[sdiy] How to design out "usb noise"?

[mskala at northcoastsynthesis.com]

On Thu, 1 Feb 2024, Mike Beauchamp wrote:

> How do you think these connections should be handled inside the synth,
> assuming a hostile environment where connections are also being made to/from a
> PC with audio cables, MIDI cables, power adapters to different
> outlets/circuits, etc.

I think the real, fundamental problem is the ground.  As long as your
synth format uses the same 0V for power return and signal reference,
you're fighting a losing battle if that 0V also has to be connected to
USB's 0V.

So if you really want to be serious about it, I guess you have to not have
that connection:  put the USB "device" side on USB's +5V/0V power, and
then optoisolate it from the synth's power system with no connections
between the two.  It might make a lot of sense to translate USB-MIDI into
the signal that would go over DIN-MIDI, send that through the
optoisolator, and then everything on the other side is the same as a
DIN-MIDI interface; however, that's not the only way that it could be
done.

As Gerry said, in the message that came through as I was writing this.
:-)

I don't know of anyone really doing that and I'm not sure it would be
commercially viable.  A weaker thing to do would be to just keep the USB
"device" side powered by USB power and have the 0V connection be the only
connection shared between the two, at which point you can try to blame any
remaining problems on the Eurorack power supply's grounding.

-- 
Matthew Skala
North Coast Synthesis Ltd.