Explain what is a clean power amplifier?

If Class D is too clean there are a few simple tweaks you might try. Obvious but slow is to just let the dust build up. If the sound is a bit dry and gritty and you would like a smoother softer focus try the Playboy Tweak, a thin coat of vaseline. Very popular all through the 80's. Keep in mind a clean amp is just the beginning. Don't forget to clay, polish and wax. 

millercarbon - you cheeky buggar! I'm still smiling.

douglas_schroeder I was sincere in my congratulations, if I were able (and able to convince my wife) to invest the time and evidently money you have I would most probably go for it. I have looked at your system page, there's some serious investment.

mahgister you have made efforts to share the benefits of setting audio equipment up and trying to make it work in your budget and house the best you can.

I see merit in both camps, and I've got my feet in both camps. After reading and learning more about electrical issues I splurged out on a device to clean up my AC for my system. I was seriously looking at Inakustik, but for less cost and I believe a better investment I went with Puritan power conditioner that also has protection built in.

Here is an ideal amp (100% perfection):

1) zero distortion.
2) zero noise.
3) No phase shift at any frequency.
4) Perfect square wave response.
5) Instant and unlimited current source.

The above is a 'clean' amplifier.  Everyone tries to achieve it, some come close.....

one that has been washed regularly, with an organic soap /cleanser, and occasionally rubbed gently with a dead sea mineral/ sea salt solution, helps electrical connectivity. Then finished with a high quality paste wax, like Mothers or Griot’s Garage Premium Carnauba Paste Wax.
Under normal usage that should keep your amp  clean and looking and sounding it's best for months at a time.