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

[Sam Lord]

On 5/18/2019 at 4:43 AM, mocenigo said:

Yes and no. Class D amps have a phase rotation that is a linear function of the frequency. This is just a delay. So in fact this is often much better than irregular phase rotations as in A and AB amps. Luckily, the rotation of the latter are much more contained.

NCore also has much smaller rotations than ICEpower and, it seems, ICEEdge - I expect the same for Eigentakt

Still, it would be VERY INTERESTING to hear Putzeys take on the matter.

Roberto

 

IIRC the phase shift at 20kHz for nCore was not consequential...below 10 degrees.  Bruno is very conscious of phase shift in both amps and speakers, I spoke with him at length about this (many years ago).

 

On 5/20/2019 at 9:54 AM, Shadders said:

...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.

 

No Class AB amplifier can be modeled analytically: all have numerous discontinuous behaviors.  Crossover notch distortion is often the largest but is far from the only one.  Transistor behavior itself, even within an fairly linear range,  is discontinuous.   

 

On 5/20/2019 at 11:05 AM, Shadders said:

All i have said is that class A/B will outperform class D, and always will do.

 

I can't find any metric which supports that view, when comparing measured performance of Bruno's Class D designs and any Class AB designs.  Note that The Benchmark AB1 is a Class H design, not Class AB.

 

On 5/20/2019 at 9:22 PM, Matias said:

I guess because he was employee at Hypex and now co-owner of Purifi. But sure, let him answer.

 

Bruno was not only the principal designer at Hypex, but the reason the company was created.  No, UcD, no Hypex.

 

On 5/24/2019 at 11:09 AM, barrows said:

@marce, typically, Mr. Putzeys' class D designs use box type polyester capacitors.  As I recall, for example, the NC-400 modules have three Wima polyester caps totaling about 2 µF in the output filter (parallel devices).  Some folks have modded these to slightly larger Wima Polypropylene parts and reported good subjective improvements....   ...Apparently the Mola Mola Kaluga monoblocks use a different type capacitor in the output filter which Bruno only describes as "monolithic"...

 

Interesting!  Monolithic ceramic caps with the C0G/NP0 rating are superb in both coupling and bypass duties.  Also X7Rs are great in spite of microphony: properly potted and/or paralleled they have no faults.  However, many have magnetic leads which are not known to their own manufacturers, whose names I won't state here (Kemet).  

 

On 5/26/2019 at 2:42 PM, jabbr said:

...Interestingly he notes that direct digital has the lowest distortion yet he doesn't like the SQ and unless we ever find out the electrical  correlate of his SQ then we have no idea whether the SQ had anything to do with direct digital (power DAC) vs some other unknown explanation. Of course the implementation remains important  

 

I would thus add the question: "Since you've said that you like the SQ of your Class D as opposed to your own direct digital/power DAC ... why? What is the electrical correlate?"

 

I think that was a very old statement from him.  Anyway, one explanation is that damping factor of his Class D circuit might have been much higher. 

 

On 5/29/2019 at 12:07 PM, shtf said:

 

Bruno, I'm curious if you've given any consideration in your designs to the digital-like bi-directional noise / distortion inherited in perhaps every Class D amp due to the high-speed switching modules?

 

IMO, Class D amplification can be phenomenal when done right.  But even some of the most naive listeners will notice this digital-like distortion and as a result will often times poo-poo all Class D designs.

 

For example.  I'm a huge advocate for superior line conditioners and in particular passive, dedicated, and bi-directional filtering types of line conditioners that actually cleanse, purify, filter, and/or condition the noisy AC coming in from the street.   My experience with Class D amplification is limited to nuforce and Wyred-4-Sound amps.   Based on my experimenting with Class D mono-blocks sharing a single line conditioner using a cryo-treated audio-grade power strip, this bi-directional noise induced by the switching modules goes up significantly when the 2 channels are sharing their bi-directional noise with each other.

