Before powering on, you should carefully check whether the cable is normal and you must ensure that all connectors are properly connected. Bass Headphone Amplifier Support a Headphone with 16‐150Ω Impedance You Can Enjoy High-Quality Sound with Various Mainstream Devices. No Sound? Please connect the input devices, like computers, mobile phones, DVDs to the Line in port, and then plug the headphones into the Line out port Correctly. Increase the volume of the input device and increase the master volume of the product. Can I use it while charging? It is not recommended to use while charging, line noise may be generated. This is why the product is powered by lithium batteries, and battery power supply can avoid line noise. Is it possible to transfer audio using the USB interface? No, the USB interface of this product only has the charging function. The device can work, but the intensity of music is not well? The battery output is not enough and needs to be charged. Why the headphone has a big buzzing sound when the input line is connected but not play? When an unshielded signal line is empty, an interference signal will enter the amplifier and be amplified. If you dislike the sound, we suggest you replace the shielded signal line or unplug the signal line. Color:Black Material:ABS Package Contents: 1 * 3.5mm Headphone Amp