[sdiy] AS3320 VCF chip - some queries

Tom Wiltshire tom at electricdruid.net
Sun Nov 11 17:55:20 CET 2018



> On 11 Nov 2018, at 16:29, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
> Hi All,
> 
> More Alfa chips! I’ve been playing with the AS3320 CEM3320 VCF clone.
> 
> I haven’t done any serious measurements like Ian F, but I’ve noticed a couple of things that I’d never noticed before, and I’d like to check this against other people’s experiences with the chip.
> 
> 1) The pass band gain drops as the resonance increases.
> I’d never really thought about this before, but the same thing happens on my Pro-One.
> Has anyone tried compensating this by feeding some of the input signal into the Resonance VCA as well?
> 
> 2) The resonance response is tilted to the high end.
> It seems to require a lot more resonance CV (ok, current) to make the chip oscillate at the bass end than at the treble end. Similarly, the amplitude of oscillation increases as the frequency rises. Why is this? Is there anything I can do about it? Should I even care?

…and also

3) The Frequency CV response works in reverse, higher voltage = lower cutoff.
This is obviously convenient for CV mixing, but I don’t see it mentioned explicitly anywhere.

Tom

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Synth & Stompbox DIY
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