This is the Mackie XLR10 mic-input expander. This unit is NO LONGER MADE and is the ONLY way to add XLR mic inputs to the classic out of production Mackie CR1604 mixing board. Simple to install, one audio connector and 4 screws. Unit is clean, no problems, and adds 10 XLR connectors to the Mackie CR 1604. This original model Mackie mixing board was still the USA made, discrete electronics mixer, and made Mackie a name for mixers. Later Mackie model mixers switched to lesser integrated circuit designs and were made in China. The original CR1604 was widely praised and adopted for studio sub-mix use and broadcast applications, and is still a loved and sought after mixing board.