The PMB-L is a box for passive mixing of line signals. It is designed with two channels. Each channel has two symmetrical XLR/f input sockets, and the input signals are mixed to an XLR/m output socket via a resistor matrix. The upper input is also galvanically isolated by a transformer. Typical applications include combining two mixing consoles into a power amplifier or mixing a stereo signal into a mono signal. The transformer technology used allows for the upper input to be connected asymmetrically while still outputting a symmetrical signal.