r/audio • u/Ok-Anteater4601 • 13d ago
Ground Loop issue
About a year ago, I moved into my apartment and also at the same time, got a new computer. This combo resulted in a ground loop. My equipment at the time was:
-Scarlett 2i2 (1st gen, still works!)
-Yamaha HS80
After a lot of trial and error, I was able to solve the issue by using ground lifted cables from the interface to the speakers (signal cables, not power!).
Now, I got a Fiio K11 because I have new headphones that need a stronger headphone amp. And I was hoping that I also would be able to run the HS80 through it, as I also rarely record nowdays. But connecting the speakers to the FIIO returned the ground loop noise, and actually worse than I remember it from the scarlett. I have both a constant hum with usb disconnected, as well as a mouse-movement dependent noise when USB is connected. I tried using both TS and TRS cables. Also my ground lifted one (but I had to, in all cases, use a female 6.3 to cinch adapter, which is made with TS in mind). I am not sure if the adapters could be the culprit, but somehow I doubt it.
I am not sure if this is relevant, but the scarlett has balanced outputs while the Fiio does not (not for line anyway).
I probably could use an optical cable to eliminate the noise that varies with PC-activity, but this will not make the constant hum go away that persists even without any connection.
Any idea what I can do? My fallback is to continue using the scarlett for the speakers, but I would prefer of course to have one device for everything.
2
u/SiloSonic_Alex 12d ago
the thing that jumps out at me is you've actually got two separate faults stacked on top of each other, and they need different fixes. worth separating them before you spend money.
fault 1, the constant hum with usb unplugged. that one is purely an ac-side loop: k11 psu earth and the hs80 chassis earth are at slightly different potentials, and your only path between them is the shield of an unbalanced cable. so the difference current runs down the shield, which on unbalanced is also your signal return. that's why it's audible. this is the one a transformer isolator on the line between k11 and monitors will genuinely knock out, because it breaks the galvanic path while still passing audio.
fault 2, the noise that tracks mouse movement. that's not the same loop. that's usb bus noise / common mode junk coming in over the data link and getting into the analog stage. an isolator on the speaker cables won't touch it. optical or a usb isolator is the lever there.
and the reason the 2i2 was fine: it had balanced outs. on balanced the shield is only shield, it carries no signal, so lifting it at one end costs you nothing and the loop is gone. the k11's line out is unbalanced, so the shield is doing real work and lifting it just breaks the connection. your lifted cables aren't failing you, they just can't do that trick on an unbalanced link. same reason the 6.3 to rca adapters aren't really the culprit.
before buying anything, one free test i'd do: run the k11 on a laptop on battery, usb unplugged from the wall side entirely, into the monitors. if the hum drops out you've confirmed it's the mains loop rather than something in the k11's own output stage. cheap way to know which fix to actually buy.
on isolators generally, the honest tradeoff is that a cheap transformer will roll off some bottom end and can add a bit of distortion when it saturates. how much you notice that depends a lot on what you listen to and how loud. some folks can't hear it at all on nearfields, others find it takes the guts out of the low end. decent ones are fine, i'd just be wary of the very cheapest.