this is a neumann cmv microphone im fixing up for a client. it came to me all messed around with and not going. somebody had attempted to modify it from its original ec92 amplifier into an ef86 without a clue as to how valves actually work!. the thing could never have gone. they were just guessing. so after some careful brain surgery it goes beautiful now with a nice simple circuit . all new components. but still has a strange spurious noise issue to solve. the noise only occurs after bassey tones and comes up in the background for about 6 seconds. and then the mic goes perfectly quiet again. what the? so after repeating and checking everything im now resolved that the capsule has a fault. it still sounds great tho as long as you dont heavy breath close up. wouldnt suit darth vader.