Portable headphone amplifier with integrated DA converter for high sound quality indoors and outdoors. Digital USB input for iPhones and Android devices (AOA-2.0-compatible Android mobile devices). HD playback at 24 bit/96 kHz via iPhones and other iOS devices (when using the TEAC HR Audio Player app for iOS for high-definition audio playback, no Apple Camera Connection Kit is required). Optical digital input for direct connection of portable audio devices or CD/DVD/Blu-ray players. High/low output gain switch. Slim profile with 21.7 mm, robust aluminium housing. Li-Ion battery rechargeable via USB (battery life approx. 8 hours) with automatic energy saving mode.