XLR Connector Pinout: 3-Pin Balanced Audio Wiring

The XLR connector has been the standard for professional audio since the 1950s because it does one thing that a standard 1/4" TS plug cannot: it carries a balanced audio signal that rejects noise over long cable runs. Studio microphone cables, stage patch bays, mixing console sends and returns, broadcast facilities -- they all use XLR. This guide covers the 3-pin XLR pinout, how balanced audio works, the XLR-to-TRS adapter, DMX lighting protocol versus audio XLR, and how to solder a cable correctly.

XLR 3-Pin Pinout

The standard 3-pin XLR pinout is defined by AES14 (Audio Engineering Society) and is consistent across virtually all professional audio equipment:

The memory aid: 1-2-3 = Ground-Hot-Cold, or "AES says 2 is hot" if you need just the key one.

Female XLR (the receptacle, typically on microphones, stage boxes, and audio equipment inputs) has three holes arranged in a D-shape. The pin numbering is stamped on the connector body and is standard across Switchcraft, Neutrik, Amphenol, and Rean/Seetronic.

Male XLR (the plug, on cables going to equipment) has three pins in the same D-shaped arrangement.

Pin 1 is the single pin on the flat side of the D. Pins 2 and 3 are on the curved side, with pin 2 on the left when you look at the solder cup side of a male connector with pin 1 at top.

How Balanced Audio Works

A balanced audio system transmits the same audio signal on two conductors -- one inverted relative to the other. Pin 2 carries the signal in phase, pin 3 carries the identical signal with its polarity reversed (out of phase).

At the receiving end, a differential amplifier (or transformer) subtracts pin 3 from pin 2:

Output = V(pin 2) − V(pin 3)

For the desired audio signal: if Pin 2 = +1V and Pin 3 = −1V, the output = 1 − (−1) = 2V -- the signal is recovered doubled (6 dB gain from the balanced differential).

For noise induced by electromagnetic interference along the cable: any external noise couples equally into both conductors, so Pin 2 noise = +0.1V and Pin 3 noise = +0.1V. The subtraction: 0.1 − 0.1 = 0V -- the noise cancels completely.

This is Common Mode Rejection (CMR). A well-designed balanced input has 60 to 80 dB of common mode rejection, which is why a 100-foot XLR cable through a lighting rig still delivers quiet audio when a similar-length unbalanced cable would pick up significant interference.

Balanced vs Unbalanced: When It Matters

For runs under 10 feet (3 m) in a low-interference environment, unbalanced (TS or RCA) is often fine. Beyond that, or anywhere near switching power supplies, dimmers, RF transmitters, or fluorescent lighting, balanced XLR is worth the extra pin and connector cost.

Consumer equipment (home audio, gaming headsets, most home studio interfaces) uses unbalanced connections. Professional equipment (mixing consoles, studio monitors, outboard gear, stage boxes) universally uses balanced XLR for line-level and microphone inputs.

XLR-to-TRS Wiring

A TRS (Tip-Ring-Sleeve) 1/4" or 3.5 mm plug also carries a balanced signal. Wiring an XLR-to-TRS adapter:

This is the standard for connecting balanced equipment with different connector types -- for example, running from an audio interface's balanced 1/4" output to a powered monitor with an XLR input using a TRS-to-XLR cable.

For an XLR-to-TS (unbalanced) connection, pin 1 connects to sleeve and pin 2 connects to tip. Pin 3 is left unconnected (floating) or can be connected to pin 1 (ground) at the XLR end -- connecting pin 3 to ground at the source end helps with some noise rejection and is generally recommended when going balanced to unbalanced.

DMX vs Audio XLR -- Important Differences

DMX512 (the lighting control protocol) also uses XLR connectors -- but they are NOT electrically compatible with audio XLR, even though they physically fit. Using an audio XLR cable for DMX can cause data errors, protocol failures, and in some cases damage to the DMX driver output stage.

Differences:

Always use cable specified for DMX (110-ohm characteristic impedance) for DMX runs. Microphone cable, which typically has 40 to 75 ohm impedance, works over short runs but can cause reflections and data errors over runs longer than 30 to 50 feet.

