XLR Connector Wiring Diagram: Balanced Audio Pin Assignment and Circuit
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An XLR diagram shows the three-pin balanced audio connector wiring standard: pin 1 ground, pin 2 hot (non-inverting), and pin 3 cold (inverting).
The XLR connector is the professional audio industry's standard for balanced analogue audio connections. It uses a three-conductor system — two signal conductors and one ground — to achieve noise rejection through common-mode cancellation. Understanding XLR wiring begins with the pin numbering convention.
Looking at the face of an XLR female socket (the receptacle into which the male plug inserts), the pins are numbered 1, 2, and 3 arranged in a triangular pattern. The convention defined by AES14 (and widely adopted as industry practice) is:
Pin 1: Shield / Ground. The cable's outer braided or foil shield connects to pin 1 at both ends (or at the source end only in some installations, to prevent ground loops). The shield provides electromagnetic shielding for the signal conductors.
Pin 2: Hot (positive, non-inverting signal). This conductor carries the signal in phase. At the receiving equipment, the differential amplifier amplifies the signal on pin 2 relative to pin 3.
Pin 3: Cold (negative, inverting signal). This conductor carries a signal of identical amplitude but opposite polarity (180 degrees out of phase) to pin 2.
The advantage of balanced operation lies in common-mode rejection. Any interference (hum from mains fields, radio frequency interference) induced on the cable affects both the hot and cold conductors equally. At the receiving differential amplifier, common-mode signals are rejected; only the difference signal between pin 2 and pin 3 is amplified. This noise rejection — quantified as the common-mode rejection ratio (CMRR) of the receiving amplifier — makes balanced XLR connections practical over cable runs of 100 metres or more.
For microphones, the XLR connection also carries phantom power (standardised at 48 V DC by IEC 61938) on pins 2 and 3 simultaneously relative to pin 1. Phantom power is used by condenser microphones to power their internal electronics. Dynamic microphones and ribbon microphones (passive types) are not harmed by correctly applied phantom power, as the voltage is presented equally on both signal pins and produces no differential current through the microphone element.
XLR connectors are rated for analogue audio use; they are not intended for high-voltage power distribution.
How to wire xlr diagram
- Strip the cable jacket Strip approximately 25–30 mm of the outer cable jacket. The outer braid or foil shield and the two inner conductor pairs will be exposed. Slide a heat-shrink sleeve over the cable at this stage if the connector shell has no integral strain relief.
- Prepare the shield Carefully fold the braided shield back over the jacket or twist the foil shield to form a pigtail wire. Trim to the correct length to reach pin 1's terminal in the assembled connector without excess slack.
- Strip and tin the conductors Strip approximately 5–7 mm of insulation from each inner conductor. Twist the strands tightly. Apply a small amount of solder to tin each conductor tip — this prevents strand splaying and improves solder joint quality in the connector.
- Solder the conductors to the correct pins Solder the shield pigtail to pin 1. Solder the positive (hot) conductor to pin 2 — typically the white or red conductor in a standard star-quad or paired cable. Solder the negative (cold) conductor to pin 3 — typically the black or blue conductor. Do not bridge solder between adjacent pins.
- Inspect and test the solder joints Each joint should be smooth and shiny. A cold (dull, granular) solder joint has poor conductivity and will cause intermittent faults. Use a continuity tester to verify: pin 2 to pin 2, pin 3 to pin 3, pin 1 to pin 1 across the cable. Verify no continuity between any pair of different pins.
- Assemble the connector shell Slide the connector body over the cable, engaging any strain relief clamp on the cable jacket — not on the inner conductors. Do not over-tighten the strain relief as this can deform the cable and cause intermittent faults.
Specifications
| Pin 1 | Shield / Ground |
|---|---|
| Pin 2 | Hot (non-inverting, positive signal) |
| Pin 3 | Cold (inverting, negative signal) |
| Phantom power standard | IEC 61938: 48 V DC ±4 V on pins 2 and 3 relative to pin 1 |
| Relevant standard | IEC 60268-12, AES14 |
| Connector locking | Latching spring pin on male connector, released by pressing the latch tab |
| Connector shell diameter | Standard 3-pin XLR: approximately 24 mm diameter male body |
Safety warnings
- XLR connectors carry audio-level signals and phantom power (up to 48 V DC). While not a high shock hazard under normal use, equipment must still be powered down before making or breaking connections during installation or fault-finding.
