Quick Answer / Summary: Wire pin 1 to the cable shield, pin 2 to the hot conductor and pin 3 to the cold conductor. Pin 2 is positive for a positive pressure wave on the diaphragm under the AES and IEC convention. Phantom power is +48 V DC on pins 2 and 3 through 6.8 kohm resistors, referenced to pin 1. Both signal legs sit at the same potential, so a dynamic microphone sees no current.
Pin numbers on an XLR are not arbitrary. Pin 1 carries the shield, pin 2 carries the hot or positive leg of the balanced pair, and pin 3 carries the cold or negative leg. Phantom power, polarity and the TRS equivalent all follow from that assignment. This article gives the pinout, the polarity trap, the 48 V path and the checks that catch a wrongly wired cable.
What Each Pin Does
The three contacts sit in a circular shell numbered clockwise from the notch at the solder side. Pin 1 is bonded to the shell on most sockets and to the cable shield at the plug. Pins 2 and 3 are the signal pair and carry equal and opposite voltages.
Gender is not a signal convention. A male plug feeds a female socket, and the pin assignment is identical on both. A turn-around adapter crosses nothing; it mates two male ends.
The balanced differential pair
A balanced line drives equal impedance to ground on both legs, and the receiver subtracts one leg from the other. Noise coupled onto the cable arrives as a common-mode voltage and cancels in that subtraction. Twisting keeps both conductors in the same field, so the cancellation holds along the run.
Pin 2 hot and the polarity trap
Pin 2 hot is the AES and IEC convention and is standard on modern gear. Some European equipment from the 1960s and 1970s was wired pin 3 hot, and a cable built for that gear inverts polarity on a modern console.
What Swapping Pins 2 and 3 Does
Swapping pins 2 and 3 inverts the signal. The receiver still subtracts, but the result carries the opposite sign, which is a 180 degree phase reversal at every frequency. One microphone on its own sounds nearly the same. Two microphones on the same source do not.
An inverted channel cancels against its neighbors where their signals overlap. On a drum kit or stereo pair the center image collapses and the low end thins out. The fault is wiring, not a phase switch on the console.
How the cancellation shows up
Sum a correctly wired pair and the level rises about 6 dB. Sum a pair with one inverted channel and the level falls, often by 15 dB or more at low frequencies. A polarity test with a known pulse makes the inversion obvious in seconds.
The 48 V phantom path
Phantom power applies +48 V to pins 2 and 3 through 6.8 kohm resistors, with the return on pin 1. Both legs sit at the same DC potential, so a dynamic coil sees no current. A condenser microphone draws its current between the two legs and pin 1.
XLR and TRS Pin Equivalence
The same three signals appear on a balanced TRS plug, so a TRS to XLR cable is a straight mapping.
Adapters and turnarounds
A TRS to XLR cable maps tip to pin 2, ring to pin 3 and sleeve to pin 1. A TS to XLR cable ties pin 3 to the sleeve, which unbalances a balanced input and loses about 6 dB. Never use that adapter on an input with phantom power engaged.
| Function | XLR pin | TRS contact | TS contact |
|---|
| Hot, in phase | Pin 2 | Tip | Tip |
| Cold, inverted | Pin 3 | Ring | Sleeve, tied to shield |
| Shield and ground | Pin 1 | Sleeve | Sleeve |
| Phantom +48 V | Pins 2 and 3 via 6.8 kohm | Tip and ring | Not available |
| Shell | Bonded at the socket | Not present | Not present |
Real Installations
Two cases where the pinout, not the microphone, was the fault.
Choir mics with a thin center image
A church installed six choir microphones on new XLR wall plates. One plate had been assembled with pins 2 and 3 reversed, and the two center microphones cancelled. A polarity check against a test source found the plate in under a minute, and rewiring it restored the image.
Ribbon microphone on a phantom input
A studio ribbon microphone failed after a session on a preamp with phantom power engaged. A strand of shield braid inside the plug was touching pin 3, so 48 V appeared across the ribbon instead of across the pair. Check for stray strands and measure pin to pin before connecting a ribbon.
Frequently Asked Questions
Is pin 2 always hot on an XLR?
On modern equipment yes, because AES and IEC specify pin 2 as the positive leg. Some vintage European gear is pin 3 hot, so run a polarity test before using unknown stock.
What happens if pins 2 and 3 are swapped?
The channel is inverted 180 degrees. Alone it is hard to hear. In a multi-microphone mix it cancels against other channels, thinning the center image and the low end.
Can phantom power damage a dynamic microphone?
Not a balanced, transformer-isolated dynamic microphone, because both signal legs sit at 48 V. It can damage unbalanced or miswired gear, and it should be switched off for ribbon microphones.
Which pins carry phantom power?
Pins 2 and 3, each through a 6.8 kohm resistor, with the return on pin 1. The voltage is common to both legs, so it does not appear as signal at the input.
Is XLR the same as TRS?
Electrically yes: pin 2 is tip, pin 3 is ring and pin 1 is sleeve. The connectors differ, and only the XLR shell is bonded to the chassis at the socket.
Related resources: XLR connector types; XLR cable shielding; XLR to 1/4 inch cable
