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[napman]

Hi pop,
I found this on the "WEB", it's not directily answer your question but I think it's interesting to know (may be you already knew)

Here it is;
OK, firstly there are 2 types of 1/4" plug - mono (2 wires) and stereo (3 wires). The stereo plug can also be used to carry balanced signals (in the TRS (tip-ring-sleeve) setup).

Guitar jacks are a two line (unbalanced) signal, XLR is a three line (balanced signal). The difference lies in two places - the actual plug type (XLR vs 1/4") and the line type (balanced vs unbalanced)

As monty said, an unbalanced line has two wires - hot and common. Any interference picked up on the hot line will be included when the signal reaches it destination (amp, pre, mixer etc.). The common in the shield, and the hot is the centre cable

In the balanced configuration, there are three lines, hot, cold and common. Hot and common are the same as above, and the cold is also a centre cable. (ie. there are two centre cables in a balanced line)

Any interference picked up on the hot (signal) line will also be picked up on the cold line.

The difference is how the signal lines are handled at the signals destiantion. In a balanced line device, the cold line is phase shifted 180 degrees before being combined with the hot line. This means (and can be proven using trigonometry) that any signal that is on both hot and cold (and it will be only the interference, not the actual guitar signal) is cancelled out.

The long and the short of it is that the interference is removed from the signal using a balanced line, while it is not using an unbalanced line.

Don't be confused between the techniques for signal transmission and the actual plugs that are used. XLR is merely a different type of plug from a 1/4" TRS plug. The XLR is used a lot because it is solid, and locks the cable into the socket. The 1/4" TRS plugs are used because they are physically smaller and cheaper.

Hope this help, pop