[RFI] stereo rfi

[Jim Jarvis]

Marv,

More information needed to diagnose the problem.

Recommend you look at Radio Works, for their ferrite
clip-ons, which are available in different mixes...with advice.
These tend to provide resistive losses in common mode sigs, 
which MAY reduce/eliminate the problem.

Suspect computer speakers and sub-woofer are different
problems.

Computer speakers are amplified.  Tend not to have rfi ferrite
on their leads, to contain computer generated RFI compliant with
part 15.  Ferrite the bejeesus out of the leads, starting at the
amplifier end of things and see what happens.  It may be that
the plastic housing doesn't provide shielding, and the rf is
getting directly into the audio amplifier.  My guess, however,
is that the speaker lead is acting like an antenna.

Sub Woofer, if not amplified, contains a high power network to 
separate audio bands.  Probability is that the speaker leads are
an antenna, bringing RF into the stereo.

Here's where it gets gnarly....I'd ferrite the bejeesus out of
those leads, AT THE STEREO end, regardless.   Can't tell if the
chassis is being common-mode excited, if it's the input which
is affected, or if it's mixing in the output stage of the power
amplifier.  May be a combination.

start with the ferrites...at least 6 of 'em of the right flavor.
(type 73?)... turn off all inputs and see if it goes away...if so,
then selectively to find the offending channel.  Likely NOT there,
though.

My bet is, mixing in the PA.

Good luck.  (I bought a stereo with metal cases, and no paint at the
case joints, and haven't had a lick of problem!)

n2ea
jimjarvis at ieee.org