[sdiy] Increasing resonance sound in 2164 VCO?

[Mike Beauchamp]

On 1/28/20 1:11 AM, Neil Harper wrote:

> I can keep changing that R1 until the resonance sound is very prominent
> and to my taste in relation to the output, but then my filter is only
> outputting half the volume of what goes in. I'm OK with bumping that up
> with an extra op-amp stage afterwards, but wouldn't I just be increasing
> the noise floor as well? Is there another way to get the same effect and
> keep my filter at unity gain?
> 
> 
> -- 
> /// Neil Harper



Hopefully someone with more knowledge of filters and 2164s can give you 
a definitive answer, but maybe self-resonance just happens at a fixed 
level and the ONLY way to change the perceived volume of the resonance 
sound is to raise/lower the input sound.

Looking at the Mutable Instruments Ripples schematic that you mentioned, 
( 
https://mutable-instruments.net/modules/ripples/downloads/ripples_v40.pdf 
) the resistor into the first 2164 cell is huge - 100K (33k expected) 
and then the output from the filter goes into a 3x opamp gain cell. 
Basically doing what you described and bumping up the apparent sound of 
the resonance effect significantly.

Whether or not that 3x gain after the filter contributes added noise, I 
have no idea.. I've never heard this filter yet. But aren't 2164's known 
to be pretty quiet? At least compared to 13700 OTAs?

Mike