The black HPA 1 by LD Systems is a headphone amplifier with high-power output for use in stage, studio, and home recording applications. It is an ideal solution for wired in-ear monitoring, and the compact design is ergonomically shaped with a rugged plastic housing. The HPA 1 has a soft-touch surface and a belt clip that can attach to the talent during a performance. 
It has locking XLR connectors for the stereo signal L/R input and a 3.5mm stereo AUX input, which can be used for playback or click. A 3.5mm stereo jack is provided as a headphone output. It has a push-button switch to select between a summed mono or stereo signals. The HPA 1 provides a built-in limiter that can give you protection against feedback and an optimal playback signal. The headphone amplifier is lightweight and can operate for up to 12 hours using a 9V battery