Benchmark AHB2 / Class D Purifi Eigentakt / Mark Levinson 333 - Listening impression & Conclusion

[audio2design]

Let's be clear: I was talking about what we hear, not about measurements or controlled testing.

In truth I don't know whether I could reliably distinguish, say, my Pass amp from my VTV in the usual type of ABX testing. But sitting through hours of listening my ears hear differences. If confirmation bias means you "hear" what you "see", how come that isn't always to the case? Why didn't I hear my $5500 Pass as better than my $1500 Purifi? What a mystery!?!

No more discussion from me on this thread: clearly I'm just hollering down a well.

You mean your brain tells you there is a difference. In between you ate food, had caffeine, stressed or destressed .... Most of all though, you are intently listening, and picking up things you didn't before, because now you are trying to.

 

[Wes]

How is that objectivists, (apparently including mastering engineers), may be assumed to be without [confirmation] bias? Perhaps they hear no differences because hearing none confirms their biases.

I would like to see a complete, stand-alone thread on this. One assumes that cognitive psychologists, if not the perfume industry, would have tested for it.

 

[rdenney]

Let's be clear: I was talking about what we hear, not about measurements or controlled testing.

In truth I don't know whether I could reliably distinguish, say, my Pass amp from my VTV in the usual type of ABX testing. But sitting through hours of listening my ears hear differences. If confirmation bias means you "hear" what you "see", how come that isn't always to the case? Why didn't I hear my $5500 Pass as better than my $1500 Purifi? What a mystery!?!

No more discussion from me on this thread: clearly I'm just hollering down a well.

With all due respect, it's always a mystery. Always. That's the point of wanting some form of controlled testing.

What we expect, and therefore what dominates confirmation bias, happens both consciously and subconsciously, it seems to me. (I am not a psychologist, but rather just a dilettante observer of human behavior, particularly my own.) I'm not sure I can predict whether the conscious or subconscious part will dominate my summary expectation and bias in any particular context. I may want the expensive amp to be better, while believing in my heart of hearts that it isn't, and that's just two of maybe four or five levels at which bias may be at work. It is indeed a mystery; were it not, there would be no need for controlled testing. I have in the past asserted that my bias was opposite of the conclusion, and therefore irrelevant to that conclusion, but I'm frankly not so shallow that I can be sure my conscious bias was really dominating my perceptions.

From the standpoint of my own preferences, I may be quite happy with one or the other. I may actually prefer coloration of a Pass amp versus a lack of coloration of a Purifi amp, for example. Or I may prefer the reverse. I can have those preferences even if I can show that I can consistently hear a difference. We live by sight and sound, so if the appearance, brand, story, and ownership experience of an amp makes it sound better to us, then, well, it does. But that doesn't mean my response is transferable.

There is nothing about blind testing that requires short listening excerpts, it seems to me. When Toole and Olive were conducting blind preference tests, they allowed the listeners to listen as long as they liked to each sample. If I listen to one for a whole week or month and write down my subjective response to it in a notebook, and then listen to a different one for a week or a month (or an hour) and write down my impressions, then listen to "X" to try and correlate it (based on my notes, after the fact) to one or the other, and keep doing so long enough for a pattern to form, there might actually be some differences that can be noted, without the need for rapid-fire ABX testing. The idea that long-term listening is required and therefore controlled testing is unhelpful is simply a mistake. The requirement is to remove sighted bias. There would need to be other controls, such as listener being unable to control volume (in order to preserve level matching), which would be inconvenient, but not fatal to the idea of a longer listening period. If the hypothesis is "with extended listening over the course of a week, Amp A sounds different than Amp B in relation to Amp X," then I can construct the necessary controlled listening test. Statistical significance would require a very long time, so most don't do it this way. But that is a matter of convenience only, and of sample size and resulting reliability of the conclusions. Such long tests would certainly lack the sample size to confirm with any confidence that A and B are the same (or different), but even the inability to confirm that easily would debunk in my own thinking any notion that the differences are profound.

For a fun read on the topic of blind testing, probably old news for most here, see: https://www.stereophile.com/features/141/index.html. That series of letters contained quite some bit of violent agreement, in addition to some incomplete understanding of statistics and some false conclusions, but I thought the 12-page back-and-forth ended well.

