The PM52 Headphone Tap is for connecting headphones to a speaker line. The unit takes a speaker level signal and allows the user to "tap in" with a pair of headphones. It's just like using a stage monitor, but using headphones instead of a heavy speaker.
The 1/4" TRS phono Mono/Stereo loop jacks are for cascading more boxes in series, or connecting to a monitor speaker. There are two headphone jacks and a volume control. The PM52 uses the speaker line signal for power, so it requires no batteries or external power.
Stereo or Mono operation
Power amplifier loop through
No batteries or AC power required