[sdiy] looking for a quad opamp

[jhaible at debitel.net]

Thanks Mike.

Yes I think this will do. I've ordered a bunch of these; if they
should not work in the 3200, they certainly make good general purpose
amps in other projects. But I think they will be good in the 3200.

I think think I found the problem behind the dramatic overshot
on fast attack times. It's not just the 324 being too slow; it's
also a large time constant (330k * 2.2nF) that makes the comparator
in the ADSR slow. And the 324's slow response does not allow
the 2.2nF to be decreased. (Korg already have decreased this from
3.3nF to 2.2nF in a revision, so I bet they were aware of
this problem!)
If everything goes as I expect, 47pF will work with a TLC274,
making the whole system fast enough.

See http://www.oldcrows.net/~jhaible/polykorg/jh_3200_gates_2of2.gif
if you're interested. Upper left corner, schmitt trigger around LM324.
the "gate-set" capacitor 2.2nF will slow down the "peak-reset" action
considerably. TLC274 allows it to be reduced to 47pF.

JH.

> JH and list,
> Texas Inst TLC274 CMOS quad comes close (or SGS-Thomson TS274)... slew 
> rate 6 V/uS when operated at 10V  - most of specs are better than LM324.
> Regards, Mike
> 
> 




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