Noisy computer (ground loop?) issues

[ttol]

So, here I thought that I could finally stop tweaking my setup.. then I get some very low volume material to listen to and find out that once I turn volume past 12 on my Singlepower amp, I can easily hear very annoying hum and beeps.

Setup:
Computer -> USB -> Stello DA100 -> Singlepower Extreme
Computer -> X-fi -> BJ Coax -> Stello DA100 -> Extreme

Everything is powered by a Belkin UPS.

To figure out what is causing the hum I first turned off my DAC: No effect on the hum. Then I unplugged ICs between the amp and DAC, hum and beeps vanished immediately.. phew, at least my new shiny Extreme isn't having any issues. Next I unhooked BJ coax cable, to my surprise the hum got significantly louder, I plugged the coax back in and unplugged the USB cable.. hum was still there but somewhat quieter. Then I unplugged both coax and usb cables, again no hum or beeps whatsoever.. Phew, also DAC seems to be physically fine.

Then I tried powering down my computer. All nasty noises disappeared again. Next I tried plugging my computer's power cord into a different wall socket.. hum got immediately worse. I plugged the computer again to the Belkin UPS and powered up, I noticed that I can hear computer's internal noises (hdd's powering up, etc.) so I turned my computer off again.. dead quiet.. then I plugged it again to a different power outlet and noticed that while the humming is definitely louder, I couldn't hear any internal noises (the beeps) anymore.

I finally decided to leave my computer plugged into the Belkin UPS, while the beeps are more annoying than a constant hum.. the hum is significantly quieter with my computer plugged into the UPS.

Any ideas how to get rid of the internal noises and hum?

 

[SonicDawg]

Sorry to hear about your problem. Is there a chance for you to try a different power conditioner? Seems like a bad case of power contamination there.

I also use my computer as source. But I never have problem with hum (except from my DAC. Long story...). Also I suggest you try using toslink connection if possible. One of its advantage over coaxial is that it doesn't transfer electric interferences.

 

[fwojciec]

If you sure that the computer is to blame, then you could try switching to an optical connection between the computer and the dac, that way you'll insulate amp and dac from the electrical mess of the computer.

 

[MCC]

Is this a laptop or a desktop? A desktop PC shouldn't have any noise issues if it's built right. If it is a desktop and it's a prebuilt PC, then the manufacturer might have used a cheap power supply that's not grounding correctly. Although the power supply is IMO the most important computer component, many prefabs skimp in this area to increase their margins.

I'm not guaranteeing that a new PSU will help, but you never know.

 

[ttol]

Thanks for the suggestions, I do have a better UPS downstairs (APC) and will check if the same hum happens with it.

Optical connection definitely kills the hum but I'd like to use it as the last option. Using both coax and usb at the same time without hum would be my preferred solution

Oh, and it's a self built desktop with a OCZ Powerstream PSU.

 

[Logistics]

Device Manager--View by connection--IRQ's, anything sharing an IRQ?

 

[ttol]

Quote:

Originally Posted by Logistics /img/forum/go_quote.gif Device Manager--View by connection--IRQ's, anything sharing an IRQ?

Holy crap! Awesome call! NVIDIA SATA controller was indeed sharing IRQ with USB controller that my DAC was connected to. Switching my hdds to the other NVIDIA SATA controller completely eliminated the internal sounds (hdd spinning up & down).

Now the only problem is the hum and occasional beeps when coax & usb are connected. If I unplug the coax the humming/beeps still gets significantly louder btw.

Thanks!

 

[ttol]

Damn.

Since I'm mighty bored I managed to bug my wife into helping me with a blind test.. turns out that I can hear the hum even using my usual listening volume.. I guess I'm stuck with optical connection unless someone smarter than me finds a way to solve the problem.

Now I'm starting to hope I had never started digging into this.. blessed ignorance etc.