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

[Mike Bryant]

There are plenty of USB opto-isolators on the market which isolate the data and ground line just fine.  However some of the cheaper ones seem to rely on both ends sourcing +5V through the USB connectors  which is a bit of a nonsense of course and can confuse some items that expect to receive +5V.  For these you'll also need a powered hub.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Mike Beauchamp <list at mikebeauchamp.com>
Sent: 01 February 2024 22:06
To: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: [sdiy] How to design out "usb noise"?

I recently stumbled across this post on reddit of someone showing usb
connection causing some serious noise:
https://www.reddit.com/r/synthesizers/comments/1aghqsa/how_to_get_rid_of_usb_noise/

Some comments suggest to use DIN MIDI instead of USB MIDI as a solution,
but it got me wondering if there's a best practice for implementing MIDI
OVER USB output that wouldn't cause this. MIDI spec includes schematics
for hardware implementation of DIN MIDI connections as we know,
including the use of opto-isolator, but I can't find the equivalent for
the USB connection.

A typical USB-B connector has the following pins:

1. VBUS
2. D-
3. D+
4. GND
5. SHIELD

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.

Mike





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