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Re: (Offtopic) Humming on ibook2 audio port?

On Wed, 9 Jan 2002, William R Sowerbutts wrote:

> Slightly offtopic post, sorry:

Hmmm, okay...

> On my iBook2 (600/DVD+CDRW) I can hear a low frequency humming on headphones
> plugged into the audio jack. The hum is only there when the system is plugged
> into the mains. I live in the UK and it sounds like it's around 50Hz, which
> would match the frequency of our AC mains supply.
> Does anyone else get this or is it just me with the dud headphones/ibook? ;)

I don't get this, but I'm sure it's the usual problem: you have grounded
your iBook with more than one wire, creating a "ground loop" into which
power supply wires can induce some current.
Typical candidates for the second wire are your ethernet or modem cable.
Try to unplug them (and anything else that could be connected to ground
level), and I'm quite sure the humming will go away, even if the power
supply is connected.
If that's it, there's not much that you can do about it, except maybe ask
an electrician for help. These phenomena could (only in very extreme
cases!) even make ethernet cables melt, so if you have a new electric
installation and there's still some warranty on it, you might want to
complain about it.
If it's an older installation, you'll probably just have to live with the
humming. It should be harmless, unless you have cables running across
several floors...

Well, now that I've listened closely to my earphones while plugged to the
iBook, I've noticed a very high-pitched sound that occurs roughly every 2
seconds and lasts for about half a second. Any guess what that could be?


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