Large hum/buzz coming from audio!!

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Muffy7

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Hi Everyone.

I have a panasonic home theatre system. It's decent, very nice to the mediocre ear. Anyway, i use my computer to play dvd's, and music, and all that jazz. So what i did, is i took an RCA to 1/8'' wire and hooked up my sound system to the sound card in my computer. Any time the volume is turned up, a hum goes up with it. Its consistent with the volume. I tried unplugging my computer's power from the wall, and left it dead. I plugged in the wire, turned it up, and it is still there! So i think that throws out electrical interference?
The weird thing, is that when i plug the same wire into my mp3 player, there is not the slightest hum at all! So i know the wire and the sound system are fine. I have a pci creative sound card (sound blaster live! 24 bit *old*) and the onboard Realtek one. I tried plugging it into both. Still the same result!

So it have to me some sort of an interference from the computer, but i can't for the life of me figure it out!

please help!

- Kevin


p.s. i thought about using an external sound card hooked up through usb (xmod for example) because if my mp3 player works... than that would have too. Well, please help me!
 

cwwozniak

Chuck
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Muffy7 said:
I tried unplugging my computer's power from the wall, and left it dead. I plugged in the wire, turned it up, and it is still there! So i think that throws out electrical interference?
Did you also unplug the AC power for any other devices, like a printer or monitor, that are connected to the PC? The chassis of the PC could have still been connected to power ground through the monitor or printer cable.
 
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Or the PC is connected too a router which is connected to cable or DSL etc.

What you have is an earth loop, arising from a connection to ground within the system that is different to that of the audio amp.
 

cwwozniak

Chuck
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Muffy7 said:
I have a pci creative sound card (sound blaster live! 24 bit *old*) and the onboard Realtek one.

p.s. i thought about using an external sound card hooked up through usb (xmod for example) because if my mp3 player works... than that would have too. Well, please help me!
A new audio card or an external audio box might still have the same ground loop / hum issues. The output grounds would probably still be connected to the computer's chassis.

Some other options if you do go with a sound card upgrade ...

Is the audio setup for your home theater simple stereo or do you have multi-channel surround sound? If your audio system has an optical or coaxial S/PDIF input, you might want to consider getting an internal card or or external box with a matching S/PDIF output. An optical connection would eliminate any possible ground loops. Not sure what the distance limits are for S/PDIF.
 

Muffy7

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306
It's been awhile since i posted this.. but for everyone to know i figured it out!

What happened was that my cable was split between my modem and my dvd player, which somehow made a large hum. After i unplugged it from the dvd player, it was completely gone!


:]

thanks for the help too.
 
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