This headphone amplifiers are designed to be used with high-impedance headphones. Headphones with an impedance of 160 ohms or higher will benefit from the use of an amplifier, as they will not be able to get loud enough without one. This amplifier has a maximum output of 40mW, which is enough to drive most high-impedance headphones to a comfortable listening level.

The amplifier also has a two-stage gain switch, which allows you to increase the output power if you need to. This is useful if you are using headphones with a very high impedance or if you want to listen to music at a very loud volume.

The amplifier is powered by a rechargeable battery, which should last for about 8 hours on a single charge. It also supports Bluetooth 5.0, so you can connect it to your phone or computer wirelessly.

Overall, this is a good portable headphone amplifier for people who have high-impedance headphones. It is small, lightweight, and easy to use, and it has enough power to drive most headphones to a comfortable listening level.