Quick Answer / Summary: On a standard XLR connector pin 1 is shield and ground, pin 2 is hot (positive) and pin 3 is cold (negative). Dynamic microphones ignore 48 V phantom power; ribbon microphones and unbalanced adapters may not. Use balanced two-conductor shielded cable for microphone runs, keep line-level sources out of mic inputs or pad them, and never plug or unplug a mic with phantom power on unless the channel is muted.
An XLR input is a balanced, latching, three-pin connector, and almost every problem attributed to a faulty input turns out to be a pinout error, a phantom power conflict or a cable with the wrong shield.
Pinout and Polarity
Pin 2 hot is the international standard, and equipment built to the older pin 3 hot convention exists in small numbers. Mixing the two produces a polarity inversion that is inaudible alone and obvious when a second microphone is added to the same source.
Pin 1 goes to the shield and to the chassis at the input. Lifting pin 1 at one end is the classic ground loop fix, but it should be done at the destination end with a proper ground-lift switch, not by cutting the shield randomly.
Balanced differential input
The input amplifies the difference between pins 2 and 3. Noise induced equally on both conductors cancels, which is why a microphone can run 30 m down a multicore next to power cables.
Latching
The latch is mechanical security, not an electrical feature. A connector that pulls out mid-set takes the channel with it, so check that the release tab engages on every cable you buy.
Phantom Power
48 V is applied equally to pins 2 and 3 relative to pin 1, so a balanced dynamic microphone sees no voltage across its coil. Condenser microphones use it to polarise the capsule and power the electronics.
Ribbon microphones can be damaged by phantom power if the wiring is faulty or the ribbon is not transformer-isolated. Check the microphone’s specification before enabling phantom, and mute the channel when connecting.
Unbalanced adapters
An XLR-to-TRS or XLR-to-RCA adapter ties pin 3 to ground. With phantom power on, that can present 48 V across the microphone output. Turn phantom off for any adapter that is not fully balanced.
Pops and thumps
Phantom power applied to a live channel produces a thump in the main outputs. Mute the channel, connect, then unmute. On a digital console, phantom is usually per channel and stored in the scene.
Levels and Gain Staging
A microphone output is roughly 1 to 10 mV, while a line source is around 1 V. That is a 40 to 60 dB difference, and plugging a line source into a mic input without a pad overloads the preamp.
Most consoles and interfaces offer a pad and a gain control. Use the pad first, then gain. If the input still clips with the gain at minimum, the source is too hot for that input, not faulty.
Cable capacitance
Long microphone cables add capacitance, which rolls off high frequencies. For a 50 m run, low-capacitance cable and a low-impedance microphone preserve more top end than an expensive connector does.
Star-quad cable
Star-quad construction improves rejection of magnetic interference in electrically noisy venues at the cost of higher capacitance. It is the right choice near lighting dimmers, not a universal upgrade.
Input Types at a Glance
What the same socket may be expected to accept.
| Input | Level | Phantom | Typical source |
|---|---|---|---|
| XLR mic | 1 to 10 mV | Yes, 48 V | Dynamic or condenser mic |
| XLR line | About 1 V | No | Mixer or outboard gear |
| XLR with pad | Attenuated 20 dB | Yes | Hot sources on stage |
| Combo XLR / TRS | Switchable | XLR side only | Mixed sources |
| XLR to USB interface | Digital out | Yes on XLR | Podcast, home studio |
Real Installations
Two deployments where the pinout and phantom rules matter immediately.
Small venue with a 20 m multicore
Use balanced star-quad for the vocal channels that run beside dimmer packs, keep phantom on for the condenser, and label pin 2 hot on the stage box. Check polarity with a test source before doors open.
Home studio with a ribbon mic
Leave phantom off on that channel, or use an inline phantom blocker. If the interface applies phantom globally, put the ribbon on a channel with a physical switch and mark the input.
Frequently Asked Questions
Which XLR pin is hot?
Pin 2. Pin 1 is shield and ground, pin 3 is cold. Equipment wired pin 3 hot is rare but exists and inverts polarity.
Does phantom power damage dynamic microphones?
No, because the voltage appears equally on pins 2 and 3 and the coil sees no differential. Ribbon microphones are the exception and should be checked.
Can I connect an XLR output to a 3.5 mm input?
Only with a proper balancing transformer or adapter that handles level. A simple cable mismatch usually produces hum and distortion.
Why does my condenser microphone not work?
Most often phantom power is off, the cable is unbalanced, or the capsule needs a moment to charge. Check the 48 V indicator first.
Is a longer XLR cable worse?
It adds capacitance and rolls off treble, but balanced operation keeps noise low. Up to 50 m is normal for a low-impedance microphone.
Related resources: 3-pin XLR wiring; XLR to RCA conversion; XLR cable length limits