The problem is really simple.
The VU meter of my PreSonus Studio Channel (PreAmp, comp) is working for 5 secondes and kinda die.
I wait 2-3minutes without using the Mic. I start again the Meter is working for 5 secondes and then the meter return to it original position and won't move so much.
Tube problem ?
When it is working, i hear in my headphone, the gain and the compression. When the meter stop, it's like my PreSonus was close and go directly through my mixer.