Sub Kick Mic A guitar pickup is actually much like a dynamic microphone coil. For decades, powerful microphones have now been wired with the style coil mounted on the primary of the microphone's transformer, and perhaps not referenced to surface (‘floating'). The microphone's situation is usually linked to the cable guard, which can be attached to the microphone amplifier's ground (see Rane's site for more discussion).
By and big, powerful microphones are extremely quiet units as a result of the combination of transformer isolation and healthy, floating indication lines throughout, as well as shielded, humbucking coils.
So why don't you instruments? Guitars are notoriously plagued by noise. Humbucking pickups are only a partial (though crucial!) solution. Well-known answer is always to float the guitar pickup to a balanced result, being a microphone. The same thought was printed this 2001 patent request like this Sub Kick Mic?