A single miswired 3-pin XLR can invert the polarity of an entire vocal channel, and the fault usually surfaces once the room is already full. Most of the confusion comes down to one question: is pin 2 hot or is pin 3 hot? The answer depends on when the equipment was built and where it came from, not on the connector itself. This guide gives you the standard pinout, explains the legacy exception in plain terms, and shows how to verify polarity on the bench before any cable leaves your shop.
Quick answer: Pin 1 is shield and ground, pin 2 is hot (positive), pin 3 is cold (negative). That is the modern convention across North America, the United Kingdom and most of Europe, and it matches essentially every current balanced XLR device. Pin 3 hot still exists on some older European and British equipment and a few legacy console outputs. If a channel sounds thin or cancels against its neighbor, check polarity first, then correct it at one point in the signal path rather than inside a working cable.
3 Pin XLR Pinout: Pin 2 Hot and the Legacy Question
A 3-pin XLR carries a single balanced analog channel. Pin 1 is the shield and the ground reference. Pin 2 carries the signal in positive phase, which the industry calls hot. Pin 3 carries the same signal inverted, which is called cold. The input stage at the receiving end subtracts pin 3 from pin 2, so noise arriving equally on both conductors cancels before it reaches the amplifier. That subtraction, not the metal shell, is what lets balanced audio survive long runs past dimmer racks and motor drives.
The latch, shell and strain relief are mechanical parts. They are not audio conductors on a correctly wired cable, and the shell should not be bonded to pin 1 at both ends of an installed run. When a cable ties the shell to ground at each end, a loop can form through rack chassis and building ground, and the symptom is hum that changes character when you touch the connector body.
Pinout Reference Table
| Pin | Signal | Balanced role | Field note |
|---|---|---|---|
| 1 | Shield / ground | Reference and chassis bond | Bond at one end on long installed runs |
| 2 | Hot (+) | Non-inverted signal | Standard on modern North American, UK and EU gear |
| 3 | Cold (-) | Inverted signal | Swap with pin 2 only to correct legacy polarity |
| Shell | Chassis | Mechanical only | Optional bond, one end only |
Treat this table as the default for every assembly you build. Deviations should be rare, documented, and never shipped inside a cable that will travel between venues.
Why Pin 2 Is Hot Today
The pin 2 hot convention is written into the wiring practice that most professional audio manufacturers follow, and it has been the norm in the United States, the United Kingdom and most of continental Europe for decades. Consoles, stage boxes, powered loudspeakers, DI boxes and interface preamps are all built to it. When you order industry-standard 3-pin XLR assemblies from a supplier who builds to that practice, pin 2 hot is what arrives.
The practical value is interchangeability. A stage box wired to pin 2 hot accepts a cable from any rental house, and polarity stays correct from the microphone capsule to the amplifier input. In a system with forty channels, the cost of one inverted channel is not the channel itself. It is the twenty minutes spent finding it while the audience is seated, plus the credibility you spend explaining why the lead vocal sounded hollow.
Balanced wiring also explains why the pinout matters more than the connector brand. Common-mode rejection depends on both conductors seeing the same interference and the input stage subtracting it. Reverse the pair and the rejection still works, which is exactly why a pin 3 hot cable passes every continuity test and still sounds wrong. The cable is not broken. It is inverted.
The Pin 3 Hot Legacy Exception
Some older European and British equipment used pin 3 as hot. The reasons were regional and historical rather than technical, and the practice faded as the industry settled on a single convention. You still meet it in older console outputs, long-serving broadcast installations, and equipment that was maintained rather than replaced. The connector looks identical, the meter beeps on every pin, and the channel still sounds thin.
The audible symptom is a vocal that loses body or a bass line that vanishes when the channel is summed to mono with its neighbor. If one half of a stereo pair cancels when combined, check polarity before you reach for equalization. Confirm it with a known-polarity source through the suspect path, then compare against a reference channel using a polarity tester or a two-channel scope on the same signal.
Correct the mismatch at one point in the signal path. Options include a polarity invert function on the console input, a dedicated in-line phase adapter, or a documented re-pin at a terminal block that stays in the rack. Never bury the fix inside a cable. A pin-swapped cable that later travels to another venue becomes someone else’s fault, and the labeling rarely survives a season of load-outs. If you must build a corrective adapter, mark it on both ends and keep it with the legacy device it serves.
