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

[Tom Wiltshire]

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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>