[sdiy] SSM2164 VCAs

[David G. Dixon]

Scott,

That's awesome!  I will have to study your circuit more closely.  I'm pretty
much sold at this point on the simple switched log/linear Bareille version
of the Gallo/Irwin circuit, and I'm thinking of just a dual VCA on a 1U
panel, and then just cranking a few of these out as needed.  Alternatively,
I might do a 2U panel and put some mixing capability in there (again, a la
Bareille, albeit a bit less complicated).  This would achieve what your
TLN-132 can do; namely, the blending of both log and linear VCA responses
for the same input signal.  I've got lots to think about, and it's making me
very sleepy...

Cheers,
Dave


> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of Scott Juskiw
> Sent: Monday, June 08, 2009 10:07 PM
> To: sdiy DIY
> Subject: Re: [sdiy] SSM2164 VCAs
> 
> With regards to the lin/log argument for VCAs, I don't think it's a
> good idea to assume that straight line envelopes should always feed
> log VCAs. I believe you should do what "sounds" best. Particularly
> with log VCAs, there are instances where 10db/volt works well, and
> other instances where 20 db/volt works well, or something in between.
> I built some VCAs that support both linear and log inputs at the same
> time which I find quite handy when I want to get really picky about
> envelope shape. Scroll down to the bottom of this page and listen to
> the two panning examples. One is 100% linear input, the other is 100%
> log input (with 16db/volt response IIRC).
> 
> http://www.tellun.com/motm/diy/tln132/TLN-132.html
> 
> In both cases a triangle wave (very linear 0-5 volts) is used to
> modulate the VCA amplitude. The results are quite different for the
> linear and log cases. If I was using this in a recording I'd probably
> use a mixture of 80% linear with 20% log.
> 
> On 8-Jun-09, at 10:25 PM, David G. Dixon wrote:
> 
> > Thanks Dave, Aaron and Tim for their excellent advice and links.  It
> > would
> > appear that the Irwin-Gallo-Lamm-Bareille axis is all I need to go
> > forth and
> > amplify!  It's interesting that the Irwin method of linearizing the
> > 2164
> > appears to be very similar to the Sims method for linearizing the
> > 13700....
> >
> > To answer Tim's concern, I was going to put in switches to have the
> > option
> > of linear or log response, for the very reasons you alluded to (analog
> > envelopes should feed linear VCAs, and triangles (such as my lovely
> > triple
> > LFO) should feed log VCAs).
> >
> > Now I've got to go and study (and possibly simulate) both Sims' and
> > Irwin's
> > schemes to convince myself that I really understand what the heck is
> > going
> > on there, and to determine whether it's strictly necessary for VCA
> > applications and therefore justifies doubling the IC requirements.
> >
> > Cheers,
> > Dave
> 
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