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

[pma]

The small (enclosed) heatsinks couldn't keep-up. The

What a shame to the designer. If this was a DIY attempt, then I would maybe understand. But, to sell this, with those 10K/W individual heatsinks - this is unbelievable.

 

[Sokel]

An amp from a renowed brand I bought new a few years back, spec'd 2×120 Wrms / 8Ω and equiped with 2 chunky 340 VA transformers. During summer, the thing shut down twice due to overheating while playing background music in my living room. The small (enclosed) heatsinks couldn't keep-up. The thermal protection sensor (thermistor) on the PCB wasn't even connected to the heatsinks.

View attachment 411215
So a bit of stress testing can't hurt I believe.

I have the exact same heatshinks at my mil spec Salas 5VDC PSU
And I can even make them go hot setting it for borderline (more than 500mA) current

 

[Old_School_Brad]

Here we go again with FTC tests in long term max power output...

This is as relevant as testing a car engine running 10.000 RPM for how long until it overheats and breaks: an useless test for an unpractical real use case. Yet the FTC specifies such test for some clueless reason, and even worst, some people insist on it...

If you insist on using car analogies; if I were looking to buy a car with an engine advertised in the brochure as capable of reaching 10,000 RPM, I would expect it to achieve that without failing.

 

[Chr1]

... But some expect to do this hypothetical 10k rpm without a radiator or fan to dissipate heat too.

Bad design. Definitely couldn't sell a car like this!

 

[NTK]

How many miles/km do you think an ICE car will last running at redline in 1st gear? Should we standardize the reliability test based on this operating condition?

 

[Chr1]

Damn nuisance car analogies...
Made even worse when e motors are thrown into the mix.
Back to amps maybe?

 

[Old_School_Brad]

... But some expect to do this hypothetical 10k rpm without a radiator or fan to dissipate heat too.

Bad design. Definitely couldn't sell a car like this!

I would naturally expect the manufacturer to have implemented the proper measures to ensure it performs as stated in the brochure without any issues.

It's quite straightforward: if it can't deliver on its promises, the product should be rated accordingly.

 

[TunaBug]

Here we go again with FTC tests in long term max power output...

This is as relevant as testing a car engine running 10.000 RPM for how long until it overheats and breaks: an useless test for an unpractical real use case. Yet the FTC specifies such test for some clueless reason, and even worst, some people insist on it...

I understand that music contains dynamic content that is not represented by a 5-minute test. But the FTC rules specifically allow manufacturers to have additional metrics that they report. If you want to also say that your 100W continuous amplifier also does 1,000W peak for brief periods measured using some test known only to you, then that number can be mentioned as well. But I definitely appreciate the baseline FTC tests that apply to everybody and that can be used to compare amplifiers.

So I call BS on your car analogy for different reasons than others. The FTC tests are not about reporting max RPM. They are about reporting continuous RPM. So by all means state that your engine allows 10,000RPM max if you want to, just only after you state that it's 7000RPM continuous.

I and I expect that vendors will do that. I'll be surprised if they don't, as they will want to find ways to distinguish themselves. Those additional numbers can be whatever they've been pushing all along. As long as they come after the FTC numbers.

I think that testers should also respect that specs that have been reported prior to the FTC rules should not be expected to meet the FTC standards.

 

[Blumlein 88]

How many miles/km do you think an ICE car will last running at redline in 1st gear? Should we standardize the reliability test based on this operating condition?

I think so. If you put a redline on my tach the engine damn well better hang together at that. I would say 5 minutes of that would not be out of line at all. Maybe not all in first gear.

 

[Mnyb]

Eh do your own tests if your not happy

Why the negativity when someone does free work for the forum

What’s done is clearly specified in the first post

 

[Chr1]

Wouldn't fancy a motor that makes half the claimed power and the engine blows up half way up to the redline...
Then you look under the hood and find there's no radiator.

 

[JustJones]

I admit to being confused , this thread was about testing to the new FTC rule yet it appears to me that stress testing to 5 minutes at MAX power while perfectly fine to do if you wish is not what the FTC rule says. What am I misunderstanding here?

(e) Any power level from 250 mW to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input.

(g) Rated power shall be minimum sine wave continuous average power output, in watts, per channel (if the equipment is designed to amplify two or more channels simultaneously), measured with all associated channels fully driven to rated per channel power.

The 5 minute test should be done at rated power which is continuous average power which is clearly stated on the NC252MP data sheet as 50 watts not 250W / 4 ohm that is Max output.

4.3. 5 minute sine test

The amplifier has not passed the 5 minute test at 2 x 250W/4ohm/1kHz. It was fine first 4 minutes, but then it shut down. Started with THD = 0.11% and reached THD = 0.5% before the shut down. The heatsink fins were slightly warmer at the end of the test period, but some hot air could be detected from the vent slots of the cover plate. After the shut down, the amplifier has recovered in a few minutes.

 

[Bruce Morgen]

I would not recommend higher supply voltage for the A07 than 36Vdc.

FWIW, I've been running two now-elderly A07s (with 50VDC rated Nichicon shunt capacitors) on somewhere between 46 and 47 volts for nearly four years with no problems at all -- not even a single protection incident, let alone an outright failure. On top of that, the two are stacked, which further degrades their already inadequate heat dissipation. I reiterate, there have been no problems at all in real world music listening.

 

[TunaBug]

Some of us feel the need of honest specifications of amplifier output power according to acknowledged documents like FTC regulations and IEC standards. The reason is to get comparable data, protect potential customers and draw attention to false claims of some manufacturers.

