Speaker background buzz, only when connected to PC

[Snakesnsparklers]

I'm using a TDA7297 amplifier hooked up to a couple 4" arcade speakers in my MAME cabinet, wired to 12V on the power supply. I get a significant background buzzing which increases with volume control when hooked up to the PC which is using a JPAC. I hooked up the amplifier to an ipod instead of the PC and it sounds great with no background buzzing. I tried some different PC speakers on the PC and they don't have the buzzing either. Ensured the monitor chassis is connected to earth ground, no difference with the ground connected or not.

What is causing the buzzing and how do I get rid of it?

[Drnick]

Search ground hum/ground loop.  Run your amp from a separate 12v and your issue will most likely go away.

[Snakesnsparklers]

Search ground hum/ground loop.  Run your amp from a separate 12v and your issue will most likely go away.

What separate 12V? I don't want to run a second power supply just for the amp... is there no way to get this to work while powered by the PC power supply? I noticed that the background noise does not change if I change the volume in windows, it's only changed when I adjust the volume pot on the amp.

[Slippyblade]

Running the audio amp on a separate power supply is pretty common.  A computer power supply is not a normal constant supply, it is a switching supply and frequently generates noise.  Just hit Goodwill or whatever thrift store is near by and grab a 12v wall wart for $1.

[Snakesnsparklers]

Running the audio amp on a separate power supply is pretty common.  A computer power supply is not a normal constant supply, it is a switching supply and frequently generates noise.  Just hit Goodwill or whatever thrift store is near by and grab a 12v wall wart for $1.

Isn't a wall wart also a switching power supply?

[Slippyblade]

Isn't a wall wart also a switching power supply?

No.  Most wall warts are little more than step-down coils with a bridge rectifier circuit.

[Ken Layton]

Sounds like you have a ground loop:

http://www.audioholics.com/home-theater-connection/ground-loops-eliminating-system-hum-and-buzz

[pbj]

http://www.ebay.com/itm/MINI-3-5MM-NOISE-FILTER-GROUND-LOOP-ISOLATOR-CAR-AUDIO-/260741338139?pt=US_Car_Audio_Video_Interconnect_Cables&hash=item3cb565141b

[lilshawn]

grounding issues are quite common between amps and computers mainly due to the computer manufactures trying to isolate the audio signal from the rest of the computer. is results in a ground difference between the ground the audio circuit uses and the ground of the computer power supply itself. it may only be a couple of micro ohms, but it's enough to cause it.

buy a noise isolator for 20 bucks at ratshack or a wall wart for 1 at goodwill... your choice. 

[Snakesnsparklers]

I tried using a separate 12V wall wart and all is well, thanks guys. Now I just need to figure out how I want to do the cabinet power wiring since I was not planning on needing an outlet inside of there initially 

[lilshawn]

if you want to ghetto rig it, you cut off an electrical extension cord plug it into the adapter and wire the cut end to the cabinet wiring.

if you want to go california ghetto rig it, you cut off a powerbar plug and wire that baby into the cabinet. then you have plugs for everything

if you want to do it the right way, you spend a couple bucks and you buy an electrical box, a duplex outlet (or 2 if you need more outlets), and a face plate. you put that in there and you plug all that stuff in real neat like.

i don't condone the use of option 1 or 2, but yes, i have shamefully done it.