Interference on sound card

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grrr_arrghh

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Hi.

Intead of cheep computer speakers, I have connected the line out on my computer to the line in on my hi-fi, to make use of the supperior quality speakers. The cable connecting these is about 10m long. Because of the length, I am used to getting some interference, especially radio signals (they always seem to be welsh radio...?).

However, recently, I have noticed something strange. This is that there is a strange noise coming from my speakers. It sounds like the wind blowing down a chimney. (It wasn't). After some tests, I discovered that this noise only happened when I accessed a hard disks.
Because of something unrelated, the internal connection to my line out does go past ONE of my hard disks (about 2/3" away), but goes no where near the other, however the noise occurs when either hard disk is accessed, and the noise is very similar.

Can anyone suggest why this might be happening? Is it magnetic interference?

Thanks.

Tim.
 
It is possibly a radiated signal from the data cable(s) for the hard disk drives or from the PCB on the hard disk drive itself.

When you say "the internal connection to my line out does go past ONE of my hard disks", are you refering to the audio cable from the CD-ROM drive to the sound card (or mainboard) audio connector?
 
ChrisP said:
It is possibly a radiated signal from the data cable(s) for the hard disk drives or from the PCB on the hard disk drive itself.
Click to expand...
that would be the obvious answer, but I was slightly confused by the fact that the interference caused by the two different hard disks (one about 2/3" away from the sounds cable at the closest point, the other about 10" at the closest point) could be indistinguishable from each other (I would have expected one to be a lot quieter, at least...)


ChrisP said:
When you say "the internal connection to my line out does go past ONE of my hard disks", are you refering to the audio cable from the CD-ROM drive to the sound card (or mainboard) audio connector?
Click to expand...
lol, its a tad complicated. I have an internal cable going from my sound card, to a headphone socket on the front of my PC, then back through my PC (using the same route as the original cable) to the line out port on the back of my PC. Does that help? Maybe the diag will help.

Thanks

Tim
 

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OK -- does the PC case have a fan at the front lower position (like in front of the hard drives)? And... are the audio cables running to/from the front panel connector shielded?
 
no fans (only fans are on proccessor and PSU)

both HDs on same channel (primary)

no, not sheilded, I suppose that was a bit of an oversight on my part. And the audio cable does run quite close to the ide cable
 
The first thing, obviously, would be to re-position the cables as possible so as to separate the IDE and audio cables as much as you can. If that solves it, fine.

If not, I would then begin to suspect that the problem may be originating on the mainboard itself. If so, there's not likely much that you can do about it, other than to replace the mainboard.

Out of curiosity, what is the make and model of mainboard in use here?
 
If you wrap the audio cable in aluminum foil that is grounded to the case you should be able to reduce the effect of radiated noise (you might want to wrap the aliminum foil in something non conductive to keep form shorting things out). At the very least you will be able to eliminate radiated noise as the cause.

Brent
 
Using shielded audio cable is the first step. If that doesn't solve the
problem, just put small capacitor accross audio input to your amplifier.
Radio signal is high frequency. Something as small as 47-330pF
should do the trick...
 
ChrisP said:
Out of curiosity, what is the make and model of mainboard in use here?
Click to expand...
its an Asus A7N8X Deluxe - with onboard sound - (i'm using the 'front pannel audio connector' to connect to the headphone socket)

thanks for the suggestions, i'll have a muck around at the weekend


gerty said:
When using shielded cable make sure to ground only one end to chassis..
Click to expand...
err, why? I prob would have anyway, but what would happen if you grounded both ends?

Thanks for all the advice

Tim
 

It 'may' cause an earth loop, which often gives a hum on the sound, by only connecting the screen at one end it prevents this - but depending how things actually are, both ends connected may work fine. In particular, if you amplifier is double insulated, and has no other earth connection, you may 'need' both ends of the screening connected.

For such a simple problem, earth loops can be extremely difficult to cure, in general you should only have a single earth connection in an audio system - for PA use this gets very hard, a common cure is to connect systems together via isolating transformers - known as 'ground breakers'.

If you still have a record deck, it may well have two phono-leads and an earth wire for connecting to your amplifier - underneath the record deck (usually inside) there will probably be an optional earth connection, from the incoming mains lead to the ground of the record deck. This connection should be made if the amplifier isn't grounded, and open circuit if the amplifier is grounded (usually! - but not cast in stone!).
 
Funny, I fixed this problem for a customer at work the other day. Exactly the same motherboard. In the end, using the latest drivers available on Microsoft WindowsUpdate seemed to fix the problem.
 
really? i don't think i've done a windows update for ages. i'll try it.

P.S. the Asus boards seem to have problems built-in. Look in any forum and the majority of questions are about Asus mobos.

Thanks everyone for the help.

Tim.
 
I have discovered something!

Stupidly, I didn't check to see if the interference was occurring on an input to the sound card. It was. It happens on the line in. (which goes nowhere near the hard disks, and doesn't go any where near the ide cables, or anywhere near the ide connections on the motherboard).

However, The line in is connected to a TV tuner card. Its a bit of a cheep model, and you have to connect the audio connection on the tv card, to the line in on your motherboard. The external connecting wire is only about 3" long. And I have replaced it with a shielded cable, and the interference still happens (even if the TV card is not connected to the aerial). Which means that the interference must either be happening on the motherboard (which I have no control over), or it is happening on the TV card (which I also can do nothing about). Simply turning down the volume on the line in stops the noise getting to the speakers, but it is a bit odd.

I just thought I'd let you guys know what I found out.

I'll try the windows update (I wont get chance until at least Monday or Tuesday).

Thanks

Tim
 
 
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