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Old 4th May 2014, 04:46 AM   #1
zcables is offline zcables  United States
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Default NAD power ratings?

Can someone explain to me NAD's power rating? They rate their average output at the same power for both 4 and 8 ohm impedance loads, but they rate their dynamic power at increasing levels as impedance drops; as shown below. I've always wondered why they do this as they clearly put effort into the power supplies and usually only cheap amps with bad power supplies don't produce more power as impedance decreases.

NAD C370
Power output RMS: 125wpc at 4 and 8 ohm.
IHF dynamic power: 210W into 8 ohms, 340W into 4 ohms, and 450W into 2 ohms.
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Old 4th May 2014, 04:54 AM   #2
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The only figure that can be used is the DIN RMS rating.

All other PMPO etc are just marketing hype, trying to make an amplifier look more impressive than it actually is.
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Old 4th May 2014, 12:15 PM   #3
tvrgeek is offline tvrgeek  United States
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NAD uses a dynamic rail boost/load impedance sensing system to give more "dynamic" power. The traditional DIN or the old FTC ratings are meaningless in this circuit. Hint: Amps do not like low impedance loads. They increases distortion and push the compensation limits. That is the technical defense. Kat is of course quite correct, they all have to play the advertising numbers game because we consumers are actually dumber than a stick in the mud.

Many amp parameters ( I won't say specs) matter. They all come down to one thing:
How does it sound in your system as you use it? The C370 is a well respected unit, much more powerful than the typical integrated amp. Don't over-think it.
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Old 5th May 2014, 10:18 AM   #4
AndrewT is offline AndrewT  Scotland
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"Don't over-think it"
Instead, just think of it as a 125W amplifier.
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Old 5th May 2014, 10:23 AM   #5
AJT is offline AJT  Philippines
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Quote:
Originally Posted by zcables View Post
Can someone explain to me NAD's power rating? They rate their average output at the same power for both 4 and 8 ohm impedance loads, but they rate their dynamic power at increasing levels as impedance drops; as shown below. I've always wondered why they do this as they clearly put effort into the power supplies and usually only cheap amps with bad power supplies don't produce more power as impedance decreases.

NAD C370
Power output RMS: 125wpc at 4 and 8 ohm.
IHF dynamic power: 210W into 8 ohms, 340W into 4 ohms, and 450W into 2 ohms.
Power output RMS: 125wpc at 4 and 8 ohm
power can be specced by a manufacturer any number of ways as long as it will pass the 1974 FTC trade regulations....
same power at 8 or 4 ohms means just big enough power transformer, output SOA, and heatsink mass for 8 ohms, otherwise if things were ideal, halving the load should double the power....not in this case and in so many others....
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Old 5th May 2014, 05:12 PM   #6
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Sizing the xfmr like that is an old trick for keeping outputs in SOA under adverse conditions when heatsinking isn't overly luxurious. (I'd rather have it like that than have the unit go poof.)
When combined with sizable buffer capacitance, it also allows for providing a fair bit of peak power at relatively modest average power - and since music tends to have a crest factor of 6-10 dB or even higher, you tend to run out of peak power first. So basically the amplifier can sound more powerful in real life without needing to have the chops to back it up.
IOW, I would expect better practical results from the combination of:
+/- 50 V (down to +/- 30 V under load), 2x 10000 F
compared to:
+/- 35 V (+/- 30 V under load), 2x 3300 F
You do pay with higher idle power dissipation and higher risk of secondary breakdown (though still smaller than with stiff +/- 50 V rails).
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