Behringer MicroAmp HA400 - ultra-compact 4-channel stereo headphone amplifier, output level control for each channel, 1x 1/4" TRS stereo input (100kohm), 4x 1/4" TRS stereo outputs (80ohm), includes 12V DC power adapter. Dimensions: 46.5 x 103.6 x 57.2mm (HxWxD