[sdiy] 13700 VCA Noise Issue

[David G Dixon]

Did you remember to use a fairly large voltage divider on the inputs?  The
input signal to an OTA should only be a few tens of millivolts (unless you
use the linearizing diodes, which I never did).  I think those dividers
generate a fair bit of noise.

I stopped using OTAs years ago, once I discovered the beauties of the 2164
VCA, so you know my advice....

 

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
> Behalf Of Tim Ressel
> Sent: Wednesday, May 17, 2017 1:13 PM
> To: *SYNTH DIY
> Subject: [sdiy] 13700 VCA Noise Issue
> 
> Hi,
> 
> So I did a design with a pair of 13700 VCAs in series and I 
> am getting a lot of white noise on the output. With the first 
> VCA closed and the second wide open I get 100-200mV of noise. 
> I made a png; where do we share these again?
> 
> Does anyone have experience with 13700 and noise?
> 
> Here's a wonk question: if I use an opamp as a transimpedance 
> amp (oh Ghod I hope I'm using the right term) on the output 
> of the 13700 to convert current to voltage, how do I 
> determine the amp's input current noise contribution to the 
> output noise? Assuming it does contribute. Or would it be 
> better to do a resistor to ground and have the amp be a non 
> inverting buffer?
> 
> Thanks!
> 
> 
> --
> --Tim Ressel
> Circuit Abbey
> timr at circuitabbey.com
> 
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