[sdiy] 13700 VCA Noise Issue

[Tom Wiltshire]

Hi Tim,

There's an excellent paper on this on Open Music Labs:

	http://www.openmusiclabs.com/files/otadist.pdf

It deals with distortion mostly, but noise is discussed. Definitely worth a read.

My take-home from it was that an op-amp I-to-V does a better job than a resistor to ground. Another reason to dump those buffers…

HTH,
Tom


On 17 May 2017, at 21:12, Tim Ressel <timr at circuitabbey.com> wrote:

> 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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