NC252MP (class D) vs. A250W4R (classAB) burst measurements into 4ohm//2.2uF load

[pma]

Not sure we can generalize beyond that.

I agree, partially. The same applies to Purifi 1ET400A which I have here as well. Not speaking about toys like Aiyima A07 or SMSL A100, that I have here as well. Yes, I have not tested "ALL" class D amplifiers. In case you have one that handles 2 ohm and complex load well, please send it to me and I will be happy to test it and post the results, good or bad ones.

Shocking news! An amplifier not designed to deliver lots of power into 2 Ω loads behaved as it was designed.

That it is not the case. The case is that ASR "think tank" creates an illusion, shared by many laymen members, and resulting in generalizations, that class D amplifiers handle difficult loads better than class AB amplifiers. Such is the atmosphere, here. The fact is that it depends on design and it is much more difficult to design class D hi-fi amplifier to do so. Again, I am waiting for just one, single example of such class D amp, supported by facts.
BTW, I was driving only one channel of the NC252MP. Because A250W has 2 independent power supplies, each for each channel, so driving both channels would give it a big advantage. The test conditions have to be fair.
Note: I know the Hypex datasheets quite well.

 

[peng]

The small difference is if the amp is oscillating at 380 kHz with resistive load or if the 66kHz oscillations occur after connecting to capacitive load, and with much higher amplitude. And such oscillations are a result of change of operating conditions of the switching amplifier. One could learn from Bruno in the Hypex Ncore thread (diyaudio, about 10 years ago) that the limit for additional capacitance that does not affect the operating conditions of Ncore is 200nF. The reason is simple, output LC filter uses 2uF capacitance and 2.2uF added in my test completely change working conditions of the amplifier. Ncore is just not designed to work with such load and speakers with similar impedance should be avoided. This information is valuable for the potential customers and not something you should fight against. You cannot protect something that is unprotectable.

You can also find a kind of load that class AB amps may not behave well. I just see no point and extremely limited value of such a test. What's the probability for someone who would suffer from the specific class D amp when used with music or movie contents? The test is certainly interesting and yes has value, just not practically speaking.

 

[tmtomh]

I agree, partially. The same applies to Purifi 1ET400A which I have here as well. Not speaking about toys like Aiyima A07 or SMSL A100, that I have here as well. Yes, I have not tested "ALL" class D amplifiers. In case you have one that handles 2 ohm and complex load well, please send it to me and I will be happy to test it and post the results, good or bad ones.


That it is not the case. The case is that ASR "think tank" creates an illusion, shared by many laymen members, and resulting in generalizations, that class D amplifiers handle difficult loads better than class AB amplifiers. Such is the atmosphere, here. The fact is that it depends on design and it is much more difficult to design class D hi-fi amplifier to do so. Again, I am waiting for just one, single example of such class D amp, supported by facts.
BTW, I was driving only one channel of the NC252MP. Because A250W has 2 independent power supplies, each for each channel, so driving both channels would give it a big advantage. The test conditions have to be fair.
Note: I know the Hypex datasheets quite well.

Just because you’re a “think tank” of one doesn’t mean you don’t have your own biases and blinders.

You draw conclusions about Class D vs Class AB, but as your own narrative repeatedly notes, the key issues highlighted by your measurements are primarily about the behavior of the power supplies.

 

[MaxwellsEq]

The case is that ASR "think tank" creates an illusion, shared by many laymen members, and resulting in generalizations, that class D amplifiers handle difficult loads better than class AB amplifiers. Such is the atmosphere, here.

I don't see people regularly making that argument.

An amplifier (AND PSU) designed to handle low impedance or complex loads will be good at it.

 

[peng]

That it is not the case. The case is that ASR "think tank" creates an illusion, shared by many laymen members, and resulting in generalizations, that class D amplifiers handle difficult loads better than class AB amplifiers. Such is the atmosphere, here.

I haven't seen evidence of that, not in terms "many". What is "laymen" members anyway? There are always going to be people on hobby forums post all kinds of things that may or may not be based on known facts, if you think doing tests that "laymen(again not sure how you define it) can prove them wrong, good luck!

