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Potential Ground Loop Problem (Help!)

Hi all,

I have a problem, so I thought I'd ask here since I got some very helpful feedback last time I had a problem.
There is a constant buzzing sound on my amp's (SMSL 98E) outputs (which scales with the volume dial) whenever I plug in a device with an AC connection. This does not happen when I plug in my phone, unless the phone is charging, in which case the buzzing persists. I have the amp hooked up to my focusrite solo, which in turn is plugged into my PC's motherboard USB ports. 
Things I have tried:
 - Using both an aux to RCA cable, and two 1/4 to RCA cables to connect the focusrite to the amp
 - Unplugging all usb and display cables from my PC except the focusrite
 - Unplugging all cables from my monitor except AC, and connecting the monitor to the amp with the aux to rca cable.
 - Plugging all components into the same extension chord / outlet. 

Interesting fact: When I move my mouse or use my keyboard, which are both plugged in through usb, I can hear the buzzing get worse for the duration that I use my peripherals.

From reading online I thought it could be a ground loop problem, which could be solved by using a ground-loop isolator, but I'm not sure and I don't want to start buying things without knowing what I'm dealing with.

Does anyone know what the problem could be?

Any help is appreciated.
santiagol
erik_squires
16,004 posts
 
PC's are notorious for causing ground loop issues. You can test this out with a laptop which can be unplugged from the wall, or by turning off the PC and disconnecting it.

If you are using a USB connector, use a USB isolator.

Best,

E
noromance's avatar
noromance
9,617 posts
 
Wi-Fi router/modem.
santiagol OP
9 posts
 
@erik_squires 
@cleeds 

I found the source of the issue: my PC.
I tried using my laptop and my phone as input sources and in both cases the buzzing was gone, even when I plugged them in to the AC. 
I'm going to blame my motherboard for it, since I already have 4 usb ports that don't work properly. A psu issue isn't out of the question for me.
I think I'm to buy a USB isolator. I'm unsure whether a pcie hub would fix it, although if it did I would be happy since I've been looking to buy buy for a while now anyways.

Thank you for the help,

Santiago
erik_squires
16,004 posts
 
I wouldn't blame your PC so much as it's power supply.  A USB ground loop isolator is the right solution, though they don't always work with every DAC.
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