[sdiy] vactrol compressor schematics?

[mike ruberto]

Well, I have spent a few hours studying various compressor designs -
some good, some bad. I see that in the better designs more serious
effort is put into the sidechain circuits. RMS converters and
precision rectifiers of varying complexity and trickyness in most of
the better circuits. However, these are mostly designed for devices
using a VCA or FET as the gain varying element.
Even the "What" circuit has a significant amount of circuitry to
process the CV. It seems to me that all of this is rather useless and
unnecessary when using a vactrol for the gain element. Due to the
sluggish response of the CDS cell in the vactrol any pre-processing of
the CV is going to be compounded and deformed by the response curve of
the CDS cell. This seems to defeat the purpose of using elaborate RMS
converters and such.

So my question is, why not use another Vactrol in the sidechain
circuit? Get rid of the precision rectifiers and let the slow CDS
response curve act as the "rectification". By biasing the the LED
drive to a certain range it might be possible to get an RMS voltage
and rectification at the same time.

Anybody have any thoughts on this? See any glaring problems with the idea?

M. A. Ruberto


On 10/25/07, mike ruberto <somnium7 at gmail.com> wrote:
> This is great! Thank you Dave!
>
> On 10/24/07, Dave Manley <dlmanley at sonic.net> wrote:
> > mike ruberto wrote:
> > > I have a few extra VTL5C3/2 vactrols and thought it would be an
> > > interesting project to build an opto-compressor with them. Anybody
> > > know of any schematic I might use for a starting point?
> > >
> >
> > There is the "What Compressor":
> >
> > http://dt.prohosting.com/hacks/what.html
> >
> > There are two different circuits on that page, the "Joe Cheep
> > Compressor" and the "What" near the bottom.
> >
> > -dave
> >
> >
>