[sdiy] Using DG-series analog switches for PWM VCA

[Mattias Rickardsson]

2164 VCAs accept supplies down to at least +/- 4 V, so it shouldn't be a
problem. They do show roughly a doubling in THD compared to the +/- 15 V
supply according to the SSI2164 data I've seen so far, but that shouldn't
really be any problem in a pedal. :-D

The PWM switch solution *might* be a better solution (for several values of
"better") considering you already have access to the digital control for
switches but perhaps not the analog CVs for VCAs, but certainly feels like
a more complex solution when coming from analog. Do it! ;-)

/mr


On Wed, 13 Jun 2018 at 12:25, Roman Sowa <modular at go2.pl> wrote:

> If you'd use 2164 or any other VCA, that's I think still simpler circuit
> that chopping switch with anti-alias and reconstruction filters. No need
> for DC/DC converting negative supply, use 4.5V for GND on VCA and AC
> couple the in/out signal. Control CV will be then between 4.5 and, say
> 7V, so easy to achieve with some biasing.
>
> Roman
>
> W dniu 2018-06-13 o 12:03, Tom Wiltshire pisze:
> > Generally speaking I’d be of exactly the same mind, David, but in this
> case this is a pedal project, so it’s a 9V single supply, which is pretty
> borderline for a 2164. Or pretty much any other obvious VCA chip except the
> LM13700, to be honest. The LM13700 is out because the chances of it *not*
> thumping with a choppy square wave modulation signal like I’m using are
> going to be minimal.  Happy to be proved wrong if anyone knows a way though.
> >
> > I could generate a bipolar supply I suppose, but then that requires
> another chip and makes things more complicated again.
> >
> > Tom
> >
> > ==================
> >         Electric Druid
> > Synth & Stompbox DIY
> > ==================
> >
> >> On 13 Jun 2018, at 04:22, David G Dixon <dixon at mail.ubc.ca> wrote:
> >>
> >> This sounds like a job for (is it a bird, is it a plane) 2164!!!
> >>
> >>> -----Original Message-----
> >>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On
> >>> Behalf Of Tom Wiltshire
> >>> Sent: Tuesday, June 12, 2018 10:33 AM
> >>> To: synth-diy at synth-diy org
> >>> Subject: [sdiy] Using DG-series analog switches for PWM VCA
> >>>
> >>> I've been working on and off on a "stutter pedal" design.
> >>> This is basically a severe volume-chopping tremolo effect.
> >>> I've experimented with using FETs to do the signal muting,
> >>> but wasn't happy with it. So I thought I'd try a PWM VCA,
> >>> since I'm controlling the mute signals from a micro
> >>> controller anyway - unlike the FET mute, I'd actually get
> >>> some control of the volume level.
> >>>
> >>> The chip I decided upon was the DSG413LE:
> >>>
> >>> http://www.farnell.com/datasheets/2311996.pdf
> >>>
> >>> Since the PWM needs to be at a reasonable frequency, I'm
> >>> unlikely to have massive control over the gain (9-bit PWM at
> >>> 62.5KHz would give me -54dB attenuation before 'Off"). But
> >>> since the alternative was a FET that was basically "on" or
> >>> "off" this still represents an improvement!
> >>>
> >>> Has anyone else done anything like this? Do you have any
> >>> experience to share or gotchas that I should avoid? How do
> >>> the DG-series chips compare with the old 4066 circuits that
> >>> I've seen this technique used with?
> >>>
> >>> Thanks,
> >>> Tom
> >>>
> >>>
> >>> _______________________________________________
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> >>> http://synth-diy.org/mailman/listinfo/synth-diy
> >>>
> >>
> >
> >
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