5-pin DMX XLR uses pins 4 and 5 for a second DMX universe. Pins 1, 2, and 3 carry the same signals as the 3-pin version.

Soldering an XLR Cable

Soldering XLR connectors requires a decent iron (60W or more with temperature control), rosin-core solder (60/40 or 63/37 tin-lead, or lead-free equivalent), and the correct technique for the solder cup style of most XLR plugs.

Tools

• Soldering iron with a 2 to 3 mm chisel tip, set to 325 to 360°C (615 to 680°F)
• Solder: 60/40 tin-lead 0.032" rosin core (or no-clean flux core for lead-free)
• Wire strippers
• Helping hands or vise
• Heat shrink tubing (1/4" for the overall jacket, 1/8" for individual conductors if needed)

Cable Preparation

1. Slide the XLR backshell and strain relief onto the cable before soldering (easy to forget until you have two connectors already done).
2. Strip the outer jacket 25 to 30 mm.
3. Unwind the braided shield. Twist the shield strands together into a single tail approximately 10 mm long.
4. Strip the inner conductors 6 to 8 mm.
5. Tin all conductors (apply a small amount of solder to make a shiny coat).

Soldering Sequence

1. Pin 1 (Ground): Solder the twisted shield braid. Pin 1 connects the shield to chassis -- this is the most important joint for noise rejection. Make it solid.
2. Pin 2 (Hot): Connect your positive conductor. In most professional microphone cable, this is the red (or white) conductor. Verify your cable's color convention -- some cables use white for hot and blue for cold, others use red and black.
3. Pin 3 (Cold): Connect your negative conductor.

Common microphone cable color conventions:

• Mogami W2534, Canare L-4E6S (star-quad): red = hot, white = cold
• Generic two-conductor cable: red = hot, black or blue = cold

Testing Before Assembly

Before closing the backshell: use a multimeter (continuity mode) to verify:

• Pin 1 to shield: continuity
• Pin 2 to your hot conductor: continuity
• Pin 3 to your cold conductor: continuity
• No continuity between any two pins (short circuit check)

Then assemble the backshell and strain relief. The cable sheath must be gripped by the strain relief, not the solder joints.

Star-Quad (Four-Conductor) Cable

Star-quad microphone cable (Canare L-4E6S, Mogami W2534) has four conductors arranged in a star pattern. For balanced audio, the two diagonally opposite conductors connect together at each end:

• Pin 2: conductors 1 and 3 (twisted together)
• Pin 3: conductors 2 and 4 (twisted together)
• Pin 1: shield

Star-quad provides approximately 20 dB additional common mode rejection compared to standard two-conductor cable, making it the choice for runs through dense RF environments.

Create Your Own XLR Wiring Diagram

Documenting your studio patch bay, stage box routing, or cable build specs keeps complex setups organized. With CircuitDiagramMaker, you can:

• Draw 3-pin XLR connector pinouts with labeled pins (1, 2, 3)
• Show XLR-to-TRS, XLR-to-TS, and DMX cable diagrams with correct pin assignments
• Create studio rack diagrams showing balanced signal routing between equipment
• Add wire color annotations for different cable types (Mogami, Canare)
• Export connection diagrams for system documentation or cable labeling

Create your own XLR connector diagram -- free

Key Takeaways

• XLR 3-pin pinout: Pin 1 = ground/shield, Pin 2 = hot (+), Pin 3 = cold (−). Pin 2 is hot -- the single most important fact to remember.
• Balanced audio works by transmitting the signal in phase on Pin 2 and inverted on Pin 3; the differential receiver doubles the signal and cancels common-mode noise.
• XLR-to-TRS: Pin 1 to Sleeve, Pin 2 to Tip, Pin 3 to Ring.
• DMX512 uses the same 3-pin XLR shell but requires 110-ohm impedance cable and a terminating resistor -- do not substitute audio microphone cable for long DMX runs.
• Star-quad cable (four conductors) provides an additional 20 dB of noise rejection over standard two-conductor cable for high-interference environments.
• Always test continuity (no pin-to-pin shorts, correct conductor-to-pin mapping) before assembling the backshell.
• Tin all conductors before soldering to the cups; heat the cup and conductor together rather than dripping solder from above.