Features 1.Stable Performance: Bluetooth digital power amplifier module features Bluetooth 5.0 with a transmission distance of up to 49 feet (unobstructed). Also, this amplifier board has a 3.5mm AUX sound input. 2.Applicable: Bluetooth 5.0 power amplifier board with 36x25x10mm / 1.42x0.98x0.39in heatsink, applicable power supply DC12?24V 5A and above (24V battery pack cannot be connected), applicable speakers 20-100W, 4-8 . 3.Multiple Protection: Bluetooth digital power amplifier module has multiple protection mechanisms to ensure its safe operation. It has short circuit protection, over current, overheat and anti reverse connection protection. 4.DC Converter Plug: Amplifier board can use commercially available DC adapter (plug 5.5mmx2.1mm) to basically meet the needs of ZK MT21 Bluetooth power amplifier board. If your existing DC power plug is not 5.5mmx2.1mm, there is no problem, because we include a DC adapter in the product. 5.Cautions: Amplifier board will only have enough output power if the sound input is sufficient and the power supply voltage and current are sufficient. The higher the power supply voltage, the higher the output power, the smaller the speaker impedance, the higher the output power. Please make sure the power of the power supply is greater than the actual power of the amplifier! specificationItem Type: Bluetooth Power Amplifier Board Material: PCB Radiator Size: Approx. 36x25x10mm / 1.42x0.98x0.39in Bluetooth Version: 5.0(Unobstructed, 15m/49.2ft) Input Mode: Aux, Bluetooth Number of Channels: 2.1 Channel Input Sensitivity: 500mV Power Amplifier Chip: Domestic Power Amplifier Chip Adaptation Speaker: 20-100W, 4-8Q Protection Mechanism: Anti Reverse Connection, Overheating and Overcurrent, Short Circuit Protection Applicable Power Supply: DC 12~24V 5A or More (Can Not Be Connected to 24V Battery Pack) Output Power: Left and Right Channel