Would someone please describe Class II specifically related only to NC400?
There is noting in the class II rules that relate specifically to the nc400, and the nc400 has no special requirements in that regard. Class II is class II.
Here is what Bruno commented on the matter on
diyaudio:
IMNSHO the word "ground" should be forcefully removed from the school curriculum. The conflation of "chassis potential", "earth potential", "power supply return" and "reference potential" into that one little sneaky cowardly word "ground" is the source of an absolutely incredible array of engineering problems the world over. Conversely, the simple act of not using the same galvanically connected network for both reference potential and any combination of the other three solves all problems. Chassis, earth and PSU null may be interconnected in any way you like provided that actual signals are accompanied by another wire carrying the reference potential of the source. The receiver, of course, should be capable of subtracting the voltages between the two wires, not attempt to take a shortcut by forcing one of the two to its own "ground" (or to try and force its own "ground" to follow the potential of the reference wire).
Class I equipment needs direct earthing of the chassis for safety, class II equipment does not. However, in the latter case you may not use earthed mains inlets. You may have noticed that mass market consumer audio gear has class II wiring and a 2-prong mains cord. This is because unbalanced connections simply do not mix easily with earthing.
If you cannot construct per class II, floating the secondary ground is a commonly used and very bad practice. Very bad because it requires star connections which are a source of HF problems. It is much better to use a differential input to float the reference terminal ie the RCA shell and sense between the shell and center pin without making a direct connection to chassis or any other of the irrelevant "grounds". One would place a cap and perhaps a resistor to chassis to limit the voltage between the two and stop the connection from becoming an antenna.
That way the differential input acts like an input transformer: only the voltage between two input pins matters, not the voltage with respect to whatever one may think is "ground". There is always an easy solution that does not require fancy floating schemes if you have a differential input at your disposal. There is neither a simpler nor a better solution than the one already in place in the UcD modules. The only thing we can do is write a very long and detailed document explaining the operation of differential inputs. Trust me, once the penny drops you'll bang your head and say "if only I knew it was that obvious". One thing you're guaranteed to do, for instance, is immediately adopt the scheme on the right hand side of the wiring application note. This is much better than any floating secondary or differential RCA connection you can dream of.
