Class D high frequency problems.

[pma]

In my opinion, any measurement of THD+N (or SINAD, if someone wishes) is pointless if the author does not declare the measurement bandwidth. Without BW declared, it is rather a promotion and marketing than a scientific valid parameter/plot.

 

[antcollinet]

@Bjorn - And again - which amp are you talking about. If it is the P400 I've shown @amirm 's test from, then that is a hypex amp.

Can you link where you got the bandwidth limited chart from?

Your chart/measurement (if it is 20kHz bandwidth) simply fails to measure distortion properly on signals starting at around 7kHz. (2nd harmonic and higher ignored), and all distortion is ignored above 10kHz (even first harmonic is outside the measurement)

NOTE - the measuremnet bandwidth doesn't specify what signals (the lines on the chart) are applied. It refers to the maximum frequency of harmonics that can be seen (measured). So if the test signal you are measuring the distortion of is 10.1kHz, then the first harmonic is 20.2kHz - and a measurement limited to 20kHz bandwidth wont see it. This is why the distortion lines on your chart start to reduce above 5kHz (where in reality the actual distortion will be increasing, as you can see happening up to 5kHz.)

This is also why Amir uses 45kHz measurement bandwidth as stated at the top of the chart I provided.


(EDITED to remove my dumbass confusion with who I was replying to )

 

[Lars Risbo]

please direct the questions and comments to the poster @Bjorn. its not my chart…

 

[Sokel]

This rise tends to be history as we go forward.
See new purifi for example.

Or better still the new icepower conductor which has the same (and better) THD+N at the worst audible case 6.67kHz than 1kHz all the way to its full power:

(link but I would love to see it verified by third parties)
(also here at an actual module)


So,we better not generalize and wait.

 

[antcollinet]

please direct the questions and comments to the poster @Bjorn. its not my chart…

Agh - sorry. My post has been edited.

 

[Sokel]

@Bjorn - And again - which amp are you talking about. If it is the P400 I've shown @amirm 's test from, then that is a hypex amp.

Can you link where you got the bandwidth limited chart from?

Your chart/measurement (if it is 20kHz bandwidth) simply fails to measure distortion properly on signals starting at around 7kHz. (2nd harmonic and higher ignored), and all distortion is ignored above 10kHz (even first harmonic is outside the measurement)

NOTE - the measuremnet bandwidth doesn't specify what signals (the lines on the chart) are applied. It refers to the maximum frequency of harmonics that can be seen (measured). So if the test signal you are measuring the distortion of is 10.1kHz, then the first harmonic is 20.2kHz - and a measurement limited to 20kHz bandwidth wont see it. This is why the distortion lines on your chart start to reduce above 5kHz (where in reality the actual distortion will be increasing, as you can see happening up to 5kHz.)

This is also why Amir uses 45kHz measurement bandwidth as stated at the top of the chart I provided.


(EDITED to remove my dumbass confusion with who I was replying to )

To be fair with the posted chart,even if the BW is restricted to 20kHz it does really good close to 6kHz where the danger zone is and H2 and H3 are well inside the BW.
I'm curious which amp is that though.

 

[Lars Risbo]

This rise tends to be history as we go forward.
See new purifi for example.

Or better still the new icepower conductor which has the same (and better) THD+N at the worst audible case 6.67kHz than 1kHz all the way to its full power:


View attachment 428426
(link but I would love to see it verified by third parties)
(also here at an actual module)


So,we better not generalize and wait.

so THD+N rising up to over 0.001% before clipping is considered good nowadays? You think this is better than gen 2 ET?

 

[Sokel]

so THD+N rising up to over 0.001% before clipping is considered good nowadays? You think this is better than gen 2 ET?

Better than the purifi?Of course not.But it's a lot cheaper too if one considers that as a criterion (242 EUR for the stereo "125" W module or 143 EUR for carton 36 pcs with PSU onboard)
But it's a great improvement in general.
The "better" in my sentence is about the comparison of the 6.67kHz with the 1kHz signal (at points any way) .

Edit:you mean 0.001% probably,so about 100dB THD+N.
Fully acceptable in my book by any amp,in fact my personal standard could be even 80dB THD+N if noise is at check and it's only the distortion that makes it so.

 

[pma]

So if the test signal you are measuring the distortion of is 10.1kHz, then the first harmonic is 20.2kHz - and

We rather use the term “first harmonic” for the signal base frekvency. So the 20kHz sine signal has second harmonic distortion component, H2, at 20kHz.

 

[Bjorn]

All class D amps based on Mosfet has rising distortion in the highs with more output.

As we can see below with Hypex with 31W and 125W and Purifi or other Mosfet class D modules have the same issue.

This is solved with GaN due to higher switching. Another benefit is square waves and slightly higher effiency. Chasing lower SINAD isn't a step forward IMO.

My conclusion based on tests today is that neither Hypex or Purifi are transparent under all conditions. There's potential audible distortion that can lead to some harshness with the right material with high enough volume (doesn't need to be super high though). May vary with speakers, difficult to say. For me this comes down to actual listening tests and not simply consider it from a theoretical standpoint. Seems like most people haven't conducted such tests. I would encourage to do so before making a conclusion.

