“Black background” — What really contributes to this phenomenon?

@tvad what kinds of mods did you undertake?

The first notable improvement in blackening background in my system came from components with robust power supplies. These changes initially came from having early source components modified with significant improvements made to power supplies. The background became blacker. No question. Improvements were easily heard. 

Bob - yes :-) 

One firm noted for early power supply work is NAIM

I like the question. I purchased components already known for their quiet background. I really like a black background and low noise floor, silent computer, etc. And after getting a black background you just found out that your new noise floor is your tinnitus...