Another USB Ground Loop Thread

ometh877

New Member
My life has been consumed over the last week and a half chasing down noise in my setup. I'll try to explain everything I've tried as detailed as I can. I'm hoping somebody can give some additional insight that might help me narrow things down better.

tl;dr Using a balanced XLR cable from AxeFx Out 1 to my RME Babyface Pro XLR input results in noise from my computer propagating into the AxeFx headphone output, and any other outputs the AxeFx is connected to. This behavior is not seen when using the unbalanced output from the AxeFx into the 1/4" input on the Babyface Pro. Changing cables/where things are plugged in has not made any impact. If the computer is powered off but the PSU is still delivering power to the USB ports, everything is silent. My laptop is quiet on battery or plugged into the AC adapter. Plugging my AxeFx into a USB port on my computer has no impact.

Gear:

Desktop PC
  • Ryzen 2700x CPU
  • ASRock Fata1ty X470 Mobo
  • Sapphire Nitro R9 Fury GPU (I disconnect the power from it during testing, no impact either way)
  • EVGA 850W Supernova G2 PSU
  • Cooler Master HAF 932 Advance chassis

RME Babyface Pro
  • Two different usb cables, no change in behavior between the two. One has a ferrite choke which is what I'm primarily using
  • Two different 12v stand alone power supplies for the RME interface, no change in behavior with either unit, no difference with PSU or no PSU

AxeFx II XL+
  • No instrument cables plugged in
  • Various XLR cables from Output 1 Left or Right
  • Sennheiser HD 280 Pro and Shure SE215 IEMs

Behavior:

Running an XLR cable from my AxeFx Output 1 (L or R channel, no change) into the XLR inputs on my RME Babyface Pro while the Babyface is connected to my desktop via USB results in a loud noise (mouse movement, CPU activity, all kinds of fun EMI types of noise) that propagates into the AxeFx headphone output, and will travel to the other AxeFx XLR output into whatever gear I plug it into, such as a mixer. Lifting the ground on the back of the XLR definitely makes things quieter, but its still very noticeable.

If I unplug the USB cable from the Babyface (with or without an external power supply driving it) the noise stops.

I have taken my AxeFx and PC to a different room/circuit, plugged them both into the same outlet and removed/unplugged everything from the PC except for the CPU fan and the NVMe drive. With the computer just idling this way I get no change in behavior. If the computer is powered off but the PSU is still delivering power to the USB ports, everything is silent.

I added a separate PCIe USB 3.0 card with the only impact being I hear less of the other USB devices coming through (RGB keyboards are really bad about this as I have found out)

I've tried to replicate this behavior with other gear and the Babyface, by swapping the output from the AxeFx with output from another piece of rack gear, but for whatever reason (perhaps other outboard gear having a higher noise floor) I don't hear/notice the same problem.

I've tried various combinations of plugging PC/AxeFx into the same power strip, outlet, different outlets, different circuits, etc. Doesn't matter.

I'm reasonably convinced the issue I have is some kind of grounding problem between my computer and the Babyface, but the unfortunate part is I only notice it with the AxeFx when its connected via the XLR inputs.

I have tried removing the shielding from the XLR cable's Pin 1 between the AxeFx and the Babyface as I've seen people on RME's forum recommend and it just made it worse.

The noise does not seem to affect my Babyface XLR outputs which drive a sub/studio monitors but I've disconnected while troubleshooting. Leaving them connected makes no difference I've noticed.

If I run a TRS or a TS cable from the unbalanced output of the AxeFx to the 1/4" inputs of the Babyface, I get no noise at all from the AxeFx. This surprised me the most because generally I would expect balanced XLR cables to not have a noise problem in the first place but I would expect unbalanced TS cables to pick up noise.

I'm going to try pulling everything out from my case tonight and re-seating everything to make sure the motherboard is properly seated. My case is also painted, so I'm going to scrape as many bare metal spots for contact between standoffs, PSU screws, etc. I suspect that this is probably a problem with the motherboard, but buying a new one seems like a shot in the dark at this point.

Any suggestions or thoughts around ways I could get around this would be very much appreciated. It may be that I'll have to just stick to using the unbalanced outputs on the AxeFx for now. I've also considered getting an external AD/DA converter (for other purposes outside of the AxeFx) and running it into the Babyface via optical ADAT, which should get around the issue as well (but won't be cheap).
 
I'm sorry that you haven't gotten any replies or help.

I get terrible noise when I have tried to USB so I stay away from it. I've gotten a few sarcastic replies when I asked about using a high end, shielded silver USB cable.

I don't know a lot on this subject but I did find this article that might be of some help.

https://forum.cockos.com/showthread.php?t=113721
 
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