Portable headphone amplifier. All aluminium-alloy body and chassis increases metal texture and increases shielding from EM interference. Toggle switches are reliable and easier to read and operate. Pre amplifier OPA1642 serves as the voltage amplifier wit great layering and medium and high frequency extension. Power amplifier AD8397 serves as the current amplifier, with great control of low frequencies and smooth drive. Bass On boosts bass effect without influencing the overall sound field. 1400 mAh built.in batteries ensures more than 16 hours of baterry life. Color: Black. SpecsModel Name/Number A3(E11K) Color BlackWeight 92 g Dimensions 91.2 mm×56 mm×13 mmAudio Input 3.5 mm stereo Jack Headphone output 3.5 mm stereo JackVolume Control ALPS Potentiometer Bass Boost 1 LevelDrive ability 16~150 (recommend) Power input recommend DC5V 1ABattery Capacity 1400 mAh Battery Life 16 hOutput Power 270 mW (32 /THD+N1%) 450 mW (16 /THD+N1%) Charging Time 4 hTHD 0.004% (1 kHz) Output Impedance 0.2 Frequency Response 10 Hz~90 kHz-3dBInput: 300mV SNR 108 dBInput Sensitivity 2.4 V (GAIN=L) 0.8 V (GAIN=H) Channel imbalance 0.3 dBCrosstalk >=72 dB (Gain=H) MAX output current 92.6 mAGain -3.8 dB (GAIN=L) 11.7 dB (GAIN=H) Overload Level 8 VrmsMAX output voltage 8.67 Vp-p