🚀 go-pugleaf

Paul Durrant <pdurrant@durrant.demon.co.uk> wrote:

> In article <1d8kpqc.dtf2qa1s5zxv4N@baw9pub65.bluewin.ch>,
> bridgeband@bluewin.ch (Bridge) wrote:
> 
> > this end to the other, there are two leads stuck together and dividing
> > into a white plug and a red plug. These two plug go into the HiFi to my
> > DAT Playback socket (which is meant for that, I think). When I have the
> > time I'll snip the earth of the audio cable, I hope it's obvious which
> > one it is.
> 
> The Earth isn't one or other of the red & white plugs - it's the shielding
> on the plugs - the cables have a central core covered in plastic surrounded
> by some shielding wire and that all inside the outer plastic cover of the
> cable. It's the shielding wire you need to make a break in.

To be precise: the red plug and the white plug each has two connections.
Assuming standard phono connectors, the central prong on each plug is
the signal connection.  The metal bits round the outside are the earth
connection.

The central prong is connected to the conductor that runs down the
centre of the lead.  The earth connection is made to the shielding that
runs around the central (insulated) wire.

This way of connecting things assumes that all the equipment connected
together by it is using the same earth potential.

In professional applications, this is often not the case, and you often
use a `balanced signal' - instead of having a single signal wire and an
earth, you have two signal wires.  When one goes up, the other goes
down, and vice-versa.  The signal voltage is the difference between the
two signal wires, so you don't have to worry about earth loops,
different earth potentials, and so on.  It's also much less inclined to
pick up noise and so on, so it's very often used on long microphone lead
runs.

If you need maximum noise immunity, the signal wires are encased in a
screen which is held at the same voltage as the signal by a buffer
circuit, the pair of screen wires are twisted together, and encased in a
screen, which is driven at the mid-point voltage of the two signal wires
by another buffer, and I suppose the madly paranoid would then encase
that in a further screen held at earth potential.  I've never met this
sort of thing in anything but high impedance, low signal level
instrumentation.

Rowland.

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