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?

 

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...)


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

Attached Images

headphone_219.gif (2.0 KB, 213 views)

 

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?

 

Also -- are these two hard disk drives on the same IDE channel -- i.e. on the same cable?

 

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

 

Is the IDE cable a 40-wire cable or is it an 80-wire cable?

 

80

 

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...

 

When using shielded cable make sure to ground only one end to chassis..

__________________
gerty

 

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


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!).

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

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.