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

[ahofer]

I feel like there might be a lot to learn here, but it is getting buried in some weird D***-measuring contest.

 

[Hapo]

Your work on this is fascinating. It may also be a turning point in identifying what measurements are sufficient when testing power amplifiers. Thank you.

...this thread was instrumental in me changing an order from a Hypex NCx500 based amp to a Purifie 1ET4070SA based one...China are getting it...

...I am not giving up on D class just yet...it is the future...the future is now...

Hypex NCx500 specs:
- 700w @ 2ohm
- 700w @ 4ohm
- 380w @ 8ohm
Purifi 1ET7040SA specs:
- 950w @ 2ohm*
- 500w @ 4ohm*
- 250w @ 8ohm*

 

[Deleted member 48726]

I feel like there might be a lot to learn here, but it is getting buried in some weird D***-measuring contest.

True. Much more than anticipated. I stick around to get some answers and learn something and because I find it interesting that we do science but not quite.. and IMO not with quite enough curiosity on some topics. There's can be an aura of "we know all that needed be known".

I don't care looking like a fool though as long as I gather some new knowledge here and there..

 

[SIY]

It is the opposite than @SIY is saying. RF susceptibility, input stage rectification, demodulation very often directly translate to audio. 20Hz - 20kHz view is short-eyed. Unfortunately, this is not a forum with many knowledgeable and experienced circuit designers.

I'll continue looking down at the ground and drooling. And retain my belief that stuff that's audible shows up in the audibility range.

 

[SIY]

Stability testing of an amplifier is hardly a parlor trick, if that's what you're implying.

It was not.

 

[Deleted member 48726]

...this thread was instrumental in me changing an order from a Hypex NCx500 based amp to a Purifie 1ET4070SA based one...China are getting it...

...I am not giving up on D class just yet...it is the future...the future is now...

Hypex NCx500 specs:
- 700w @ 2ohm
- 700w @ 4ohm
- 380w @ 8ohm
Purifi 1ET7040SA specs:
- 950w @ 2ohm*
- 500w @ 4ohm*
- 250w @ 8ohm*

What do the * refer to?

 

[JRS]

An automated version of Amir's cube with say,1000 most populars speaker's parameters (of various types) taken from their measurements and all that in a sequence would be too much to dream on?

This seems unwieldy. Instead I would suggest looking at the impedance plot of a couple of hundred moving coil speakers and perhaps a dozen e stats. It may well be possible to sort them into 3 bins:easy, moderately difficult, and ball busters. Then average elements of each bin. Shouldn't take too long to cycle through the 3 dynamic dummy loads. I'm not sure one would need to show all graphs for all three. Instead focus on typical use case with detailed msmts like those used here and perhaps spot checks of distortion and FR of difficult loads. I thinks its safe to say easy loads would reflect even better msmts. Finally for amplifiers whose cost and performance suggest it might be chosen to drive e-stats, then a fourth load would be tested. Thankfully all the FR ribbons are mostly resistive and apart from the notoriously difficult to drive Apogee Scintillas, dong drop to one ohm!

It's a bit of deja vu--I remember similar conversations 30 years ago. One would think we'd have universal standards. Instead its back to the 1960s when all manner of ridiculous specs were posted. Might as well be quoting 110ac line voltage at 60 Hz. Now figures offeredbthat even exceed 1500 or so watts available at 15 amp leg, almost as if converting mass to energy.

 

[Hapo]

True. Much more than anticipated. I stick around to get some answers and learn something and because I find it interesting that we do science but not quite.. and IMO not with quite enough curiosity on some topics. There's can be an aura of "we know all that needed be known".

I don't care looking like a fool though as long as I gather some new knowledge here and there..

 

[antcollinet]

I feel like there might be a lot to learn here, but it is getting buried in some weird D***-measuring contest.

12, if anyone is interested

 

[Hapo]

What do the * refer to?

...???...I just noticed that....

 

[Sokel]

I read somewhere in the thread that there's not much energy above 10Khz and I agree but that's not always the case and since we're talking about extremes in this tread here's a couple (REW's WAV analysis of the actual tracks,NOT acoustic measurement,forget the shown levels):


Morning Mr Magpie (Nathan Fake Harshdub RMX) by Radiohead

Gigantic 18Khz peak,let alone the lows who are frightening in high levels.


The torture (for gear and ears) called Pan Sonic-Suhteellinen (see the red line)

Same group,Pan Sonic-Virta 1 (red line)

Extremes,I know,but they are there,in all it's glory,and there's many more,so let's better not be too assured.


Edit:Fun fact that their album cover looks like this:

 

[Ted G]

Best thread ever.

 

[SIY]

12, if anyone is interested

Is that Celsius or Fahrenheit?

 

[Hapo]

Purifi 1ET7040SA specs:
- 950w @ 2ohm*
- 500w @ 4ohm*
- 250w @ 8ohm*
*Full power output now achieved with new SMPS*

Just to clarify to those that my 7040 amps can reach full power (whereas others who use the standard Hypex SMPS cannot)

 

[Buckeye Amps]

What do the * refer to?

