optocouplers for VCAs?

[David Halliday (Volt Computer)]

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
> 
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> Steven Curtin  
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