Question to audio experts... background noise

[phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org]

I would *guess* that the issue is the shielding of the cable that you plug
into the jack. If the cable is not shielded, it will act as an antenna and
in the downtown Toronto area, there are huge RF signals. (From the window
where I'm sitting, the CN Tower is visible...).

I used to work in sound reinforcement in Toronto theatres, and RF pickup
was a major problem.

Grounding is usually not a solution to RF pickup problems, but it could be
an issue if there is an existing shield and it's not connected to ground.
Ground is a slippery concept. What's the ground on a laptop that's
operating off a battery? ;). In the case of a laptop, it's the metal
enclosure or plate.

If the headphone lead is acting as an antenna, there are a couple of
possible cures. You can loop the headphone wire a couple of times through
a ferrite donut or cylinder. You sometimes see these ferrite cores on
video or USB cables, you might be able to salvage something from a surplus
shop (eg, Active Surplus, Above All, Creatron, or the reincarnated
Supremetronic). More complicated, you can solder a small (50 or 100
picoFarad) capacitor across the earphone connector.

Peter
who top-posts without shame ;)

> Hi all,
>
> I don't have much experience with what is normal for sound card.
> So, I thought I should ask audio experts here...
>
> I get high-frequency background noise when I plug in my earphones
> directly into "front line-out" (green) of integrated sound card.  I can
> hear the noise change as I move mouse, type something on keyboard,
> or do something on screen.  My guess is "grounding" problem.  But,
> when I plug in my external 2.1 speaker system, the high-pitch noise
> becomes noticeable only at max volume.
>
> Is this normal for all sound card or just integrated ones?
> Maybe one shouldn't plug earphones/headphones directly into front
> speaker jack?
>
> --
> William
>
>
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-- 
Peter Hiscocks
Syscomp Electronic Design Limited, Toronto
http://www.syscompdesign.com
USB Oscilloscope and Waveform Generator
647-839-0325

--
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