[sdiy] 4-Quadrant VCA?

[Tim Ressel]

Ah, so that is what they are doing in the LM13700 datasheet when they 
have a single 13700 doing a 4-Q multiplier!

--Timbo


On 9/13/2017 12:54 PM, Olivier Gillet wrote:
>> I know I could use AD633s but they are really pricey. Any other clever ways
>> of pulling this off?
> Add enough DC offset to one of the signals to make it unipolar.
> Subtract the other signal from the result. Choose wisely which branch
> of your circuit is labelled as the "control" path and which one is the
> "audio" path.
>
> https://forum.mutable-instruments.net/t/blinds-how-does-it-work/8287
> https://mutable-instruments.net/modules/blinds/downloads/Blinds-v60.pdf
>
> Pros: no distortion, no odd behaviour at zero-crossings, doesn't cost
> more than a normal VCA circuit.
> Cons: need a couple of precision resistors, non-ideal behaviour at
> high frequencies.
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com