Neumann M147 DIY with Arienne K87 (add comparison with u87ai sound files)

[oscarhuang]

How have you determined that's because it's an impedance-balanced output? Does the noise go away if you use a 1:1 or 2:1 transformer?

Although I haven't done any experiments with transformers yet. But I think the noise will disappear after adding an output transformer. I have made several fet unbalanced output microphones before and this has not happened. So I don't know what the problem is.