[sdiy] 1496 VCA?

[Ian Fritz]

At 02:15 PM 6/13/2008, Dave Manley wrote:

>I think here, "null out" means to set 0 gain for 0 CV.

Right. But with a 4Q multiplier you trim out x feedthrough with y at zero 
*and* vice versa.


>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.

Right again (of course). But at this point I think you are better off using 
a 13700-based VCA.

For the best of both worlds, look at my switchable 2Q/4Q multiplier 
circuit.  (EN #113).

Ian