Audio from the Computer to Receiver

[whmartin]

Hopefully someone out there can help me trouble shoot this problem:

I have my entire CD collection now on my hardrive. I wanted to hook it up to my receiver so I could cue up music on the machine and let it play through my main system. Got a miniplug extension and a stereo mini plug to RCA adapter. Ran that from the output on my soundcard (same output that usually runs the PC speakers and subwoofer) and hooked the other end into an unused line input on my Pioneer receiver....

Problem is it puts out a TERRIBLE hum through the receiver. The hum is there no matter what I switch to on the receiver.... Line, DVD, VCR... the hum is there. If I unplug the cord at the computer the hum stops... but if I touch the plug to a metal part on the back of the computer the hum picks up again.... like the computer is not grounded properly or something. Both the computer and the receiver (and all components) are plugged in to line filter/surge protectors and all appear to be properly grounded (according to my little outlet tester).

Any ideas on how to get rid of the hum??

 

[Techno Freak]

Do you have access to another soundcard incase it is that?

It may be that the hum was always there but you don't notice it through the little computer speakers.

 

[Chipster]

Have you tried unplugging all your other inputs to your receiver as you may have some sort of 'earth loop' where too many things are earthed. Sometimes if more than one piece of equipment in a system is earthed, you will get a hum.

You could also try running an earth cable to your receiver grounding post if it has one.

Get expert advice though before removing any earth wires as they are there to potentially save your life!!!

Bad card or cables??

Improperly seated card??

 

[philsparks]

It's almost certainly an earth loop - basically your PC and your stereo are both grounding the negative side of the signal but there's a small difference between them which is giving you the mains (50Hz) hum. The way to confirm this is to remove the earth wire from the plug in your PC (just for a minute while you check, don't leave it like this). Remember not to leave anything else with a full 3-pin mains supply connected to your pc such as printer, monitor etc as all these could also be grounding the pc.

Actually getting rid of it can be a bugger. Some really good hi-fi (well Naim, I don't know about the rest) don't actually ground the signal in the amp but rely on one of the sources to do it.

try some of these:
- try and isolate which bit of other equipment is causing the loop - CD player, turntable etc. If you unplug one of these from your amp you may get rid of the loop, however if the amp itself is grounding the signal you may struggle
- try pluggin your pc and amp into the same outlet with a double adaptor (to minimise the loop). Or maybe try a totally different plug - maybe even using a long extension cable to try an upstairs socket. Remember to do this for all your pc equipment at the same time - printer, monitor etc.
- If your amp has an optical input you could link the optical out from your pc to that - no electrical connection, no ground loop
- I think you can get isolating transformers that pass the signal but which don't have a direct electrical connection. To be honest I think they don't do the sound quality much good, but presumably if you've compressed your CDs and are playing it back through a <£100 sound card you're not expecting to get anywhere near stand alone CD player sound quality anyway.

hope this helps
Phil

 

[whmartin]

Thanks Guys....

As you suggested, it was a "ground loop" (same as an "earth loop" right?? I'm in the US!) Anyway, What I did to test it was to plug the computer (temporarily) in to a 3-prong to 2-prong adapter, removing the ground from the equation. The hum stopped. Now I have to determine if this is safe, both for me and the equipment. When hooked up this way, are the computer and peripherals now grounded through the AV system? And even if they are, is this a unwise thing to do?

I will try the extension cord idea this weekend. If that also takes care of the problem, I could just have an electrician come in and wire a separate breaker for the outlets in my office to separate them from the outlets in the room with my receiver.

 

[philsparks]

... not really

It's true that the PC is now effectively grounded through your amplifier rather than through it's own earth connection - however the skinny little cable and plugs between the two won't be able to carry the high current that could flow to earth in a fault situation. Now you could take that view that the risk of the PC PSU developing a fault is small and live with it - but I'd talk to a proper electrician first.

Phil

 

[cyberheater]

Do not operate any electrical device that is designed to have a ground without it! Please. I know it's annoying but not as annoying as copping 240 volts!

If you have spdif on your audio card then use that. BTW, have you tried plugin both systems into the same extension cable.