optocouplers for VCAs?

[mark verbos]

Also, we must not forget the fact that optoisolators are not as quick in
their response. OTAs are better at allowing crazy amplitude modulation,
like from other audio signals.

Mark

David Halliday (Volt Computer) wrote:
> 
> My main thought would be that optoisolators don't track each other very
> well - they would be fine for VCA applications but not for multi-stage
> filters.
> 
> Linearity is another issue - again, amplitude is not as critical as
> frequency.
> 
> Another problem that I have heard of is that the resistance of the cell
> changes as a function of the voltage applied to it.  This is otherwise
> known as distortion and is generally a no-no unless we add it ourselves.
> 
> > -----Original Message-----
> > From: Steven Curtin [SMTP:sdcurtin at lucent.com]
> > Sent: Wednesday, August 20, 1997 2:37 PM
> > To:   synth-diy at horus.sara.nl
> > Subject:      optocouplers for VCAs?
> >
> > Hi-
> > I'd like to have lots of VCAs in a system and was thinking of just
> > using a
> > bunch of optocouplers- they provide variable resistance in response to
> > an
> > input voltage, etc.  Is there some reason why the use of an OTA is
> > preferable?   I know mainly digital circuitry and tend to cookbook the
> > analog stuff.
> >
> > Steve C
> >
> > --------------------------------------------------------------
> > Steven Curtin
> > http://www.emf.org/people_curtin.html
> > Lucent Technologies - Bell Labs Innovations
> > rm. 3C-208, 200 Laurel Ave S
> > Middletown, NJ 07748-4801  U S A
> > ph: (908)957-2996   fax: (908)957-6878
> > --------------------------------------------------------------