[net.audio] Long interconnection question...

rafaeld@teklabs.UUCP (Rafael De Arce) (06/11/85)

I've just gotten into building up my stereo system and will not pretend to 
have answers to your particular problem but I will pass some info to you
that may help.

I'm a ham (WD6CMX) and have had the problem of decoupling my stereo from my
transmitters for years. It's not any big deal once you know what you are doing.
Harmonic suppression above 30 Mhz. is around 100 db. plus/minus 10 db. Still-
in-all the RF funnels it way thru to the stereo from time to time..

So how do I prevent it!

First of all I keep all lines (speaker wires, phono inputs, tape in/outputs,
etc.) as short as possible. This is to keep all lines from becoming antennas.
Yes! Antennas.

All metal objects act as antennas. The longer the piece, the better the possi-
bilities are that it will resonate at a fundemental or harmonic frequency. The
shorten it is, the least likely it will resonate (at freguencies that will 
bother you).

Spurious emissiom (as the FCC refers to them) entering the final amp will be
amplified and the final amp can't tell the difference between the intelligence
(the music) and noise. That is not to say that all noise heard on the speakers
come from RF sources. The Stereo itself creates its own noise as well as the
speakers distorting. (Speakers are the worst offenders.)

One last comment.

RF frequencies and audio frequencies are magnitudes apart. Most well designed
electronic equipment selectively allows the desired signal into the cir-
cuit and filters out the unwanted. Once the signal is selected, little filter-
occurs there after. Your final amp is not a filter. Therefore you want to keep
the signal as clean as possible prior to the final boost.

Keep the line between the pre-amp and final amp as short as possible.