Rick "who doesn't have the money to waste on stuff that is merely expensive" Denney

 

[Phorize]

I guess the problem also seems to be that class d is more difficult to handle then traditional amps to reach reference performance and there is a wider room for error in the design. There are probably more different Class D layouts considering all integrated devices than there are A or AB. But to be honest, if I hadn't upgraded my speakers further while testing the other high end class D amp to this day I wouldn't have noticed the difference. So this whole topic has become really high end nowadays compared to the earlier days of class d.

For some time now the advantages in terms power efficiency, lower heat output and miniaturisation have out weighed trade offs in audible output, and now there are no trade offs. Looking at the performance figures for SOTA class d I’d be totally stunned if people could distinguish them under controlled conditions.

Its about to become academic anyway, all developed economies are going to have to ban the production of all consumer products with class a/b levels of energy wastage to meet carbon reduction targets. I’d recommend that anyone who is concerned about the issue to buy your class a/b devices now whilst they are available.

 

[mocenigo]

Also the discussion about class D here makes no sense. There are huge differences between different class D amplifiers. Same for class A and AB. I've seen class A amplifiers that are utter garbage, but I don't use those as proof dat alle class A sucks.

In my arguing I was assuming we talk about “good” Class A, AB, and D products. Of course this is also difficult to define, but little chip amps whose maximum wattage is measured at 10% THD are out of the question.

 

[mocenigo]

True, you did come right out and admit “I am sharing point of views and experiences which are clearly described as sighted and not controlled.”

A hug (sincerely!).

 

[mocenigo]

True, you did come right out and admit “I am sharing point of views and experiences which are clearly described as sighted and not controlled.”

Also, I know that the amplifier I built myself is the best amplifier on the planet because when I see it I know it is mine, the one borne out of the work of my hands, with Purifi modules and the Neurochrome Universal Buffer! HA! ;-)

 

[SIY]

Also, I know that the amplifier I built myself is the best amplifier on the planet because when I see it I know it is mine, the one borne out of the work of my hands, with Purifi modules and the Neurochrome Universal Buffer! HA! ;-)

Now that is something I understand! It's a corollary of Olson's Law. Unfortunately, you're wrong and the best amplifier on the planet is my little EL84-based tube amp.

 

[mocenigo]

Now that is something I understand! It's a corollary of Olson's Law. Unfortunately, you're wrong and the best amplifier on the planet is my little EL84-based tube amp.

In italy it is called also “Effetto scarrafone”, I.e. the Cockroach Effect in Neapolitan dialect. There is a saying in Neaples: “ogne scarrafone è bello a mamma soia” i.e. “every cockroach is a beauty in its mom’s eyes.”

 

[SIY]

In italy it is called also “Effetto scarrafone”, I.e. the Cockroach Effect in Neapolitan dialect. There is a saying in Neaples: “ogne scarrafone è bello a mamma soia” i.e. “every cockroach is a beauty in its mom’s eyes.”

I now learned a new word in Italian, mille grazie!

 

[Random Lunatic]

I have these 3 amplifiers and am curious how they compare in my environment.

Equipment setup:

CD/SACD player: Oppo BD105

Stereophile’s Test CD2 , Track 15 pink noise, , for level matching the three amplifiers​

Volume set 72dBC on track 15 before playing songs B - F​

Volume set to 82dBC on track 15 before playing songs G-H​

​

Standard Music :​

• B - SACD Norah Jones, Come away with me
• C -SACD Andrea Bocelli, Melodramma
• D -SACD Dire Straits, Walk of Life
• E -SACD Pink Flyod, Time
• F -CD Ultimate Demonstration Disc: Chesky Records’ Guide to Critical Listening, Track 3 Spanish Harlem

Life Classical Recording Music:​

• G - SACD Telarc Tchaikovsky 1812 overture, Track 7 Cossack Dance from Mazeppa
• H -SACD Telarc , Donald Runnicles , ORFF Carmina Burana , track 10 were diu werlt alle min

Blu-Ray Movies:​

• I -John Williams Live in Vienna, Track 19 Imperial March , watching in 2ch mode
• J -Patriot, Uncompressed LPCM Audio track, Scene 6

Apple TV 4k:

• 1. Streaming Apple music (various pop songs Taylor Swift, Marron 5, etc)
  2. YouTube podcast (for center channel compare)
  3. HBO Max Movies (for center channel compare)

Pre-Pro Anthem AVM50v, XLR audio input from oppo.
802D3 Speakers (Front) , HTM1D3 (Center) , old DM640i (Surround back)
Amplifiers under test:

1. Mark Levinson No 333
2. Benchmark AHB2
3. VTV Purifi Eigentakt EVAL-1

Listening Impression (Stereo 2ch mode):

