[sdiy] Blackmer VCA cell

[Mike Bryant]

A standard comparator based PWM circuit fed from one voltage drives a MOSFET switch fed with the other voltage and that feeds the averaging filter.   Just one FET more than a normal PWM.

I'm not sure what the original person's application was, just pointing out that it isn't hard to do what he seemed to be after.


-----Original Message-----
From: Brian Willoughby [mailto:brianw at audiobanshee.com] 
Sent: 23 October 2021 23:41
To: Mike Bryant
Cc: *SYNTH DIY
Subject: Re: [sdiy] Blackmer VCA cell

Did someone link to a PWM circuit that multiplies two voltages? That sounds like an expensive circuit.

It seems that I'm not following what you're suggesting. Are you talking about an EG that tied to a specific VCA? ... or a generic EG that can be patched anywhere, such that the VCA could be controlled by multiple CV sources at once?

B.

On Oct 23, 2021, at 15:34, Mike Bryant wrote:
> Because as someone pointed out it's hard to voltage control the parameters correctly into an exponential VCA.  PWM solves that as it multiplies one voltage by another.  And it's a single PWM, not several.  
> 
> Of course it can be a single multiplying DAC as well so no need for any sample and holds involved.