weird stuff

[ninja_x]

I've got an iPod and a Total BitHead amp. I got a case which can hold the two together. However, when I used it, I heard a very high pitched, audible whine. Never having heard this sound from my equipment before, I separated the amp from the case, and the whine instantly disappeared. It turns out that the volume of the high pitched whine is inversely correlated to the distance between the underside of my amp and my iPod, completely disappearing (to my ears) when they were about an inch and a half apart. I figure this must be caused either by interference with the electric signal in the amp caused by the magnetic field generated by the iPod's electric currents, or magnetic interference in the iPod's audio circuit caused by the amp's current. Not really much of a question here, although if anybody has more wisdom on this topic and would like to share feel free to do so. Also, does anybody know if/how I can magnetically shield the iPod case (it's a hardcover that folds over so I don't have to worry about seeing the screen). Is it normal for a portable amp to be this sensitive so as to have it not able to be put near the iPod? I guess in theory magnetism would affect all parts of an electric signal in an audio system, so it would sound best if everything were really far apart or shielded (or ingeniously positioned so as to always have the field parallel to the currents, but that would be pretty much impossible).

 

[ninja_x]

I think I have a better explanation as to the source of magnetic interference: the motor that drives the iPod's hard drive.

 

[GreatDane]

I use my iPod in my truck using the headphone out into an Eclipse head unit and I can hear the hard drive starting up, a very slight whine as it first starts.