Setup and Verification Sequence
- Test continuity pin to pin: 1 to 1, 2 to 2, 3 to 3, using a meter with an audible continuity mode and fresh leads.
- Confirm there is no short between pin 2 and pin 3, and no short from either signal pin to pin 1 or the shell.
- Check shell bonding. On installed runs, the shell should be bonded at one end only; on touring cables, follow the house convention and label it.
- Feed a known-polarity test signal through the full path and read the output on a polarity tester, keeping the hot lead leading at the destination.
- Record the result on the cable label and in the build sheet, including any deliberate pin swap, so the next technician inherits information rather than a mystery.
What Buyers Ask Before Ordering 3-Pin XLR
Sourcing managers usually want three things confirmed before a purchase order goes out: that pin 2 is hot as standard, that the same pinout is held across every length and color in the order, and that the build sheet states it in writing. Ask for the wiring declaration on the quote, not just on the datasheet, because a supplier who assembles from mixed stock can drift between lots.
The second question is about termination quality, since the pinout is only as good as the solder joint or crimp behind it. For fixed installs, solder-cup chassis connectors with a proper strain relief outlast molded ends that get flexed daily. For touring, molded or overmolded ends with a flexible boot survive cable wraps better. Specify which one you want per position instead of accepting a single default across the whole order.
Finally, ask how custom pinouts are handled. A supplier should be able to build a documented non-standard assembly on request and mark it clearly, and should refuse to quietly mix it into standard stock. That discipline protects you from the worst outcome in this category: a correctly built cable that is wrong for the rack it is plugged into.
Three Field Scenarios
- Touring vocal package with a digital console. Every cable is pin 2 hot and the console has a polarity display per channel. The risk here is a single mislabeled spare in the cable trunk, so every assembly gets a continuity and polarity check at the top of each leg.
- Houses of worship mixing new and inherited gear. A modern digital mixer feeds an amplifier or processor from the 1990s. Check the legacy device for pin 3 hot before assuming the new console is at fault, then correct once at the processor input and document it in the rack log.
- Rental inventory shared across venues. Cables move between rooms with different house conventions. Standardizing on pin 2 hot for all stock, plus a labeled inventory of legacy adapters, prevents the slow accumulation of mystery faults that only appear on other people’s stages.
Sourcing Notes for Installers
Order connectors and cable as a matched set. The XLR cable wiring reference covers the conductor-to-pin mapping in detail, and the balanced XLR cable guide explains why the pair must stay together from end to end. Mixing two-conductor plus shield cable with three-conductor stock in the same order is a common cause of assemblies that meet the pinout on paper but not in the hand.
For the connector side, choose XLR connectors rated for the environment: die-cast shells and metal latches for stage use, panel-mount receptacles with solder cups or PCB pins for chassis work. Document the pinout on the purchase order, keep a sample from each lot, and test the sample before releasing the rest of the shipment to a job site.
FAQ
1. Is pin 2 always hot on a 3-pin XLR?
On modern equipment, yes. Pin 2 hot is the working convention across North America, the United Kingdom and most of Europe, and it is what current consoles, stage boxes and powered speakers expect. Pin 3 hot survives on some older European and British devices, so verify inherited gear rather than assuming the convention holds across a mixed rack.
2. What happens if pins 2 and 3 are reversed?
The channel still passes audio and still rejects noise, but its polarity is inverted relative to every other channel. Alone it may sound thin or lack low-end weight. Summed with a correctly wired neighbor, low frequencies cancel and the source seems to disappear. It is a wiring fault, not a broken cable, and a continuity meter will not reveal it.
3. Should pin 1 and the shell be connected?
Pin 1 is the shield and signal reference; the shell is a mechanical part that can optionally be bonded to it. Bonding the shell at both ends of an installed run can create a ground loop through rack chassis and building ground. On touring cables, follow the house convention and label any deliberate difference so the next user understands it.
4. How do I test polarity without a dedicated tester?
Send a known-polarity signal, such as a polarity test pulse or a symmetrical waveform, through the path and compare input and output on a two-channel scope. The hot conductor should lead at the destination. If you have no scope, compare the suspect channel against a reference channel on the same source and listen for low-frequency cancellation when both are summed to mono.
5. Can a supplier build a custom pinout for us?
Most can, but require it in writing on the purchase order and on the cable label. A custom assembly that looks identical to standard stock is a liability once it reaches a stage. Ask for the wiring declaration with the quote, keep a sample from the first lot, and test that sample before the balance of the shipment goes to site.