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XLR connector

The XLR connector is an electrical connector design. XLR plugs and sockets are used mostly in professional audio and video engineering applications for a variety of purposes including power connections and both analog and digital audio signals.

The connector has been called a cannon plug or cannon connector in reference to its original manufacturer, James H. Cannon, founder of Cannon Electric in Los Angeles, California (now part of ITT Corporation.) Originally manufactured as the Cannon X series, subsequent versions added a latch (Cannon XL) and then surrounded the female contacts with a resilient polychloroprene, which resulted in the part number prefix XLR.[1][2] The number of pins varies from three to seven. Many companies now make XLR connectors.

They are superficially similar to the older and smaller DIN connector range, but are not physically compatible with them.

XLR connectors are covered by an international standard for dimensions, IEC 61076-2-103[3]

Patterns of XLR connector
Variety of male and female XLR connectors with different numbers of pins

The most common is the three-pin XLR3, used almost universally as a balanced audio connector for high quality microphones and connections between equipment. XLR3 was also used to transmit MIDI data on some Octave-Plateau synthesizers including the Voyetra-8. Most of the XLR types made by different companies will mate with others of the same number of contacts.

XLR4 (with four pins) is used for ClearCom and Telex intercom headsets and handsets, DC power connections for professional film and video cameras, older versions of AMX analog lighting control and some pyrotechnic equipment. XLR5 is the standard connector for DMX512 digital lighting control and is also used for dual-element microphones and dual-channel intercom headsets. XLR6 is used for dual channel intercom beltpacks. XLR7 is used on several generations of LeMaitre (now Ultratec) fog machines for remote input and control.

Many other types of connectors using the XLR type shell exist, with various pin numbers. Most notable are two now obsolete three-pin patterns manufactured by ITT Cannon. The power Cannon (also called the XLR-LNE connector) had shrouded pins and red insulation, it was intended as a mains power connector, but has been superseded by the IEC 60320 series of connectors and increasingly, more recently, the PowerCon connector developed by Neutrik.

The loudspeaker Cannon had blue or white insulation (depending on its gender), was intended for connections between audio power amplifiers and loudspeakers. At one time XLR3 connectors were also used extensively on loudspeaker cables, as when first introduced they represented a new standard of ruggedness, and economic alternatives were not readily available. The convention[citation needed] was that a two-conductor loudspeaker cable had XLR3 female connectors on both ends, to distinguish it from a three-conductor shielded signal level cable, which has an XLR3 female at one end and an XLR3 male at the other. Either pin 2 or 3 was live, depending on the manufacturer, with pin 1 always the 'earthy' return. This usage is now both obsolete and dangerous to equipment but is still sometimes encountered, especially on older equipment. For example, some loudspeakers have a built-in XLR3M as an input connector. This use was superseded in professional audio applications by the Neutrik Speakon connector.

The female XLR connectors are designed to first connect pin 1 (the earth pin), before the other pins make contact, when a male XLR connector is inserted. With the ground connection established before the signal lines are connected, the insertion (and removal) of XLR connectors in live equipment is possible without picking up external signals (as it usually happens with, for example, RCA connectors).

Lighting control for entertainment applications is widely connected using five pin XLRs. Only three pins are used to carry the DMX512 signal, including systems implementing Remote Device Management (RDM). Using XLR5s also prevents users from confusing lighting with common XLR3 audio cables. Unfortunately, five pin XLRs still allow the use of lower-grade (non-110 Ohm) microphone cable for transmission of signals. Some manufacturers of DJ lighting and professional lighting are still using three-pin connectors as their standard. Manufacturers such as Leviton and Lightronics have even established new protocols not compatible with DMX512 that use three pin XLR to control lighting devices (primarily dimmers made by the same manufacturer).

Rechargeable devices exist that use three-pin XLR connectors. These can be found on electric powered mobility wheelchairs and scooters. The connectors carry from 2 to 10 amps at 24 volts.

Some audio equipment manufacturers reverse the use of pin 2 (properly the normal input) and pin 3 (inverting input). This reflects their own previous usage before any standard existed. Pin 1 is always ground, and many connectors connect it internally to the connector shell or case.

Although covered in AES48-2005 and in AES54-3-xxxx, there is still some disagreement on the best way to handle the usage of pin 1 at both ends of a cable, particularly with respect to the cable shield, the connector's shell, signal ground, and a third cable conductor connected to pin 1, which may (or may not) be connected to the shield. The main controversy is whether the shell of the connector should be connected to pin 1 or the shield, or left floating. AES standards mentioned above recommend that shells of cable-mounted connectors should never be connected to pin 1 or the shield, because inadvertent contact of the shell with another grounded surface while in use can create unwanted current paths for fault current, potentially causing hum and other noise. On the other hand, equipment containing active circuitry should always have pin 1 connected to the conductive enclosure of the equipment as close as possible to the point where the signal enters the enclosure. The argument centers around the radio frequency shielding provided by the shell of the connector, which may be reduced if it is left floating. An alternative solution is to connect the shell to pin 1 and the shield through a small value capacitor, providing RF shielding but allowing very little audio-frequency current to flow. This capability can be built into a fixed jack or a cable terminated with XLR connectors.

An XLR3M (male) connector is used for an output and an XLR3F (female) for an input. Thus a microphone will have a built-in XLR3M connector, and signal cables such as microphone cables will each have an XLR3F at one end and an XLR3M at the other. At the stage box end of a multicore cable, the inputs to the mixing desk will be XLR3F connectors, while the returns to the stage will be XLR3M connectors. Similarly, on a mixing desk, the microphone inputs will be XLR3F connectors, and any balanced outputs XLR3M connectors.

Neutrik also offers several models of combination jacks that accept both XLR and 0.25 in TS or TRS plugs.

Phantom power

Some microphones such as condenser microphones require power. An alternative to battery power is phantom power, which consists of direct current applied equally through the two signal lines of a balanced audio connector (in modern equipment, usually an XLR connector). The supply voltage is referenced to the ground pin of the connector (pin 1 of an XLR), which normally is connected to the cable shield or a ground wire in the cable or both. When phantom powering was introduced, one of its advantages was that the same type of balanced, shielded microphone cable that studios were already using for dynamic microphones could be used for condenser microphones as well, in contrast to vacuum-tube microphones, which required special, multi-conductor cables of various kinds.

With phantom power, the supply voltage is effectively invisible to balanced microphones that do not use it: e.g., most dynamic microphones. A balanced signal consists only of the differences in voltage between two signal lines; phantom powering places the same DC voltage on both signal lines of a balanced connection. This is in marked contrast to another, slightly earlier method of powering known as parallel powering or T-powering (from the German term Tonaderspeisung), in which DC was overlaid directly onto the signal in differential mode. Connecting a dynamic microphone (especially a ribbon microphone) to an input that had parallel powering enabled could very well damage the microphone severely, but this is not normally so with phantom powering unless the cables are defective or wired incorrectly.

See also

TRS connector
RCA connector
DIN connector
RF connector


^ Rane Professional Audio Reference description
^ Rayburn, Ray (December 16, 2008). "A brief history of the XLR connector". Sound First. Archived from the original on February 22, 2011.
^ http://webstore.iec.ch/webstore/webstore.nsf/Artnum_PK/31858
^ Audio Engineering Society. AES14-1992 AES Standard for professional audio equipment—Application of connectors, part 1, XLR-type polarity and gender.

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