Questions For Interview With Bruno Putzeys & Lars Risbo About Purifi Audio

[psjug]

12 minutes ago, Matias said:

 

I refer to class A and AB with linear power supply, which together should account for something like 90% of the high end market.

 

As for references, check out the THD x power graphs, or 19+20kHz x frequency graphs, that Stereophile, SoundStage and Audio Science Review forums have, and compare nCore against similar prices or even ultra expensive amps.

 

Not that I am a hardcore objectivist but still.

If you are comparing THD you should compare the best against the best.  I think the Class AB from Benchmark and Neurochrome  might beat nCore in this regard, or at least they all measure extremely well.

[Matias]

1 minute ago, psjug said:

If you are comparing THD you should compare the best against the best.  I think the Class AB from Benchmark and Neurochrome  might beat nCore in this regard, or at least they all measure extremely well.

Agree, but they are 2 amps out of a million class A and class AB models. And not only nCore, but also other class D modules from ICEpower or Pascal measure better than the majority of ABs out there.

[psjug]

2 minutes ago, Matias said:

Agree, but they are 2 amps out of a million class A and class AB models. And not only nCore, but also other class D modules from ICEpower or Pascal measure better than the majority of ABs out there.

I don't think that is a valid reason to regard one class superior to another.

[Shadders]

20 minutes ago, Matias said:

 

I refer to class A and AB with linear power supply, which together should account for something like 90% of the high end market.

 

As for references, check out the THD x power graphs, or 19+20kHz x frequency graphs, that Stereophile, SoundStage and Audio Science Review forums have, and compare nCore against similar prices or even ultra expensive amps.

 

Not that I am a hardcore objectivist but still.

Hi,

The new Purifi module preliminary data states that 1kHz THD for 10watts into 4ohms is 0.00026%. My basic class A/B design has a THD @ 1kHz into 4ohms of 0.000184% (simulated). My design is simple using a single pre-driver for the emitter follower output stage. I can easily enhance the performance by adding another pre-driver, creating a triple EF output stage.

 

Class A/B will always outperform class D, when comparing the best designs of both.

 

Regards,

Shadders.

[psjug]

18 minutes ago, Shadders said:

.

Class A/B will always outperform class D, when comparing the best designs of both.

 

I don't see how you can know that either.  And anyway at what point do you say THD+N is good enough and start looking at performance in other areas?

[opus101]

21 minutes ago, Shadders said:

 

The new Purifi module preliminary data states that 1kHz THD for 10watts into 4ohms is 0.00026%. 

 

No, the plot on their website shows that number is THD+N - at 10W its clearly noise limited.

 

https://www.purifi-audio.com/eigentakt/

[Matias]

@psjug and @Shadders I think you both are missing my point. It is not that class D always measures better in band than all class A and class AB out there. But my point is that they usually measure better than the majority of class A and AB out there.

 

Here are some examples I found on the solid state amplifier reviews on Stereophile, just the top ones reviewed and measured there, all in 4 ohms.

 

Verity Monsalvat: starts at 0.09% THD and reaches .025% at 10W.

McIntosh MC462: starts 0.0065% THD and reaches .001% at 10W.

FirstWatt SIT-3: starts 0.05% rises to .65% at 10W.

Constellation Centaur II 500: starts 0.02% and 0.09% at 10W.

Simaudio Moon 888: starts 0.015% and 0.025% at 10W.

Benchmark AHB2 I searched for, since it is so good: starts with 0.0005% and reaches 0.0001% at 10W.

 

Now take an ICEpower 125ASX2 in SE for example: starts at 0.008% and reaches .002% at 10W.

Or Pascal U-PRO2S: starts 0.01% and reaches 0.07% at 10W.

And finally Purifi 1ET400A: starts at 0.008% and reaches 0.00025% at 10W.

 

Sure there are better class A and AB out there, but the class D is very low while A and AB are not usually so.

 

And of course listening is critical.

[Shadders]

1 minute ago, psjug said:

I don't see how you can know that either.  And anyway at what point do you say THD+N is good enough and start looking at performance in other areas?

H,

Since class D is an approximation and discontinuous system, whereas class A/B is continuous, and feedback can always be used to reduce further if so desired, while still allowing for the amplifier to be stable. Linearising techniques in class A/B are well known, and the performance in this area allows for minimal feedback in most basic amplifiers, which still out perform class D.

 

Regards,

Shadders.

[Matias]

More examples from Soundstage Network reviews (BHK Labs measurements), still always 4 ohms.

 

Ayre VX-R: starts at 0.015% THD, rises to 0.025% at 10W.

Bryston 4B3: starts at 0.02% THD, reaches 0.003% at 10W.

Hegel H360: starts at 0.015% THD, reaches 0.005% at 10W.

Luxman M900u: starts at 0.04% THD, reaches 0.004% at 10W.

Parasound Halo A23: starts at 0.03%, reaches 0.09% at 10W.

