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Discussion Starter · #1 ·
I found a thread on a similar subject in the Amps/Receivers forum, and posted my issue in that thread, but that forum just moves soooo fast that the thread ends up off the page within an hour or so. Maybe someone here can help?


I have a tower PC I built back in mid-2006 on one side of my living room. My TV and Onkyo 7.1 receiver are on the other side of the room. I cut a plate with RCA jacks into the walls on each side of the room, and connected those wall plates through my attic with RG6 cable terminated with RCA connectors. I have a stereo mini-jack-to-RCA cable from my computer's motherboard to the RCA wall jacks, and another RCA cable from the wall jacks on the other side to the Onkyo receiver.


I keep the computer's volume usually below 1/2, and I can hear a high-pitched whine through the stereo speakers that gets louder as I turn the receiver volume up. I'm wondering if this is some kind of electrical interference from my computer's power supply? I'm using an Antec 450W computer power supply, which is one of the more well-known, well-regarded brands of computer power supplies, at least from what I could tell from my research when building the system. Also, the computer is plugged into an APC battery backup/surge suppressor, which is then plugged into the house wall outlet.


The thread I posted in earlier had a link to a Radio Shack ground-isolating RCA cable. If I installed this between the wall and the Onkyo receiver, would help with the problem?

http://www.radioshack.com/product/in...entPage=search
 

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Discussion Starter · #2 ·
well, the ground isolating RCA cable didn't help. I tried it on the amplifier-side of my attic cable runs, and also on the computer side, no change.


I did notice that the high-pitched sound seems to come from the center-channel speaker only.


I can also hear a similar high-pitched sound coming from the computer tower itself, although not as loud as the sound from the speakers at my normal listening volume. I removed the tower side panel, and the sound seems to be coming from the power supply. Could the Onkyo receiver actually be amplifying this sound from the computer power supply? Perhaps I just need to replace the power supply?
 

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Is the audio output from the computer coming from onboard audio at the motherboard, or a separate sound card? In either case, are you sure you are connected to the audio line out, and not the headphone out? It sounds like you could have a poor quality line audio output from the computer, or possibly a bad connection. Those 1/8" minijacks can be of very low quality and don't hold the plugs very well, and low quality computer soundcards can sometimes have very poor signal-to-noise ratio, though there's no excuse for that in this day and age.


All that said, I suppose it's possible the issue is stemming from a bad computer power supply, but I doubt it.


You could consider getting a new sound card (or motherboard if you really want to go crazy) with a coaxial digital output. Then you could use the same RCA cable in your wall to run digital audio into the Onkyo with no noise whatsoever. That's how I do it with both of our computers into my Onkyo receiver, just using standard RCA cables.
 

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The first thing you need to try is to get yourself an external USB sound card. PC's inherently give off a hum and will then be amplified on your receiver. If you are still experiencing problems then there is a ground loop issue. The easiest way to troubleshoot this is to bring your receiver over and plug it into the same receptacle as the computer. If the hum is gone then you know it is a ground loop. If the hum is still there, it will be the PC mini jack out that I mentioned earlier.


Good Luck

G-Man
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by Aaron Gilbert /forum/post/15468959


Is the audio output from the computer coming from onboard audio at the motherboard, or a separate sound card? In either case, are you sure you are connected to the audio line out, and not the headphone out? It sounds like you could have a poor quality line audio output from the computer, or possibly a bad connection. Those 1/8" minijacks can be of very low quality and don't hold the plugs very well, and low quality computer soundcards can sometimes have very poor signal-to-noise ratio, though there's no excuse for that in this day and age.


All that said, I suppose it's possible the issue is stemming from a bad computer power supply, but I doubt it.


You could consider getting a new sound card (or motherboard if you really want to go crazy) with a coaxial digital output. Then you could use the same RCA cable in your wall to run digital audio into the Onkyo with no noise whatsoever. That's how I do it with both of our computers into my Onkyo receiver, just using standard RCA cables.

I don't think my motherboard has a line-out jack. There is microphone, headphone, line IN, and then 2 additional jacks for the option of an analog 5.1 setup (using all 5 jacks together). I dunno, all 3 of the other jacks besides Mic and Line-in say Line-out, so maybe I should try all of them.


Also, this sound I'm hearing from the speakers can also be heard coming from inside the computer case. The same high-pitched sound, same frequency, can be heard inside the case, and I think it's the power supply.
 

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Quote:
Originally Posted by PatrickGSR94 /forum/post/15469784


I don't think my motherboard has a line-out jack. There is microphone, headphone, line IN, and then 2 additional jacks for the option of an analog 5.1 setup (using all 5 jacks together). I dunno, all 3 of the other jacks besides Mic and Line-in say Line-out, so maybe I should try all of them.


Also, this sound I'm hearing from the speakers can also be heard coming from inside the computer case. The same high-pitched sound, same frequency, can be heard inside the case, and I think it's the power supply.

I wouldn't rule out an impedance mismatch between the output jack and your receiver, but it could indeed be a problem with your power supply. Good power supplies are reasonably cheap these days (though you can buy a whole case for about the same money, sometimes with a crap power supply already). There are several reliable and quiet power supplies on the market, a couple include Sparkle and Fortron Source (FSP Group). Just don't buy into the hype that you need a 600 or 700w power supply, and read the current output specifications - some 400w power supplies output as much as some so-called 450w or even 500w supplies.
 

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One other source of noise is the hard drive (s). I tried a series of different units and found the new Maxtor (Seagate) SATA 3.0 drives give off the least amount of noise. I also used a shielded set of SATA cable connectors. They came with my Intel motherboard and are manufactured by Eltop Electronics. The part number is D10910-001 BAFO 06 04. The BAFO 06 04 may be the manufacturing date. But the cabling inside the blue sheath is clearly shielded and the board end connector has a locking mechanism. The older black and red SATA connectors aren't as well shielded.


This may or may not get rid of the whine you're experiencing but it worked for me.
 

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Discussion Starter · #9 ·
I may try some shielded SATA cables. I just wish I had some spare parts laying around (power supply, hard drive) that I could swap out to verify the source of the noise, but I don't have any spare parts at all.



That's why I'm trying to narrow this down so I know exactly what I need to buy.
 

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Discussion Starter · #10 ·
I also can't figure out why the amplified high-pitched noise is only coming out of my center channel speaker...
 

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Discussion Starter · #11 ·
Update on my issue: I just installed a Diamond Audio Xear3D CMI 8768 PCI sound card into my computer, and it has completely eliminated the noise coming through the RCA cables into my AVR and center channel speaker.


However the high-pitched noise is still present from inside the tower case. It almost seems like it's coming from the mother board itself. I can hear a high-pitched noise (not sure if it's the same) when the computer is completely shut down, but still plugged in (little green LED on the mobo is still lit).
 
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