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:

Pin Signal Also Called
Pin 1 Shield / Ground GND, screen, chassis
Pin 2 Hot / positive signal + (plus), non-inverting
Pin 3 Cold / negative signal − (minus), inverting

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:

XLR TRS
Pin 1 (Ground) Sleeve
Pin 2 (Hot +) Tip
Pin 3 (Cold −) Ring

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:

Audio XLR DMX512 XLR
Connector 3-pin XLR 3-pin or 5-pin XLR
Cable impedance 40-80 ohms 110 ohms (EIA-485)
Signal type Balanced analog audio RS-485 differential digital
Pin 2 Hot (+) audio Data +
Pin 3 Cold (−) audio Data −
Termination Not required 120-ohm resistor at last fixture

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

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:

Testing Before Assembly

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

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:

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:

Create your own XLR connector diagram -- free

Phantom Power (P48) and the XLR Pins

Phantom power is 48V DC (commonly written P48) sent from a mixer, audio interface, or preamp down the same two signal pins used for audio -- pins 2 and 3. Both pins carry +48V relative to pin 1 (ground), so there is no voltage difference between pin 2 and pin 3. Because a balanced input only responds to the difference between the two pins, the phantom voltage itself is invisible to the audio signal path -- it just supplies power to a condenser microphone's internal electronics or capsule.

This only works correctly through a proper balanced connection: pin 1 (ground) needs a solid, continuous path back to the phantom power supply, and pins 2 and 3 both need to be intact. A broken shield or a cable wired unbalanced (with only one of pins 2/3 connected) can turn a clean phantom power feed into a source of noise or, in some cases, a pop or thump when connecting.

Dynamic microphones designed for balanced operation are generally unaffected by phantom power, since the identical voltage on both signal pins does not drive current through their circuits. Ribbon microphones are the exception to be careful with: standard ribbon mics have no phantom power protection, and an unbalanced connection, a wiring fault, or a damaged cable while P48 is active can send current through the ribbon element and damage it. Unless a ribbon mic is explicitly built with phantom power protection, leave phantom power off on that channel until the mic is disconnected.

Common XLR Failure Modes

Most XLR problems trace back to one of a small number of causes. This table covers the symptoms you're most likely to run into:

Symptom Likely Cause How to Check
Crackling or dropout when the cable is moved or flexed Cold solder joint, or a broken strand where the conductor exits the strain relief Wiggle-test each end while monitoring signal; inspect solder cups under magnification
Complete signal loss Open connection somewhere along the run Continuity-check pin 1, 2, and 3 individually from end to end
Hum or buzz Broken or lifted shield connection at pin 1, or a ground loop between two grounded devices Check pin 1 continuity first; if the shield is intact, try lifting ground at one end or using a ground-isolation device
Signal present but very quiet or thin-sounding Only one of pins 2/3 is actually connected -- cable wired unbalanced by mistake Check that both pin 2 and pin 3 show continuity to the correct conductors at both ends
Signal present but out of phase with other channels Pins 2 and 3 reversed at one end of the cable Compare polarity against a known-good cable using a phase check or by ear on a mono source

A cheap continuity-testing multimeter resolves most of these in a few minutes -- work pin by pin rather than guessing based on the symptom alone.

5-Pin XLR Beyond DMX

DMX512 is the most common reason you'll see 5-pin XLR in the field, but it is not the only one. Some broadcast and professional audio gear uses 5-pin XLR connectors for combined stereo or dual-microphone connections, intercom headsets, or proprietary microphone/headphone combo jacks. Unlike the 3-pin audio pinout or the 5-pin DMX pinout, these uses are not standardized across manufacturers -- the same 5-pin shell can carry completely different signals depending on the device. Never assume a 5-pin XLR cable is safe to connect between two different devices just because the connector fits -- always check the specific pinout diagram for the equipment on both ends first.

Key Takeaways

Frequently asked questions

Is it safe to leave phantom power on all the time, even with nothing plugged in?

Generally yes on modern audio interfaces and mixers -- most are designed so an open (unconnected) XLR input with phantom power on does not cause damage. The bigger risk is hot-plugging a mic that is sensitive to phantom power, or plugging in a device that isn't designed for it, while P48 is already active on that channel.

What happens if phantom power reaches a ribbon microphone by mistake?

Standard ribbon microphones have no phantom power protection. Since P48 puts 48V on both pins 2 and 3, a fault, an unbalanced cable, or a bad connection while phantom power is active can send current through the delicate ribbon element and destroy it. Keep phantom power off for any ribbon mic that isn't explicitly built with phantom protection.

Can I plug a 3-pin audio XLR cable into a 5-pin DMX fixture?

Physically the connectors often mate, but electrically they are different systems -- DMX512 uses RS-485 differential digital signaling at 110-ohm impedance, not balanced analog audio. A 3-pin cable will only carry pins 1 through 3, so it may work for basic DMX on some fixtures but is not a substitute for proper DMX-rated cable, especially on longer runs.

What gauge wire should I use for an XLR microphone cable?

Most standard microphone cable uses 22 to 24 AWG stranded copper conductors for the signal pair, with a braided or foil shield tied to pin 1. Thinner conductors are fine for typical mic-level signal runs; wire gauge matters far more for speaker cable carrying higher current than it does for line- or mic-level XLR signal.

Why does my XLR cable cut out only when I wiggle it near the connector?

This almost always points to a cold solder joint or a strand of conductor that has broken right where it exits the strain relief inside the connector shell. Open the backshell and check each solder cup and the strain relief grip -- a joint that looks fine visually can still be mechanically cracked and only lose contact under flex.

Can I run digital AES/EBU audio over a standard XLR microphone cable?

AES3 (AES/EBU) digital audio uses the same 3-pin XLR connector but is specified for 110-ohm cable. Standard microphone cable (typically 40 to 75 ohms) can work for short digital runs, but the impedance mismatch risks signal reflections and errors over longer distances or at higher sample rates -- the same caveat that applies to using mic cable for DMX.

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