> each.

Many people here said a polyphonic analog synth *needs* some sort of
autotune. Well, mine has none... It works ok-ish for 9 of the VCOs, one
is drifting heavily. I still have to try and replace this 3340. It's not
perfect without autotune, but hell, this is analog... :-)

Ingo