 

[voodooless]

For me this comes down to actual listening tests and not simply consider it from a theoretical standpoint.

And you did those double-blind?

 

[antcollinet]

This is solved with GaN due to higher switching. Another benefit is square waves and slightly higher effiency. Chasing lower SINAD isn't a step forward IMO.

My conclusion based on tests today is that neither Hypex or Purifi are transparent under all conditions.

Please show evidence of GAN devices as a category showing better measurements across the board using the same test conditions.

Because this one does not.

Peachtree GAN400 Amplifier Review

This is a review and detailed measurements of the Peachtree GAN400 stereo balanced (input) amplifier. It is on kind loan from a member and costs US $2,499. I am not generally a fan of peachtree audio product looks but this one in coffee stain looks pretty good. Other than a power switch, not...

www.audiosciencereview.com

Nor does this:

LSA Voyager GAN 350 Review (Stereo Amplifier)

This is a review and detailed measurements of Living Sound Audio Electronics Voyager GAN 350 stereo amplifier. It is on kind loan from a member and costs US 3,000 from the company. I really like the high-end look of this amplifier case: Strange though as there is no power indicator, nor...

www.audiosciencereview.com

And nor does this:

Premium Audio Mini GaN 5 Review (Stereo Amplifier)

This is a review and detailed measurements of the Premium Audio Mini GaN 5 Stereo Class D power amplifier. It was kindly sent to me by a member and costs US $799 (recent price increase). The GaN 5 comes in a compact enclosure with plenty of ventilation at the cost of decent looks: Beside...

www.audiosciencereview.com

That's three out of three.


And you still haven't told us which amp, or which tests, your first chart was from.

 

[Lars Risbo]

@Bjorn : how do you do a GaN class D amp without GaN MOSFETs?

Almost any amp has HD rising with frequency irrespective of the operating class. if not it probably has too much to start with anyway.

GaN FETs are just another variant of transistors and offers different trade offs compared to silicon. Certainly attractive for high voltage /power use.

However, it’s the modulator and feedback loop that is the big differentiator.

 

[Ropeburn]

Good luck hearing -100dB of distortion when your amp is pumping out 70W.

Lol indeed. In any scenario short of technobunker/concert/full blast orchestra levels, that isn't just inaudible. It's physically nonexistent. If max is 100dB peaks and distortion is -100, exactly zero of it is in the air.

 

[MaxwellsEq]

There's potential audible distortion that can lead to some harshness with the right material with high enough volume (doesn't need to be super high though).

Nonsense. You don't understand audibility of artefacts.

 

[Bjorn]

The graph I showed earlier of a GaN amp (prototype that doesn't exist on the market and may perhaps never be released) was shown with 22 KHz, which is typically the accepted standard. Sure, with higher bandwidth the distortion would be higher. But we don't see the same rise as we do with silicon MOSFET amps. And that's my point.

We can look at a measurement conducted for both a Orchard Starkrimson GaN and Purifi 1ET400A by Audioexpress.

The Starkrimson GaN:

And the Purifi 1ET400A:

Source: https://audioxpress.com/article/fre...d-audio-bosc-and-purifi-audio-eigentakt-eval1

Notice that with the Purifi the distortion rises much quicker at higher frequencies. This would also be much worse for the Purifi above 2 KHz with a higher bandwidth. I don't know whether Audioexpress measured with 20 KHz or 22 KHz but it wasn't 45 KHz.

A poor implemented GaN amp obviously doesn't prove anything. There's no doubt that a well implemented GaN has advantages. Less rise in distortion at higher frequencies, close to a perfect squarewave and more efficient. What it comes down to if what's audible and that requires proper testing. People need to conduct that for themselves.

As mentioned before, I see no benefit with newer silicon MOSFET class D amps with simply lower SINAD numbers.

 

[Buckeye Amps]

From the review article itself:

Any measurement differences seen here fall orders of magnitude below human hearing thresholds.

 

[Bjorn]

From the review article itself:

Right and since the author didn't hear any difference between the amps, that is of course an objective truth for all humans at all ages with all music materials with all speakers at all level as well.

 

[kyuu]

Right and since the author didn't hear any difference between the amps, that is of course an objective truth for all humans at all ages with all music materials with all speakers at all level as well.

Ok... so why do you seem to be pointedly ignoring the question of whether these audible differences you claim exist have been proven in a double blinded listening test?

It's also weird that you are claiming that further improvements in SINAD are useless, while simultaneously touting the benefits of... improving SINAD but only at the highest frequencies where the benefits are the most dubious.

 

[Buckeye Amps]

Right and since the author didn't hear any difference between the amps, that is of course an objective truth for all humans at all ages with all music materials with all speakers at all level as well.

Feel free to set out to disprove if you'd like.

GaN has its obvious advantages. But transparent is transparent. Whether Purifi, Hypex, or a properly implemented GaN amplifier. It just so happens one of these options costs considerably more. Maybe that's why you're pushing it?