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

[cheater cheater]

How do they prevent aliasing there?

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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