With the HeadAMP 4 you have got the possibility to connect up to 8 different headphone models with varying impedances. Features: [ Four stereo 6.3-mm plus four parallel stereo 3.5-mm TRS outputs [ each with individual volume control [ Stereo 6.3-mm and parallel 3.5-mm inputs [ Handles line level or headphone amp level input signals (up to 20dB of additional gain) [ All-metal, stackable chassis [ Power Requirements: 12V DC (adapter included) [ Dimensions (W x D x H): 107mm x 89mm x 45mm [ Weight: 0.61kg