Note: This pre stage board is suitable for NE5532 NE5534 and OPA series op amps. Note that AD797 cannot be placed in the front position. It can be used for the inverting output at the back. If you replace different op amps, the sound will have different changes. You can buy it yourself. Op amp of the OPA series to adjust your favorite bass. 3 frequency balance, good sound density, strong treble extension, sweet vocals, and deep low frequency dive. Specification: Item Type: Amplifier Board_x000D_Material: PCB_x000D_Working Voltage: DC12-24V Features: 1[Durable and Effective]?Digital stereo amp module is made of high quality resistors and capacitors, which are durable and effective. 2[For Sound System]?Pre stage board is for retrofitting into your own pre stage, and it can also be adapted to sound system of all audiophiles. 3[Front Input and Output]?Amp board front input is buffered, 2x amplified output, buffered output, and inverted 0.2x output. 4[4 Level Control]?A channel with 4 level control can make the output sound quality density, sound field, and dynamics better! 5[Easy Installation]?Bass adjustment amplifier board is easy to install, it can be used after wiring. DC12?24V working voltage. PackageList: 1 x Amplifier Board 1 x Knob Cover 1 x Power Cord 1 x Nut 1 x Gasket