Electrical hum from topanga

[mattpitts74]

In the last few months I have built a topagna following the recipe here on CA.

 

my only alterations are with a bigger case and the addition of a PPA usb card. I have recently noticed that there is quite a lot of electrical hum coming from the computer if I put my ear to the case :-(

 

i was wondering if anyone could make any recommendations as to how I might go about fixing this?

[goldsdad]

Easy - take your ear off the case.

 

Sorry, couldn't resist.

[The Computer Audiophile]

Can you find the location of the hum? This has come up before with other servers and people were able to locate where the hum was coming from and post pictures here of the location on the board. This usually helps find the issue.

[bluesman]

If you're using a monitor or TV for both your computer and video entertainment, this may help you. I have an odd hum that only appears when I connect my computer source to my monitor. When I first noticed it, I thought it had to be one of my aging components, so I ran the usual troubleshooting measures for audio. The power amp was silent with open or shorted inputs. But when I plugged the preamp back into the amp, the hum returned and was present regardless of the input selected (with the DAC on or off). So I concluded (prematurely) that it was the preamp and ordered a new DAC-preamp (well it was a really great excuse...)

 

An hour after ordering the new unit, it occurred to me that I hadn't checked the entire system thoroughly enough to be sure of the noise source - and I'd have felt just terrible if I bought a new DAC/preamp that I didn't really need. So I unplugged everything from every input in the chain and started connecting sources one at a time, even running the DAC directly into the power amp and using my Nuforce iDo as the signal source. Long story short, the hum disappeared when I disconnected my computer's digital out (coax or USB) from my DAC, and I discovered that it was only present when my computer (at that time a PC) was connected to the monitor (regardless of video connection - HDMI, component and VGA all brought back the hum). So I put one of my old, small flat monitors on a shelf and used it instead of the monitor we use for TV viewing to display my music GUI.

 

When I built my BeagleBone, I thought I'd be fine again and connected the mini-HDMI out to the good monitor - and the hum came back. I still don't know why plugging the video output of whatever computer's sourcing my music into the monitor on my rack causes a hum, but it definitely does. As far as I can tell, there's no conductive path between the monitor and the rack rails or any component mounted to them. There's absolutely no metal-to-metal contact between the BBB and the rack - it's sitting on a hard rubber isolation pad at the back of a shelf.

 

Bottom line - see if the hum goes away when you disconnect your computer from your monitor.