Because this is a 2.1-channel integrated front and rear speakers, the gain is sufficient, eliminating the need for a preamplifier; analog signal sources can be directly input. The and left and right channel tones can be adjusted independently to meet your different speaker configurations and produce balanced and pleasant sound. The subwoofer is rated at 200W into 4 ohms and 100W into 8 ohms. The left and right channels are rated at 70W into 4 ohms and 50W into 8 ohms. The subwoofer uses a BTL output; the positive and negative output terminals are connected to the amplifier circuit. Do not ground the "BS-" terminal. Color:Black Material:PCB+Metal Package Contents: 1 * Power Amplifier Board 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.