It seems a bit like a related case where people who think the "trust your ears" is golden vs "measurements/DBT are the way", probably have posted million times on how/why all amps sound the same was wrong, when rarely anyone on sites like our ASR has ever make such a claim. Sort of make up something that they need to contradict when there is no need to because there is almost nothing there to begin with. Just making their points without trying to contradict something that don't exist, would have been much more enjoyable to read, but okay that's just my opinion so ymmv.

 

[IPunchCholla]

The case is that ASR "think tank" creates an illusion, shared by many laymen members, and resulting in generalizations, that class D amplifiers handle difficult loads better than class AB amplifiers.

Is it? I have not encountered that.

 

[IPunchCholla]

Just to make sure I am understanding what is going on here. The A/B amp has a linear supply and the D amp a switching supply. This burst test is draining the capacitence of the switching supply causing voltage sag leading to much higher (and less stable) distortion during the test due to higher clipping caused by the voltage sag? Or is there something in the amplifier topology itself causing this?

If my understanding is correct. Shouldn’t the test, if it is exploring topology, examine the amps using identical PSUs?

 

[Frank Dernie]

The tests are slightly technically interesting but practically, for my physiology as an old bloke and my interest in mainly classical music, not of much relevance.

I probably can't hear 10kHz, I gave up turning the volume up testing myself for fear of damaging my tweeters. So the fundamental is inaudible to me, never mind any harmonic distortion products.

Also a look at the frequency content of the music I listen to shows most level between 50Hz and 3kHz with low level harmonics up to around 8kHz, and very low any higher, so an amps distortion at 10kHz and 20kHz I don't care about. At all.

Even 1kHz, the bog standard test signal ever since I first took an interest in the 1960s has always seemed a bit high to me, the fundamental being about ¾ of the way up our piano keyboard never mind the harmonics.

I am more interested in how kit performs around 100 to 200Hz, not least since pretty well all the overtones of these notes are in the audible and sensitive area of my ears, so any harmonic distortion will alter timbre.

 

[Chr1]

I find these tests, and consequent discussion very interesting but unfortunately I definitely am in the ASR "layman" category. Such that I am unable to distinguish when/if a test such as this, is testing the amplifier class/module or the type of power supply. Or both. I would be very grateful for clarification on this. Plus thanks to Pavel, as I think that it is actually quite hard for us laymen to understand the real world power of some amplifiers. Particularly relating to difficult loads and extended high output.
Mainly due to the inconsistent, (random) nature of their official/claimed power ratings.

 

[ZolaIII]

Shocking news! An amplifier not designed to deliver lots of power into 2 Ω loads behaved as it was designed.
View attachment 472505

Why not try something designed for it, such as:
View attachment 472506

You call that much? Let me remind you how scalable AB class is and what designed for low loads is.

Dynacord L3600FD.

 

[atmasphere]

1) It is a myth that class D amplifiers are better in handling low impedance load,
2) It is a myth that class D amplifiers are better in handling complex loads (see post #1).

Based on the limited sample size my feeling about this is there's a good chance you're committing a logical fallacy of the same name. IOW what you've posted is true only for the two amps you measured.

For any amplifier the power supply has to be built to maintain the amplifier circuit within its design parameters. Obviously there's more current involved driving 2 Ohms. So what is needed is to confirm that the power supply used with the module is actually capable of supporting the amplifier while driving 2 Ohms. I think a lot of class D amps have insufficient power supplies simply because the person that bought the module and put it in a box made the assumption that because class D is so much more efficient that they didn't need such a beefy power supply. IME the power supply needs to be as beefy or even more so than you see and a class AB amp of the same power. I say moreso simply because the variation of current load on the supply varies more than any other kind of amp.

That variable needs to be securely nailed down.

 

[ZolaIII]

This isn't any kind of class D (H actually) amplifier, it's glorified by you Brunos design, yes it's limitation of PSU but same is complementary one specifically tailored for it by the same designer.

 

[IPunchCholla]

You call that much? Let me remind you how scalable AB class is and what designed for low loads is.
View attachment 472521
Dynacord L3600FD.