 

Having forgotten all about the bi-directional noise issue some years ago I had purchased a high-powered Class D integrated amp and though it was connected to a superior line conditioner, I noticed very audible distortions that was causing the presentation to be very unmusical though the int. amp was clearly doing its job otherwise quite well.  Then I recalled this bi-directional noise issue with Class D and swapped out the int. amp for a pair of mono-blocks (same mfg'er, same wpc, same Class D modules) with seemingly no such digital-like distortions.

 

What I realized from this Class D int. amp experience was that not only were the 2 Class D modules sharing their switch module digital-like bi-directional noise at the IEC inlet but the distortions were significantly compounded over and above due to the fact that the active pre-amp gain stage had to borrow AC power from one of the channels so now the pre-amp section was getting a double dose of this bi-directional noise and then amplifying it at the gain stage.

 

My lesson learned then and there was to never ever purchase a stereo 1-chassis 1-IEC inlet Class D amp or integrated amp because the consumer can do nothing to reduce this internal sharing of this bi-directional noise.  On the other hand, Class D mono-block amps with superior bi-directional filtering line conditioners are for me the cat's meow. 

 

For 20 years now, all my playback systems have included superior line conditioning because of what they do to treat the noisy AC coming in from the street.  But even with Class D mono-block amps, I find superior line conditioners absolutely mandatory to keep the digital-like bi-directional noise from going back into the AC outlet, some say even back to the AC service panel, and then induce its digital-like noise into other components.

 

That said, I see this very real digital-like bi-directional noise as perhaps the single greatest shortcoming for Class D for most consumers so my question to you is this.  Since few are aware of this distortion and perhaps even fewer are aware of superior line conditioning, what if anything, has Purifi done to address this very real distortion with Class D amplification?

 

Bruno has stated that his nCore circuits have *very* low HF components either radiated *or* transmitted onto the AC line.  His extremely adept use of differential signals in both the SMPS and amp module are the reason.  But still, any garbage on the line is bad and minimizing it is important.  Recently Bruno demonstrated with Shunyata, with whom I worked under contract from my old company for a couple years (no financial ties now), and their non-reactive, environmental HF reduction is a great antidote to line- and component- generated noise.

 

On 5/31/2019 at 9:16 AM, Shadders said:

Hi, A few more questions: Is the voltage gain specified (12.8dB) based on the opamp being in circuit, or out of circuit ?

Are the THD figures also based on the opamp being in circuit or out of circuit ?

Can the module be used without the opamp in circuit ?

What opamp is provided with the module ?

Is the loop gain based on the opamp being in circuit ?

 

Really good point Shadders!  Many of the measurement improvements disappear when one adds another stage to replace the lost gain!  Are the Purifi modules really an improvement over nCore?  Another 13dB of gain would knock S/N down by about 4-5dB, right where the NC500 measured.   

 

However, the concept of lowering amp gain makes sense, given the excessive output of many high-end DACs.  On the third hand, 13 dB is too low.  On the fourth hand, you'll *never even nearly* clip the amp when your DAC sends a maximum signal.  But fifthly, I'm guessing that an opamp *is* meant to be added to the front of this circuit.

[Sam Lord]

Since all of you good folks are captive now, waiting for Bruno's response, I'll spew some debris about my experience with class D, in fact an older and lesser variety: 1st gen Icepower in Bel Canto amps.

 

1) Class D has very low output impedance.  If you want to hear them at their best, USE IT!  Don't use a stereo amp, use monoblocks with very short speaker cables. Or do what I do, vertically biamp with a stereo amp on each side.  This prevents cabling from halving your amp's output impedance, or worse!

 

2) As above, use that low output Z to maximum benefit: bi-amp if possible, or at least bi-wire, because the difference between 2ft and  6ft of shared speaker cable makes a measurable and audible difference in performance.  Separate circuits make an even bigger jump.  Bruno emphasizes biwiring for the same reasons, but any IMD between transducers is eliminated with multi-amping.

