[sdiy] Blackmer VCA cell

[mskala at northcoastsynthesis.com]

On Mon, 25 Oct 2021, Gordonjcp wrote:
> On Sat, Oct 23, 2021 at 06:18:37PM -0400, Matthew Skala via Synth-diy wrote:
> > A capacitor charging from a voltage source through a resistor will change
> > its voltage fast at first, when there's a large drop across the resistor
> > and therefore a large current, and then slower as it approaches the target

> It's a little more complicated than that because in a "real" envelope
> you have the timing cap charged off the full positive rail (either 12V
> or 15V) but the comparator that flips to the decay phase set for 10V.

What I wrote is true - it's faster at the start and slower toward the end.
The fact that the voltage source used for charging is beyond the target
voltage does make the difference between the start and end smaller; it's
less concave down, and closer to linear, than it would be with a voltage
source nearer the target voltage.  With the voltage source exactly at the
target voltage, it theoretically never completes at all.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before tribes.
https://ansuz.sooke.bc.ca/