[sdiy] Korg Poly 61 mod help

[Tom Wiltshire]

Travis,

It doesn't look too hard from the schematics, although I haven't  
found a decent copy of those.

http://www.dompselaar.org/Korg/Poly61/poly61c.jpg

(the others are in this same folder)

As you say, it's a matter of figuring out where the control voltage  
comes from the cpu
and goes to the analog chips. In the case of filter frequency (Fc) I  
think it's at the bottom of IC42 (uPD-8255, top RHS) where 6 digital  
lines feed an op-amp mixer to make a very basic DAC. You could feed a  
voltage into the op-amp mixer (IC38? 36? can't read it clearly).
The set up for resonance is very similar and just below on the  
circuit diagram.

Making this modification will allow you to change the cutoff without  
stepping, so I say go for it.

Hope this helps,
Tom


On 5 Nov 2008, at 16:13, Travis Thatcher wrote:

> I've seen several places where people have managed to mod a Korg Poly
> 61 with pots for both cutoff and resonance control.  I imagine it is a
> matter of figuring out where the control voltage comes from the cpu
> and goes to the analog chips. I don't have a schematic and would love
> to know if anybody has done this mod, or has any tips for doing it.
>
> -Travis
>
> -- 
> http://www.judichicago.com
> http://www.myspace.com/judichicago
> http://www.recompas.com
> http://voiceofsaturn.blogspot.com
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>