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Purifi 1ET400A with linear PSU tested to comply with FTC rule

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@Buckeye Amps , why do not you rather concentrate on better amplifier testing and understanding how to make a test system rather than spending time in pointless discussion? Learn and grow, and you would not face the Stereophile fiasco again.

@pma , please stop trolling.
 
If the personal attacks continue. You will receive a Warning and a perm thread ban. Stop trolling and communicate with respect and professionalism.

No further warnings will be given. ;)
 
How does one become compliant with "shall be obtainable at all frequencies" if not by actually obtaining, while testing? ;)


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Through statistically significant testing and probability. I believe we can all agree that it's impossible to to test an infinite number of frequencies at an infinite number of power levels. So what you do is design a set of tests at specific frequencies and power levels that give you a mathematical model of your device. The engineers, mathematicians, and lawyers sit down and decide if that model is good enough for performance and liability reasons.

As a quick crude example you would just test the four corners of your design spec. Think power on the vertical and frequency horizontal. i.e. 20Hz 250mW, 20kHz 250mW, 20Hz rated power, 20kHz rated power. Not a lot of data, hard to prove that the device complies if challenged.4 data points wouldn't give me a warm fuzzy feeling.

So now we add more data points. Let's step out min and max power by one third octaves. Now you've got more data points to fill in the line between 20 and 20kHz at min and max power. Now let's step power by some arbitrary amount, how about a 3dB power increase from 250mW to rated power at 20Hz and 20kHz. We now have a performance box outlined with a number of data points. By no means a complete and full test but enough to define boundaries of performance. Probably want to do some testing inside the box so maybe 6 dB power steps across octaves, decades might be a little far apart.

Now you've a bunch of data points that show the operation of the amp at the extremes and inside of it's operating spec. So the mathematicians do their thing analyze the data and say yes or no to the spec you want to use and a confidence interval for the data set. Then the lawyers decide if the CI is good enough to defend if challenged in court.

Don't forget that it's the FTC that has to test and prove the amp isn't meeting the spec. They would have to prove beyond a reasonable doubt that it was intentionally advertised wrong.
 
If an amplifier can produce rated power at 20 Hz and at 20 kHz for 5 minutes, then why would the rated power not be "obtainable at all frequencies"? I don't remember seeing an amplifier produce less power at some random in between frequency.
 
Now you've a bunch of data points that show the operation of the amp at the extremes and inside of it's operating spec. So the mathematicians do their thing analyze the data and say yes or no to the spec you want to use and a confidence interval for the data set. Then the lawyers decide if the CI is good enough to defend if challenged in court.
Are you kidding? You want amplifier makers, many of them small outfits, to hire lawyers and mathematicians just to meet the FTC rule? You don't think it makes more sense to write the test procedure into the rule so that it can easily be followed? Then mathematicians and lawyers can do some more worthwhile work with their talents.
 
If an amplifier can produce rated power at 20 Hz and at 20 kHz for 5 minutes, then why would the rated power not be "obtainable at all frequencies"? I don't remember seeing an amplifier produce less power at some random in between frequency
In theory you are right, however, there are the distortion requirements to account for as well. For example, 20kHz is an interesting test point The rated power needs to include a THD+N measurement at 1%. But none of us can hear distortion from a 20kHz signal because the 2nd harmonic is at 40kHz. Quite a lot of people think 6.6kHz is a more useful test for devices for humans because many of us will hear the 2nd harmonic and 3rd harmony distortion.
 
Would you mind posting the graphs like the one above (switching frequency amplitude) with calibrated Y axis? Like dBV, V, anything. The plot in dBrA does not allow to read the switching frequency amplitude, it is important to know.
While agreeing with you that any time a graph is shown as dBrA or dBrB, A or B should be present, I disagree that at the levels typically seen with quality Class D amps that it's important.

In any case, although I'm sure you already knew the answer and the question was just for effect, here you go:
1736381686380.png
 
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What are we concerned about if not audibility? There are of course engineering reasons to look above 20kHz, its possible they can affect whats going on under 20kHz, but at the end of the day the most important thing to consider is what we can hear.
In this case, the 'standard' ostensibly to be only concerned with how much 'power' an amplifier will put out under a very narrowly defined condition.
 
