The Samson S-amp is a portable, 4-channel headphone amplifier featuring individual output volume control knobs. The input and output connectors are of the 1/4" stereo type and the S-amp works with a wide variety of headphone models and impedances.
Samson SASAMP Features
Four channel stereo headphone amplifier
Maximum output power on each channel regardless of different headphone impedances
Four 1/4-inch stereo headphone outputs
Individual volume control for each headphone output