[sdiy] lots of VCAs on one PCB

[Kyle Stephens]

Optocoupler, Vactrol/roll-your-own, etc. in the feedback loop of an op amp to linearize the response? Your specs are pretty much limited to those the op amp then.

If there's a quad channel opto out there that'd be of interest. I know a single channel type was discussed in the past in regards to the possible ban on Vactrols in Europe and elsewhere due to RoHS...though I never did find out what the verdict was on that... Just throwing more ideas out there at this point.


Seems as it stands, the 4049 design (why not a 4069 btw - they're newer, and cheaper, and iirc, are more linear when (ab)used in this fashion), or some SMT option seems best don't it? I'd try my hand at a layout myself but my own Eagle skills, well, are more befitting a chicken.

Joergen does mention that the SSM2024 was just what he had at the moment - there's the SSM2018, which *is* linear, though is but one VCA per 16 pin IC - said IC has some useful, otherwise external elements built in though.

http://www.analog.com/static/imported-files/data_sheets/SSM2018T.pdf

Hope you find some solution :]


_Kyle

--- On Tue, 11/24/09, Oscar Salas <osaiber at yahoo.es> wrote:

> From: Oscar Salas <osaiber at yahoo.es>
> Subject: Re: [sdiy] lots of VCAs on one PCB
> To: synth-diy at dropmix.xs4all.nl
> Date: Tuesday, November 24, 2009, 2:37 AM
> 
> 
> --- On Tue, 11/24/09, Derek Holzer <derek at umatic.nl>
> wrote:
> 
> > From: Derek Holzer <derek at umatic.nl>
> > Subject: Re: [sdiy] lots of VCAs on one PCB
> > To: synth-diy at dropmix.xs4all.nl
> > Date: Tuesday, November 24, 2009, 11:52 AM
> > Thanks to everybody who replied so
> > far! I'll try to run down the possibilities so far in
> this
> > email:
> > 
> > 1) Oscar Salas: "Tessera" quad VCA
> > 
> > I initially looked at Marc Bareille's Quad VCA, and I
> would
> > have to pass on this VCA setup for the same reason. It
> needs
> > too many PCBs. I use a fairly shallow case and mount
> all my
> > boards parallel with the faceplate. There would not be
> room
> > for four (or eight!) PCBs stacked up, especially
> considering
> > the space needed for the joysticks, jacks and pots
> behind
> > the board as well.
> > 
> > 2) Kyle Stephens / Gergo Palatinszky / Andreas
> Wetterberg
> > 
> > Four seems to be a common number when dealing with
> groups
> > of joysticks (see Tessera, Bareille's Quad etc etc.
> The THAT
> > 2181 looks interesting, however I specifically
> mentioned
> > using it for control voltage and this one is
> exponential.
> > 
> > 3) Mark Verbos
> > 
> > 4049 hex VCA looks great from the angle of low parts
> count
> > and cheap. Heck, with SMD it would be almost
> > microscopic!!!!! I just wonder how it sounds? I
> wouldn't be
> > using it for audio rate modulation, however some of
> the
> > gestural stuff with the joystick could get pretty
> fast.
> > Anyone know how well this VCA design sounds?
> > 
> > 4) Tim Parkhurst / John Mahoney
> > 
> > The SSM2164 was indeed the first chip I looked at, and
> yes
> > it is exponential. My other joystick based project is
> in
> > fact a quad spatializer, and nothing could be easier
> than to
> > use 8 2164 ICs and be done with it. The fact that they
> must
> > be doubled to get a linear response adds quite a bit
> of
> > board real estate to the problem, and is basically the
> same
> > as the Tessera that Oscar mentioned, and the same as
> > Bareille's Quad VCA. If I could find a board layout
> small
> > enough (my Eagle/Kicad skills are very poor) then I
> would
> > certainly consider such an option. Ideally, I'd love
> it if
> > someone with better PCB laypout skills than me wanted
> to
> > take either the Tessera or the Quad VCA and SMD-ize
> them
> > ;-)
> > 
> > 5) Jason Proctor
> > 
> > I'm trying to avoid any digitization of the signal for
> the
> > moment. Programming too. I got into analog synths to
> get
> > away from digital music (Pure Data programming
> mostly).
> > However I'll keep it in mind.
> > 
> > 6) Kyle Stephens
> > 
> > The SSM2024 also looks interesting, however the first
> thing
> > that the Bergfotron page you directed me to says is
> that the
> > performance is quite poor. Too bad, a single IC with
> four
> > linear VCAs would be a good solution!
> > 
> > 7) Nathan Trites
> > 
> > Two boards of 8 would be just fine with me. I figure
> that I
> > have room for two PCBs "under the hood", but not four.
> If
> > you were interested to help with this project, let's
> talk!!
> > 
> > Best!
> > Derek
> > 
> > --::: derek holzer ::: http://blog.myspace.com/macumbista ::: http://www.vimeo.com/macumbista :::
> > ---Oblique Strategy # 140:
> > "Reverse"
> > 
> > 
> > 
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> > 
> 
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