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

Guy McCusker guy.mccusker at gmail.com
Wed Dec 12 16:07:15 CET 2018


On Wed, Dec 12, 2018 at 2:52 PM <rburnett at richieburnett.co.uk> wrote:
>
> I haven't done the calculations, but I'm left wondering whether or not
> you can do this "multi-input crossfade scanner" thing well enough using
> just fast PWM of the analogue switches themselves, and ditch the VCA's
> altogether.

Interesting idea. But how would we overcome the clicking issue?

Grant Richter's Electro-Optical Mixer used an LM3914 with a
"dithering" i.e. PWM controller to create crossfades using vactrols.
https://web.archive.org/web/20110720183735/http://www.musicsynthesizer.com/Corpse/VCEOM.html
Somehow the PWM idea feels similar to that. Richter's circuit takes
advantage of the slow response of the vactrols to smooth out the
response. Presumably your idea would involve some explicit integration
for the same purpose? Could that also reduce the clicking, without
low-pass-filtering the audio too much?



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