[Shadders]

3 minutes ago, opus101 said:

 

No, the plot on their website shows that number is THD+N - at 10W its clearly noise limited.

 

https://www.purifi-audio.com/eigentakt/

Hi,

Yes, but again, my design is basic, and for the Purifi plot, look at the step up in THD at about 15watts - you do NOT get this with a class A/B design. Why the sudden jump in THD at this point ?

 

Class A/B will always be superior.

 

Regards,

Shadders.

[opus101]

1 minute ago, Shadders said:

... for the Purifi plot, look at the step up in THD at about 15watts - you do NOT get this with a class A/B design. Why the sudden jump in THD at this point ?

 

Suggest you get acquainted with measuring real-world amps (not sims) and you'll find the answer for yourself. There's a very simple explanation for that which has nothing to do with the amp itself and everything to do with the measurement device (Audio Precision).

[Shadders]

2 minutes ago, opus101 said:

 

Suggest you get acquainted with measuring real-world amps (not sims) and you'll find the answer for yourself. There's a very simple explanation for that which has nothing to do with the amp itself and everything to do with the measurement device (Audio Precision).

Hi,

I stand corrected - i just examined a 1990's DIY design with low THD and the slight rise for that amplifier at similar power output.

Regards,

Shadders.

[mocenigo]

I do not see why. With a higher switching speed also the noise between 22 and 80 Khz will be brought down, and also Class D measurements should look better. Maybe it won't, but I do not see how this should be a priori discounted.

 

At this level of 0.0000...% THD further improvements do nothing audible. At some point perhaps D and AB will get indistinguishable and what will count are weight, size, and power consumption. At which point Class D will win.

 

Note I do not care much about the winning topology. As long as I can get detailed, neutral, silent, dynamic amplifiers at reasonable prices, I do not care what's under the hood.

 

 Roberto

 

49 minutes ago, Shadders said:

Class A/B will always outperform class D, when comparing the best designs of both.

 

Regards,

Shadders.

 

[Shadders]

11 minutes ago, mocenigo said:

I do not see why. With a higher switching speed also the noise between 22 and 80 Khz will be brought down, and also Class D measurements should look better. Maybe it won't, but I do not see how this should be a priori discounted.

 

At this level of 0.0000...% THD further improvements do nothing audible. At some point perhaps D and AB will get indistinguishable and what will count are weight, size, and power consumption. At which point Class D will win.

 

Note I do not care much about the winning topology. As long as I can get detailed, neutral, silent, dynamic amplifiers at reasonable prices, I do not care what's under the hood.

 

 Roberto

 

 

Hi,

Since class A/B is continuous - class D which is discontinuous will always be an approximation.

 

The measurements of class D amplifiers restrict the bandwidth to 22kHz, yet many class A/B amplifiers have a measurement bandwidth of 80kHz. Maybe this is why people state class D is better than the majority of class A/B........

 

Regards,

Shadders.

[mocenigo]

Sorry but this does not make sense. Class A/B may be "continuous" but it is STILL an approximation. A different one, that does not require quantisation, but it is still an approximation, because it adds noise nonetheless. Yes, a different profile of noise but it is still noise.

 

As I told above, a higher switching frequency would easily push the noise further up. Also when you write "the measurements of class D amplifiers restrict the bandwidth to 22kHz" this is not 100% clear to me as well. Re: the MEGAschino, for instance, I only read "bandwidth 150Khz" and then a THD+N measurement, not specified as in audio band. Similarly, I often see measurements of Class A or AB amps restricted to the audible band only...

 

 Roberto

 

2 minutes ago, Shadders said:

Hi,

Since class A/B is continuous - class D which is discontinuous will always be an approximation.

 

The measurements of class D amplifiers restrict the bandwidth to 22kHz, yet many class A/B amplifiers have a measurement bandwidth of 80kHz. Maybe this is why people class D is better than the majority of class A/B........

 

Regards,

Shadders.

 

[Matias]

17 minutes ago, Shadders said:

Hi,

Since class A/B is continuous - class D which is discontinuous will always be an approximation.

 

The measurements of class D amplifiers restrict the bandwidth to 22kHz, yet many class A/B amplifiers have a measurement bandwidth of 80kHz. Maybe this is why people class D is better than the majority of class A/B........

 

Regards,

Shadders.

 

If you think about it, a pair of transistors per channel, one recreating the positive signal, the other the negative signal, and blending both with crossover distortions, is also not very continuous.

[psjug]

16 minutes ago, Shadders said:

Hi,

Since class A/B is continuous - class D which is discontinuous will always be an approximation.

 

The measurements of class D amplifiers restrict the bandwidth to 22kHz, yet many class A/B amplifiers have a measurement bandwidth of 80kHz. Maybe this is why people state class D is better than the majority of class A/B........

 

Regards,

Shadders.

