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WATTS: Derate for 1khz vs music. Derate for Class A vs D.

It is a proper word at proper place. Manufacturers are obliged to specify the rated power and there are IEC and FTC standards how to measure it. Not that we have "various measurements", that is a lame excuse. If the amplifier fails to fulfil the standards, then the claimed rated power must be lowered to the level when it fulfils the standards. In other words, derated.
Having one standard to measure against, and finding differences to whatever the manufacturer stated are valid as long as the same standard is applied. Measuring something else and finding other performance figures can have numerous reasons, some stemming from the core amplifier design, others may be design decisions based on budget, or whatever other reasons. Not all of these do actually affect the actual performance of the amplifier with music. A "derate" will tell you exactly nothing in that regard, and that is why it's so pointless. It's far more important to understand these differences, and how they would impact the actual performance of the amps with music. if you are about informing consumers, then this should be a priority. It's just as pointless as only looking at SINAD. At face value, a 110 SINAD is just as pointless as a 30W derate.
ASR should protect the rights and interests of the customers, but, for some suspicious reasons, it rather seems to protect some manufacturers and OEM assemblers and their marketing and business interests. Why? There seems to be a reason.
I think there is no issue in exposing the shortcomings of the current measurement method, also given the issues we've recently seen with the clearly inadequate B100 amp. For sure, things should be improved to get a clearer picture of what the amps are capable of, but it should also be made clear how these measurements relate to the actual performance of music, similar to how it should be much clearer that SINAD is more a (limited) measure of engineering excellence, and much less something relevant to the audible performance (within reason). And yes, there is no discussion that adequate power delivery is also part of engineering excellence... But I guess with the SINAD craze ASR fell victim to its own success... it's not a bad thing perse, because it means we can repeat this again with other metrics. There just needs to be the willingness to do so.
 
It's pretty clear to me that a continuous power rating isn't all that useful in the context of music, which has a pretty high crest factor.

However I'm okay with a continuous power rating as it basically represents a worst case scenario in terms of what it's required to deliver.
 
it basically represents a worst case scenario in terms of what it's required to deliver

Exactly. Minimum requirements for any advertised amplifier over a few (2) watts.

By all means extol the virtues of high dynamic/short term power and how important that is blah blah. NAD had no problem selling their power tracker (later called power envelope) in vast numbers into the market even with fully compliant FTC ratings AND a very high rated dynamic output. So did Proton, Hitachi, Pioneer, Marantz, Kenwood and Yamaha. They all had ranges of conservative FTC rated amps with very high short term ratings. Mostly achieved with commutating designs with high voltage secondary rails.

Personally, I love those designs. They are cool running, offer considerably more than their continuous ratings, and then you get obscene short term swings when you need it.
 
It's pretty clear to me that a continuous power rating isn't all that useful in the context of music, which has a pretty high crest factor.

However I'm okay with a continuous power rating as it basically represents a worst case scenario in terms of what it's required to deliver.
Absolutely. Choosing an amplifier based on continuous power ensures you’ll have ample headroom in any situation.
That’s my perspective as well. A reasonable compromise could be selecting an amplifier with a lower continuous power rating but substantial dynamic power reserves. Brands like Yamaha, NAD, and Onkyo have produced excellent amplifiers with this design philosophy. One might even argue that this approach reflects thoughtful consideration of the demands of musical signals in their design and rating processes.

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I use WATTrms for ratings and calculations. Some experts here say it is a fantastical number that serves little to no purpose. They want average, real and or apparent used instead.
I"ve always understood it that the strictly technical view is RMS in relation to watts is not applicable, because it is a specific technique to obtain the DC equivalent for an AC waveform (One that goes negative as well as positive). Power is never negative so the root of the square is not necessary. Just the mean is.

My personal view is that it doesn't matter because the result is the same, and "RMS" has just become an indicator of "Average, not peak"
 
Just to make the point about gain even clearer…


Maybe we should ask “Scientific Audiophile” to rerun his test with the preamp from that thread in circuit. Of course all we’d get is a video about how nasty the clipping is with that cheap Fosi amp…
 
Thanks @GXAlan for the m-noise video. Although m-noise is focused more on speaker testing and calibration, it does seem relevant to amp testing for long term power. The other thread on the FTC rule is a bit polluted so bringing my thoughts here instead!

