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Join Date: Jun 1999
Location: West Hartford, CT; USA 06107
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Better power supplies are always better for a number of reasons: lower distortion, generally less heat output, bettersound, more listening power. WPC RMS gives the amps ability to produce a sustained level of wattage. This is very useful if you listen to sine waves; not music or movies, which constantly vary in level.
A better power supply means that the amp can put out peak power far beyond the WPC RMS. NAD excels at this; others don't. If you have a lousy power supply that can generate 100wpc, but little beyond that for peaks, you'll get clipping (amp running out of power and putting out square waves instead of sine waves) and distortion.
Yes, others fudge their specs. You supposedly can't for RMS, as that is dictated by the FTC. But you can give the spec w/1 or2 or 7 channels running, at 1k Hz (easy to produce) or 20-20k Hz, and at any level of distortion you choose. That looseness in the FTC RMS spec allows for what amounts to false claims of power, and makes it extremely difficult o compare products objectively.
If you have ever seen a review of a "100 watt per channel rec'r" that does 100 WPC with one or two channel runnings, and drops to something like 33 wpc with 5 or7 channels running, you're reading a review of an amp with a poor power supply.
There once was a spec. widely used called dynamic headroom (in dBs), which measured the amps ability to put out the peak power referred to above. Very few use this spec anymore, probably because they'd be so poor. At least NAD gives IHF power, which gives you an idea of what the peak power capabilitites of its equipment are.
Incidentally, NAD is the only company I've seen which gives power ratings in WPC and dBW. There may be others.