Tube Pre-Amp Question

If the hum changes with an increase in volume it is likely that it occurs in a source/pre-amp connection, or a component part or tube in the unit that preceeds the line amplifying section of the pre-amp. I'm not familar with the VTL but if it has one a rectifier tube could be a problem as could a tube in the phono stage (if it has one).

I would suggest that you disconnect all of your sources and see if the hum goes away. If it does then add them back one at a time checking the results.

That will get you started.

I would also try floating the AC ground on your power amps. You might be experiencing a ground loop if the power amps are grounded through the AC cords.

Thanks for the feedback. The "Hum" is actually more like the sound of air/ static...nothing really. Not really a hum, more like nothingness/ sound. If that makes sense.

You are probably hearing tube 'rush' from less than the quietest tubes, or you are hearing the pre-amps' intrinsic noise floor. Do you only hear this with you ear within inches of the tweeter? If so I wouldn't be concerned, its not unusual.