 

3) Class D circuits, moreso than Class AB, ramp up in distortion in an abrupt way, usually around 1/2 of the power at clipping (1% THD).  If you listen at very high levels, as I do (I have very inefficient ATC monitors), Get at least 2x the amp power you expect to need.  Then your loudest passages will truly be pristine.  

[Matias]

39 minutes ago, Sam Lord said:

3) Class D circuits, moreso than Class AB, ramp up in distortion in an abrupt way, usually around 1/2 of the power at clipping (1% THD).  If you listen at very high levels, as I do (I have very inefficient ATC monitors), Get at least 2x the amp power you expect to need.  Then your loudest passages will truly be pristine.  

 

Maybe older class D did ramp up THD with power increase rather quickly, specially on the highs (look at ICEpower 1000ASP datasheet 6.67kHz cuve).

But not anymore, ICEpower 125ASX2 and 1200AS are already better behaved, and specially Hypex nCore NC400/NC500 and now Purifi 1ET400A, their THD x power remains very low until rising to clip at the 1% THD standard threshold.

[Shadders]

3 hours ago, Sam Lord said:

I can't find any metric which supports that view, when comparing measured performance of Bruno's Class D designs and any Class AB designs.  Note that The Benchmark AB1 is a Class H design, not Class AB.

Hi,

Due to the excessive noise on a class D output which is present permanently, the measurement of the THD uses a 22kHz bandwidth filter. The class A/B amplifiers use 80kHz in the measurements.

 

3 hours ago, Sam Lord said:

No Class AB amplifier can be modeled analytically: all have numerous discontinuous behaviors.  Crossover notch distortion is often the largest but is far from the only one.  Transistor behavior itself, even within an fairly linear range,  is discontinuous.   

A class A/B amplifier output is a continuous function of the input. Your reference to "Crossover notch distortion" is a continuous function in a correctly biased class A/B amplifier - it is non-linear, but the feedback reduces this to a minimum, as does multiple transistors in the output stage.

 

The transistor is not a discontinuous device, as it operates entirely with a continuous non-linear function when forward biased.

 

3 hours ago, Sam Lord said:

Monolithic ceramic caps with the C0G/NP0 rating are superb in both coupling and bypass duties.  Also X7Rs are great in spite of microphony: properly potted and/or paralleled they have no faults.

Please see :

https://linearaudio.nl/cyril-batemans-capacitor-sound-articles

 

All ceramic capacitors have inherent distortion which exceeds all others. Polyester capacitors have significant distortion. Polypropylene and polystyrene capacitors have the lowest distortion.

 

Regards,

Shadders.

[Matias]

20 minutes ago, Shadders said:

Hi,

Due to the excessive noise on a class D output which is present permanently, the measurement of the THD uses a 22kHz bandwidth filter. The class A/B amplifiers use 80kHz in the measurements.

 

Low pass filters outside the audio band do not interfere with measurements in the audio band. High frequency noise is not reproduced by the tweeters, let alone heard.

 

23 minutes ago, Shadders said:

A class A/B amplifier output is a continuous function of the input. Your reference to "Crossover notch distortion" is a continuous function in a correctly biased class A/B amplifier - it is non-linear, but the feedback reduces this to a minimum, as does multiple transistors in the output stage.

 

The transistor is not a discontinuous device, as it operates entirely with a continuous non-linear function when forward biased.

 

 

Then the amplifier classes are always defined as follows:

Class A: – The amplifiers single output transistor conducts for the full 360o of the cycle of the input waveform.
Class B: – The amplifiers two output transistors only conduct for one-half, that is, 180o of the input waveform.
Class AB: – The amplifiers two output transistors conduct somewhere between 180o and 360o of the input waveform.

 

https://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html

[Shadders]

2 minutes ago, Matias said:

Low pass filters outside the audio band do not interfere with measurements in the audio band. High frequency noise is not reproduced by the tweeters, let alone heard.

Hi,

This is about performance, not whether the tweeter can or cannot reproduce the signal. The performance of a class A/B amplifier exceeds the class D amplifier. The issue is that the extra noise in the audio band 22kHz+ for class D, exceeds class A/B amplifiers noise.

