[sdiy] OTA performance (was SSM chip reissue)

[Mattias Rickardsson]

On 25 April 2017 at 13:15, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> You raise an interesting possibility though - it could be that variations in gain matching at large attenuations are one reason why it's harder to make 2164-based SVFs resonate at the low end than at the high end. Previously when this has been discussed, phase lag has been proposed as the likely culprit. But if the gains match well at 0dB, pretty well at -20dB, and not so well by the time you're down at -80dB, then you'd expect resonance to drop off at lower frequencies.
>
> Incidentally, Oberheim managed to make an SVF with CA3080s in the OB-X, and they're not matched at all (unless they matched them?). The filter is quite highly thought of. Ultimately, it's not always about technical perfection.

Interesting. I've had some filters sometimes lacking resonance in the
low end, and the increaswingly unmatched 2164s could be a reason. But
wouldn't the capacitors need to be matched just as good? AFAIK only
the RC constant determine the pole frequencies, so if one of the caps
are 5 % off, then the filter could perform worse if the gain cells are
perfectly matched - compared to having them 5 % off in the other
direction.

How well do you specify the tolerance of your SVF capacitors? :-)

/mr