The B 29 L powers one or two C 4.. L version MicroMic III Series microphones (except for the D 409 L which requires no phantom power). The B 29 L features an on/off switch and status LED as well as a mic/line selector for matching the output level to the input of the connected mixer or recorder, etc. The B 29 L operates on one standard 9-V battery. Average battery life is 50 hours. Two volume controls allow you to balance the levels of the two microphones. A supplied clip makes it easy to attach the B 29 L to a belt or guitar strap, etc.