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supply, but rather with the fact that when you are plugged in your laptop
is connected to your electrical system's "ground." That can sometimes
produce a "ground loop" (if some other spot in the system is also connected
to "ground," for example a powered set of speakers). Ground loops are
notorious for producing hum, since they are in effect large loop antennas
that pick up the 60Hz AC electromagnetic fields from the power lines all
around us.
Again, this is pure speculation. But it may suggest some things to look at
and/or try to get rid of potential ground loops. If you have the hum
problem and have access to an "isolation transformer" you might try
plugging in the laptop to the isolation transformer and plugging it into
the line. That should break the ground loop while still providing
essentially the same AC power to the power supply. If you do this, please
let us all know how it works out. (Send me e-mail directly, please, as I
may not be able to monitor this list much longer. Heavy deadline pressures
are building in my life and this is too high an activity list for me to
monitor during the depths of a crunch.)
John
At 11:19 AM 7/14/98 +0300, you wrote:
>
>>I've seen the low hum people are referring to on many different laptop
>>computers. Its origin is naturally mysterious as the AC power supply
>>shouldn't be having a problem, yet it is known that some of these "humming"
>>computers stop buzzing if run only on battery power. There is one theory
>Well I am one of the people that have the problem with a dell laptop. And I
>can tell you that the hum is significantly reduced when you remove the power
>supply. I know this does not make sense as the power is DC by the time it
>gets to the PC but as you say it may not be a poor laptop power converter.
>That was using VV and the recognition was bad. I now have an IBM from work
>and loaded NS Preferred. As I don't have the adaptor necessary I am using
>the PCs internal mike, which works amazingly well. Voice recognition with no
>external mike!
>If anyone is interested I can send them a sound file to demonstrate this
>problem
>I am obviously not happy with my Dell at the moment as it seams to be
>unusable for VR.
>
>Tony Swales
=======
John M. Goodman, Ph.D., author of "Peter Norton's Inside the PC,"
Seventh Edition (Sams 1997, ISBN 0-672-31041-4)
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