KNACRO Wireless Bluetooth 4.0 Audio Receiver Board Stereo Digital Amplifier Module Mini USB 5V Audio Input: Bluetooth 4.0.Bluetooth Chip: CRS8635. Impedance Range: 4-8 ohm, best for 3W. What is included:1 * Bluetooth 4.0 Power Amplifier Board . PCB Board Size: 60 * 35mm / 2.36 * 1.4in (L * W ). Applicable speaker impedance: 4/6/8 ohm.