You don’t have to settle for wimpy, muddy sound just because you’re on the go. The AT-PHA100 Portable Headphone Amplifier is small (width and length comparable to a smartphone) but packs a powerful punch. Engineered using select audio components, and enclosed in all-aluminum casing to protect the circuitry, the AT-PHA100 gives headphones a rich, detailed boost throughout the sonic range with ultra-low distortion. The AT-PHA100 is equipped with both analog and digital inputs (3.5 mm jack and USB micro-B, respectively) and 3.5 mm headphone jack. It also features a high/low gain switch, machined aluminum volume knob, and five-stage sampling indicator for digital input. The internal lithium polymer rechargeable battery lasts up to 14 hours when amplifying an analog signal, and up to 6 hours when amplifying a digital signal. The amplifier comes with two rubber bands and a rubber mat for strapping the unit to a smartphone or other portable device, a 1.0 m USB cable (USB 2.0 to USB micro-B) and a 10 cm audio cable terminating in a 3.5 mm gold-plated stereo mini plug at each end. 

Specifications 

System Requirements: PC: with built-in USB port corresponding to USB 2.0 CPU: Intel Core2 CPU2.2 GHz or equivalent RAM: 32-bit OS 2 GB or more, 64-bit OS 4 GB or more Supported OS: Windows XP (32-bit)*, Windows 7, Windows 8, Windows 8.1 Mac OSX Mavericks (10.9) * Technical support by Microsoft is no longer available. Corresponding Headphone Impedance: 10 – 300 ohms Maximum Output Level: 100 mW + 100 mW (10% during 16 ohms, THD) 80 mW + 80 mW (10% during 32 ohms, THD) 10 mW + 10 mW (10% during 300 ohms, THD) Frequency Characteristic: 10 Hz – 100 kHz (-1 dB) Signal-to-noise Ratio: 110 dB (A-weighted) Total Harmonic Distortion: <=0.001% (32 ohms 10mW output) Input Connector: Analog: 3.5 mm (1/8") gold-plated stereo mini jack Digital: USB (micro-B)/asynchronous mode/ DSD128 (DoP), DSD64 (Native / DoP): 24 – 32 bit/ PCM 384kHz, 352.8kHz, 192kHz, 176.4kHz, 96kHz, 88.2kHz, 48kHz, 44.1kHz, 32kHz: 16 – 32 bit Output Connector: 3.5 mm (1/8") gold-plated stereo mini jack Power Supply: 5V DC, 500 mA bus power system (PC)/rechargeable lithium polymer battery (BATTERY) Charging Time: Up to 10 hours (DC5V, 500mA) Battery Life: Digital about 6 hours (JEITA) / analog about 14 hours (JEITA) Operating Temperature: 41 – 104° F (5° – 40° C) Dimensions (excluding protrusions): 1.1" (27 mm) H × 3.0" (77 mm) W × 4.6" (116 mm) D Weight: About 240 g Accessories Included: 1.0 m USB cable (USB 2.0 to USB micro-B), 10 cm audio cable (3.5 mm gold-plated stereo mini plugs x 2), rubber mat, two rubber bands Common spec for analog/digital without annotation Fs=384 kHz, 32-bit for digital input