Need help with ground loop/noise in PC

[hans132]

I recently bought a new PC and had some noise when connecting my IEMs to the headphone output. Those IEMs are super sensitive and many devices can't drive them without some audible noise, so I didn't think much about it.

That however changed, when I connected active monitors to the line out of the motherboard and heard some pretty nasty noise coming from them. Connecting my smartphone, laptop, any other device to the monitors I didn't have any issues besides the hiss normal for those kind of class-d amp monitors. Connected to the PC there was unbearable noise, while I identified the same noise on the IEMs, but much more quiet in comparison to the monitors.

I did some research and found many people have that problem and it is described as GPU ground loop. The noise changes frequencies with changing fps/v-sync. There doesn't seem to be a definitive way to fix that problem. Changing power socket for PC and/or monitors, using balanced connections, floating grounds, using usb interfaces... the all may or may not help. I was hoping to fix the issue with a USB interface, but the noise still persisted. Even connecting my smartphone (which is connected to the monitors - sounding great) to my PC via USB to charge, starts messing up the smartphone output.

With the help of a cable, which had an isolation transformer incorporated, I was able to fix the issue with the monitors, but now I am wondering how I will be able to drive my 250Ohm headphones...

I would like to ask you some questions:

1. I read that isolation transformers have a negative effect on the sound. Are there any measurements as to how much it gets changed?

2. I tried an usb interface with a seperate power source, but the ground loop messes up the interfaces output even then. There are devices like the ifi defender, which some reviewed to not work at all or work, but introducing a new source of hiss...
From what I understand about USB connections: The ground loop can't manifest via the 2 data pins, as the deliver a digital signal. Instead it must manifest via the GND and +5V pins. Coudln't you just make a y-cable, which gets the data connection from the pc and the power via a seperate usb power supply? If this would not work, why? If it does work, why doesnt anyone else offer this solution?

3. While everyone talks about ground loops in this context, how can this affect the headphones? From what I understand, ground loops occur if an unbalanced cable is used to transmit a analog signal between devices with seperate power sources, but the headphone has no seperate power source... why can I still hear the same noise then with my IEMs?

4. I tried a different (my old) GPU and it creates even more noise than my old GPU, despite not having these issues in my old PC. While there must be a connection to GPU, what do you think is most likely the real source? The PSU? The motherboard?

I would greatly appreciate if someone could help me out.

 

[sandymc]

I had a similar problem with a 65" inch OLED smart TV and a pair of Focal active monitors. Very bizarre - the noise from the speakers would actually vary with the displayed picture. Difficult to trace because there was also a whole lot of other equipment in the room. But I eventually traced it to power supply noise - basically, high frequency noise contamination was flowing over the power lines from the smart TV, and creating noise on the active monitors. Filters on the power line helped, but eventually we just got rid of the Focal monitors, and replaced them with KRK V series monitors, which gave no problem at all.

In my experience, a lot of people talk about ground loop noise, but unless it's at 50/60Hz, it probably isn't an actual ground loop.

In your environment, I'd suggest not driving the headphone direct from the PC - get an external DAC/Amplifer. A good one won't have any power supply issues.

 

[hans132]

In your environment, I'd suggest not driving the headphone direct from the PC - get an external DAC/Amplifer. A good one won't have any power supply issues

If that would work, then I wouldn't even consider having a problem. However I already tried an USB interface and it did not work. It even had a selectable power source. You could select between usb bus power and battery power and neither worked. The noise transmitted through USB. Also searching on the internet many people also claim, that usb dac/amps didn't solve the issue. Would you say there is a criteria for which usb interfaces do and don't solve the issue and if so, what would that be?

If you think it is an issue in the power line, then I believe that isn't the source problem either. If I connect the monitors to my smartphone headphone port it plays fine. If I connect the smartphone usb then to charge via pc usb, there is a lot of noise. If I connect the smartphone to a cheap phone charger instead (on the same powerline) there is no issue.

 

[somebodyelse]

This deserves an FAQ entry. The monitor problem seems like a typical ground related noise issue - in this case probably leakage current modulated by varying load from the cpu or gpu, which is why it's not mains frequency related. You can find out all the gory details, and a number of solutions, in the application notes from Jensen Transformers - AN007 probably has everything you need and more. Among the solutions are balanced interconnects (assuming no Pin 1 problems - see AN007 again), toslink (optical) or transformer isolated SPDIF, and galvanic isolators for USB - note that the cheap ones can't usually manage USB2 speeds.

