hum on U87 when touching Characteristic-Switch
Author: Florian Pilz
Date: 04/05/2014
Hello there,

this is my setup :
Mic : Neumann U87 AI
Preamp : Focusrite Liquid CHannnel

This is my problem :
there must be a "ground-Problem" or something with the 50hz coming out of the power supply.
I also have the "feeling" that i have some sistortions in the High-mids or the highs. Sometimes it sounds a bit like a saw.
The hum (50hz) is very small when i do not touch the Characteristic-switch, but when i do it getīs much richer.
It would be no good solution, just saying, "donīt touch it", because, as in the upper lines written, it sounds a bit harsh an not very clean
When i connect my TLM 103 it sounds much richer in the bass and the Highs seem to be cleaner.
I also brought my setup into the "Bayerischer Rundfunk" (bavarian public radio), where i work, to test, wether there is also a hum or not. There is NO hum. I also testet (at home) another Preamp - same Problem.
I also tested other U87 on my Equipment - same Problem

My question would be :

1. Is the U87 so sensitiv?
2. Does anybody know a solution, to get rid of this problem?

I tried everything to ground my equipment, have bought a transformator to clean up my Power supply, nothing helped.
The only thing that helps best is to use the TLM 103 or my Brauner Phantom (Both have no characteristic-switches)

Hoping :-)
Best regards
Florian Pilz
Martin Schneider/Neumann