[sdiy] THAT 2181C VCA's

[Steve Allen]

Thanks Craig,
 I checked Romans site, and it looks like I'll be
spendin the weekend breadboardin and solderin : )
 YES!!!!
 Oh yea, and Thanks Roman and all those who sent a
reply.
This list ROCKS!!!
--- Craig Critchley <craigc at nwlink.com> wrote:
> You can linearize a VCA response by putting a second
> VCA in feedback loop -
> EDN has a short article on doing this with the
> SSM2164 which also has
> exponential response. Tracking is very good,
> especially if you use two VCAs
> on a single chip, but of course you double the
> number of VCAs you need.
> 
> The article may be found here:
> 
>
http://www.reed-electronics.com/ednmag/index.asp?layout=article&articleid=CA233728&rid=0&rme=0&cfd=1
> 
> For VCFs and VCOs, having an exponential response
> might get rid of needing
> an external expo converter, but you'll still have
> the temperature
> coefficient to deal with (at least, that's what it
> looked like with the
> 2164.) I'm not sure how good the log conformance is,
> I haven't tried myself.
> 
> Roman Sowa's site has VCFs and VCOs built with the
> SSM2164 here:
> 
> http://www.sowa.synth.net
> 
> I would imagine these circuits could be adapted to
> other audio VCAs.
> 
>                 ...Craig
> 
> ----- Original Message ----- 
> From: <WeAreAs1 at aol.com>
> To: <snd_audio at yahoo.com>;
> <synth-diy at dropmix.xs4all.nl>
> Sent: Monday, November 03, 2003 8:41 PM
> Subject: Re: [sdiy] THAT 2181C VCA's
> 
> 
> >
> > In a message dated 11/3/03 8:06:44 PM,
> snd_audio at yahoo.com writes:
> >
> > << Hello,
> >  Wondering if anyone here has worked with the THAT
> > 2181 VCA's. I have 200+ of these and would like to
> use
> > a couple of them for VCF's and VCO's as well as
> VCA's.
> > Any idea's, suggestions...? >>
> >
> > Hi Steve,
> >
> > Isn't the 2181 an exponential-only control
> response?  That makes it very
> easy
> > to use it in audio apps such as compressors and
> volume control, but makes
> it
> > a little complicated for use in filters, VCO's, or
> for attenuating control
> > signals such as envelopes and LFO's.  Yes, it's
> true that we want
> exponential
> > response on our VCF's and VCA's, but we need to
> have a lot of control over
> the
> > design parameters of the exponential amp, and if
> I'm not mistaken, the
> 2181
> > doesn't really give you much access to the expo
> amp section.  If you want
> to use
> > it a VCA for attenuating (DC) control signals,
> it's almost always better
> to
> > have a linear response VCA for that purpose. 
> There might be some way to
> > "linearize" the control input on those chips (by
> building some kind of
> external
> > anti-log amp), but that also seems like a lot of
> trouble, and I'm not sure
> you could
> > ever really get the linearity to exactly track.
> >
> > Maybe you could build a nice analog mixer fader
> automation system with all
> > those chips!
> >
> > Michael Bacich
> 



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