Before powering on, you should carefully check whether the cable is normal and you must that all connectors are properly connected. 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, to in port, and then plug the headphones into 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 . 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 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 Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.