Bad Hum/Buzz from USB Powered DAC

[reeseslover531]

Hello,
 
I have a headroom Total Bithead. It's a USB powered DAC/AMP combo. I'm using a Macbook Pro Retina 13" and I'm getting very bad buzz/hum in the headphones out. This comes out of both headphone ports and whether it's plugged into the laptop directly or through a powered hub. It's definitely related to things being displayed on the screen because when certain things happen on my computer the type of buzz is changes. I've also just set it up away from any thing else on my bed.
 
Is this just a penalty of a USB powered DAC and I should move up to a external powered DAC? WIll a USB Isolator actually help?
 
Thanks,
Joe

 

[MrScratch]

It seems a ground loop issue. Do you have other USB devices connected to your Mac while using le Total BitHead?
Have you tried this setup with your Macbook running on batteries?
 
Do you have access to another Mac or a PC?

 

[reeseslover531]

I do have other devices connected. I have a mouse/keyboard.
 
I'll try it not plugged in when I get home tonight and I'll also try it on another machine.
 
Is it possible that this gets solved if I used a DAC/AMP that had it's own power supply?

 

[HPiper]

You might want to try a different usb cable if you have one also.

 

[reeseslover531]

Yeah I've tried different USB cables

 

[ab initio]

Yeah I've tried different USB cables

Try connecting your DAC to a usb hub that has its own power supply. That should isolate your dac from the computer's power supply

Cheers

 

[Jd007]

it seems to be a ground loop. you won't be able to get complete galvanic isolation from the computer if you go through usb, but there are ways to address the problem still. try a usb cable with a choke? see https://en.wikipedia.org/wiki/Ferrite_bead
 
if that doesn't work there are usb ground loop isolators that you can get

 

[reeseslover531]

Thanks everyone for your help!
 
I've tried different cables and laptop plugged in or not plugged in. 
 
Before I spend a decent amount of money on a USB isolator ($45?!?) I'm probably going to buy a powered DAC/AMP combo anyways in the near future. Would having that on separate power solve this issue do you think?

 

[reeseslover531]

Tried that. No change

 

[reeseslover531]

http://www.amazon.com/Multi-purpose-USB-Isolator-Built-in-DC-DC/dp/B00899UVGW
 
Is that a decent isolator?

 

[Jd007]

Quote:

Tried that. No change

Separate power does not get rid of ground loop noise. If your DAC/amp and PC are all grounded (i.e. use 3-pronged plugs), you need your DAC/amp to have complete galvanic isolation from your PC to remove the ground loop noise, which means no electrical ground connection between them. USB, digital coaxial, and analog RCA all carry ground which will not help with ground loop noise. The only guaranteed way is to use optical S/PDIF, as the connection is optical with no electrical signal at all. This is the route I went for in trying to get rid of my ground loop problem, I bought an external DAC that had optical input, and used it to connect to my PC's optical out. I believe a USB isolator would work as well but I never used one (so I'm not sure if the one you linked is good or bad), as I wanted to upgrade my DAC anyway.
 
Of course if your DAC/amp is not grounded (i.e. use 2-pronged plugs) then you should not have ground loop noise, but this is rare as most DAC/amps I've seen are grounded. I tried this "fix" with my amp (bought a 3-prong to 2-prong cheater plug), and my humming was gone. This however is not recommended for long-term use as it makes potential malfunctions in your equipment very dangerous (if something shorts inside then the outer case could be carrying 110V socket power!).

 

[reeseslover531]

Used the usb isolator and it didn't work

 

[ab initio]

Quote:

Used the usb isolator and it didn't work

Is your Dac still under warranty? It sounds like your dac is damaged.
 
Cheers