Mackie HM-4, Compact 4-Way Headphone Amplifier, Share a single stereo source with up to 4 headphone pairs, 1 x 6.3 mm jack stereo input and 4x 6.3 mm jack stereo outputs with individual volume controls, Dimensions: 51 x 109 x 58 mm, Weight: 200 g, Includes 12V power supply