Power amp + computer = bleh

[danvan]

Basically I get a hum out of the amp when my computer is attached.

I'm using a Harman/Kardon Citation 16 which has worked very well with my NAD 7225 preamp and Wayne J's Eros loudspeakers. Very clean in every way through the radio or stand-alone CD player. However when it is connected to my computer through the NAD I get a loud hum from both speakers, but especially in the left one. THis happens when connected thorugh my H/K AVR-7200 as well, so its not a preamp issue. I've tried both the dedicated RCA outputs on my sound card (M-Audio Audiophile 24/96) and the headphone jack from my motherboard and get the same thing. Signal cables are of decent quality and have never given me troubles in the past and (as far as I can tell) don't run past anything that they should be picking up any noise from. The hum stays roughly constant regardless of volume of music, so its not a big deal if I'm listening at decent levels but when I'm watching a movie it is definitely annoying. Oh yeah, my old Klipsch Promedia speakers do nothing of the sort, so its not the computer fault (at least theres nothing I can fix on it)

I believe the amp did the same thing when connected to my older TV and Satellite receiver, so I don't know what to do to fix it. Is there some kind of filter that I can put it in line with the signal? Not sure where else to go on this.

Anyways, thanks for any thoguhts. I've put up with the problem for a while now and my heads starting to hurt.

[quasi]

Have you tried conneting both chassis together? I.e. the compter chassis to the power amp chassis via a fly lead?

Cheers

[Zen Mod]

try to connect audio gnd and chassis (of your amp) with power resistor of several ohms-4,7 to 10,like Nelson does in his amps via thermistor
next solution is to use signal xformers for your PC audio output ;(

[danvan]

Seems to help somewhat, probably need a better connection on both ends. Where would the best place on my computer be-directly on my audio card? Or should I scrape some paint off of my case and solder a lead directly on there?

[Zen Mod]

Originally posted by danvan
Seems to help somewhat, probably need a better connection on both ends. Where would the best place on my computer be-directly on my audio card? Or should I scrape some paint off of my case and solder a lead directly on there?

I meant on audio gnd and chassis,both in your amp;goal is to differenciate audio and safety ground in your amp ,because in PC they are same

if you didn't tried that already (seems you didn't) ,just connect chassis of your PC (under any screw ) and amp chassis (under any screw) with piece of wire;
who knows-maybe it help,but I suspect that ground loop will be even worse than now

just for test (I repeat -for test) try to lift safety ground on pc OR on amp; I'm sure that hum will vanish......

[danvan]

Certainly helps a great deal, I'll have to find an unpainted piece of metal on my PC and it should be perfect. Thanks a bunch guys!

[theAnonymous1]

I had a similar ground loop problem from my pc , I had to remove the ground from my rca cables.

[Zen Mod]

Originally posted by danvan
Certainly helps a great deal, I'll have to find an unpainted piece of metal on my PC and it should be perfect. Thanks a bunch guys!

any screw at back of your PC is "enough unpainted"

[DragonMaster]

Are both on the same power socket, just like this? It happens to me with my synth when it's plugged on a different circuit than the PC. What else, your PC is making too much RFI.