Power amplifier tests with respect to FTC: 16 CFR Part 432 (July 5, 2024) requirements on output power claims

[Rick Sykora]

If we insist on using car analogies for some reason, I believe it’s more like a 200 HP engine that overheats and breaks down on the highway, even though the car was driving within the speed limit and only using 50 HP.

Not quite, but agree it is an oversimplification. Edited my post to reflect.

 

[Rick Sykora]

If we insist on using car analogies for some reason, I believe it’s more like a 200 HP engine that overheats and breaks down on the highway, even though the car was driving within the speed limit and only using 50 HP.

How about I drop the analogy and just go with "correlation is not causation".

 

[JustJones]

It’s e that I find confusing. The intent seems clear. If after pre conditioning, you can throw any arbitrarily selected frequency at it for 5 minutes at full power and it maintains less than 1% THD+n, your good. It needs to be able to do this for any frequency between 20 and 20k. Where I get confused is devising a reasonable test regime that I can be pretty certain the amp will then be able to pass that bar, as I obviously can’t test all the frequencies. What is the fewest number of frequencies and which ones can I test and be reasonably sure any frequency will then work?

No idea they don't explain. White noise maybe ? ?

 

[Mschn]

Long time back we were selling computers to Nasa for flight simulation. They were used on the Shuttle program. All the gear they were using from us were long discontinued. They had tested them, and verified them so they used them. New gear no matter how much better, was unproven and could not be deployed without years of testing. Again, different world than consumer products where the typical product cycle is as fast as 6 months.

This is typical for space industry in my experience.

30+ years ago I designed a LNA for the Cassini-Huygens project. The customer (ESA) dictated which transistors to use and they were old already back then but they were proven. You don't send a repair crew to Saturn...

/Martin

 

[restorer-john]

The regulations keep getting misunderstood. Which isn't surprising. Here's the relevant part of the new regulations . It defines rated power in section (g). The 1 hour warm up is 1/8 rated power not max power, it is supposed to be up to the manufacturer to disclose the power ratings of their amplifiers but according to Hypex on their spec sheet the continuous average power(rated power) of the NC252MP is 50W. So if you go by 50W the warm up would be 1/8 x 50 = 6.25W for 1 hour.

We get all that. It's been pointed out for years.

Trouble is, the assemblers (all of them) advertise and sell their products using the maximum power rating- not the 50W rating. That is the issue, not Hypex's butt-covering, hand-waving disclaimers and fine print excuses for designing modules that are drag-strip queens, not endurance racers.

 

[antcollinet]

The regulations keep getting misunderstood. Which isn't surprising. Here's the relevant part of the new regulations . It defines rated power in section (g). The 1 hour warm up is 1/8 rated power not max power, it is supposed to be up to the manufacturer to disclose the power ratings of their amplifiers but according to Hypex on their spec sheet the continuous average power(rated power) of the NC252MP is 50W. So if you go by 50W the warm up would be 1/8 x 50 = 6.25W for 1 hour.



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Right - but you are looking at the module power ratings.

Most amps using that module don't mention the 50W continuous output power and only reference the max output power. They specify themselves as a 250W amp.

Having said that - I've little doubt with this module that if it was integrated with sufficient cooling (a big enough heatsink, with adequate thermal coupling to the module) it could sustain the max power rating for the necessary 5 minutes (note 1 includes: "Max output power is time limited due to thermal properties"). But how many OEM's integrate sufficient cooling?

 

[IPunchCholla]

We get all that. It's been pointed out for years.

Trouble is, the assemblers (all of them) advertise and sell their products using the maximum power rating- not the 50W rating. That is the issue, not Hypex's butt-covering, hand-waving disclaimers and fine print excuses for designing modules that are drag-strip queens, not endurance racers.

I mean, I don’t know anyone at Hypex to characterize their behavior, but I did learn to spec heat sinks from them, back when I was playing around with building amps (my own circuits using existing TI A/B ICs). They do seem to at least try to get the info out there. They were the first resource that popped up when I was searching.

https://www.hypex.nl/media/b8/33/ac/1686146768/AN_Thermal_design.pdf

 

[Multicore]

We get all that. It's been pointed out for years.

Trouble is, the assemblers (all of them) advertise and sell their products using the maximum power rating- not the 50W rating. That is the issue

Yes. And I'm now of the opinion that unless Amir wants to take on the job of fixing that by enforcing FTC rules for them I'm not going to badger him about it.

 

[somebodyelse]

Trouble is, the assemblers (all of them) advertise and sell their products using the maximum power rating- not the 50W rating. That is the issue, not Hypex's butt-covering, hand-waving disclaimers and fine print excuses for designing modules that are drag-strip queens, not endurance racers.

At least one of them seems to have done extended testing around full power to prove their thermal design:
https://www.audiosciencereview.com/...-ncore-amplifiers-overheat.49087/post-1758153

 

[amirm]

I just think it would be nice to check if these things can do the max power (as determined by Amir) for a few minutes.

Why a few minutes? It won't resemble any real life usage.

