"infamis" wrote in message
om...
The AC signal is carried on the inner pin of the RCA jack
and the ground provides the return path for the complete
circuit. Just as the body of your car carries the return path
for the battery power that runs the starter motor, the power
that runs your lights, and even the audio that goes to the
rear speakers, etc.

The inner pin is just one conductor, correct? Where's the other conductor
at?
Is it ground? If that's so, that's what I'm not getting. If ground means
there's a rod stuck in the earth, how can that be generating the other
"half"
of the AC signal?

Ground does not mean a rod stuck in the earth. Ground simply means common.

Let me explain the 3 meanings of ground in electronics.

(1) A rod stuck in the earth, either for lightning/high-voltage safety, or
to use the earth as part of an antenna system.

(2) The chassis of equipment. This is usually connected to (1) indirectly
through the power lines, but it need not be; the equipment works just as
well without doing that (e.g., portable, battery-operated equipment); we
usually tie (2) to (1) through the power line for high-voltage safety, to
better control what would happen if things inside got accidentally connected
to the case or chassis.

(3) A reference point in a circuit.

Consider an imaginary amplifier that consists of a 4-terminal black box.
The input signal goes to terminals A and B. The output signal is taken from
terminals C and D.

Suppose now that inside the amplifier, B and D are connected together. That
is in fact the way amplifiers are usually built.

In that case we will say B = D = ground. It need not be grounded in sense
(1) or (2), although in fact, for hum protection, it is usually connected to
ground in sense (2).

"Ground" merely means "shared by the input and the output."

Now... This amplifier still has 4 terminals (2 wires for input and 2 wires
for output) even though the input "ground" wire is connected to the output
"ground" wire.

Is this making things any clearer? The AC that comes in through an RCA plug
requires 2 conductors, which are the pin of the plug and the outer shield of
the plug. The AC that comes out to drive the next device also requires 2
conductors, the pin of its plug and the outer shield of its plug. It
happens that, the way amplifiers are built, the outer shields of the 2 plugs
are connected together and are considered "ground."

I should perhaps work through all this with batteries and light bulbs, but
it would require some diagrams.