I think you really need to find a better word than "approximation".  I get it that you don't like the discoontinuous nature of Class D - why don'y you leave it at that?  And  you did not answer my question in the other thread: do you also dislike DSD and sigma delta converters?  Do you only like analog source for your music?

[Shadders]

49 minutes ago, mocenigo said:

Sorry but this does not make sense. Class A/B may be "continuous" but it is STILL an approximation. A different one, that does not require quantisation, but it is still an approximation, because it adds noise nonetheless. Yes, a different profile of noise but it is still noise.

 

As I told above, a higher switching frequency would easily push the noise further up. Also when you write "the measurements of class D amplifiers restrict the bandwidth to 22kHz" this is not 100% clear to me as well. Re: the MEGAschino, for instance, I only read "bandwidth 150Khz" and then a THD+N measurement, not specified as in audio band. Similarly, I often see measurements of Class A or AB amps restricted to the audible band only...

 

 Roberto

 

 

Hi,

Class D is an approximation since it is a pulse width modulation signal. It requires filtering to average the signal between the PWM samples.

 

Class A/B is a continuous function - there are no discontinuities. The noise is either component noise, or derived from the continuous function (polynomial) that adds the harmonics.

 

If you examine the output of class D, then for a 1kHz signal, there is the signal, the harmonics of the signal, and a lot of non-harmonically related noise at a very high level. (neglecting component noise)

 

If you examine the output of class A/B, then for a 1kHz signal, there is the signal, the harmonics of the signal. (neglecting component noise).

 

Class A/B performance will always exceed class D.

 

Regards,

Shadders.

[barrows]

2 hours ago, psjug said:

I don't think that is a valid reason to regard one class superior to another.

No one is suggesting that class D amps are better BECAUSE they are class D.  In fact, Mr. Putzeys himself often says that his class D amp designs perform well in spite of the fact that they are class D.  This thread is about the new Purifi amp design (and subsequently its predecessor, Ncore) and NOT about class D in general. 

[barrows]

1 hour ago, Shadders said:

Hi,

The new Purifi module preliminary data states that 1kHz THD for 10watts into 4ohms is 0.00026%. My basic class A/B design has a THD @ 1kHz into 4ohms of 0.000184% (simulated). My design is simple using a single pre-driver for the emitter follower output stage. I can easily enhance the performance by adding another pre-driver, creating a triple EF output stage.

 

Class A/B will always outperform class D, when comparing the best designs of both.

 

Regards,

Shadders.

Ahhh, simulations do not count!

[Shadders]

34 minutes ago, Matias said:

 

If you think about it, a pair of transistors per channel, one recreating the positive signal, the other the negative signal, and blending both with crossover distortions, is also not very continuous.

Hi,

If that were the case, then the THD would be very poor. It is not for a class A/B. Through output stage bias, multiple devices, and feedback, the crossover distortion can be reduced to insignificant levels.

 

The signal output of the class A/B amplifier is a continuous signal, whereas for class D, it is an average of the discontinuous signal.

 

Regards,

Shadders.

[mocenigo]

Of course Bruno is also fishing for compliments 😉

 

4 minutes ago, barrows said:

No one is suggesting that class D amps are better BECAUSE they are class D.  In fact, Mr. Putzeys himself often says thta his class D amp designs perform well in spite of the fact that they are class D.  This thread is about the new Purifi amp design (and subsequently its predecessor, Ncore) and NOT about class D in general. 

[Shadders]

1 minute ago, barrows said:

Ahhh, simulations do not count!

Hi,

Of course they do. Examine books by Robert Cordell and Douglas Self - all their work is confirmed by simulation versus experimentation.

 

What does seem to be happening on this thread is people using real world measurements of class A/B at 80kHz measurement bandwidth, against the bench testing of a module with a measurement bandwidth of 22kHz - not like for like.

 

Regards,

Shadders.

[Matias]

5 minutes ago, barrows said:

This thread is about the new Purifi amp design (and subsequently its predecessor, Ncore) and NOT about class D in general. 

 

Actually this thread is for question to Bruno and the Purifi team hehe.

[barrows]

1 minute ago, Shadders said:

Hi,

Of course they do. Examine books by Robert Cordell and Douglas Self - all their work is confirmed by simulation versus experimentation.

 

What does seem to be happening on this thread is people using real world measurements of class A/B at 80kHz measurement bandwidth, against the bench testing of a module with a measurement bandwidth of 22kHz - not like for like.

 

Regards,

Shadders.

You cannot fairly directly compare a sim with a working amplifier on the bench.  Simulations are good tools for development, but are not entirely accurate, as I am sure you realize.  This apples to oranges.

Have you ever done a fair comparison, a listening test, of a well implemented Ncore amplifier vs. a comparable class A/B design (approximately the same power output in the same system)?  If not, I would suggest that you do so, as you appear to have a theoretical bias against class D, you might just change your mind if you listened.