L. Ha wrote:
>
> Hi,
>
> I hope that your guys can help me out with the problem. I recently
> purchase a computer and hooking it up to an AC wall outlet. Everytime I
> try to use an electric fan (which hooks up to a different AC wall outlet),
> the computer speakers make constant static noise. When the fan turned off,
> so was the noise. Also, turning on/off the light introduces a loud
> popping noise on the speakers (Altec Lansing 4.8).
>
> The question are:
>
> 1. How can I get rid of the noise on the AC power outlet,
> which my computer is running from?
> 2. Can a UPS and/or surge protector resolve this problem if I install a
> UPS and/or surge protector between the AC power outlet and my computer?
> 3. And finally, can this problem does any latent damage to my system? I
> have the system for approx. 1 month.
>
> -Thanks, Loc
Had a similar problem, last summer, with a fan I added to my cubicle in
an electronics lab area. When I first plugged in the fan and turned it
on, my trusty multimedia computer started having singing speakers (at 60
Hz). Since the fan was the new object in the roon, and it had a
non-polarized plug (both prongs were the same size), I tried reversing
the plug in the outlet, but that didn't work. I had to position the fan
away from the speakers and speaker wire to eliminate the hum. I guess
that the fan had a shaded pole motor that was really radiating noise.
(I later tested it with an oscilloscope, and found it to be very noisy,
hence, my speakers, being magnets, were being modulated by the radiated
signal and 'humming'). The fan switch, in this case, caused the
speakers to POP (instead of a light), because the fan was a two speed
fan. Everytime I switched the fan switch, the speakers popped. Again,
I tested the radiated signal around the fan and learned that the fan
switch was an un-insulated (not enclosed in metal) cheap switch that
created a lot of high frequency harmonic energy every time it changed
position (it arced a lot). That energy was radiated and the speakers
being sensitive devices, picked it up and reacted to it - as the pop I
heard.
Will the POP hurt the speakers or your system? No.
Can you get rid of the hum? If reversing the fan plug in the AC outlet
does not work, try moving the fan further away from the speakers and
speaker wire (3 feet or 1 meter) does not do the trick, get a new (and
better quality) fan. It is the quality of the motor and its ability to
not radiate AC interference signals that will determine if the speakers
hum or not.
Recently, there was another problem with speakers and a fan and hum, and
I suggested reversing the plug. Never heard back.
so in answer:
1. The noise may not be "on the outlet". It may be (and most likely
is) being radiated and picked up.
2. A UPS and/or surge protector can eliminate high frequency noise or
impluse noise on a line, but it cannot stop radiated noise from entering
your system.
3. Latent damage to your system? Probably not. (Note: It is highly
unlikely that anything will happen. But in electronics, I will never
bet that if I switch off a light, that the light WILL come back on when
I place the switch back to the ON position. There are NO guarantees in
electronics!)
One last note: The AC line current is 60Hz? The hum in the speakers is
LOW frequency (60Hz?). So filters on the line to block the hum will
also degrade the AC Current! The UPS would have to be a type that takes
the AC current and converts it to a DC current which then converts it
back to an AC current to power your system. Those UPS systems are not
cheap. And if the interference signal is entering your system by
radiation, then distance is the only solution. (Put the fan on an
extension cord and slowly bring it near your computer system and see
when the speakers start to hum. That is one way to find out if it is
radiated or through the AC wiring!)
HTH
--
Jean Bourvic :>))
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