[sdiy] Help with noisy VCA

Jay Schwichtenberg jschwich53 at comcast.net
Fri Sep 1 01:00:56 CEST 2017


You want about 100mv pp of signal on the input pin for 1% distortion. If my calcs are right that would be 4.8 Vpp on the input.


The gain in the output amp seems really high. Vo = I*100000, so to get about 5 Vpp output you need about 25ua into the op amp.


So I'd guess the noise is from the high gain in the output stage. You'd need that if the input is really low level or the Iabc current is low.


Like I said this is an off the top of my head guess.


Jay S.

> 
>     On August 31, 2017 at 2:09 PM Tim Ressel <timr at circuitabbey.com> wrote:
> 
>     Hi,
> 
>     I am still having trouble with this VCA design:
> 
>     https://drive.google.com/open?id=0B2yaoNYlV1nMWFhSRWUwdlU3TzQ
> 
>     It is noisy, and it gets worse as you turn up the gain. I tried
>     switching to a 2164 design but its no longer available in SMT.
> 
>     Any ides?
> 
>     --
>     --Tim Ressel
>     Circuit Abbey
>     timr at circuitabbey.com
> 
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>     Synth-diy mailing list
>     Synth-diy at synth-diy.org
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> 
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