-75 db Background Noise for Avalon , is this normal ?

[Barbad]

Hi Friends ,

When I Turn off my Avalon 737 preamp , the digital level meter on input channel shows -inf , OK !
when I turn on the preamp with lowest output level ( Mute ) , input level meter
shows -85 db ... and when I put the output level of preamp to "0" then level meter shows -75 db and ffffffff noise start and I don't like that ...

are these numbers normal for pro analog devices & connections ?
is ( -12~-6db : -75~-70db ) ratio normal for ( audio signal : Noise ratio ) ?

if these numbers are not normal , then what should they be ?

All Inputs&Outputs&cables are balanced ... Tubes are NEW ...
I used a spectrum analyzer and noticed that I have some noise below 100 Hz around -90db ... is this AC hum ? Ground loop ? then why do i hear that like white noise ?

Thanks for your helps .

[amarshism]

Probably dirty power, which depending where you reside usually sits between 50-60hz. Ours reads -inf off and on.

[nosebleedaudio]

First; is anything plugged into mic pre input? Need a 150 ohm load to really do noise level check...
2nd; the 737 is not real quiet..(specs from web site)
And not sure what the 0dB means on the 737, could be unity gain, could be min gain, which could be SOME gain..if you know what I mean...
The -dB gain could indicate padding the input...again not sure without looking at schematic..Some Tube pres are done very differently from solid state pres..
My guess would be its OK...
Plus; is the noise white noise? Hiss?
If so I would doubt its a AC problem.