My wife takes her cheapo kindle fire when on the metro, and likes to watch movies on it, and uses an old pair of headphones, the Sony MDR-XB300. Problem - with the noise on the metro, she can barely hear the sound. So I thought of getting her a headphone amplifier. But she doesn't want to carry anything as big as my Superlux HA3D, so I need something really small, like no bigger than about 2" - 2.5" along the biggest dimension. The impedance of the Sony MDR-XB300 is 24ohm. I know nothing about small consumer amps, so I turn to you guys here. My budget is no bigger than about $60.