Are you kidding? You want amplifier makers, many of them small outfits, to hire lawyers and mathematicians just to meet the FTC rule? You don't think it makes more sense to write the test procedure into the rule so that it can easily be followed? Then mathematicians and lawyers can do some more worthwhile work with their talents.

Not kidding, that's just my answer as to how a company could attempt to comply with the regulation.

Not my problem if a small company can't comply with rules and regulations. They can't then they don't advertise power.

The rule sucks, poorly written, should be redone. A well written rule costing less money to comply with benefits all parties. I'd much rather see compliance costs spent on UL and FCC certification. Safety and benign interference/compatibility are much more important IMO.
 
Are you in the United States? I wouldn't lose in court since I wouldn't be involved. The regulation doesn't require infinite number of frequencies only those between 20hz-20khz at rated power for 5 minutes.
There *ARE* an infinite number of different frequencies between 1,000 and 1,000 Hz. Let alone between 20 and 20,000 Hz. That's just basic mathematics (Density Theorem).

But this thread has ceased to be interesting for me.
 
How does one become compliant with "shall be obtainable at all frequencies" if not by actually obtaining, while testing? ;)


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Regulations are often not concrete in their wording -I get it. I work with standards regularly in my field within the energy sector.

Because of this, guidelines, addendums, or supplementary documents addressing specific questions about the regulation or standard are frequently provided. These resources aim to reduce ambiguity and prevent multiple interpretations.

The FTC regulation is no exception.

"Shall be obtainable" means exactly that. If an amplifier is picked up by anyone, and the manufacturer claims on the packaging that it complies with FTC regulations, it should be capable of being tested at any frequency between 20 Hz and 20 kHz while delivering the rated power and distortion figures.

This testing could be carried out by the commission itself (as is done in the EU with random inspections) or by any third-party tester.

However, this does NOT imply that manufacturers are required to test their amplifiers at every frequency in that range. The regulation doesn't specify that.

If a manufacturer is confident in their design, they might only test at 20 Hz and 20 kHz and rate the amplifier based on FTC guidelines.

This approach makes sense. It's rare for an amplifier to exhibit low distortion at 20 Hz, high distortion at 1 kHz, and low distortion again at 20 kHz.
 
This approach makes sense. It's rare for an amplifier to exhibit low distortion at 20 Hz, high distortion at 1 kHz, and low distortion again at 20 kHz.
It is routine for class d amp to have unpredictable distortion vs frequency vs power.
 
be capable of being tested at any frequency between 20 Hz and 20 kHz while delivering the rated power and distortion figures.
Government provides no specification for how that distortion is measured. I can pick very high bandwidth and invalidate most such ratings by companies.
 
Regulations are often not concrete in their wording -I get it. I work with standards regularly in my field within the energy sector.

Because of this, guidelines, addendums, or supplementary documents addressing specific questions about the regulation or standard are frequently provided. These resources aim to reduce ambiguity and prevent multiple interpretations.

The FTC regulation is no exception.

"Shall be obtainable" means exactly that. If an amplifier is picked up by anyone, and the manufacturer claims on the packaging that it complies with FTC regulations, it should be capable of being tested at any frequency between 20 Hz and 20 kHz while delivering the rated power and distortion figures.

This testing could be carried out by the commission itself (as is done in the EU with random inspections) or by any third-party tester.

However, this does NOT imply that manufacturers are required to test their amplifiers at every frequency in that range. The regulation doesn't specify that.

If a manufacturer is confident in their design, they might only test at 20 Hz and 20 kHz and rate the amplifier based on FTC guidelines.

This approach makes sense. It's rare for an amplifier to exhibit low distortion at 20 Hz, high distortion at 1 kHz, and low distortion again at 20 kHz.

This regulation is so poorly written that you need to try to re-interpret words, like "obtainable" to even begin to agree as to what the regulation actually requires.

Reminds me of an ex US president who, with a straight face, said this in his defense: "It depends on what the meaning of the word 'is' is" :)
 
This regulation is so poorly written that you need to try to re-interpret words, like "obtainable" to even begin to agree as to what the regulation actually requires.

Reminds me of an ex US president who, with a straight face, said this in his defense: "It depends on what the meaning of the word 'is' is" :)
Weren't we just trying to figure out what the word "all" means?
 
I have a strong urge to start quoting Jean-Paul Sartre from the "L'Imaginaire" but I strongly resist :p
 
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