[sdiy] Help, I'm Desperate! (Charge Injection with DG408)

[Michael E Caloroso]

On 12/14/18, Rutger Vlek <rutgervlek at gmail.com> wrote:

> Ha, I totally agree! I once explored an approach to ring-modulation using a
> single VCA and an inverting switch. It seemed like a nice, cost-effective,
> approach (especially since I wanted to use a discrete VCA that would be too
> bulky for another approach). After two prototypes of this circuit, I simply
> gave up. In the analog domain it was simply too difficult to trigger the
> switch exactly at the point where the VCA was fully closed, due to circuit
> accuracy and noise. It was a hard lesson in the reality of analog
> electronics. I went down the route of simply duplicating the discrete
> circuit for the negative quadrants, and it works extremely well albeit not
> super-linear, but that was a deliberate choice.

Don Buchla stated in 1982 that he had tried to design a multiplier
that could function as both VCA and ring modulator, and he couldn't
come up with a suitable design that balanced low distortion, ample CV
rejection, and linear/nonlinear operation in both modes.  Mixing the
control and audio realms in the audio domain can force some
compromises.  And this is a designer who sought multiple functions out
of a single module.  Yes PAiA had a 47xx module that did both, but not
that well either.

MC