Features: The 2.1 Channel Preamp Board features a NE5522 operational amplifier for precise auditory signal processing. Integrating low pass filtering and subwoofer optimization in a single power design. Main function of this tuneded version of the passive mixing board is to adjust the high and low frequencies of the input auditory signal, which is then send to the amplifier board for amplification. The principle of this product is that the auditory signal is filtered directly through filter and the desired high and low frequencies obtained through capacitors. The sound board not require a power supply, but the processed sound will be much lower. Specifications: Product name: NE5532 Passive Preamp Board Adjustable items: Total sound Treble bass Number of channel: 2.1 channel Knob spacing: 22.5mm Type: XH2.54-3Pin Size about : 82x30mm/3.23x1.18in Weight: 24.5g Power: 10-25V Package Includes: 1Set 2.1 Channel Preamp Board note: Please allow 1-2cm errors due to manual measurement. Please allow for slight color differences due to different display resolution.