XLR Connector (3-pin Audio) Symbol
Definition: The XLR Connector (3-pin Audio) symbol represents a balanced, shielded 3-pin audio interconnect in circuit diagrams, denoting a connector used to carry balanced differential audio signals between microphones, mixing consoles, amplifiers, and professional audio equipment; the connector is referenced in IEC 61076-2 and EIA RS-297-A and its three pins are designated Pin 1 (Shield/GND), Pin 2 (Hot/+), and Pin 3 (Cold/-).
Also known as: XLR plug, Canon connector, balanced audio connector, mic connector, 3-pin audio plug, professional audio connector.
What the XLR Connector (3-pin Audio) symbol means
The XLR Connector symbol in a schematic identifies a 3-pin balanced audio interface point. Pin 1 carries the cable shield and chassis ground, Pin 2 carries the positive (hot) audio signal, and Pin 3 carries the negative (cold) audio signal. The balanced differential signal on Pins 2 and 3 allows common-mode noise rejection: any interference induced on the cable affects both conductors equally and is cancelled by the differential input of the receiving equipment.
XLR connectors are the professional standard for microphone connections, stage and studio wiring, and any application requiring reliable, low-noise audio over cable runs exceeding a few metres. The symbol is used in audio system block diagrams, stage wiring schematics, recording studio patchbay layouts, and live sound reinforcement documentation.
How to identify the XLR Connector (3-pin Audio) symbol
The XLR Connector symbol is typically drawn as a small circle or D-shaped outline representing the connector body with three numbered pin indicators inside or adjacent to it. In simplified schematic form it may appear as a rectangular block labelled 'XLR' with three labelled lines exiting it: Pin 1 (Shield/GND), Pin 2 (Hot/+), and Pin 3 (Cold/-). In some diagrams it is represented by a triangle or trapezoid outline with three terminal lines, visually distinguishing it from 2-pin or multi-pin connector symbols.
Function in a circuit
The XLR connector provides a mechanically locking, environmentally robust electrical connection for balanced audio signals. The three-pin balanced configuration allows the connected equipment's differential input amplifier to subtract the identical noise voltage induced on both signal conductors (Pins 2 and 3) from the desired audio signal, achieving typically 40–80 dB of common-mode noise rejection ratio (CMRR). The locking mechanism (a spring-loaded tab) prevents accidental disconnection on stage or in rack systems. XLR connectors also carry 48 V phantom power from mixing consoles to condenser microphones via Pins 2 and 3 simultaneously (with Pin 1 as return).
Standards: IEC vs ANSI
| IEC 60617 | IEC 61076-2-103 specifies circular connectors used for audio and similar applications. XLR physical and electrical characteristics are also described in IEC 61076-2. The symbol used in IEC-style schematics is a circle with three pin stubs labelled 1, 2, 3. |
|---|---|
| ANSI/IEEE 315 | ANSI/EIA RS-297-A defines the XLR-type connector dimensions and pin assignments, establishing Pin 1 = ground/shield, Pin 2 = hot (+), Pin 3 = cold (-). IEEE 315-1975 (ANSI Y32.2) defines the generic connector symbol used for XLR in ANSI-style schematics. |
| Key difference | IEC and ANSI connector symbols for XLR are effectively identical in schematic use — both show a circular or rectangular outline with three numbered pin terminals. The pin-numbering convention (1=GND, 2=Hot, 3=Cold) is universal and does not differ between standards. |
Terminals / pins
| Pin | Name |
|---|---|
| gnd | 1 (Shield/GND) |
| hot | 2 (Hot/+) |
| cold | 3 (Cold/-) |
Typical values
Impedance: microphone output typically 150–600 Ω balanced; line level 600 Ω or 10 kΩ+ load; phantom power: 48 V DC (IEC 61938) or 12 V / 24 V variants; contact resistance: < 10 mΩ; rated current: 15 A (power variants up to 5-pin); frequency response: DC to >100 kHz; cable: typically 2-conductor shielded microphone cable (Belden 8451 or equivalent).
Where the XLR Connector (3-pin Audio) symbol is used
- Professional microphone connections to mixing consoles, preamps, and audio interfaces in recording studios and live sound
- Stage patch bays and multicore stage boxes (stage snakes) carrying multiple balanced audio channels
- PA system amplifier inputs and processor interconnections in live event production
- Broadcast audio — outside broadcast (OB) vehicles, broadcast consoles, and tie-line panels
- Phantom-power delivery (48 V) from console or preamp to condenser and ribbon microphones
- Intercom systems (production talkback, show relay) using modified 3-pin or 5-pin XLR wiring
- DMX512 lighting control (using 3-pin or 5-pin XLR as a physical interface, though not an audio signal)
Example
In a live stage audio schematic, a condenser microphone is shown connected to a mixing console preamp input via an XLR Connector symbol pair: the microphone output XLR female (pins 1, 2, 3) connects through a balanced microphone cable to the console input XLR male (pins 1, 2, 3). A notation at the console input indicates +48 V phantom power is enabled, supplying the microphone via Pins 2 and 3 simultaneously relative to the Pin 1 shield.
