The PM50s mixes a stereo or mono line-level Monitor signal with a mic level XLR microphone signal to a set of headphones or earphones. It has a monitor level control, mic level control, mic pass through XLR jacks, two headphone output jacks, and a stereo TRS 1/4" monitor input jack. Possible users may be drummers who need to hear a click track, choir singers who need to hear themselves, etc. The power adapter is included.