This type of tuning board is a passive tuning board, the main function is to adjust the input audio signal high and low volume, and then send it to the power amplifier board for amplification. The principle of the product is to pass the audio signal through the resistance-capacitance element directly through the brush selection to filter out the desired high and low sounds. The tone board does not need power supply, but the volume be much smaller after processing. Product name: Passive tone board bare board Adjustable items: total volume, bass, treble Number of channels: two channels Knob spacing: 22.5MM Socket type: 2.54-3P Colour: Random Color, don't accept the specified color Material: Plastic+Metal Package Contents: 1 x Passive tuning 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.