Creative abuse of the USB standards like the Y-cable you propose may or may not work - some parts of the newer USB standards can check resistance between data lines and ground so your 'broken' cable may have compatibility problems, particularly with newer ports.

The quality of onboard audio is something of a lottery as it's barely even an afterthought for manufacturers. It's quite possible to have load-related noise issues due to poor ground routing in the audio part of the motherboard, or even in the cabling to the front panel connectors. You'll find references to the importance of the layout in Bruno Putzeys' The G Word and in Tom Christiansen's discussion on how not to mess up your LM3886. If they've got audible problems with headphones plugged in directly to the motherboard then there's not a lot you can do other than get another audio interface that doesn't have these problems.

 

[hans132]

Thanks for the references. It will take me some time to work through, but they look pretty relevant. I will have a deeper look!

I was hoping to get something like a topping e30/l30 or a schiit magni/modi, but as I said: Based on testing one USB interface, my hopes are quite low that they would solve the issue. Would you happen to know about an interface which would most likely solve my issue or what to look out for in an interface when having this problem?

My other plan was to get something like a Behringer UCA222 to use the toslink out or to get one of those usb isolators, but as you pointed out, those devices get quite expensive if you would like them to support more than CD quality.

 

[somebodyelse]

I completely forgot about the transformer performance question - this thread has some measurements. Short version: they distort a bit, and low distortion ones tend to bet expensive, but they do work.

I assume from the question that your motherboard isn't one of those that includes digital outputs, and that you're after both headphone and monitor outputs, but don't need inputs.

I've got an old UCA-202 from when they were still using the genuine TI codec chip, and it works as a basic optical output. I'd probably give the Fun Generation UA-202 a try now - same TI codec, and transformer isolated coax output rather than optical, but cheaper than the Behringer. The transIt doesn't have a headphone output, As you've noted they've got limited capabilities though.

If you want something with a faster digital output and feed the Topping or Schiit I think Topping's D10s has a transformer coupled digital output. I'm sure there must be cheaper alternatives that can do USB to digital at higher rates, but it's not something I've looked at. You need to be careful about the isolation for coax, and the speed of the toslink transmitter - many will do 96 kHz but not 192kHz if that's important to you.

Assuming your monitors have properly implemented balanced inputs you could pick one of the pro audio interfaces like the MOTU M2 - balanced line outs for the monitors, and a halfway decent headphone amp. More 'hifi' style options with balanced outs tend to be more expensive. There's a new D10 version on the way with balanced outputs, and the new Khadas Tone2 looks good on paper with balanced outputs and a headphone amp. Khadas' own published measurements look good, but we haven't seen external verification yet, and I'm not a fan of their new 'balanced RCA' connectors given what they're charging. Topping are sticking to standard 1/4" TRS sockets.

 

[hans132]

Thanks for the extended reply.

Correct, my mainboard lacks optical out and I am looking for a way to connect headphones and monitors.

I didn't know that coax outputs are isolated on such devices. Good to know! I would be happy with 24bit/96khz.

The motu m2 was also on my list (and my monitors do have balanced inputs), but the problem I see is that there is no coax/toslink in. So I would feed the noisy usb signal straight into the headphone out.

I thin I will go for the recommended UA-202. In regards to dac/amp I will wait for prices of the new topping pro models.

 

[somebodyelse]

Coax digital outputs aren't always isolated, especially when present on motherboards, so you need to check. The transformer is usually a rectangular block next to the coax socket - in the internal pic of the UA-202 linked above you'll see it in the top right corner with 'UT15612' printed on the top. I think I've seen a similar one on the internal pics of the D10. The receiving end sometimes has a transformer, but that's less common.

The headphone output on the M2 should be fine with USB so long as you're using it for headphones. The problems come when you give the leakage currents a route to somewhere that's also part of the signal, which you aren't doing with headphones or with balanced interconnects. If you use the headphone output or RCA output to an amp or something then you might have a problem again. I have a similar situation with my Focusrite Forte with some PCs.