Audiophile CMOY headphone amplifier USA made with high quality parts-Altoids Wintergreen Alps volume control with built in switch, Japanese made, very high quality Designed for Over Ear and On Ear headphones, may not work well with lower impedance in ear monitors NJM4556 op amp, TLE2426 Rail Splitter 8 Pin DIP socket allowing op-amp rolling Battery Not Included, Works with headphones from 30-300ohms