The pickups used to amplify a banjo are completely different than for guitars and other instruments. Compared to a guitar, a banjo head has significantly higher and more percussive resonance and is also in a higher frequency range. Slapping a guitar pickup on a banjo will result in a very tinny, thin sound with a tendency to clip, distort and feedback significantly.
We recently received a call about amplifying a dance floor for a tap-dancing performance. The dance floor was a full-floating hardwood floor (with a pad underneath), and the idea was to attach pickup sensors to the floor at various points and then run them all into a PA system for amplification....