 

Regards,

Shadders.

[barrows]

50 minutes ago, Shadders said:

This is about performance,

Hahaha!  No it is not.  this website is called "Audiophile Style"  Nothing discussed here is about some kind of non real world theoretical "absolute" performance completely unrelated to the actual performance as it relates to the listening experience by Audiophiles.  You are playing some kind of weird thought process game which is not relevant to actual performance when listening to music through loudspeakers.  I have no interest in wasting Mr. Putzeys' time discussing "performance" variables which have no relation to at the actual experience of playing music through loudspeakers and listening to it.

[Matias]

1 hour ago, Shadders said:

This is about performance, not whether the tweeter can or cannot reproduce the signal.

 

Wow, I have no words to reply to this! 😂

[Shadders]

19 minutes ago, barrows said:

Hahaha!  No it is not.  this website is called "Audiophile Style"  Nothing discussed here is about some kind of non real world theoretical "absolute" performance completely unrelated to the actual performance as it relates to the listening experience by Audiophiles.  You are playing some kind of weird thought process game which is not relevant to actual performance when listening to music through loudspeakers.  I have no interest in wasting Mr. Putzeys' time discussing "performance" variables which have no relation to at the actual experience of playing music through loudspeakers and listening to it.

Hi,

This is an open forum where all views are allowed. The fact that you have no interest, does not make the points being discussed irrelevant.

 

Questions to the designer whether technical or other are pertinent, since they claim :

 

"This  corresponds to an unprecedented 110MHz Gain-Bandwidth Product and produces consistent ultra-high performance across the audio spectrum unmatched by audio ampliers of any technology or operating class."

 

I do not think we should let such a designer tell everyone what to think.

 

For your statement on "weird thought process" :

• The class D modules are measured with a measurement bandwidth of 22kHz. Why ? (i have answered this).
• No reviewer or audio enthusiast has ever complained about the excess noise above 20kHz
• Class A/B amplifiers are regularly reviewed with measurement bandwidth of 80kHz.

Essentially, class D amplifiers are getting preferential treatment, else the performance of the two cannot be compared, and given that there is excessive noise above 20kHz which no one has ever complained about - means you just cannot hear it. The "golden ears" reviewers and enthusiasts, quite simply, do not have "golden ears".

 

Not sure where you are getting the non-real world from - Purifi quote real world figures, make exotic claims regarding those measurements, and these are being discussed.

 

Would you prefer it that we just accept what the manufacturers, reviewers, sellers, and fanbois say without critical discussion ?

 

Regards,

Shadders.

[barrows]

@Shadders, Real world is listening to the amplifiers playing music in an audio system.  I would also consider measurements which are relevant to the listening experience real world as well.

 

I have actually listened to Ncore amplifiers playing music  through some very fine loudspeakers including the Raidho C 1.1, the Vivid Audio Giya 2 and the Focal Ultima Diablo Utopia (I think that is the correct name).  That is what I would consider real world.  The results were on par with any other amplifiers of my experience, which includes all the usual suspects of Class A/B, like Pass, Soulution, dartZeel, Constellation, etc...

 

I really do not understand the need to consider performance parameters which are irrelevant to audio performance, audio performance is what I am interested in.

[rickca]

15 minutes ago, barrows said:

Focal Ultima Diablo Utopia

They are just called Focal Diablo Utopia.  Here they are in my living room paired with Focal subwoofers.

 

[Shadders]

45 minutes ago, barrows said:

@Shadders, Real world is listening to the amplifiers playing music in an audio system.  I would also consider measurements which are relevant to the listening experience real world as well.

 

I have actually listened to Ncore amplifiers playing music  through some very fine loudspeakers including the Raidho C 1.1, the Vivid Audio Giya 2 and the Focal Ultima Diablo Utopia (I think that is the correct name).  That is what I would consider real world.  The results were on par with any other amplifiers of my experience, which includes all the usual suspects of Class A/B, like Pass, Soulution, dartZeel, Constellation, etc...

