On Sat, 07 Feb 2004 19:43:32 GMT, "gix" wrote:

Hi
i'm an italian student and exuse for my english;as from object i have a
question for the audio line of my panel audio(GMA 340 garmin),exsit a really
advantage to use bipolar shielded wire twisted respect a normal bipolar wire
shielded for reduce the noise in my headphones.
If you have a document on this matter for me is very important
Thank you in advance
Bye Luigi


Buon Giorno, Luigi.

I will try to write this so it can be translated clearly.

Pairs of wires inside a grounded shield are made for amplifier outputs
that drive the wires in opposite directions at the same time. In
English this is often called "push-pull" or "double-ended." In this
type of design, neither signal is related to ground.

In a cable with only one wire inside the shield, the amplifier output
drives the voltage on the wire with reference to ground. This kind of
design is subject to "common-mode" interference -- the noise is picked
up on the signal wire. Double-ended systems reject this kind of noise
because the noise voltage has the same polarity on both wires, while
the signal has opposite polarities on the two wires. But this is a
result of system design. You can not achieve it by changing headphone
wires.

In fact, I think the noise may be entering the radio very far back in
the chain of amplifiers inside the radio. The noise may even enter on
the positive power wires. If the noise is really bad, you will need
a good technician to remove it.

Ciao,
Don