I agree with the need for honest measurements. I'm glad for the new FTC rules, and definitely appreciate your time and effort in testing.

But I also think that in all fairness to some of these amps, if their ratings were created prior to the FTC rules that the reports should state that very clearly. In other words, you're expecting them to pass a test that they never claimed they would pass. As a consumer I appreciate knowing that the amp doesn't meet the expectations implied by the FTC, but it's unfair to the engineers who created these products to say they are failing when they never claimed that they would pass.

 

[Chr1]

Agreed. The question is whether some were really even "fit for purpose" tho. A few appear not to be imho.

 

[Sokel]

I agree with the need for honest measurements. I'm glad for the new FTC rules, and definitely appreciate your time and effort in testing.

But I also think that in all fairness to some of these amps, if their ratings were created prior to the FTC rules that the reports should state that very clearly. In other words, you're expecting them to pass a test that they never claimed they would pass. As a consumer I appreciate knowing that the amp doesn't meet the expectations implied by the FTC, but it's unfair to the engineers who created these products to say they are failing when they never claimed that they would pass.

I agree in general.
But it's one thing to design a product according to needs an a whole other thing designing it by exploiting the weaknesses of measuring systems,like the very short testing time.
(something like the decision of the 5V output new DACs,right where the AP555 makes them shine the most)

I still can't get it,there's no shame at all producing a 20-30-50 W amp,it will find its place just fine if it's nice and reliable.Why the need for such outrage?

(*I'm staring at my 1200as's with their peaks p/c at their naming and their 280 W continuous in their data sheet * )

 

[DonH56]

I admit to being confused , this thread was about testing to the new FTC rule yet it appears to me that stress testing to 5 minutes at MAX power while perfectly fine to do if you wish is not what the FTC rule says. What am I misunderstanding here?

The 5 minute test should be done at rated power which is continuous average power which is clearly stated on the NC252MP data sheet as 50 watts not 250W / 4 ohm that is Max output.
View attachment 411228

First, this is a general thread, not specific to one manufacturer.

But, that is a good point, and one manufacturers should adhere to as well. The problem arises when product data sheets are not accurate. This is one for a fairly recent well-regarded amplifier using Purifi modules:

• Rated output power into 8 Ohms and 4 ohms(Stereo mode) 80 W (ref. 20 Hz-20 kHz at rated THD, both channels driven)
• >200W into 8 Ohm, >380W into 4 Ohm
• Rated output power into 8 Ohms (Bridge mode, ref. 20 Hz-20 kHz at rated THD, both channels driven)
• >700W into 8 Ohm

Confusing since the 80 W in the line is followed by >200/>380 W right below, and the bridge mode does not have that (so I suspect 80 W is a typo). Nothing said about continuous, just "rated output power" which the FTC (and I) would argue means "continuous". Especially since this particular amplifier also lists Clipping and IHF dynamic power:

• Clipping power (Stereo mode, at 1 kHz 0.1 % THD)
• >210 W (0.1 % THD 1 kHz 8 ohms)
• IHF dynamic power (Stereo mode, at 1 kHz)
• 8 ohms: 260 W
• 4 ohms: 520 W

Perhaps the power supply and heat sinking (thermal management) is sufficient to meet the FTC ratings (very well might in this case). If not, then the continuous spec can be derated with a 7 dB headroom spec added (in this example, that is already covered by the clipping and IHF dynamic specs). A quick search shows to me a number of products using Hypex and Purifi modules that are not clear with regards to maximum and continuous output power. The FTC rule will help avoid this sort of confusion.

Edit: IIRC, some Hypex modules were limited by the output capacitors self-heating, not thermal management, but either way the FTC spec applies since it does not care the underlying cause for the limit.

 

[JustJones]

Thanks for explaining. I know the thread isn't specific to one manufacturer but the NC252MP was easy to find and was one tested. It looks like you're using the Nad M23 and where it doesn't say continuous in the specs they do in the literature. ¯\_(ツ)_/¯

Conservatively rated at 2x200W continuous into 8 ohms and 2x380W into 4 ohms,

It would be nice if everyone would get in the same boat as it makes it hard for those of us who aren't as savvy.

 

[Sokel]

Also,the "music" argument (and the reduced power needs) is not as solid as we think and depends on the application.
At this thread for example tests were made with LFE channel material of Interstellar's Wormhole Scene which proved to be specially demanding.
They were not for 5 min though,but for about 1 minute,but at least way more than the usual few ms we see around.

(an icepower module found faulty and a Hypex NC502MP died during the tests,@StigErik can tell us more about it)

Edit: Interstellar's WS :

 

[DonH56]

Thanks for explaining. I know the thread isn't specific to one manufacturer but the NC252MP was easy to find and was one tested. It looks like you're using the Nad M23 and where it doesn't say continuous in the specs they do in the literature. ¯\_(ツ)_/¯

NP. And yes, I had it in mind due from some other research, not really a great example though I do wonder if it meets the revised rule. There are tons of amps using Hypex (etc.) modules that do not spec them properly, but I was too lazy to go deeper in the Duck Duck Go search to copy and paste. Not really relevant; what matters is having and meeting a defined spec.

It would be nice if everyone would get in the same boat as it makes it hard for those of us who aren't as savvy.

That's what the FTC is trying to do. A lot of us were quite annoyed when they "dumbed down" the spec many years ago to bow to the AVR manufacturers; this is a very welcome revision for "old-school" folk and anybody who values reliability and output power defined per spec and not marketing.