Assuming the same levels of distortion, while that is a more powerful amp overall, it is actually performing slightly worse/ basically the same in terms of lower resistance increase in power (the ideal of halving of power from 2 to 4 to 8)? I might not understand the point you are trying to make?

 

[ZolaIII]

Assuming the same levels of distortion, while that is a more powerful amp overall, it is actually performing slightly worse/ basically the same in terms of lower resistance increase in power (the ideal of halving of power from 2 to 4 to 8)? I might not understand the point you are trying to make?

Those series are limited by ADC to 80 dB SINAD. Particularly that one is light for what it gives (18.2 KG) considering it's power supply is torodial (and still again limiting factor). It's G class typology based. Point is by coupling transistors you can get a design that can output KW-ats and it's still serviceable, rest is determined by design goals. No OEM nonsense how you can't get replacement SPS when capacitors run dry and so on.

 

[IPunchCholla]

Those series are limited by ADC to 80 dB SINAD. Particularly that one is light for what it gives (18.2 KG) considering it's power supply is torodial (and still again limiting factor). It's G class typology based. Point is by coupling transistors you can get a design that can output KW-ats and it's still serviceable, rest is determined by design goals. No OEM nonsense how you can't get replacement SPS when capacitors run dry and so on.

Ok. That makes sense. That amp is definitely a cover almost any power need amp. Personally, if I am getting an amp for my home use, it is totally overkill. I am a big believer in adequacy. Define your use case and get exactly what you need to meet it. No more. No less. I personally would choose one of the recent TPA 3255 amps, as knowing my listening levels and distortion sensitivities, it more than meets my use case and is 10% the price. I believe we are better off reducing the materials we use over making them repairable but using far more materials. Reduce, Reuse, Recycle. In that order. Overbuilding a product increases costs at every single step of the use-life of that product.

 

[MaxwellsEq]

Such that I am unable to distinguish when/if a test such as this, is testing the amplifier class/module or the type of power supply

At its simplest - when testing the limits of a power amplifier, you are testing the limits of the power supply. A perturbation such as this makes the amplifier swing between the power supply rails and forces the output stage to pass as much current as the power supply can sustain (initially) and the overall design can handle in extracting heat.

Power supplies sag. Some are regulated (most SMPS are reasonably regulated) which means they use silicon devices to maintain volts and amps and minimise sag. Classic linear PSUs are not regulated and depend on a reservoir of energy stored in capacitors, topped up at 50/60 Hz or 100/120 Hz.

So Pavel has made a logic (category) mistake. He is NOT able to draw the conclusion he has drawn (about amplifier classes). Unless he undertakes a test with a class D and class AB with identical linear or SMPS PSUs.

I should add - I applaud the use of perturbation tests of this nature and would like to see more.

 

[Chr1]

Thanks.

Quick question : What, if any, are the disadvantages of SMPS PSUs?

All my amps are more than 10 years old and all have torroids. Used to be the case that a hefty torroid transformer was a sign of good amp. Seems times have changed.

 

[MaxwellsEq]

Thanks.

Quick question : What, if any, are the disadvantages of SMPS PSUs?

All my amps are more than 10 years old and all have torroids. Used to be the case that a hefty torroid transformer was a sign of good amp. Seems times have changed.

Done really well SMPs have no significant audio disadvantages over linear PSUs. They are obviously smaller and lighter. They are more complex and so in principle have more ways to fail.

 

[Chr1]

Thanks again. I guess this begs the question : Cost vs Failure Rate?

Are there any reasons not to use SMPS?
(Transient plus long duration, high output power requirements etc...?)

I am kind of old school and would rather sacrifice a bit of (possibly inaudible) SINAD for reliability when it comes to amps.
Failing power supplies are a no no for me. Unless they are cheap and easily replaceable.
My 2c.

 

[atmasphere]

Thanks.

Quick question : What, if any, are the disadvantages of SMPS PSUs?

All my amps are more than 10 years old and all have torroids. Used to be the case that a hefty torroid transformer was a sign of good amp. Seems times have changed.

In our research we found that to get the most out of the amp module, the SMPS really needs to be designed for the application. That is often true of toroidal transformers too, which leads to the second disadvantage: cost. If you are having a custom SMPS made you'll need to make a good number of them to make it cost effective.