[sdiy] 1496 VCA?

[Ken Stone]

the ETI (international) VCAs doubled as ring modulators by switching in or
out an extra circuit to deal with the 2 quadrant/4 quadrant issue.
As ian said, they don't null very well. You can't shut the damn things up.
There is a notable amount of signal bleed through. I have several of them in
my system and I have used none of them in years.

Ken

>John Mahoney wrote:
>> Ian Fritz wrote:
>>> The 1495/6 approach was almost instantly dropped when OTAs became 
>>> available.  They require quite a few external parts, they have to be 
>>> carefully trimmed, and unless you hand pick selected units they typically 
>>> don't null out very well.
>> 
>> To "not null out" means to allow CV feedthrough, is that right? 
>
>I think here, "null out" means to set 0 gain for 0 CV.
>
>Also there is the issue that a balanced modulator is a 4-quadrant 
>multiplier, while a VCA is a 2-quadrant multiplier.  This means if the 
>CV is negative, the 4-quadrant multiplier inverts the input signal, and 
>so requires an additional circuit to prevent output when the CV is 
>negative (IC1+diode form a rectifier clamping negative CV to 0).  VCAs 
>don't have this problem.
>
>-Dave
>
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Ken Stone   sasami at hotkey.net.au
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