A socket that accepts both an XLR plug and a 6.35 mm jack. The XLR path goes to the microphone preamp with phantom power; the jack path goes to a line or instrument input, and they are not the same circuit.
Why it saves space
Two sockets in the footprint of one, which is how a compact interface offers both a microphone and an instrument input on a front panel a few centimeters wide.
The switch that matters
Instrument or line. A guitar into a line input sounds thin and quiet because the impedance is wrong; the Inst or Hi-Z position fixes exactly that.
What phantom power does here
It applies to the XLR path only. A jack in a combo socket is never carrying 48 V, which is why nothing is at risk from leaving it switched on.
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
Does the interface know which I plugged in?
Mechanically, yes — the two plug types make different contacts. What it cannot know is whether your jack is a line source or an instrument, which is why there is often a switch marked Inst or Line.
Can I use both at once?
No. One combo socket is one input, whichever plug is in it.
Last reviewed 2026-08-19