- Phantom power can damage some ribbon microphones (active ribbon types are usually protected; passive ribbons with unbalanced transformers may be at risk). Verify microphone compatibility before enabling phantom power.
- Do not use XLR connectors or cables for mains power distribution — they are not rated for mains voltages or currents.
- In installed permanent wiring, ensure cable routes comply with applicable building wiring regulations, particularly regarding segregation from mains power cables to prevent induced interference.
- Use only electronics-grade solder and appropriate ventilation when soldering. Lead-containing solder poses a health hazard; wash hands thoroughly after handling.
Tools needed
- Soldering iron (temperature-controlled, 25–40 W)
- Electronics-grade solder
- Wire strippers
- Small flat-head screwdriver (strain relief)
- Continuity tester or multimeter
- Flux pen (optional, for improved solder flow)
- Polarity checker (for installed cable verification)
- Heat gun (for heat-shrink tubing)
Common mistakes
- Reversing pin 2 and pin 3, producing a polarity-inverted signal — inaudible in isolation but causes cancellation in summed signals.
- Connecting the shield at pin 1 at both ends in an installation with multiple earth points, creating ground loops and induced hum.
- Using instrument cable (single-conductor with shield) instead of balanced two-conductor cable — the single-conductor cable has no cold conductor and provides no common-mode rejection.
- Over-tightening the strain relief clamp on the cable's inner conductors rather than the jacket, causing short circuits or open circuits with slight cable movement.
- Using insufficient heat to form a proper solder joint, producing a cold joint that intermittently loses contact.
Troubleshooting
- Cable passes signal but hum is present on the audio signal
- Cause: Ground loop from pin 1 connected at both ends, or shield not connected at all Fix: Lift pin 1 at the destination end to break the ground loop. If hum increases with shield lifted, the hum is from elsewhere; restore pin 1 connection and investigate source.
- No signal at destination despite cable apparently connected
- Cause: Open circuit on pin 2 (hot) conductor, cold solder joint, or pin 2 not connected at one end Fix: Measure continuity between pin 2 at each end of the cable. Check solder joints at both connectors. Re-solder any suspect joints.
- Intermittent signal loss when cable is moved
- Cause: Strain relief clamped on inner conductors rather than jacket, or cold solder joint Fix: Open the connector at the suspect end and verify strain relief is clamping the jacket. Inspect solder joints and re-solder if joints appear dull or cracked.
Frequently asked questions
What is the XLR pin assignment standard?
The standard assignment per IEC 60268-12 and industry practice is: pin 1 = shield/ground; pin 2 = hot (non-inverting, positive); pin 3 = cold (inverting, negative). This standard applies to both male and female connectors. Looking into a female XLR receptacle, pin 1 is at the bottom, pins 2 and 3 at the top left and right respectively.
What is phantom power and which XLR pins carry it?
Phantom power (IEC 61938) is a 48 V DC supply applied equally to pins 2 and 3 relative to pin 1 (ground). It powers condenser microphones and active DI boxes without a separate power cable. The voltage is common-mode on the signal pins, so correctly wired balanced equipment is unaffected by it.
Why do some installations connect pin 1 at the source end only?
Connecting shield pin 1 at both ends creates a conductive loop between the equipment earth points at each end. If those earth points are at different potentials — common in large audio installations — circulating current flows in the shield, inducing a 50/60 Hz hum. Lifting pin 1 at the destination end breaks the loop while retaining shielding effectiveness.
What happens if pin 2 and pin 3 are swapped (polarity reversed)?
Reversing pins 2 and 3 produces a polarity-inverted (phase-reversed) signal. In a single channel this is inaudible. In a multi-channel system where channels are summed (e.g. a mono mix of two microphones), out-of-phase signals can partially cancel each other, causing thin or hollow sound and reduced bass. Polarity reversal is confirmed using a polarity checker or pulse test signal.
Can XLR cables carry unbalanced audio?
Yes, but the noise rejection benefit of balanced operation is lost. A typical unbalanced-to-XLR conversion pins pin 3 to pin 1 (ground) and uses pin 2 as the signal. This is acceptable for short cable runs in low-noise environments but defeats the purpose of using XLR connectors for long runs.
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