• For songs B-F , level match volume based on Track 15 pink noise (A1 above) , resulting in typical music volume swings around 80dB-86dB. They all sound good. The Benchmark and Levinson sounds very similar in tonal balance, my son (blind test) could not tell them apart. The Benchmark AHB2 sounds very clean on E) Time , the ring sounds the clearest. On v vocal on AHB2 sounds a little bit less weight (Andrea Bocelli voice sounds less vibrato) compare to others. Levinson sounds very similar to AHB2 but the vocal is is more full and the bass has more weight. The Class D Purifi Eigentakt tonal balance has stronger mid-bass/low midrange so the vocal sounds more forward and closer but the upper treble is rolled off. The sound of cymbals are not as clear and not as distinct compare to levinson 333 or benchmark. AHB2.
• For songs G-I, volume knob has to increase by 10dB (A2 above) to compensate for the recording sound level. The Class D Purifi Eigentakt sounds compressed (lack impact), at loud level, the sounds of each instruments are not as delineated, and the high frequency triangle and cymbals are not very clear in comparison to benchmark AHB2 or levinson 333. Both levinson 333 and benchmark AHB2 sounds very similar, but when the dynamic sound peak at 94dB, the 333 sounds more at ease and each individual instruments details are more distinct (more details of cello vibration and triangle resonance) than the AHB2.
• It is hard to tell apart AHB2 vs 333 but easy to identify the Class D Purifi once we have heard all three on the same or specific songs. The Class D Purifi has rolled off treble and forward midrange that is its strong signature (by comparison, it sounds neutral/normal on its own when there is nothing to compare). This roll off treble reminds me on my previous Krell KSA-200s sonic signature.
• The life recording song G-H has very wide dynamic (55dB – 94dB swing). Since my son played at the orchestra, I know what orchestra sounds like sitting in front rows. In my observation, to reproduce this life-like sounds of life orchestra is probably the most demanding for high resolution speakers and amplifiers. When playing loud level , songs G-I , the old Levinson still sounds the best.
• When playing loud dynamic music song G-I, we heard changes in Class D Purifi tonal balance, the peak sounds certain instruments are level off compare to AHB2 or 333. Could the Class D PWM sampling be manipulated so the peak musical waveform dynamic is lost to bias for more midrange clarity ? Or is there soft clip mode where certain peak music waveform is “clipped” so they sound “compressed” . I don’t know but what we heard is a more compressed dynamic relative to AHB2 or 333 on song G-I.

Listening impression (Movie, using it to drive center channel)

• Playing with K-M, AHB2 (mono bridge mode) and 333 sounds the same.
• Playing with K-M, even level matching with AVM50v built-in level calibration (per SPL meter), the dialogue still sounds louder with the Class D Purifi. It correlates with our stereo experience where purify midrange is more forward sounding but less treble.
• This Class D Purifi amp is good match for center channel or a PA system, it accentuates midrange voice (in comparison, sounds "neutral"/normal when listening to it without any comparison). So the dialog is more clear (e.g. comparison on streaming podcast from apple TV).
• Try watching the Blu-ray Patriot movie Scene 6; It has both uncompressed 5.1 PCM and standard Dolby Digital 5.1. The dialogue on Dolby Digital 5.1 is more clear due to compression (special effects, music, weapons sounds are compressed) . However, if one has dedicated room , speakers and amps, one would want to watch it in uncompressed PCM for more immersive and open sound.

My personal conclusion:

1. Class D amplifiers have improved a lot of the years but Class D Amps are still no match to good design Class AB Amp.in term of sound quality and dynamic handling
2. Benchmark AHB2 is more versatile (good for all music) and more dynamic than the Class D Purifi Eigentakt
3. Class D Purifi Eigentakt is suitable for center channel, its slight compression and unnatural bias toward midrange makes dialogue more clear It is not an ideal amp for life classical music reproduction.
4. Mark Levinson 333 is the best despite its old age. It is the most life-like, with more weight on vocal , and more at ease when playing life recording classical orchestra at higher volume level
5. There needs to additional scientific measurements that can explain why the benchmark AHB2 sounds better than Purifi Eigentakt in my environment and why the levinson sounds more dynamic and detailed on loud classical music. Traditional SINAD, THD , IMD measurement using sinewave do not have the musical waverform complexity and can not explain the contrast of what we heard among these amplifiers in our environment. What we heard can not be explained with just THD measurement as they all sound good (not distorted) but different. As below certain THD, the delta is not audible.

