Audio Connections

Here are pin-outs for common audio connectors and how to make certain audio cables: Before I list them, it is important to point out the difference between balanced and unbalanced signals. Balanced signals have two conductors for the signal - a positive (hot) and a negative (cold). Balanced connections help to reject outside noise from the system and are mandatory for longer runs of cable where the signal is not amplified. This is because the two conductors are summed in inverse at the other end, so any noise picked up along the length gets cancelled out. An unbalanced signal does not have a second conductor, so as the signal is amplified, the noise is also amplified. Unbalanced cables should only be used for short runs.

Signals on hot and cold connections with 180 degree phase inversion

Noise introduced equally on both original and inverted connections

At destination inverted signal is put back into phase causing noise on that connection to be out of phase

Resultant signal cancels out noise and boosts amplitude of original signal

XLR connector

The XLR connector is used commonly for balanced audio connections such as microphones and professional audio components.

Tip = positive (hot)Ring = negative (cold)Sleeve = groundFor stereo connections, tip is Left and ring is Right.For insert connections, tip is Send and ring is Return.Microphone cables

Mic cables have a male XLR connector on one end and a female XLR connector on the other end. The pins are wired straight through, i.e. pin 1 goes to pin 1, etc. Although some people connect the chassis of the connector body to pin 1 (ground) I don't usually follow that procedure because it can lead to unwanted results with ground loops when mic cables are used to interconnect other equipment.

Direct box

When an unbalanced signal, such as one coming from an electric guitar, is connected to a microphone input on a mixer, the signal must be modified for impedance and balance. Most 1/4" TS connections have an unbalance signal between 10,000 and 50,000 ohms. A direct box has a transformer that converts this signal to balanced outputs having an impedance between 150 and 600 ohms. It also has a ground lift switch to isolate AC hum where ground loops are a problem.