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

[Roman Sowa]

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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>>> Synth-diy at synth-diy.org
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>>>
>>
> 
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