 

I really do not understand the need to consider performance parameters which are irrelevant to audio performance, audio performance is what I am interested in.

Hi,

I am not disputing anyones experience. In fact, their experience has shown that frequency bandwidth above 20kHz is not required. I think this fact, is a definitive reason to claim that high resolution in respect to sampling frequency, really is not required.

 

It is Purifi who have made the "exotic" claim that their amplifier is the best ever (my summary). They, through their measurements and "exotic" claim have made the decision for you, that you cannot hear anything above 20kHz, nor can the class D noise above 20kHz affect the in band performance.

 

So, for class D and class A/B comparison, class D gets preferential treatment for the measurement bandwidth. In addition, the module specifications is a standalone measurement, such that enclosure, power supply (to some extent), wiring, placement, are optimal in every case. A class A/B amplifier is always measured based on the manufacturers offering which include the aforementioned, and its distortion mechanisms.

 

Regards,

Shadders.

[Matias]

Purifi has stated frequency response up to 60kHz before 2nd order roll off. This is reasonable, as there is music content above 20kHz. But the switching frequency is around 500kHz, which is way above. Not even bats hear that, or plasma tweeters reproduce it.

[Shadders]

1 minute ago, Matias said:

Purifi has stated frequency response up to 60kHz before 2nd order roll off. This is reasonable, as there is music content above 20kHz. But the switching frequency is around 500kHz, which is way above. Not even bats hear that, or plasma tweeters reproduce it.

Hi,

Do you believe that the output of class D is solely the music input replicated with the specified THD, and a 500kHz switching frequency ?

 

Regards,

Shadders.

[Matias]

7 minutes ago, Shadders said:

Hi,

Do you believe that the output of class D is solely the music input replicated with the specified THD, and a 500kHz switching frequency ?

 

Regards,

Shadders.

And a little IMD and THD, yes. If you don't believe their datasheets, here are some independent measurements with top of the line Audio Precision of a popular NC500 module.

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-nord-one-nc500-amp.7704/

[Shadders]

30 minutes ago, Matias said:

And a little IMD and THD, yes. Here are some measurements with top of the line Audio Precision of a popular NC500 module.

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-nord-one-nc500-amp.7704/

Hi,

The measurement bandwidth is 22kHz in some cases, and 40kHz in others for THD versus frequency, and 61kHz in others.

 

For the 61kHz measurement bandwidth (the last graph) shows that the amplifier THD is 0.1% to 0.2% at 20kHz, yet the specification states 0.001% typical for 20Hz to 20kHz, using a the IMD test. The specification for the Hypex NC500 states :

 

"Note 2: At higher audio frequencies there are not enough harmonics left in the audio band to make a meaningful THD  measurement. High frequency distortion is therefore determined using an 18.5kHz+19.5kHz 1:1 two-tone IMD test."

 

So, do you accept that class D manufacturers are right and decide for you that 20kHz+ frequencies are meaningless, or is this just to make their numbers look better ?.

 

They certainly claim the superiority when it suits them (Purifi "exotic" statement).

 

The graph with the full spectrum without any filter (3rd from last), shows that for an 80mV input signal. There is significant noise from 20kHz to 100kHz, hence the poor THD with 61kHz measurement bandwidth (100x worse than IMD).

 

Does this energy from 20kHz to 100kHz affect the tweeter ?. What about the higher frequencies 100kHz to 400kHz ?

 

Is there such a thing as sub harmonic distortion in tweeters ?

 

EDIT : To add - the intermodulation distortion graph, second from last - the 35kHz to 45kHz intermods are 40dB worse than the benchmark amplifier. Is it possible that the tweeter is affected by these intermods at the level that they appear ? What about lower intermods, such as 9kHz+10kHz tests ?, or 12kHz+13kHz tests ?

 

Regards,

Shadders.

