Just in case anyone is having trouble understanding how/why there can be two signal wires in addition to ground, it's the same thing as bridging amplifier channels, except on a smaller scale.

One channel carries the signal as normal, and the other channel has the identical signal with the polarity opposite (180 deg, out of phase), meaning when one output goes +, the other one goes -.

The result is that the output, taken from one amp's + terminal to the other amp's + terminal, has twice the overall voltage with the same input signal, which doubles the speaker's current level.

The result is a quadrupling of power, if the amp is capable of doubling its power into a load of half the impedance. That, and the amp's - terminals are (or can be) tied together.

Since current is not really relevant in line-level signals, the main benefit is less noise because (a) of the higher signal-to-noise ratio and (b) because the shield is not a signal-carrying conductor.

In what is often called "true balanced circuit topography", the + and - signal pathways are carried by "mirror" circuitry. Again, the result is that ground is never a signal reference.

In most balanced circuits, either polarity's signal actually could be referenced to ground (like a pair of amps) and two signals could theoretically be had at the same time, one + and one.

So, one can use either the + (pin 2) OR the - (pin 3) as a signal output, as long as pin 1 is used as the ground. Just keep in m ind that the two hots are of opposite polarity (phase).

This message was edited by Larry Fine on 08/23/04 22:23 ET.