Key facts
- The XLR Connector (3-pin Audio) symbol represents a balanced audio connector with Pin 1 = Shield/GND, Pin 2 = Hot (+), and Pin 3 = Cold (-), following the ANSI/EIA RS-297-A and IEC 61076-2 pin assignment standard universally used in professional audio.
- Balanced wiring via the 3-pin XLR connector achieves 40–80 dB of common-mode noise rejection ratio (CMRR) at the differential amplifier input, making it essential for long cable runs in electrically noisy live and studio environments.
- Pin 1 on an XLR connector carries the cable shield and should connect to chassis ground at the input (receiving) equipment only, not at the output (sending) equipment, to avoid ground loops — a principle known as 'Pin 1 Best Practices' (AES48-2019).
- 48 V phantom power (IEC 61938) is delivered via the XLR connector's Pins 2 and 3 simultaneously (equal positive voltage on both signal conductors relative to Pin 1), allowing condenser microphones to operate without a separate power supply.
- The XLR connector was originally designed by James Cannon (hence 'Canon connector') in the 1950s and later evolved into the ITT Cannon XLR standard; the female connector is used on microphones and the male on console inputs, following the convention that signal flows into female connectors.
- The locking mechanism on XLR connectors (a spring-loaded release tab) provides a secure mechanical connection that resists accidental disconnection under tension — a critical requirement for stage and broadcast applications.
- DMX512 lighting control protocol uses 3-pin or 5-pin XLR connectors as a physical interface (EIA-485 differential signal), which means DMX wiring uses the same XLR symbol in schematics as audio, distinguished only by the protocol annotation.
Diagrams that use this symbol
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- xlr wiring diagram
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- xlr cable diagram
- xlr pin diagram
- xlr to mono jack wiring diagram
Frequently asked questions
What does the XLR connector symbol mean in a circuit diagram?
The XLR Connector symbol in a circuit diagram means a 3-pin balanced audio connection point. It identifies where a microphone cable, line-level interconnect, or DMX cable attaches. The three pins are always Pin 1 (Shield/GND), Pin 2 (Hot/+), and Pin 3 (Cold/-), providing a balanced differential signal path with noise rejection.
What does the XLR connector symbol look like in a schematic?
The XLR Connector symbol is drawn as a circle or rectangular outline representing the connector body with three terminal lines labelled 1 (GND/Shield), 2 (Hot/+), and 3 (Cold/-) exiting it. In block diagrams it may appear as a small labelled box with three connection lines. The symbol is distinguished from other connectors by the explicit three-pin numbering and the 'XLR' label.
What is the pin numbering for an XLR connector?
XLR connector pin assignments are: Pin 1 = Shield/Ground (cable screen), Pin 2 = Hot (positive signal, +), Pin 3 = Cold (negative signal, -). This convention is defined in ANSI/EIA RS-297-A and followed universally in professional audio worldwide. The female connector is typically on the microphone or signal source, and the male on the input or destination.
What is the difference between IEC and ANSI XLR connector symbols?
The XLR connector symbol is effectively identical in both IEC (IEC 61076-2) and ANSI (ANSI/EIA RS-297-A, IEEE 315) representations: both depict a circular or rectangular connector outline with three numbered pin terminals. The pin assignment (1=GND, 2=Hot, 3=Cold) is universal across both standards and all regions.
What is phantom power and how does it relate to the XLR connector?
Phantom power (IEC 61938) is 48 V DC supplied by a mixing console or preamp through the XLR cable to power condenser microphones. The 48 V appears on both Pin 2 and Pin 3 simultaneously (equal voltage on both, referenced to Pin 1), so it does not unbalance the signal. Dynamic microphones and passive ribbon microphones are unaffected by phantom power because they present no DC path between pins.
What standard defines the XLR connector symbol?
The XLR connector's physical and pin-assignment standard is ANSI/EIA RS-297-A and IEC 61076-2-103. The schematic symbol for connectors in general is defined in ANSI Y32.2 / IEEE 315-1975. The professional audio industry also follows AES48-2019 for best practices on Pin 1 grounding and balanced interconnection.
Why is the XLR connector used for microphones instead of a simple 2-pin connector?
The 3-pin XLR is used for microphones because the balanced differential wiring (Pin 2 and Pin 3 carrying equal and opposite signals) allows the receiving preamp to reject common-mode interference induced on the cable, achieving 40–80 dB noise rejection. This is critical for long cable runs in electrically noisy environments. The 3rd pin (Pin 1) provides a dedicated shield ground path separate from the signal conductors.
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