Class D amplifier - the real characteristics vs specification

Ren Kitchener

Ren Kitchener

Junior Audioholic
My point was, that spike on the THD vs F graph is not really there because the X-Axis is the test frequency, not the actual frequency you would be playing when listening to music.

For clarity, when you apply a 6.5 kHz signal, you get that spike, but the magnitude of the spike, looks to be about just over 0.002% is the "Total harmonic distortions" so it included all the harmonics in the ultrasonic band that is likely well pass the audio band of 20,000 Hz. ASR uses 45 kHz or higher, but in Hypex's, that did not specific the test bandwidth, and that's part of the reason I can only take an educated guess.

Another point to note is, that spike was there when tested at 200 W output. There are no such THD+N spikes at 2 and 20 W output level.

It would have been nice if Hypex published the FFT too, like ASR typically do, then you can see the frequency of the actual distortions. As it is now, you are only seeing the total, you cannot tell what that 0.002% is made up of, and as I said, if I guessed right, it would be made up of harmonics at frequencies much higher than 20,000 Hz so you wouldn't have to worry about the 2nd, and 3rd (12, 18 kHz).
PENG, this is terrific information. The distortion figures, from memory, are calculated using the root-sum-squared equations of the numerous harmonics. So you are right, you don't know how many of the inaudible harmonics are used and at which amplitude. Personally, I would have used only the highest 2nd or 3rd harmonic - whichever the higher, at this frequency rage.
 
P

PENG

Audioholic Slumlord
PENG, this is terrific information. The distortion figures, from memory, are calculated using the root-sum-squared equations of the numerous harmonics. So you are right, you don't know how many of the inaudible harmonics are used and at which amplitude. Personally, I would have used only the highest 2nd or 3rd harmonic - whichever the higher, at this frequency rage.
My guess is based on the fact that such class D amplifiers use output filters to get rid of the switching noise that are high frequency noises. Bruno Putzeys has an article right here on AH:

Switching Amplifier (Class D) Basics | Audioholics

In that article, he noted the following on residual noise as well:

"In a switching audio amplifier, the output signal is a low-pass filtered version of the high-powered PWM voltage produced by a switching power stage. The bottom 20kHz of the signal spectrum is the audio signal. The high-frequency portion usually starts at a few 100kHz and consists of the switching frequency along with its harmonics and sidebands. These high-frequency components are a necessary by-product of trying to amplify a continuously variable signal using only two voltages. They need to be removed afterwards because it's only the audio we are interested in. A switching audio amplifier invariably ends in a passive LC filter intended to do just that.

Unfortunately, there's no filter that can totally block parts of the spectrum. Only attenuation is possible. So, the output signal is necessarily accompanied by some remnants of the unwanted high-frequency content of the PWM signal. These remnants are called the residual. "

That 0.002%, being so minute, could have been mostly residual noise in the Ultrasonic band.

I may email Hypex and ask them about the bandwidth they used for those graphs. The Marantz example from ASR was from the measurements using 90 kHz bandwidth.
 
mazersteven

mazersteven

Audioholic Warlord
I seriously doubt that .........
10 years ago class D amps weren't even a consideration now we're talkin about them and the cost of them is coming down and the technology is getting better so I can see no reason why in 5 years class D amps not becoming popular as class A/B amps today.
 
Mikado463

Mikado463

Audioholic Samurai
10 years ago class D amps weren't even a consideration now we're talkin about them and the cost of them is coming down and the technology is getting better so I can see no reason why in 5 years class D amps not becoming popular as class A/B amps today.
Ok, too that I agree, but in no way will ALL of us be using Class D amps in 5 years.

like automobiles there is also a transitional 'hybrid stage' .............

 
lovinthehd

lovinthehd

Audioholic Jedi
10 years ago class D amps weren't even a consideration now we're talkin about them and the cost of them is coming down and the technology is getting better so I can see no reason why in 5 years class D amps not becoming popular as class A/B amps today.
You'll have to pry that Pass out of Mikado's cold dead hands....
 
ryanosaur

ryanosaur

Audioholic Spartan
To answer the earlier question...
I chose Hypex NC400 and SMPS600N400 due to the cost and reviews. They do not require any additional parts in the way of Input Buffers/OP Amps the way that the Purifi and OEM NC500s seem to.
So as a DIY project, especially for a non-EE, the NC400s as Stereo or Monoblock Amps will be the absolute easiest to assemble.
At the Hypex Affiliate/Sister Company, DIYClassD, you can buy a complete Monoblock kit including a chassis. You can also buy several different styles of Chassis from Ghent in China (including single-chassis dual and triple monoblock configurations).

Toid123 did a video on an ICEPower class d build:

At the time I was considering this, I had not seen any reviews of the ICEPower options. Ithink this has changed on ASR, now, but cannot confirm.

