[sdiy] CMOS Switch as VCA?

[nicolas]

You might be able to get something vaguely usable by using the cmos switches in pairs, put one switch in the negative feedback loop of an opamp servo type circuit and use that to inform the CV input to the other switch which actually does the VCA thing.  Might work if the two switches are within the one chip and are reasonably well matched.  To make sure you get the most unbuffered and simplest cmos switch you might want to use the 4007 which can be configured as such.  Good luck.  Worth a go :)

Cheers,
Nicolas


--- On Tue, 9/2/10, Scott Nordlund <gsn10 at hotmail.com> wrote:

> From: Scott Nordlund <gsn10 at hotmail.com>
> Subject: RE: [sdiy] CMOS Switch as VCA?
> To: 
> Cc: synth-diy at dropmix.xs4all.nl
> Received: Tuesday, 9 February, 2010, 11:15 AM
> 
> The 4016 isn't buffered though, that's primarily the one I
> was thinking about.  The only thing I had in my mind about
> the 4066 was its lower on resistance, but yeah, it is
> buffered so never mind.  The 4016 does have an inverter to
> drive the P-MOSFET so I would expect some nonlinearity due
> to that.  I'm not hoping for anything approaching hi-fi,
> but I think the idea would be useful in some way even if it
> only barely works.
> 
> ----------------------------------------
> > Date: Mon, 8 Feb 2010 13:53:11 -0800
> > From: dlmanley at sonic.net
> > CC: synth-diy at dropmix.xs4all.nl
> > Subject: Re: [sdiy] CMOS Switch as VCA?
> >
> >
> >>>> Forgive the dumbness of the question, but
> has anyone tried using a standard CMOS switch (4016/4066) as
> a "sort of" VCA? I mean with an actual linear CV input, not
> using PWM. I haven't tried it and I've never seen any
> reference to it, but I can picture it almost working, though
> probably not in an optimal kind of way. At least it wouldn't
> have the CV feedthrough problems of a single transistor
> VCA....
> >>>>
> >>>> Any ideas?
> >>>>
> >>>>
> > Per the datasheet the 4066 control inputs are buffered
> through 3
> > inverters. You won't get any kind of linear response
> using this part.
> > Most of the "oddball" CD4xxx circuits that use
> "digital" parts for
> > analog purposes use the "UB", or "unbuffered" parts
> which allows them to
> > be used, pretty much, as a bunch of transistors in one
> package. Google
> > "cd4069 linear" for some relevant info.
> >
> > -Dave
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