Magnetic interference from Amplifier + Hard disk damage?

hob said:

I recently had my powerbook overhauled, there was damage to the casing, but also the ram and hard-disk was mysteriously damaged. (Long story, but yes the casing was my fault, but the rest was completely random!)

What I suddenly realised was, that my setup in my room is a desk with two monitor-speakers either end of the room, and a central amplifier. I used to leave my powerbook ON TOP of the amp. No wonder I got hard disk damage, right? The magnetic interference from the amp? Or am I talking rubbish?

I've just bought a Lacie External hard disk and was wondering how far away from my amp on my desk I should leave my (repaired) powerbook and new hard drive? Or if it doesn't mate a difference?

Cheers,
Hob

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Get yourself a magnetic compass and test it while the gear is on. If it doesn't make the compass twitch then there is little to no possibility of damage to your electronic devices.

Well, considering that amplifiers normally have one or more big ass magnets in them, it is probably not a good idea to put a computer on top of one.

It IS possible for damage to occur

EMR (Electro Magnetic Radiation) is a common problem that can affect certain sensitive components. I have recently set up (for a client) 14 46" Plasma screens, using very high quality interconnects, and under certain conditions, somebody standing closeby with a Mobile (Cellular for you Yanks ) phone cause interference on SOME of the screens - depends on positioning etc. One of the screens developed vertical stripes after this problem and had to be replaced. In a larger desktop case (a la G5) the components are pretty well shielded by a Faraday shield, this is less easy to implement successfully in a laptop form-factor and so these machines are a little more susceptible to these types of problems.

Hope this helps

You are forgetting one thing. Not only does a amplifier become magnetic (not much) from the power cores, but it also seaks its earth through the metal casing. So your powerbook, being all metal, could have had an earthing shock...

Wouldn't the magnets on the monitor speakers be a hell of a lot more powerful than anything in teh amplifier? My monitors are self-powered, so it's all the same thing, but my guitar amp, on the other hand...

Actually my monitors are shielded pretty well (they can go right next to the CRT without causing any discoloration), so my only real concern is that guitar amp. I keep it on the other end of the room, though, 'cause I don't want any mics to pick up any more of the computer fan noise than they absolutely have to.

To (not) answer your question: I have no idea.

MacBandit said:

Get yourself a magnetic compass and test it while the gear is on. If it doesn't make the compass twitch then there is little to no possibility of damage to your electronic devices.

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Of course, the damage could be done by an oscillating EM field, which might not cause the needle to visibly fluctuate. In general, I think it's a bad idea to set computers on top of amps for many reasons....

Redboy said:

Wouldn't the magnets on the monitor speakers be a hell of a lot more powerful than anything in teh amplifier? My monitors are self-powered, so it's all the same thing, but my guitar amp, on the other hand...

Actually my monitors are shielded pretty well (they can go right next to the CRT without causing any discoloration), so my only real concern is that guitar amp. I keep it on the other end of the room, though, 'cause I don't want any mics to pick up any more of the computer fan noise than they absolutely have to.

To (not) answer your question: I have no idea.

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As you stated most high end modern speakers are shielded so they typically aren't a worry but that of course is not guaranteed. Amplifiers on the other hand typically have no shielding whatsoever to protect their very large magnets from damaging outside devices. The electromagnet that is the power supply or supplies can be larger than most speaker magnets.

jsw said:

Of course, the damage could be done by an oscillating EM field, which might not cause the needle to visibly fluctuate. In general, I think it's a bad idea to set computers on top of amps for many reasons....

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Very true in which case it probably oscillates at a frequency too high for any cheap compass to detect.

I find that an old monotone CRT makes a great EM field detector. You can't hurt them and they are very sensitive to gauss.