AM422 is a passive DI box. Unlike an active DI box, it does not require any external power supply to operate (such as phantom power or batteries). DI boxes are mainly used to convert high impedance instrument signals (such aselectric guitars, piano, etc.) to low impedance balance signals and output them to PA or recording systems. The advantage of impedance matching is to avoid signal loss. Unbalance to balance avoids noise caused by long distance line transmission. A ground lift is installed to eliminate the hum caused by the ground circuit between the input and output. Use the "Merge" function to switch the THRU output to input to combine stereo input (such as keyboard) into a balanced mono output.