[sdiy] Voltage vs current, was Low voltage synthesis?

Paul Perry pfperry at melbpc.org.au
Tue Jan 18 21:47:20 CET 2022


"Common impedance coupling"
Yeah, and it's a lot more "common" than I would like!
A ring modulator board I made had persistent feedthrough - culprit  was a
little bit of common impedance (that is, PCB ground) with the power supply
rectifier and this resulted in the local oscillator mixing with 50Hz and
generating two sidebands that sounded like leakage from the oscillator
(down in the noise, so you couldn't see it on a scope, but you could hear
enough to be infuriating.)
Could have sorted it with that probe, I expect. Lucky nobody offered me one
for $1,200 that day...

paul perry melbourne australia


On Wed, Jan 19, 2022 at 1:41 AM Neil Johnson via Synth-diy <
synth-diy at synth-diy.org> wrote:

> > Could even apply to DC scenarios. Imagine the CV input line to your VCO
> is shared with a line that carries a few amperes of DC current (or, more
> likely, the ground reference for the CV input).
>
> "Common impedance coupling".
>
> Neil
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