Lastly, importing the Amp and Power Modules from Hypex or Purifi, into the US should be Duty Free. I cannot speak toward the Chassis from Hypex. Aluminum is a touchy subject. :) There will be some fee for importing the Chinese Chassis from Ghent audio, so keep that in mind when planning your purchase.
 
Ren Kitchener

Ren Kitchener

Junior Audioholic
I seriously doubt that .........
I thought that too Mikado463 - but the specification of these new class D amps look superb - plus, they run cooler with less aluminium (or copper). The added plus is the high damping factor along with the low noise. Having said that - I have not had a good enough class D amp to compare - so this will be put right next week.
 
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Ren Kitchener

Ren Kitchener

Junior Audioholic
Lastly, importing the Amp and Power Modules from Hypex or Purifi, into the US should be Duty Free. I cannot speak toward the Chassis from Hypex. Aluminum is a touchy subject. :) There will be some fee for importing the Chinese Chassis from Ghent audio, so keep that in mind when planning your purchase.
Yes, the harmonised tariff/commodity code for importing amps into the US is 8518500000 - which I think is at 0% - if this number is included in the documents from any supplier, it should sail through.....
 
Mikado463

Mikado463

Audioholic Samurai
I thought that too Mikado463 - but the specification of these new class D amps look superb - plus, they run cooler with less aluminium (or copper). The added plus is the low damping factor along with the low noise. Having said that - I have not had a good enough class D amp to compare - so this will be put right next week.
look at my previous post , #45. I have listen through the Rogue Hybrid Class D amps and thought quite highly of them. But then as 'lovin' said, it's highly unlikely my Pass amps are going anywhere........
 
ryanosaur

ryanosaur

Audioholic Spartan
:)
My only experience with anything related to Pass Labs was a First Watt Amp that the host of my Phil3 audition used. Seriously cool gear.
Hell, I look at my Outlaw 2200s with great affection. So those... ;) I get it.

When I am finished with my job in another week, I will get off my @$$ and solve my chassis issue for the Hypex Amps. I’m hoping I can get a DIY Audio Store Chassis modded to accept a 5-channel monoblock layout. The hole pattern for both the Amp and PS modules are non-standard and specific.
Once I get that resolved, or order from Ghent, it should only take a day to get everything assembled. *fingerscrossed
 
Paul DS

Paul DS

Audioholic
10 years ago class D amps weren't even a consideration now we're talkin about them and the cost of them is coming down and the technology is getting better so I can see no reason why in 5 years class D amps not becoming popular as class A/B amps today.
I suspect that a lot of people on this site buy their receivers by weight. In short, if it isn't heavy, it isn't any good. Class D receivers are very light. For my money, they sound every bit as good as an A/B receiver.
 
A

Audioholic opaleski

Audiophyte
I suspect that a lot of people on this site buy their receivers by weight. In short, if it isn't heavy, it isn't any good. Class D receivers are very light. For my money, they sound every bit as good as an A/B receiver.
The sound is there, up to about 80db. After that a class D will not get much further. I am currently comparing a 1500 watt Class D to a 700 Class A. The Class A will blow away the Class D in Volume, but, if you listen to music above 100db too long, you will soon not hear anything!! Weight wise you have 200+ pounds vs maybe 50.
 
Ren Kitchener

Ren Kitchener

Junior Audioholic
The sound is there, up to about 80db. After that a class D will not get much further. I am currently comparing a 1500 watt Class D to a 700 Class A. The Class A will blow away the Class D in Volume, but, if you listen to music above 100db too long, you will soon not hear anything!! Weight wise you have 200+ pounds vs maybe 50.
I'm not familiar with the technologies at these awesome power levels, but a 700 Watt Class A, shouldn't 'blow away' a 1,500 Watt Class D in terms of volume? - Watts are Watts, whichever the class, if comparing sinewave apples with apples. So, I can only guess (and it is a guess) that the class A is distorting the signal - perhaps in a compressed way to give a 'loudness maximiser' effect. This suggest to me that the Class D is much more transparent (assuming the specs are both r.m.s., or both peak, and that they are 'truthful').
 
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Ren Kitchener

Ren Kitchener

Junior Audioholic
The Hypex amps all seem to measure incredibly well. I will be thrilled when the price reaches the point where NCores are more mainstream.

I'm not planning to replace the Parasound until it croak, but whenever that day comes I'll be looking for a Hypex-based replacement as long as it has the same features.
I've just received my Hypex MC122MP (with it's control pcb) - I'll fire it up today if I can get the time. But my speakers are active - so I'll have to get a move on and make some cabs for the drivers and crossover I purchased last year. In the mean time, I have two 4 Ohm loads bolted to a substantial heat sink - so I can at least 'scope' the outputs. Thanks 'Kvn'.
 

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