"James Sweet" wrote in message
news:48jwf.13937$ya4.5646@trnddc03...
Karl Uppiano wrote:
"Alan Holmes" wrote in message
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"Dave Plowman (News)" wrote in message
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In article ,
Alan Holmes wrote:

More precisely, make sure that your stereo amplifier and your computer
are connected to the same ground. Even a few millivolts of AC
difference in ground potentials can cause lots of 60 Hz hum.

But only if you live in the US of A, if you live in other parts of the
world, it will be 50 hertz.

Neither. The hum you hear in the UK is actually 100 Hz.

How do you work that out?


Second harmonic of 50 Hz. A lot of the hum you hear in the US is actually
120 Hz for the same reason. Most objects, including speakers, really
don't radiate that well at 50 - 60 Hz fundamental, but can and do radiate
pretty well at some of the higher harmonics.

I always thought the 60Hz caused core laminations, coil windings, etc to
smack into each other at both peaks of the waveform, hence the 120Hz sound
from a 60Hz source. I could be off on the process, but I do know that if I
use a sound editor on my computer to produce a 120Hz sine wave it sounds
just like the 60Hz hum from transformers.

Yeah, I think a magnet or buzzer (like in an old alarm clock) will be
attracted by both peaks of a 50 or 60 Hz input, and oscillate at the second
harmonic.