Common Pin Allocations
We mainly use two types of connectors for signal transmission: XLR and jack. An audio signal can be transferred in two ways: unbalanced and balanced. The unbalanced transmission requires two wires. The balanced transmission requires three wires. An XLR connector has three poles to connect the wires to. A jack has either two poles or three poles.
For the unbalanced signal transmission, the useful signal is sent via one wire, while the other wire is used as signal ground. For the balanced transmission, the useful signal is also transmitted via a third wire, but the phase is reversed by 180°.
After signal transmission, the negative phase is reversed again at the input transformer and is then added to the positive signal wire. This way, interferences are eliminated. A balanced cable link is a lot less susceptible to noise.
The XLR Connector
There are two different XLR connectors: the male connector and the female connector. The XLR output is male, the XLR input is female. The XLR output of a microphone is male, while the XLR input of a mixing console is female. The following graphic shows the XLR pin allocation:
| # | unbalanced | balanced | speaker cable |
|---|---|---|---|
| 1 | shield and signal ground | shield | negative wire (–) |
| 2 | signal | positive wire (“hot”) (+) | positive wire (+) |
| 3 | bridged with pin 1 | negative wire (“cold”) (-) | free |
The Jack Connector
In audio engineering, we mostly deal with two variations: the 3.5 mm jack (i.e. on an iPod) and the 6.35 mm jack (i.e. on a guitar cable). Both sizes are available as two-pole and three-pole variations. A two-pole jack connector consists of a tip and a sleeve. A three pole connector has a ring between the tip and the sleeve.
In an unbalanced transmission, the tip is used for the signal and the sleeve is used as signal ground. In a balanced transmission, the ring is used for the negative signal wire.
A three-pole connector can be used for the unbalanced transfer of a stereo signal (i.e. headphones). The left signal is connected to the tip, the right signal is connected to the ring and the ground of both signals is connected to the sleeve.
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sig = audio signal GND = signal ground |
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L = left audio signal R = right audio signal GND = signal ground of both channels |
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L = negative signal R = positive signal GND = signal ground of both channels |