That sensation of compression and slightly subdued top end reflects my experience with the Purifi as well, and I've bee racking my brain for months now, trying to figure out what is going on - because it seems like an abnormality compared to other amps I've heard, but at the same time the Purifi's specs, and Bruno's expertise would lead me to think the Purifi is the more correct presentation... But it just doesn't sound quite right when compared directly to others somehow.
As you say its a minor difference, but enough that over longer periods I think I have the same reaction as someone else said: Believe in audible differences in these types of amps or not, but whatever its doing, it makes me listen less to music - now this in my case isn't specifically about the Purifi, I don't think its that bad by any means, but it does seem to have some slightly unusual character to it.
The NCore in the NAD M10 has some of the same character, but it is much more pronounced in the Purifi... I don't know what's causing it, but its clearly something Bruno is doing, and is doing more of in the Purifi than the past nCore designs.

Its leving me confused whether the Purifi is the one true gospel, based on Brunos immense expertise, and all the other amps are 'off'... or whether I should take a hint and look elsewhere, like the Orchard amps or Benchmark if I could afford it... Or even a monstrosity like the ML

 

[SIY]

That sensation of compression and slightly subdued top end reflects my experience with the Purifi as well, and I've bee racking my brain for months now, trying to figure out what is going on - because it seems like an abnormality compared to other amps I've heard, but at the same time the Purifi's specs, and Bruno's expertise would lead me to think the Purifi is the more correct presentation... But it just doesn't sound quite right when compared directly to others somehow.
As you say its a minor difference, but enough that over longer periods I think I have the same reaction as someone else said: Believe in audible differences in these types of amps or not, but whatever its doing, it makes me listen less to music - now this in my case isn't specifically about the Purifi, I don't think its that bad by any means, but it does seem to have some slightly unusual character to it.
The NCore in the NAD M10 has some of the same character, but it is much more pronounced in the Purifi... I don't know what's causing it, but its clearly something Bruno is doing, and is doing more of in the Purifi than the past nCore designs.

Its leving me confused whether the Purifi is the one true gospel, based on Brunos immense expertise, and all the other amps are 'off'... or whether I should take a hint and look elsewhere, like the Orchard amps or Benchmark if I could afford it... Or even a monstrosity like the ML

Can we assume that these “comparisons” were done without basic controls? That’s the most likely explanation.

 

[Purité Audio]

I get melons with a raspberry top note and a bitter chocolate finish.
Keith

 

[Phorize]

I don't know what's causing it, but its clearly something Bruno is doing, and is doing more of in the Purifi than the past nCore designs.

I’m wondering if you could shed some light on this. If we take basic the measurements for the purifi amp at face value we have to rule out audible artefacts if any kind being produced by the amp. If we have doubts, then a controlled test is the only way to validate them. As far as I can see there is nothing else to do, and yet quite regularly people conclude that their uncontrolled observations overrule rigorous test data. Can you see the conundrum? How do we encourage people to seek real evidence rather than just saying that a whole field of engineering is based on a delusion.

 

[Random Lunatic]

I’m wondering if you could shed some light on this. If we take basic the measurements for the purifi amp at face value we have to rule out audible artefacts if any kind being produced by the amp. If we have doubts, then a controlled test is the only way to validate them. As far as I can see there is nothing else to do, and yet quite regularly people conclude that their uncontrolled observations overrule rigorous test data. Can you see the conundrum? How do we encourage people to seek real evidence rather than just saying that a whole field of engineering is based on a delusion.

Oh I entirely see the issue - it’s a big part of why I myself am rather confused by this. If I hadn’t seen other completely separate accounts of the same experience, I’d have chalked it up to some odd interaction with my speakers or my taste. But I’ve seen a couple accounts of this experience with it - anecdotal of course. My experience that the same sort of thing, whatever it is, was shared to a lesser extent by Bruno’s earlier designs also somewhat reinforced it. In my case, much like this chap, it was just a rudimentary at home blind tests against some other amps.

Having looked rigorously at the Purifi amps measurements as well as listened to Bruno, whose expertise seemingly knows no bounds, is to a great extent why I’m left quite confused with what I’m experiencing, and have heard others describe - because on paper this amp should be as near as makes no difference perfect - so I’d almost have assumed it was the one sounding correct and my other amps were wrong. But then here it’s being compared to the only amp to my knowledge that beats it on paper, with the same result.

