[sdiy] THAT 2181C VCA's

[Peter Cornell]

Hi list

THAT have some great app notes. Chack them out here :

www.thatcorp.com

Peter

----- Original Message -----
From: "Steve Allen" <snd_audio at yahoo.com>
To: "Craig Critchley" <craigc at nwlink.com>; <WeAreAs1 at aol.com>;
<synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, November 04, 2003 8:26 AM
Subject: Re: [sdiy] THAT 2181C VCA's


> 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=CA
233728&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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