update on alternator noise over speakers

[Ti Kan]

=?iso-8859-1?q?mike?= writes:
> yep...can see that the battery acts as capacitor if
> the EMF is coming from the alternator...but still
> don't see what the conection point of the earth wires
> has to do with it

First of all, we're not talking about EMF here.  It's about actual
voltage fluctuations on the power and ground lines due to voltage
drop caused by the resistance of the wire, which is proportional
to the current that the wire carries.  That current will only be
the stereo's own current consumption if the stereo has its own
power and ground wires direct to the battery.  If the power and ground
are tapped off some other location which is shared with other electrical
devices, then the current will also include those of the other devices.
Power and ground lines are symmetrical, one is a feed and one is a return
to the battery.  Any voltage fluctuations in either of these will
be "noise".

The ground line is just as likely to get noise as the power line.
When the ground line gets noise (which can occur if you ground
your amplifier, say, in your trunk on the car body, and that same
body is used to ground other devices such as lights, fuel pump,
ignition, etc., and now your amplifier's ground return to the
battery includes the tiny voltage perturbations created by all the
other devices' ground returns as well), that noise in the ground
line will be "seen" as part of the input to the amplifier, and
amplified to your speaker as noise.  The car body, even as big as
it is, is not a zero ohms return to the battery.  For the purpose
of lights or other devices, some noise in the power and ground
lines is inconsequential.  For a stereo, that noise can wreak havoc
in the sound.

-Ti
01 S4 2.7 biturbo quattro
84 5000S 2.1 turbo
80 4000 2.0
96 A4 2.8 quattro (sold but not forgotten)
-- 
    ///  Ti Kan                Vorsprung durch Technik
   ///   AMB Research Laboratories, Sunnyvale, CA. USA
  ///    ti at amb.org
 //////  http://www.ibiblio.org/tkan/
///