[sdiy] AS3320 VCF chip - some queries

Florian Anwander fanwander at mnet-online.de
Tue Nov 13 12:01:22 CET 2018

Am 11.11.2018 um 17:29 schrieb Tom Wiltshire:
> 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?
Doepfer mentions this behaviour also in the manual for his A-121:

http://www.doepfer.de/a100_man/A121_man.pdf page 4

"The A-121’s resonance is not frequency dependent to any significant 
degree. As long as resonance is kept below the self-oscillation level, 
any variation is imperceptible. The one exception to this is at high 
levels of resonance, coupled with a high cut-off frequency setting, when 
an increase in resonance can lead to a small drop in the sine-wave 
output’s frequency. This is a characteristic of the CEM 3320 filter IC, 
and is not due to a design fault in the A-121’s control system"



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