PA-1 Personal Headphone Monitor from Whirlwind is a high-output, low-distortion, portable monitoring device with multiple inputs, so it can be used with a variety of headphone signal distribution systems and is suitable for critical listening in any professional audio environment. The PA-1 is a great choice for boosting weak headphone signals when working in a loud environment. It will accept balanced or unbalanced line-level stereo signals through a pair of 3-pin female XLR inputs or a single 1/4" TRS input, while 3.5mm and 1/4" outputs let you use any pair of headphones.
It has volume and balance controls and a stereo/mono switch, and it can be powered by two optional 9V batteries or the included external power supply. The integrated belt clip allows for hands free operation, while keeping the volume and balance controls at hand.