 

[restorer-john]

Yes. And I'm now of the opinion that unless Amir wants to take on the job of fixing that by enforcing FTC rules for them I'm not going to badger him about it.

Enforce? Nah, just test continuous power and don’t recommend any product that doesn’t meet its advertised specifications.

That should be the bare minimum for a reviewer looking to retain credibility.

 

[amirm]

Enforce? Nah, just test continuous power and don’t recommend any product that doesn’t meet its advertised specifications.

If a product is excellent, you want me to say it is not because of what is written on their website? We call this biting your nose despite your face.

That should be the bare minimum for a reviewer looking to retain credibility.

My testing already goes well beyond what most people do with these amps, both in severity and length. Going beyond that to a spec written by people who don't even know how one measures or uses an amplifier shows incompetence by the reviewer, not anything else.

 

[amirm]

Those of us who care to test amplifiers properly will continue to do so.

Yet you haven't produced a single test using the new FTC ruling.

As to @pma, I have no idea what he thinks he is running with 4 ohm loads, no 5 minute duration, made up notions of warm up, etc. Nor has he shown designs that pass that people would want to buy.

ASR is just a fringe enthusiasts' website. It has zero presence outside our little obsessive bubble of an echo chamber. We are fringe, let's be honest.

Non-enthusiasts either don't know what a watt is, or how much they need. They would have no clue with "FTC" means either. They are going to shop by features, marketing, etc.

Enthusiast on the other hand, care about reviews. Any search of products that I have tested shows up on top of Google searches as Google considers us one of the trusted forums in this regard. Here is a quick search on my latest review:

We show up as the top organic search result. Our impact is quite wide and is the very reason I don't jump to run crazy, one-liner tests to please some bureaucrat in Washington DC. They are going to click on the review and see full performance of the product including proper power measurements.

That said, regulatory bodies do care.

They don't really. FTC's first line in request for comment was whether they should get rid of this ruling, likely because its time had come and gone. Folks, with good intentions but lack of knowledge in audio testing helped them create a far worse regulation than the original. So here we are. I wish them luck in enforcing a rule that is so ambiguous. And when companies find out they can't pass them and are loathe to derate their gear in advertising.

Your schtick seems to be to act hostile and demand that people run a test you have not run or thought through yourself. This kind of approach doesn't work with me.

 

[pjug]

Why a few minutes? It won't resemble any real life usage.

It at least hints at the degree of thermal management. Your readers can care about that or not.
edit: I know that you already typically mention whether the amp is cool or hot after the testing so this would just be a little more.

 

[USER]

Your schtick seems to be to act hostile and demand that people run a test you have not run or thought through yourself. This kind of approach doesn't work with me.

He has three amps in storage waiting to be tested...

 

[amirm]

It at least hints at the degree of thermal management. Your readers can care about that or not.
edit: I know that you already typically mention whether the amp is cool or hot after the testing so this would just be a little more.

These devices have robust protection circuits that shut them down if they get too hot. So there should be little worry about short term failure in this regard. Long term failure is another matter one that is not caught by this 5 minute, one time test.

That said, I am interested in tests that perform some level of design verification. My thought was to stress the amp thermally but also check for transient conditions (e.g. power cycles, shorts, etc.). I would then let such a test run overnight and see if it survives. For this to happen, someone needs to step up and build an automated fixture for it. I can't tie up my lab gear this way for this long. Need to connect, push a button and go to sleep and have results tomorrow. Once there, companies can then build such a box themselves or buy it.

 

[pjug]

These devices have robust protection circuits that shut them down if they get too hot. So there should be little worry about short term failure in this regard. Long term failure is another matter one that is not caught by this 5 minute, one time test.

That said, I am interested in tests that perform some level of design verification. My thought was to stress the amp thermally but also check for transient conditions (e.g. power cycles, shorts, etc.). I would then let such a test run overnight and see if it survives. For this to happen, someone needs to step up and build an automated fixture for it. I can't tie up my lab gear this way for this long. Need to connect, push a button and go to sleep and have results tomorrow. Once there, companies can then build such a box themselves or buy it.

I had a Class D desktop amp die when I shorted the outputs even though it claimed to have "Perfect protection circuit for overheating, overcurrent, etc." For sure I consider it my fault. But I don't know if protection by itself is the best answer, at least not for everyone.

 

[Rick Sykora]

I had a Class D desktop amp die when I shorted the outputs even though it claimed to have "Perfect protection circuit for overheating, overcurrent, etc." For sure I consider it my fault. But I don't know if protection by itself is the best answer, at least not for everyone.

Which amp was it?

 

[mhardy6647]

I am not outraged. Are you outraged? I will fake some outrage as an excuse to have a beer to calm me down though.

I like your thinking!

 

[pjug]

Which amp was it?

i didn't want to say since it was my fault. SMSL A300. The scheme with grounded + on one of the outputs bit me. I knew about it but trusted my memory on which channel. Memory was shit!

This example is not really on point for the continuous power issue except to say protection can't always be trusted. Also to look at it another way maybe playing these amps at max power for a few minutes will verify that protection is triggered!