[marce]

13 hours ago, Shadders said:

 

 

Please see :

https://linearaudio.nl/cyril-batemans-capacitor-sound-articles

 

All ceramic capacitors have inherent distortion which exceeds all others. Polyester capacitors have significant distortion. Polypropylene and polystyrene capacitors have the lowest distortion.

 

Regards,

Shadders.

Not COG/NP0, class 1 ceramics.

[Shadders]

2 hours ago, marce said:

Not COG/NP0, class 1 ceramics.

Hi,

Thanks - i missed that.

Regards,

Shadders.

[Matias]

13 hours ago, Shadders said:

Hi,

The measurement bandwidth is 22kHz in some cases, and 40kHz in others for THD versus frequency, and 61kHz in others.

 

For the 61kHz measurement bandwidth (the last graph) shows that the amplifier THD is 0.1% to 0.2% at 20kHz, yet the specification states 0.001% typical for 20Hz to 20kHz, using a the IMD test. The specification for the Hypex NC500 states :

 

"Note 2: At higher audio frequencies there are not enough harmonics left in the audio band to make a meaningful THD  measurement. High frequency distortion is therefore determined using an 18.5kHz+19.5kHz 1:1 two-tone IMD test."

 

So, do you accept that class D manufacturers are right and decide for you that 20kHz+ frequencies are meaningless, or is this just to make their numbers look better ?.

 

They certainly claim the superiority when it suits them (Purifi "exotic" statement).

 

The graph with the full spectrum without any filter (3rd from last), shows that for an 80mV input signal. There is significant noise from 20kHz to 100kHz, hence the poor THD with 61kHz measurement bandwidth (100x worse than IMD).

 

Does this energy from 20kHz to 100kHz affect the tweeter ?. What about the higher frequencies 100kHz to 400kHz ?

 

Is there such a thing as sub harmonic distortion in tweeters ?

 

EDIT : To add - the intermodulation distortion graph, second from last - the 35kHz to 45kHz intermods are 40dB worse than the benchmark amplifier. Is it possible that the tweeter is affected by these intermods at the level that they appear ? What about lower intermods, such as 9kHz+10kHz tests ?, or 12kHz+13kHz tests ?

 

Regards,

Shadders.

 

You are right that THD increases with frequency faster than class AB, although its significance is also lesser. First that 20kHz tone the 2nd harmonic is 40kHz and 3rd harmonic 60kHz, so useless for hearing. Even 10kHz harmonics of 20kHz and 30kHz are not very relevant. Second that our hearing is more sensitive on the midrange, so that say a 1kHz and its harmonics are the very sweet spot of hearing sensitivity. And there is where class D is usually cleaner. 

 

 

You are also right that the Purifi statement is a little over the top, but its their marketing. How many other amplifiers have not state they were the best in the world bla bla?

 

The extra energy of the switching frequency is turned to heat on the tweeter, but low level of power. It is not going to burn anything.

 

If there were "sub harmonic distortions" it would be show in the 19+20kHz dual frequency IMD tests, and it does not.

 

Benchmark AHB2 is indeed and excellent measuring amplifier.

 

But enough for graphs, if you consider how good ncore sounds even compared to big names, as @barrows, this is what really counts. Specially factoring the price, size, weight, efficiency, etc.

[Shadders]

6 minutes ago, Matias said:

 

You are right that THD increases with frequency faster than class AB, although its significance is also lesser. First that 20kHz tone the 2nd harmonic is 40kHz and 3rd harmonic 60kHz, so useless for hearing. Even 10kHz harmonics of 20kHz and 30kHz are not very relevant. Second that our hearing is more sensitive on the midrange, so that say a 1kHz and its harmonics are the very sweet spot of hearing sensitivity. And there is where class D is usually cleaner. 

 

 

You are also right that the Purifi statement is a little over the top, but its their marketing. How many other amplifiers have not state they were the best in the world bla bla?

 

The extra energy of the switching frequency is turned to heat on the tweeter, but low level of power. It is not going to burn anything.

 

If there were "sub harmonic distortions" it would be show in the 19+20kHz dual frequency IMD tests, and it does not.

