These are the industry standard microphone connectors, robust and relatively simple to install. There are a number of ways in which they can be wired.
(i) BALANCED operation
Pin 1 connects to screen (Signal earth)
Pin 2 connects to signal + (Live)
Pin 3 connects to signal - (Return)
(ii) UNBALANCED operation
Pins 1 & 3 connect to the screen of the cable
Pin 2 connects to signal conductor
The PIN numbers are identified on the XLR plug and an easy way to remember how they should be wired is:
X = Earth (Pin 1)
L = Live (Pin 2)
R = Return (Pin 3)
An unbalanced microphone can only be used up to a maximum of 10 meters away from the amplifier. Any more than this and noise problems become apparent. A balanced microphone will allow cable runs of up to 100m without any loss of performance. .For unbalanced operation, a single core screened microphone cable can be used, but for a balanced line a twin core screened cable is required.