So NC500 can do 400 watts at 1khz and 1% thd. And therefore this figure would be substantially lower at 0.01% thd and 20hz to 20khz?
Probably, you would have to see the frequency vs output curve for the actual numbers. More later..
What does Continuous Output Power mean?
Good question, this is one of those specs that frustrate people like me who are obsessed with accuracy, definitions etc.. Like "power consumption" specs, different manufacturers seem to use definitions of their own, and worse still they usually don't even tell you what their basis are.
Some of the choices, or preference you can choose from, based on my search on the internet would include but not limited to the following:
1) "continuous output power" may mean the output power measured at a specific sine wave frequency that is a continuous signal, so that could range from just a few seconds, 10 seconds, 10 minutes, or literally continuous, i.e. forever!!
2) It could also mean using a continuous sine wave signal at a specified frequency, usually 1 kHz, for a specified duration. If the duration is not specified, it could be anything, for example if the manufacturer follows the FTC rule that is not compulsory as far as I know, it will be for not less than 5 minutes.
Note that Hypex does not provide "continuous" ratings. I read it somewhere that they leave such spec to the manufacturers since the real (i.e. literally) "continuous" rating would depend on the cooling provided, such as heat sinks.
Rated power shall be obtainable at all frequencies within the rated power band without exceeding the rated maximum percentage of total harmonic distortion after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input.
Now, back to the Hypex amps, again just the Hypex amp modules based on Hypex data sheets:
For the NC400:
If you look at the red curve, it would be about 400 W, 4 ohms, 1 kHz, and a little more for 6 kHz. The 6 kHz curve is good because it would include the typically dominant 2nd and 3rd harmonics. You can find out the same about the NC502MP by looking through the downloadable data sheets.
I wish all power amp manufacturers would provide as much details as Hypex, for their midrange and up models, sadly, very few do.