Behringer HA400 4-Channel Headphone Amplifier, Black Behringer HA400 Features: 4 stereo headphone outputs with volume control Small and compact DC 12 V adapter included. Behringer HA400 Specifications: Input Channels: 1 Output Channels: 4 Analog Inputs: 1 x Stereo Analog Outputs: 4 x TRS Controls per Channel Volume Form Factor: Desktop Height: 1-5/6" Depth: 2-1/4" Width: 4-1/16".