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Dear all,

I am just setting my recording studio, I hope you can help me and accept my very basic questions.
My devices consist in:
AKG 414 LTD mic;
SPL Channel One preamp;
Fireface 400 UCX;
MacBook Pro.

The mic is connected to the pre-amp through a XLR cable. From the output of the pre-amp a balanced cable goes to an analog input of the Fireface.
Now I am trying to record, with the Phantom switched on, and what I see is that if I increase (after 30 dB) the mic-gain in the Channel One I start hearing a quite strong low frequency disturb. I need to increase the gain because otherwise the signal is very weak.
With this interference the quality of the recording would be unacceptable
May you shine a light on what is happening?
It would be great.