[sdiy] PWM VCA was: CMOS Switch as VCA?

[Magnus Danielson]

cheater cheater wrote:
> How do they prevent aliasing there?

Synthesis filters after the VCA as I recall it.

Check the schematics yourself. I have them online.

Cheers,
Magnus

> D.
> 
> On Sun, Feb 14, 2010 at 23:30, Magnus Danielson
> <magnus at rubidium.dyndns.org> wrote:
>> Scott Nordlund wrote:
>>> 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?
>> The Sennheiser VSM-201 vocoder uses CMOS switches as VCAs through PWM.
>>
>>> I've also seen a completely bizarre 4049/4069 hex-VCA that uses the power
>>> pins as the output, but this has the obvious disadvantage that all the
>>> signals are mixed together.
>> The 4069UB is cheap. Use several if it bothers you. Those VCAs uses the fact
>> that a FET transistor can be made into a linearised voltage-controlled
>> resistor.
>>
>> The internal logic of 4016 or 4066 does not allow similar tricks. You are
>> essentially bust on that quest. I will look again, but I am pretty sure.
>>
>> Cheers,
>> Magnus
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