Im of course not suggesting anyone take these anecdotes as ‘fact’ per se, but it does make me wonder what might be the cause or explanation, assuming we aren’t all sharing some mass audio delusion of course

I migh have a look if there is some metric/flaw that the Benchmark has in common with most amps that the Purifi doesn’t. Though I don’t really expect to find an answer without the level of expertise these amps designers have.

For now all I know is that the Purifi don’t quite sound as clear/impressive as I would have expected, comparatively to other amps - though I suppose that to an extent just speaks to the level of transparency most modern amps already possess.

 

[mocenigo]

I now learned a new word in Italian, mille grazie!

Technically, it’s Neapolitan.
Scarrafone (Neapolitan) = cockroach (English) = scarafaggio (Italian)

 

[MasterApex]

That sensation of compression and slightly subdued top end reflects my experience with the Purifi as well, and I've bee racking my brain for months now, trying to figure out what is going on - because it seems like an abnormality compared to other amps I've heard, but at the same time the Purifi's specs, and Bruno's expertise would lead me to think the Purifi is the more correct presentation... But it just doesn't sound quite right when compared directly to others somehow.
As you say its a minor difference, but enough that over longer periods I think I have the same reaction as someone else said: Believe in audible differences in these types of amps or not, but whatever its doing, it makes me listen less to music - now this in my case isn't specifically about the Purifi, I don't think its that bad by any means, but it does seem to have some slightly unusual character to it.
The NCore in the NAD M10 has some of the same character, but it is much more pronounced in the Purifi... I don't know what's causing it, but its clearly something Bruno is doing, and is doing more of in the Purifi than the past nCore designs.

Its leving me confused whether the Purifi is the one true gospel, based on Brunos immense expertise, and all the other amps are 'off'... or whether I should take a hint and look elsewhere, like the Orchard amps or Benchmark if I could afford it... Or even a monstrosity like the ML

Thanks for sharing.
Last night, I invited my son friend (not an audiophile) to listen.
We used the telerac 1812 overture SACD, playing the songs 2 times and ask him to focus on the dynamic and details.
He was able to detect difference between AHB2 and Purifi.
But when I used my old entry surround speakers as test, none of us could tell the difference. So high resolution speakers matter.

I believe we need to develop new measurement method that explains WHAT we HEAR
Current measurement of freq response , IMD, THD based on sinewave and dummy load is single dimension and do NOT fully explain what we hear.

 

[SIY]

Thanks for sharing.
Last night, I invited my son friend (not an audiophile) to listen.
We used the telerac 1812 overture SACD, playing the songs 2 times and ask him to focus on the dynamic and details.
He was able to detect difference between AHB2 and Purifi.
But when I used my old entry surround speakers as test, none of us could tell the difference. So high resolution speakers matter.

I believe we need to develop new measurement method that explains WHAT we HEAR
Current measurement of freq response , IMD, THD based on sinewave and dummy load is single dimension and do NOT fully explain what we hear.

So no controls AND coaching. The explanation for what you “hear” is quite straightforward.

 

[Wes]

how is asking him to focus on the dynamic and details a problem?

 

[SIY]

Oh I entirely see the issue - it’s a big part of why I myself am rather confused by this. If I hadn’t seen other completely separate accounts of the same experience, I’d have chalked it up to some odd interaction with my speakers or my taste. But I’ve seen a couple accounts of this experience with it - anecdotal of course. My experience that the same sort of thing, whatever it is, was shared to a lesser extent by Bruno’s earlier designs also somewhat reinforced it. In my case, much like this chap, it was just a rudimentary at home blind tests against some other amps.

Having looked rigorously at the Purifi amps measurements as well as listened to Bruno, whose expertise seemingly knows no bounds, is to a great extent why I’m left quite confused with what I’m experiencing, and have heard others describe - because on paper this amp should be as near as makes no difference perfect - so I’d almost have assumed it was the one sounding correct and my other amps were wrong. But then here it’s being compared to the only amp to my knowledge that beats it on paper, with the same result.

Im of course not suggesting anyone take these anecdotes as ‘fact’ per se, but it does make me wonder what might be the cause or explanation, assuming we aren’t all sharing some mass audio delusion of course

I migh have a look if there is some metric/flaw that the Benchmark has in common with most amps that the Purifi doesn’t. Though I don’t really expect to find an answer without the level of expertise these amps designers have.

For now all I know is that the Purifi don’t quite sound as clear/impressive as I would have expected, comparatively to other amps - though I suppose that to an extent just speaks to the level of transparency most modern amps already possess.

Much handwave. No controls. Had you considered running an actual experiment before making extraordinary claims?