Korg Poly800/EX800 Users

>Here's some tech overview of what happens in there: for resonance you >have 
>current input to the chip, hence 10k res and 10k trimpot fed by >CV. Old 
>mod used pot instead pot and all you got is lowering maximum
>resonance to some level (as 10k is left in). Atom's mod take different 
> >approach, it attenuates incoming res CV and feeds old 10k res. So you 
> >get the same max resonance as before but now you can fully shut 
> >resonance, old mod took it to some level but here you can get 0 
> >resoance. My mod is somewhat different. I installed the switch to >choose 
>between original line (10k trimpot and 10k res) and new one >(100k lin pot, 
>10k trimpot, 1k res), that way I got higher resonance >(set by trimpot and 
>res, pot to 0), and it goes almost to 0 res (pot at >the max). Pot is 
>configured as variable resistor.

that's a really good idea....much better than the way the normal mod works.

>Cutoff is bit different. I suspect it's OTA input as it's fed by again
>current from +V, lower leg with res and cap is for stabilisation.
>Atom's mod substitutes it for voltage divider and feeds current input
>with voltage. In theory that would be a problem. Can't say more. I'd
>toss in resistor inbetween pot wiper and chip input, 1k or so.
>Haven't tried it. Now, if you look at the borad you'll see silkscreened
>short link for bypassing trimpot to +V. Hmm, so maybe it really works.
>You might even not need 470ohm res he suggested.

makes me really wish there was actually a datasheet available.

you should try giving the filter a 2-pole switch as well.

>Strange, mine oscillates witout any input, no problem. And it's quite
>nice chip, I like selfocs resonance. Sounds much better than CEM VCF >chip 
>IMO.

I agree.  Best filters I've ever heard, particularly right on the edge of 
self-oscillation.  The same filters are also used in the DW-8000 and I think 
they sound a bit better there....too bad the DW-8000's waveforms have no top 
end.  Interesting that yours would oscillate with no input....

and sorry about the technical errors...never saw the schematics so it's 
really just guessing.

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