Explain what is a clean power amplifier?

Amps that are not clean, just need an intervention.
Once clean, they can relapse  But so many amps are in denial.  

Nordost QX4. Enough said.

The devialet expert 120 I'm selling is one CLEAN sounding amp! 

...an absurdvation for one that doesn't use or even have a pre-amp....

I can turn my volume to max....and nothing....even with my low-rent IC's.

AB SS amps....nothing pedigree....SS 'pro' Eqs'....

The RTA sez their's a 'noise floor'....but I can't hear it.

*shrug*  Maybe I'm just lucky....or in a local focal locus that allows such.

If so....no, you can't move here....*G*

Obviously I don't Dare touch anything other than 'volume'.....

One false move...*poof*