Input ground loop hum only when p10 cables or XLR without phantom power are connected

Yep, switching USB cables alone will not help you. There is a known problem with laptop power supplies and ground loops.  I can't answer your questions because I'm pretty confused and don't know all the details. However, the easiest, and least likely to interfere with your sound quality is isolate the USB line. If disconnecting the USB makes your problem vanish, that's what you need to isolate. It's not just a problem for audio. The device I list is actually for medical products, which suffer the same way.

Stereophile does all their USB DAC testing with a laptop  running from battery power. I think it's a boneheaded way to test DAC's, but that's their standard exactly because of this issue.


Best,


Erik

In fact, most of the time, ground loops are independent of cables (unless wired wrong).

A ground loop can't be fixed by noise filters or switching cables, or better shielding. You have to break the metallic contact in the loop.

Best,

Erik

Thanks, Erik, I'll try the isolator then...I can't really disconnect the USB because the Scarlett 2i4 has no external power source, it's powered solely through USB, so I need it connected in order to hear anything. The hum goes away when I disconnect my notebook power cord, using the battery...But anyhow, I had not heard about these USB galvanic isolators, I'll give them a try.

Good luck, and let me know how it works for you.

Best,


Erik

Hey pedro!

You may need to get the extra power supply for it if your laptop does not provide a high-current port. Just FYI.

Best,


Erik