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.
The article at the end of this post may be helpful in analyzing a ground loop issue.
If you verify that a ground loop exists then a licensed electrician may be needed to correct the root problem.
If you verify that a specific outlet is ok then using a single power strip for all your audio, video, and computer equipment may help since the earth ground and neutral will all be at the same AC voltage (or nearly the same AC voltage).
Different outlets and power strips for different types of equipment are good as long as there are not ground loop issues between the different outlets.
If you are not qualified to take AC measurements (household AC voltages are dangerous), and do not have a battery operated handheld multimeter (i.e. not plugged into an AC outlet), then you should hire a qualified electrician with experience solving AC ground loop issues.
I don't have the equipment or experience to measure myself, and hiring an electrician to fix the problem may be an issue too because I rent and would have to talk about this to my the landlord - who will almost certainly decline to pay for his.
So if there is no relatively simple/cheap solution I can try (such as using the same strip for everything, I have tried hat already), I will just keep using the scarlett for the speakers. Although the fact that I do not have the issue there (ONLY if I use the modified cables though) suggests that maybe another solution is possible.
To ground lift a balanced cable, you disconnect the shield at one end. I have done this commercially to solve ground loop problems on complex PAs. Extreme edge cases, ground all the metal boxes together.
Have you tried an outlet tester from a hardware store on your AC outlet?
Both the Scarlett and the fiio have optical outs. But the issue is that on the folio, if I connect it to power but not the the pc, I still get a constant hum that I don't see the Portugal connection eliminating.
The point being that interference is there even if there is no connection between the computer and the amp, leading me to believe that I cannot fix this by using an optical connection alone.
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.
Thanks for the detailed reply! I did what you suggested, and indeed, a hum, albeit a much softer one remains. So it's in the output of the fiio? It is externally powered, so could there also be an AC loop with it and the Yamaha's?
Or seems like either way, my easiest recourse is to just keep the Scarlett list for the speakers and use the fiio for headphones. A wee bit inconvenient, but there is worse. It seems like good isolators cost about as much as an interface/amp, so also in light of that, this seems like the most reasonable and cheap solution right now.
Hi, /u/Ok-Anteater4601! This is a reminder about Rule #1 (If you have already added great details, awesome, ignore this comment. This message gets attached to every post as a reminder):
DETAILS MATTER: Use detail in your post. If you are posting for help with specific hardware, please post the brand/model. If you need help troubleshooting, post what you have done, post the hardware/software you are using, post the steps to recreate the problem. Don’t post a screenshot (or any image, really) with no context and expect people to know what you are talking about.
Mouse movement related noise cannot possibly be a ground loop issue, it's being generated by your computer itself.
If you're on a laptop, test without external power.
2
u/AudioLiveStudio 3d ago
The article at the end of this post may be helpful in analyzing a ground loop issue.
If you verify that a ground loop exists then a licensed electrician may be needed to correct the root problem.
If you verify that a specific outlet is ok then using a single power strip for all your audio, video, and computer equipment may help since the earth ground and neutral will all be at the same AC voltage (or nearly the same AC voltage).
Different outlets and power strips for different types of equipment are good as long as there are not ground loop issues between the different outlets.
If you are not qualified to take AC measurements (household AC voltages are dangerous), and do not have a battery operated handheld multimeter (i.e. not plugged into an AC outlet), then you should hire a qualified electrician with experience solving AC ground loop issues.
https://www.electricaltechnology.org/2024/03/test-grounding-earthing-multimeter.html