[sdiy] OTA performance (was SSM chip reissue)

[David G Dixon]

Same. 

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
> Behalf Of Tom Wiltshire
> Sent: Wednesday, April 26, 2017 6:42 AM
> To: Roman Sowa
> Cc: Andre Majorel; synth-diy at synth-diy.org
> Subject: Re: [sdiy] OTA performance (was SSM chip reissue)
> 
> 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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