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XLR
Cannon XLR connector — IEC 61076-2-103

XLR is a type of electrical connector, developed in the 1950s by Cannon (ITT) and primarily used with audio-visual and stage lighting equipment. The circular connectors have between 3 and 7 contacts, and are also used for control, low-voltage power supplies and other applications [1].


Although the official name for these connectors is XLR – named after Cannon's X-series connectors – they are also referred to as Cannon connectors. They are made by many manufacturers though. Below are the most common pin layouts and wiring schemes.


When describing the gender of the connectors (pins or holes), it is common to add a suffix to the plug name, such as '/M' (male) or '/P' (plug) for pins, and '/F' (female) or '/S' (socket) for holes. In the descriptions below we use '/P' and '/S', e.g. XLR-5/S for a 5-pin female XLR connector.

Layout
Audio
Headsets
Lighting
Power
  


Layout
XLR 3
This is arguably the most common type of XLR connecor. It is used for balanced audio signals in microphones, mixers, amplifiers, etc. It is also used for intercoms and for low-voltage power supplies, although in the latter case the pinout is not unambiguous.   
3-pin XLR (female) socket

XLR 4
The 4-pin XLR is often used for low-voltage power supplies – typically 12V DC – and is used with professional audio and video equipment, in particular with camera's. The pin-out is unambiguous and it should be preferred over 3-pin XLR.

4-pin XLR is also used for headphones and headsets, in particular with stage intercoms.
  
4-pin XLR (female) socket

XLR 5
The 5-pin XLR is most commonly used for lighting control, in particular when using the DMX512 standard. They are also used for stereo microphones (using two balanced pairs and a common ground) and for various kinds of DC power supply.

In some cases, this connector is also used for intercoms, especially when stereo is required.
  
5-pin XLR (female) socket


XLR 6
6-pin XLR is commonly used for dual-channel intercom systems and for stage lighting control applications. It is also used for professional stereo headphones with a balanced microphone (boom), and for a variety of special purpose devices.   
6-pin XLR (female) socket


XLR 7
7-pin XLR is used for the connection of (some) valve-based condenser microphones, and carries their signal as well as the LT and HT voltages for the valves (tubes). It is also used for the remote control of certain Le Maitre and Ultratec fog machines, and for a variety of special purpose devices.

Crypto Museum has adopted the 7-pin XLR for the connection of vintage POTS telephone sets to (wartime) speech scramblers, such as the SA-5030 dial phone and the Frequency Changer 6AC.

  
5-pin XLR (female) socket


Audio
Mono balanced audio   XLR 3
This is the most common XLR plug for audio signals. It can be used for microphones as well as line-level signals. Male chassis parts are normally used for output (e.g. at the bottom of a microphone), whilst the input is isually a female socket (e.g. on a studio mixer).

  1. Ground (shield)
  2. Audio (+) (H) (hot)
  3. Audio (–) (L) (cold)
    3-pin XLR (female) socket
Mono unbalanced audio   XLR 3
If an unbalanced source (e.g. a microphone) is connected to a balanced input, the shield (ground) should be connected to pins 1 and 3.

  1. Ground (shield)
  2. Audio (+) (H) (hot)
  3. Connected to 1
    3-pin XLR (female) socket

Headsets
Intercom headset   XLR 4P
This is the most common wiring for a stage intercom, such as Clear-Com and other Clear-Com compatible wired intercoms. In most cases the headset cable is fitted with an XLR-4/P connector.

  1. MIC GND (shield)
  2. MIC signal (hot)
  3. Headphone (H)
  4. Headphone (L)
    4-pin XLR (male) socket
Despite the commonly accepted standard shown above, some manufacturers, in particular the largest one – Riedel – uses XLR-4/P connectors on its equipment, in which case the headset cable has to be fitted with an XLR-4/S connector. The pinout is identical however.

  1. MIC GND (shield)
  2. MIC signal (hot)
  3. Headphone (H)
  4. Headphone (L)
    4-pin XLR (female) socket
Stereo headset with microphone   XLR 5
This is the most common wiring when a 5-pin XLR is used for intercom applications, but note that the microphone is unbalanced. A standard DMX extension cable can be used for the wiring.

  1. MIC GND
  2. MIC signal
  3. Headphone common
  4. Headphone Left
  5. Headphone Right
    5-pin XLR (female) socket
Stereo headset with balanced microphone   XLR 5
This wiring scheme is used by Beyerdynamic, for example when its DT-290 headset is used with the K 190.41 cable. A 5-pin male connector is used on the headset cable, and a female socket on the equipment. This scheme should be used when the headset has a balanced microphone. Note that a common ground (3) is used for microphone and speakers.

  1. MIC-H
  2. MIC-L
  3. Headphone & MIC GND
  4. Headphone Left
  5. Headphone Right
    5-pin XLR (female) socket
Stereo headset with balanced microphone   XLR 6
  1. MIC-L
  2. MIC-H
  3. Headphone common
  4. Headphone Left
  5. Headphone Right
  6. MIC ground
    6-pin XLR (female) socket
Stereo headset with balanced microphone   XLR 7
  1. MIC GND
  2. MIC-H
  3. MIC-L
  4. Headphone Left (L)
  5. Headphone Left (H)
  6. Headphone Right (H)
  7. Headphone Right (L)
    7-pin XLR (female) socket


Lighting
DMX512
  1. Signal Common
  2. Data 1 (–) (primary data link)
  3. Data 1 (+) (primary data link)
  4. Data 2 (–) (optional secondary data link)
  5. Data 2 (+) (optional secondary data link)
    5-pin XLR (female) socket
DMX512 alternative
This connector is not endorsed by the DMX512 standard, but is nevertheless commonly used.

  1. Signal Common
  2. Data 1 (–) (primary data link)
  3. Data 1 (+) (primary data link)
    3-pin XLR (female) socket


Power
Below are some wiring schemes for supplying low DC voltages (typically 12V DC) to (professional) equipment. Although 3-pin XLR is often used as a low-cost power connector, it is recommended to use 4-pin XLR instead, as its wiring scheme is unambiguous. The receptable that is fitted to the chassis of the device that must be powered, is always of the plug-type (male), as shown here.

12V DC   XLR 4P
  1. 0V (ground)
  2. not connected
  3. not connected
  4. +12V
    4-pin XLR (male) plug, commonly fitted in the chassis of the device that is to be powered
Low-cost wiring   XLR 3P
Although the wiring scheme below is often used with (professional) equipment, it is by no means standard. The use of 3-pin XLR for power supply is therefore strongly discouraged.

  1. 0V (ground)
  2. not connected or +12V 1
  3. +12V
    Recommended wiring when using 3-pin XLR for power supply
  1. When using this wiring scheme, it is recommended to connect pin 2 to pin 3, so that they both carry 12V. This allows a standard microphone cable to be used for supplying power to a device, and avoids damage should it accidentally be plugged into a microphone.

UK wiring   XLR 3P
Even worse than the above wiring scheme, is the British one for using XLR3 for power supply, as the (+) and (-) terminals are reversed. This might cause serious damage to equipment to which it is connected. Unfortunately, this 'standard' has meanwhile been adopted by manufacturers of cheap power supply units, especially from China. Avoid this wiring scheme whenever possible.

  1. +12V
  2. +12V
  3. 0V (ground)
    3-pin XLR (female) socket


References
  1. Wikipedia, XLR connector
    Retieved April 2021.

  2. Wikipedia, DMC512
    Retieved April 2021.
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Crypto Museum. Created: Friday 02 April 2021. Last changed: Monday, 06 September 2021 - 09:40 CET.
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