*Full power output now achieved with new SMPS*

Just a small tidbit below the specs since we are now using the Micro Audio SMPS

 

[antcollinet]

Is that Celsius or Fahrenheit?

Inches or cm is probably a far more pertinent question.

But my lips are sealed.

 

[ctrl]

[off-topic]

I read somewhere in the thread that there's not much energy above 10Khz and I agree but that's not always the case and since we're talking about extremes in this tread here's a couple (REW's WAV analysis of the actual tracks,NOT acoustic measurement,forget the shown levels):

It seems that something went wrong with your analysis. If one takes your most extreme example, Pan Sonic-Suhteellinen, the sound pressure spectrum for the entire track looks like this:


... and if you consider only the last extreme four minutes still like this:


If we ignore the extreme low end SPL around 20Hz, then the high end around 10kHz is still about -15dB lowered compared to the bass range (100-200Hz) - which is significant.

Of course, this is less sound pressure level drop than pink noise (-10dB per decade) and significantly less than average music - but even this extreme music is still far away from white noise (what your analyses of the song is indicating).

"Normal" music vs pink noise spectrum:

 

[Sokel]

[off-topic]


It seems that something went wrong with your analysis. If one takes your most extreme example, Pan Sonic-Suhteellinen, the sound pressure spectrum for the entire track looks like this:
View attachment 277129

... and if you consider only the last extreme four minutes still like this:
View attachment 277132

If we ignore the extreme low end SPL around 20Hz, then the high end around 10kHz is still about -15dB lowered compared to the bass range (100-200Hz) - which is significant.

Of course, this is less sound pressure level drop than pink noise (-10dB per decade) and significantly less than average music - but even this extreme music is still far away from white noise (what your analyses of the song is indicating).

"Normal" music vs pink noise spectrum:
View attachment 277131

I just put the WAVs in the REW's WAV analyzer,that's all.
Thing is that it sounds that way too,way too exaggerated on the edges.
I was so curious about it so I switched of lows (<220Hz in my actives) so to listen what are they doing up there,
If someone doesn't know what happens with that album he will scare that something got wrong with it's gear,specially the songs with the simulated 50Hz mains sound.

(spikes in Vitra 1 appear on the acoustical measurements with REW's RTA too,I can't hear them as definite sound,is if someone blows a sharp blow).

Edit:That's what I get acoustically (about a minute's peaks,where the "blow" is),it's certainly not at the (enormous) lows level,but still I rarely see such a thing:

 

[Rottmannash]

I know this continued discussion is frustrating for some. Especially given the brilliant and essentially "free to me" work from @amirm and others who have the equipment and patience to run tests on real world products without any reward from advertisers and manufactures. In my experience of HiFi I've never been so blessed with excellent information and guidance.

I have a mental model of a Class D (which is not the same as the classic block diagrams) of a black box that provides gain in the audio frequency bands superimposed with an RF device producing Radio Frequency signals which cannot be played by our speakers and which we cannot hear and which is mostly blocked from reaching our speakers by the output filter.

What this thread seems to be about is - perturbations to the RF amplifier - 1) whether a real world device can cause an interaction and 2) whether such an interaction perturbs the RF device, 3) how would we sensibly test and present this.

What is perhaps relevant is how many people are really satisfied with their Class D amps in the real world. Obviously, the vast majority of purchasers can not measure how well the amp works, but if there are real world perturbations to the RF device that folds artefacts such as noise and distortion back into the audio bands, we're not encountering complaints...

I have 5 channels of Purifi and 2 channels of NC252MP, 2 IcePower monoblocs, a Topping PA5 and maybe others I can't recall at this time but I have had zero issues either sonically or w/ reliability with any of them. I couldn't be happier with any of the Purifi or 252 amps but the Icepower monoblocs (of which one was measured by @amirm) do sound harsh at high volumes-none of the other class D amps I have exhibit this type of audible distortion and to my ears are faultless, even at very high volumes.

 

[charlielaub]

Friends, there is no "problem" with the Hypex NC252MP. ZERO.

The OP postulated some hypothetical and pathalogical test load that drops the impedance below 2 Ohms at 20kHz AND keeps dropping it to ZERO Ohms above that point. As far as I can tell there has been exactly ONE speaker that has such a pathalogical load, some electrostatic. The solution is that the designer of that speaker should be SHOT, and NOT that the world needs to design audio amplifers that can operate into a dead short above 20kHz, where there is no audible output anyway.

But now the OP has insinuated that the Hypex amp in question is somehow deficient. Hey the Hypex amp also won't work well as the power supply for a DC welder. But that is not the intended use. And driving loads that fall below what it is rated for is also not an intended use. So you can say that OP is "misusing" the amplifier. While I compliment the OP for his amplifer design that does better under these circumstances, I really question why he had to make such a comparison.

On a related note to @amirm - the people who are asking for amplifier performance measured into a dummy loudspeaker test load aren't crazy. While it is nice to see testing into various resistive loads, the sometimes widely varying phase angles of a loudspeaker with a passive crossover can also deteriorate the perfomance of an amplifier when it drives a predominantly capacitive or inductive load. Large phase angle in combination with low impedance magnitude represents a challenging test of any amplifier's capabilities. A related post on the subject can be found HERE.