How to Wire a XLR Plug

Balanced Professional Audio Connections use 3-Pin XLR Connectors

Jun 5, 2009

Wiring balanced audio 3-pin XLR connectors is straightforward but it is important to get it right, else phase errors may occur.

The 3-Pin XLR connector is widely used in the professional audio world to carry single-channel balanced audio signals. Originally manufactured by Cannon Electric in California, now part of ITT-Cannon, this connector is rugged enough to take the knocks of outside broadcasts and stage use, and reliable enough to perform well for many years.

In general, for audio connections male connectors are used for an output and female connectors are used for the input. This is why a signal source, such as a microphone, has a plug on the end whereas a mixer or recorder has sockets.

This is the opposite convention to power connectors, where safety considerations mean that power sources come on sockets, rather than on plugs where the pins may short if they come into contact with stray metal objects. However, since phantom power is sometimes supplied by the receiving device, this convention works out well in practice.

XLR Connector Pin Allocation for Balanced Audio Use

How to Solder the 3 Pin XLR Connector

First run the cable through the rear cap, cable retaining claw and connector shell. It is maddening to solder the pins only to find out that it has to be redone because one of these components is not already in place on the cable or they are not in the right order.

How to Solder the Cable to the XLR 3 Pin Audio Plug or Socket

Strip about 2cm (3/4 inch) of the outside insulation from the cable. Experienced wiremen often use a knife, but a rotary cable stripping tool can make it easier to remove this without nicking the strands of the shield with the knife. Tease the strands of the shield apart to expose the inner twisted pair, then twist the strands of the shield together and tin the ends to keep the strands together.

Strip about 1/4 cm (1/8 inch) of insulation from the inner twisted pair, and using a soldering iron of 25W to 50W tin the exposed ends, and tin the solder bucket terminals of the connector. If making up an XLR plug, it can be a good idea to insert the plug into a spare socket connector (not one that is part of any piece of equipment or live circuit). The stops the pins shifting if the thermoplastic disc they are set in softens if the iron is kept on them too long.

It is usually easier to solder the twisted pair to pins 2 and 3, then solder the shield to pin 1. Whatever colour code is used, it must be used consistently. A common one is red for hot, to pin 2 and black for cold, to pin 3. It is essential to get this consistent between both ends of a cable, otherwise a phase reversal will occur, which can cause all sorts of subtle problems in mixdown. A general consistency in the studio means that is an XLR cable has to be repaired, the colour coding is known, without having to chase down the other end of the cable to find out how it had been wired up.

A well made XLR audio connector will give years of reliable service even under the rigours of stage usage.

The copyright of the article How to Wire a XLR Plug in Music Studios/Recording is owned by Richard Mudhar. Permission to republish How to Wire a XLR Plug in print or online must be granted by the author in writing.