Handy Andy wrote:

"tony sayer" wrote in message
...
In article , Pinot
Grigio pinotgrigio@somewhere.? writes
Whenever we turn a light on or off, an electrical sound can be heard from
the PC speakers.
I assume we have a faulty connection somewhere.
Any suggestion as to the best place to start. Is it more likely to be
the
lighting circuit?
I suspect the answer is that it could be anywhere but just thought I'd
ask!


Don't worry about it. PC speakers are of such **** poor quality they
respond to anything like the slightest amount of RF energy. Trust me I'm
a radio comms engineer)
--
Tony Sayer


I would have thought that the 'problem' is an amplifier one rather than
speakers.

True. Talking about "speakers" is misleading, because the problem is
definitely not in the loudspeakers themselves, but most probably in the
amplifiers (a stereo pair) that drive them, and/or their power supply.

However, before running away down that path, we need to take a step
back, and ask the OP:

* Does any other audio device in the house (TV, mains-powered radio,
hi-fi) show the same problem when you switch things on and off? Do the
lights flicker?

If not, it's highly unlikely to be a major fault in your mains wiring.

Small disturbances on the mains are normal, whenever you switch anything
on and off. What seems to be abnormal is that your amp/speakers are very
sensitive to them.

Assuming the answer to the first set of questions was No, then try to
narrow it down further.

* Borrow a completely different set of speaker/amps and power supply
from another PC. Is the problem still there, or is it specific to your
set?

* Aside from the specific problem you reported, is the audio background
dead quiet, hum-free and undistorted? Or is the sensitivity to mains
switching part of a wider problem?

There are two connections to the speaker/amps system: the mains power
supply and the audio input from the PC. The electrical noise could be
getting in either way, so:

* Unplug the audio input lead from the PC. If the problem is still
there, the interference is coming in through the power supply.

* If the problem goes away when you unplug the audio lead, it could be
either at the PC end, in the lead or its connectors, or the amplifier
end (though I'd bet on the last two).

Given the answers to these questions, several people here might be able
to help you further.


--
Ian White
Abingdon, England