The R&D behind m-noise tells us that peak levels are the same across the spectrum, but crest factor drops. In the video the example of a snare drum is used - it's loud but only briefly. We essentially need four tests to characterise an amp then:
  1. 1KHz 5W THD+N to set a baseline
  2. Stepped sine testing at a range of frequencies (32 is usual) between 20Hz and 20KHz to determine 1% THD power at each frequency. This can use very short (20-100 cycles) tone bursts and will not thermally stress the amp
  3. 5W Multitone testing at the same frequencies to identify IMD issues. Short duration with no thermal stress again, 1 second should probably be enough to get a noise floor that compares with (1)
  4. Thermal testing with m-noise. Not sure what the procedure should be but it feels reasonable to start with the signal set to the same total power as the 1KHz sine max discovered in test 2? An "ideal" amp for music/movie playback should be able to do this forever, so run until protection kicks in or the chassis reaches 60C?
Note that I have not included a worst case thermal stress test of running at full 1KHz power with a sine. It's informative to designers and testers but very misleading for consumers I think.

Thoughts?
 
I use WATTrms for ratings and calculations. Some experts here say it is a fantastical number that serves little to no purpose. They want average, real and or apparent used instead.
There are no RMS watts. RMS volts, sure -- not watts, though.
Continuous watts, yes -- that's what half of this thread's about! ;)
The other half is about (more or less) instantaneous watts. EDIT: with some discussion around how instantaneous is instantaneous: msec, usec, sec, min (etc.)

If the claimed output power exceeds the steady-state capacity of the mains circuit feeding it (e.g., a nominally 120 VAC, 15 amp circuit in the US) -- I get kind of skeptical of the claim.
 
I see now all Erins amp reviews after Jan. 2024 (about 2 reviews to date) show the max output for 1khz and for multitone, so you can see the difference (the derate) going from 1khz to multitone. It is the only place I know of that does that. It would be great if we do that at ASR too.

Erins tests show NAD C 3050 dropped 3%. Not bad.

I checked the definition of "derate" and I think i used it correctly. What word do you prefer for this reduction in power output? I don't care what word we use as long as it is not misleading.
 
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It's not derating per se, I would say. The challenge is definitional. At least in the FTC '74 heyday, there was a rule of thumb that one might expect ca. 3 dB more power output at 1kHz at a given THD level relative to the 20-20kHz power output for an "average" mid-1970s stereo amplifier (at the same THD limit).
In other words, an amplifier that put out, e.g., 50 watts at 1 kHz at <0.1% THD was probably capable, under the same assay conditions, of 25 watts from 20-20kHz at <0.1% THD.
Looked at one way, it's a 50 watt amplifier.
Looked at another way, it's a 25 watt amplifier.

This High Fidelity magazine cover from 1973, which I posted to the "FTC power" thread, illustrates the challenge as it manifested itself back then (and, it appears, once again nowadays).
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Come to think of it, there's another way to look at the hypothetical 25 watt amplifier I... umm... hypothesized above:

  • 50 watts 1 kHz
  • 25 watts 20 to 20kHz
  • 25 watts with 3 dB headroom
;)
 
If the claimed output power exceeds the steady-state capacity of the mains circuit feeding it (e.g., a nominally 120 VAC, 15 amp circuit in the US) -- I get kind of skeptical of the claim.
Haha, yeah. Some capacitance-related wizardry comes into play, and you end up delving into compromises and millisecond signaling.
This isn’t inherently bad, but it’s important to consider how the ratings were determined.


Come to think of it, there's another way to look at the hypothetical 25 watt amplifier I... umm... hypothesized above:

  • 50 watts 1 kHz
  • 25 watts 20 to 20kHz
  • 25 watts with 3 dB headroom
;)
Like it, until recent, has been for forty years. :)
 
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