XtremPro Portable Headphone Amplifier Aluminum body w/ L-Shaped Plugs - Black (M1) Portable Headphone Amplifier Aluminum Body L&#45;Shaped PlugsSpecifications Audio Input&#58; 3&#46;5mm stereo jack Volume Control&#58; ALPS Potentiometer Drive ability&#58; 16&#45;150 Ohms&#40;recommend&#41;