[sdiy] OTA performance (was SSM chip reissue)

[Tom Wiltshire]

I've tried those alternative approaches of putting diodes in the feedback path with the 2164 SVF and never had any luck with them at all. Periodically, I think "No, it really *ought* to work…" or wonder "Oh! What if I try X instead?" and go back and give it another try, but so far, it's just lead to frustration.
The zeners across the BP cap isn't perfect by any stretch, but it's simple, reliable, and it works.

Tom

On 26 Apr 2017, at 14:20, Roman Sowa <modular at go2.pl> wrote:

> The idea of using zeners is to limit the signal inside the integrator and keep it away from overdriving it that leads to nasty squeeky noises out of tune. Doing that outside integrator is totally different approach of keeping SVF stable, more like addition of diodes in the feedback of the filter.
> 
> Roman
> 
> W dniu 2017-04-26 o 14:02, Andre Majorel pisze:
>> On 2017-04-26 10:06 +0200, Roman Sowa wrote:
>> 
>>> At low cut off frequency, when integrator currents are really
>>> small, Zeners are damping the oscillation, because most of the
>>> current is eaten up by the zener, not the cap - at that small
>>> current their voltage is way much smaller than, say, at 1mA,
>>> the top of VCF frequency.
>> 
>> Any possibility of putting an op amp between the BP output and
>> the Zener diodes to buffer the signal ?
>> 
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