A 48 V supply the interface sends up the XLR cable to run a condenser microphone’s electronics. Dynamic microphones do not need it, most condensers will not work without it, and it only travels over XLR.
Why it exists
A condenser capsule needs a polarizing voltage and its internal preamp needs power. Rather than a battery in every microphone, the interface supplies it through the same cable that carries the signal.
Why only XLR
The three-pin balanced connection has the conductors to do it. A jack cable does not, which is why an XLR-to-jack adapter leaves a condenser completely silent.
The practical rule
Connect the microphone first, then switch phantom power on, then raise the gain. Doing it in that order avoids the thump that goes through your headphones.
Check your own manual before you plug anything in. Voltage, polarity and current draw differ from model to model, and the manufacturer’s figures take precedence over anything written here. A supply of the wrong polarity can damage a pedal in seconds, phantom power is safe for most microphones but not for every one, and the required voltage is printed next to the socket or stated in the manual — not inferred from a connector that happens to fit.
The questions players ask
Where is the switch?
On the interface, usually marked 48V or P48, sometimes per channel and sometimes for both. On a two-channel interface it often applies to both inputs at once.
Is it safe to leave on?
For condensers and dynamics, generally yes. Some ribbon microphones are the exception, so check the manual for anything unusual before connecting it.
Last reviewed 2026-08-19