This is a finished power amplifier board that has been welded. Please use a suitable transformer for power supply. Our power amplifier board has its own rectifier and filter. Our power amplifier board uses double-bridge rectification to provide power. , not a simple diode superposition!! Before turning on the power, be to check whether the wiring is correct. Be careful of short circuit. Connecting the wrong wiring will easily burn the chip. When the power amplifier board is working, it will heat up. 't worry, the heat of this chip is normal. Do not touch it!! The power amplifier board generates a lot of heat! Please pay attention to ventilation and heat dissipation! For a long time or ~ you can add a cooling fan or change to a larger heat sink. The main parameters Product name: 2.1 channel subwoofer power amplifier board Chip specification: LM1875 (domestic chip) Product size: 110mm x 77mm x 47mm (excluding potentiometers and other protruding parts) Output power: 3X20W LM1875 Power supply voltage: double power transformer 11V~15V Potentiometer spacing: 24mm24mm Driving capacity: It is recommended to use a full-range speaker with a size of 4~8 above 4 inches for the left and right channels, and a long-stroke -diameter subwoofer with a size of 4~8 above 6 inches is recommended for the subwoofer. Remember! Please do not use small speakers! Ordinary small speakers are not good! In general, we do not recommend customers to make their own subwoofers unless they are very proficient in speaker parameter selection and cabinet processing. Limited to the actual conditions, it is difficult for ordinary players to make their own speakers with very good results. It is recommended to buy finished boxes to make speakers! Choose -, high-sensitivity speakers as much as possible. Material: plastic colour: black Package Contents: 1 x 2.1 channel subwoofer power amplifier board Only the above package content, other products are not included. Note: Light 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.