Vacuum Tube Headphone Amplifier with hi-fi sound that turns listening to music into a true audio experience. It has a durable metal body with transparent tube cover, volume control, output power 180mW x2 (16 load) and 22mW x2 (300 load), Headphone impedance of 16 ~ 300 and a frequency response of 10Hz ~ 65kHz. It can be charged via USB or micro USB inputs, has a headphone jack output and two audio inputs. Battery capacity is 16 ~ 18 hours. The package includes a USB cable and audio cable. Dimensions: 125.6 x 78 x 16 mm. Weight: 150.5 g. Color: Black.