brand new and high quality Features: 5.0 Bluetooth-compatible version has for high fidelity and two-channel stereo sound quality, with higher efficiency and farther transmission distance. Capacitor 470uf 35V solid capacitors ensure power storage and heat dissipation, and stable power supply is a prerequisite for good sound quality. The copper for DC connector is used to withstand high current and no heat. Free for DC for head lead, for the input power interface of this product, even if you don'for t have a for DC for head adapter or battery, it can be easily wired. It also comes with a volume adjustment function, which rotates the chirp potentiometer clockwise to zoom in and counterclockwise to decrease. Great for DIY speakers. Specification: Model: ZK-502L Bluetooth-compatible version: 5.0 Material: Fiber glass board and electronic component Size: app.55 x 38 x 17mm/2.17x 1.50 x 0.67in Adaptation supply voltage: 5-24V(optional 9/12/15/18/24V adapter, high power recommended high voltage) Adapter speaker: 30-200W, 4,8 Number of channels: Left and right stereo(stereo) Bluetooth-compatible transmission distance: 15m(without occlusion) for Protection mechanism: Self-recovery overheat for protection, self-recovery short circuit protection Color: As picture shown Quantity: 1 Pc Tip: To have enough out put power if the audio input is sufficient and the supply voltage/current is sufficient. The power supply voltage is higher and the relative power will be larger. The speakers with different impedances will have different output power. In the for case of sufficient voltage and current, the larger the ohms of the horn, the smaller the relative sound powre. Please pay attention Power supply voltage: 12V--8 ohm speaker/12W(left channel) + 12W(right channel), 4 ohm speaker/20W + 20W 15V--8 ohms/18 + 18W, 4 ohms/greater than 30 + 30W 19V--8 ohms/32 + 32W, 4 ohms/greater than 45 + 45W 24V--8 ohms/38 + 38W, 4 ohms/greater than 50 + 50W Precautions for use: The power switch on the board is the standby switch. After the switch is turned off, the machine is in a low-power standby state. To completely turn off the power or unplug the for DC plug on the machine for a long for time. Question and answer: 1. How to choose a power supply? The power supply with the board is critical. The higher the voltage, the higher the current and the better the output power. If you only have 12V 1A, you can bring a 3-4 inch speaker. If you are 19V 5A or above, there is no problem with 8-10 inches, and the power supply must be highly valued. If the voltage is too low, the sound will be distorted after the sound is amplified. If the current is too small, the speaker will pull the voltage low, work abnormally or the sound quality will deteriorate. It is recommended to use 18V19V24V power supply with current above 3A. If you only have 9V12V or 1A 2A power supply, it can also be used but the power is small. Please pay attention to the maximum volume when using it, which may affect the sound quality. 2. How to choose a speaker? Commonly used speakers are generally 8 ohms, can not distinguish between positive and negative, the effect is the same, 4 ohm speakers can also be used. If your speaker power is small, it may be used between 10W-30W. The power supply voltage is small to prevent the amplifier from burning out after burning. For example, select a power supply below 15V. If you are a 50W-200w speaker, don'for t worry about the speaker burnout. You can choose 12-24V power supply. The higher the voltage you choose, the louder the output sound or power. 3. How to connect to Bluetooth? Power on the power amplifier, connect the speaker, turn the audio knob blue light to turn on, turn on the phone settings - Bluetooth-compatible - search for "BT-WUZHI", and then click the connection, there will be a beep when the connection is successful, this When it is in Bluetooth-compatible mode, you can for play music. The next for time you power on, it will automatically connect with the phone. 4. When the sound becomes louder, the phenomenon of turbid sound appears. The sound is distorted. Please change the adapter power supply with a higher voltage rating. 5. After the sound becomes louder, the sound is stuck. The input power is insufficient, and the power supply itself is intermittently powered off. Please replace the power supply with a larger power.Or the output power is too large, the power amplifier board is seriously heated, and thermal for protection occurs, reducing power usage or enhancing heat dissipation. Note: Please allow 0-1cm error due to manual measurement. pls make sure you do not mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item.