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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.<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Mike Beauchamp <list@mikebeauchamp.com><br>
<b>Sent:</b> 01 February 2024 22:06<br>
<b>To:</b> synth-diy@synth-diy.org <synth-diy@synth-diy.org><br>
<b>Subject:</b> [sdiy] How to design out "usb noise"?</font>
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<div class="PlainText">I recently stumbled across this post on reddit of someone showing usb
<br>
connection causing some serious noise: <br>
<a href="https://www.reddit.com/r/synthesizers/comments/1aghqsa/how_to_get_rid_of_usb_noise/">https://www.reddit.com/r/synthesizers/comments/1aghqsa/how_to_get_rid_of_usb_noise/</a><br>
<br>
Some comments suggest to use DIN MIDI instead of USB MIDI as a solution, <br>
but it got me wondering if there's a best practice for implementing MIDI <br>
OVER USB output that wouldn't cause this. MIDI spec includes schematics <br>
for hardware implementation of DIN MIDI connections as we know, <br>
including the use of opto-isolator, but I can't find the equivalent for <br>
the USB connection.<br>
<br>
A typical USB-B connector has the following pins:<br>
<br>
1. VBUS<br>
2. D-<br>
3. D+<br>
4. GND<br>
5. SHIELD<br>
<br>
How do you think these connections should be handled inside the synth, <br>
assuming a hostile environment where connections are also being made <br>
to/from a PC with audio cables, MIDI cables, power adapters to different <br>
outlets/circuits, etc.<br>
<br>
Mike<br>
<br>
<br>
<br>
<br>
<br>
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