Fosi Audio N2 Headphone Amplifier Portable Amp Gain & Bass Switch Audio Hi-Fi 3.5MM Earphone Headset Powered Dual-Output with Lithium Battery for iPhone, iPod, iPad, MP3 and Computers

Audio input: 3.5mm headphone port Headphone output: 3.5mm headphone port Charging port: Type-C Volume adjustment mode: High precision volume knob Power supply: DC 5V 1A Internal voltage?±9.5V Op amp: OPA1642 Current amp: 1W triode to tube Battery capacity: 2200mAH Battery Life: about 12h Magnification (Av): GAIN=L:3 GAIN=H:6.8 Low-frequency gain?BASS=ON?: +6dB Frequency response: 10Hz-25KHz SNR...