 

Benchmark AHB2 is indeed and excellent measuring amplifier.

 

But enough for graphs, if you consider how good ncore sounds even compared to big names, as @barrows, this is what really counts. Specially factoring the price, size, weight, efficiency, etc.

Hi,

The point is, Purifi make exotic claims, and these should be scrutinised - stating theirs is better than anyone elses whatever the amplifier, is more than promoting a specific attribute the amplifier has.

 

What class D sellers/manufacturers say regarding THD, is purely based on their desire to ignore the usual measurement bandwidth because it makes their product look worse.

 

We have people selling RF absorbent materials stating that they are beneficial when placed inside or near an amplifier, yet for some reason, the 20kHz+ mush from class D which is always there regardless whether a signal is being amplified, seems to be irrelevant.

 

For the sub-harmonic, this was relating to tweeter mechanical - i have seen discussion on it - but i would not know if it occurs.

 

The nCore tests showed the IMD signals repeated at 40kHz and was quite high in energy. What this means is that does IMD occur with lower frequencies causing the IMD to be inband - such as 5kHz+6kHz ? Does the IMD in the mid 20kHz cause metal dome tweeters to ring ? since they have resonances here ?

 

I agree, that it is really the subjective listening that matters - do you like it, but we cannot pick and choose which measurements matter, because the ignored set make the product look worse, yet still apply the ignored set to other amplifiers.

 

Regards.

Shadders.

[barrows]

20 hours ago, Shadders said:

So, do you accept that class D manufacturers are right and decide for you that 20kHz+ frequencies are meaningless, or is this just to make their numbers look better ?.

I choose to back up theory such as this with actually listening to the amplifiers through loudspeakers.  In comparison to trad class A/B amps I hear no faults-good enough for me for very high end system and serious audiophile loudspeakers.  I ma entirely satisfied that amps such as the Mola Mola Kalugas offer everything I need in an amplifier, and thta additional resources are much more wisely spent elsewhere.

[Shadders]

13 minutes ago, barrows said:

I choose to back up theory such as this with actually listening to the amplifiers through loudspeakers.  In comparison to trad class A/B amps I hear no faults-good enough for me for very high end system and serious audiophile loudspeakers.  I ma entirely satisfied that amps such as the Mola Mola Kalugas offer everything I need in an amplifier, and thta additional resources are much more wisely spent elsewhere.

Hi,

Your subjective listening neither confirms or refutes the objective measurements. You will not know whether you can hear 20kHz+ or not.

 

Again, if you are happy that the manufacturer decides for you regarding your hearing, or that 20kHz+ has no effect in the system reproduction, then ok.

 

The issue is that they present measurements that make their amplifier look better than the usual class A/B amplifier. They restrict the measurements to make their product look better, then claim no other amplifier can be better. I do not think class D should be given such preferential treatment - we should therefore be asking all reviewers to use the 22kHz measurement bandwidth, to level the playing field.

 

Another aspect is the very low output impedance of the unit. I think the performance of the Purifi module is excellent in this regard, but this is at 1amp output current (rms assumed) which equates to 6.83volts peak output into 4ohms. If we have a transient of 20.5volts peak, which is 3amps (rms) into 4ohms, is the output impedance the same ?. At 1amp, the damping factor is 12,000 which is vastly greater than any other amp.

 

The objective measurements are used to present an expectation of performance, and subsequently the listener will hear accordingly. I do not think our hearing is as good as we believe it is.

 

Regards,

Shadders.

[DuckToller]

Guys, 
please don't get nervous. Answers are coming.😌
Lars and Bruno have sent back more than 15 pages of response to the most important questions, and the article is in the making.😋
Stay tuned, it's something quite special ! 😍
Best, Tom

[Ralf11]

should we start a betting pool on whether @jabbr gives up his Pass amps?

[jabbr]

50 minutes ago, Ralf11 said:

should we start a betting pool on whether @jabbr gives up his Pass amps?

 

As long as I keep them, hell will never freeze over!