Features: Applications: Ultra compact stereo headphone amplifier for studio and stage applications. 4 Channels: With 4 headphone output channels and 1 input channel. The volume of each output channel can be controlled independently. Good Quality: Provide the highest quality for each headset even at maximum volume. With Adapter: The 4580 operational amplifier has excellent performance. A DC 12V power adapter is included. Rust Proof: This amplifier adopts high quality material which will avoid rust well. Specifications: Input type: line in (o in) Output type: line out (o out) Built in battery: n Recommended maximum impedance of earphone: 65-80 ohm Amplifier type: Min Model: ha40 Bluetooth: No Wireless network: no Power adapter: EU plug/US Plug Commodity size: about 10.5 * 5.5 * 4.5cm / 4.1 * 2.2 * 1.8inch Color: Black Material: Metal includes: 1 * Amplifier 1 * Power adapter 1 * English manual