[sdiy] 4-Quadrant VCA?

Tom Wiltshire tom at electricdruid.net
Wed Sep 13 23:38:32 CEST 2017


Sorry, forgot to say: Page 55.


> On 13 Sep 2017, at 22:34, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
> There’s are examples in Ray Marston's Audio IC user’s handbook with both CA3080 and LM13700 - both very similar:
> 
> https://www.scribd.com/document/253630610/Audio-IC-s-Users-Handbook-Marston-pdf
> 
> I have to agree with David D. though - this is better done with the 2164. You’ll get a better result. The feedthrough and distortion on the LM13700 means it’s always a high to get it “good enough”.
> 
> 2 cents,
> Tom
> 
> ==================
>       Electric Druid
> Synth & Stompbox DIY
> ==================
> 
>> On 13 Sep 2017, at 20:54, Olivier Gillet <ol.gillet at gmail.com> 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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> 





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