Ferrari Mailing List: Re: Need help with stereo in Ferrari

[Charles Perry (charles]

Just for everyone's future reference, the basic problem with all car
audio systems with respect to noise is that car audio is unbalanced by
design (meaning the music's electrical return path and ground are the
same conductor). A properly balanced system (most pro-audio equipment)
uses three conductors (positive, negative, ground), rather than an RCA
line's two conductors (positive, negative/ground).

The signifigance is that the "shield" of RCA wires is not actually a
shield since it is carrying the music signal. That is also why it is so
prone to picking up noise. This is why things like Monster Cable
interconnects are complete wastes of money. Extra layers of shielding
are, by definition, not shielding in car audio, nor in the vast majority
of home audio (anything with RCA connectors). 

This is also the hint of truth in Jeff's suggestion for using network
cable. Network cables are balanced and use their twist as part of a
noise rejection scheme (same as balanced pro-audio cables). This works
in networks due to the balanced electronics on both ends. Using network
cable for car audio will not give you the same benefits because the
electronics at both ends are unbalanced. It will still work, but no
better or worse than regular RCA cables.

In the 90's Rockford Fosgate tried to introduce balanced audio into the
car stereo world in their upper-end lines but it was expensive and
poorly understood and did not catch on.

My current favorite scheme is using fiber-optics as interconnects, but
this requires equipment that is designed for that, which is expensive.

-- charles



-----Original Message-----
From: Jeff Greenfield [mailto:coyote [at] acme-ltd.com] 
Sent: Saturday, March 07, 2009 10:24 PM
To: Charles Perry
Cc: 'The FerrariList'
Subject: Re: [Ferrari] Need help with stereo in Ferrari

Three things come to mind. 

One is that you are picking up RF noise from through your RCA cables.
Believe it or not, I have read that the best thing to use for to connect
components in a car is CAT 5 Network Cable. I've used this (making my
own
cables) on the last few installs I've done and have had no interference
problems at all. Sometimes the shielding in shielded cables will
actually pick up noise. 

The other possibility is that you are having a ground loop problem. This
occurs due to a very small difference in potential (essentially voltage)
when components are grounded at different points on a cars chassis. You
can try a ground loop isolator to see if it reduces or eliminates the
noise. 

One last thought, if your sub uses speaker level inputs from your head
unit, sometimes this causes random popping usually when switched on and
off. If there is any way you can use line level inputs to the sub (I
assume you are using a sub that has its own amp) you would be much
better off. 

Jeff