An exceptionally natural, acoustic tone can be achieved by properly mixing the signal from the Biesele magnetic coil array pickup and that from a typical bridge mounted piezo-electric pickup (such as the Underwood or Fishman). The pre-amplifier/mixer was designed for just this purpose. The pre-amplifier/mixer circuit for both models consists of a volume on/off control, a signal blend control, an auxiliary input, and a selectable gain auxiliary range switch. Each coil array is provided with an inversion switch to maintain phase alignment between the two signal sources. 

Two models are available; the MT, a single unit that contains the pre-amplifier/mixer; and the DP, a model that separates the coil array from the pre-amplifier/mixer. The DP configuration reduces the physical mass of the assembly that mounts on the fingerboard by half. Its pre-amplifier/mixer can be strapped to the tailpiece or placed off of the instrument altogether.

And if you forget to turn off the switch when you're packing
up after the gig you won't kill the battery, the power to the 
circuit is also disconnected when the cord is unplugged from 
the output jack on both models.