Amplifier Specs

A sincere thanks to everyone for the free education. Almarg, thank you for the links.

Correction: The link in my previous post labelled "this text of the regulation" should have been http://edocket.access.gpo.gov/cfr_2009/janqtr/16cfr432.2.htm

Regards,
-- Al

Here is a link to the revised FTC regulation which "exempts sellers who make power output claims in media advertising from the requirement to disclose total rated harmonic distortion and the associated power bandwidth and impedance ratings."

It is actually 16CFR432 (Title 16, Part 432 of the Code of Federal Regulations), not 46CFR432 as referred to in the CEA document I linked to in my preceding post. The effectivity date is indicated as 60 days following publication in the Federal Register, which apparently was 12/22/2000 as indicated at the end of this text of the regulation.

BTW, the CEA was at that time a sector of the EIA, so Bob's comment was essentially correct.

Regards,
-- Al

Why would a company like B&K provide amplifier specs that use "cheater" measurments like "150 watts @ 1 kHz into 8 ohms"?

I believe the answer is simply that they are conforming to Consumer Electronics Association standard CEA-490A, previewed here, which is the currently applicable, and apparently voluntary, standard for specifying audio power amplifier ratings. As you'll see in the sidebar on page 2 of this article, only the 1kHz ratings are called for.

I believe that the 20Hz-20kHz ratings that were legally mandated by the FTC in 1974 were revamped ca. 1998 and in effect superseded by the CEA spec.

Regards,
-- Al

Mordenmail - I don't think 20Hz-20kHz is "given" since full power at 20kHz is absolutely useless. For class D it could not be possibly specified for the reason I mentioned before (full power at 20kHz would damage output filter).

Average music power is only few percent of max power. No need to design class AB amplifiers for sustained max power - otherwise they would have same size heatsinks as class A amps. Maximum current available is what counts.

First, I had no idea my question would evoke such a visceral reaction from some. It was not exactly my intention to accuse B&K of "cheating", hense the quotation marks used in my question. Martykl was exactly right in his interpretation of my question. I am a novice compared to most of you regular Audiogon posters, though an expert compared to most normal people, and have always understood that the most acurate measurment of power that an amplifier can deliver must be consistent at all frequencies. I have read material from various sources over the years that has indicated this to be the case. Clearly, my understanding appears to be somewhat an oversimplification. None the less, I have always wondered why B&K would give a rating such as the one cited in my question, while my Adcom amplifier is rated over the full spectrum of frequencies. It seems that specifiying power output at just 1kHz could suggest that the amplifier would not do as well at other frequencies. If this is not the case, why not just specify a rating at full range?

Interestingly, I have always felt like my B&K out-performs my Adcom and I have never felt like it was short of power. So, I don't believe that B&K makes junk...

Kijanki: You know a lot more than I do. However, I wonder if companies like Krell, Rowland, and Bel Canto, all companies that I consider much more high-end than B&K, might not specify frequency range because it is a "given" at that price point. You know what you are buying and you are paying for it. Just a thought.

Question is different from accusing somebody of cheating.

B&K amp in question is most likely class D amp where output circuitry (Zobel network) would burned out at full power at high frequencies. It is irrelevant since there is very little power in music at these frequencies but there is no easy way to specify it (it's a curve). It might apply as well to class AB amps since most of them has inductor on the output.

Most of manufacturer's don't even specify frequency range for the power. Not only class D (Rowland, Bel Canto and most likely hundred of others) but also other classes amps (Krell for instance) don't have frequency specification for the power at all. Are they all accused of cheating as well?

I think the question Morden asked is "Why isn't the amp's output spec'd into the usual 20-20k, 8ohm load"? It's a fair question. Note that the amp makes no claims to deliver the rated output ABOVE or BELOW 1kHz (where it may well be needed) and could, theoretically roll off steeply at, say 10kHz. The lack of further description of the 8 ohm load, while both annoying and less informative than it might/should be, is SOP.

Unless there is an accompanying power bandwidth spec (I'd double check for this), I'd agree that this is a misleading spec for a high end amp.

Marty

I'm not sure I understand: why do you think "150W @ 1kHz/8 0hm load" a cheater spec?
It is unlikely that this is a misrepresentation... it may not mean much (i.e. 8 ohms resistive, average? what about @ 20kHz, etc) -- but cheating?

Do not call it cheating unless you can explain why you need 150W above 1kHz.