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

tvrgeek

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But several milliohms in cables, as you mentioned the output network, then crossover. Likely several 100 before you get to the diver. Point is, in the real world, a DF of 20 or 20,000 is irrelevant. I am more concerned with the PS ability to remain stiff under dynamic peaks.
 

rdenney

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Well, I have been building speakers and amps for 40 years, so I rest on my experience.
I am looking at objective measures. Always first. I then listen, but invariably, my ears usually follow the specs until you get to a "good enough" threshold. Loads have HUGE differences on ampler performance. If you have ever done a Spice model of an amp with various realistic loads, you would see it in the FFT big time. Now, before the "good enough" everyone has their choice of what faults are least objectionable.

One of the things I do not understand yet in ClassD is how distortion varies with current. AB is usually far worse with a "4 Ohm nominal" load than an 8. Sometimes by an order of magnitude.

Super low output Z is no holy grail. If you have ever built a speaker you would know it is darn near BS.
The data sheet for the 1ET400A shows output power with respect to distortion, which should say what needs to be said about how distortion varies with current. The module is noise-constrained until an output power of 100 watts or so at 8 ohms (200 watts at 4 ohms, and about 150 watts at 2 ohms) after that, distortion becomes the dominant feature until clipping. The point where clipping becomes significant is an opinion, of course. Distortion starts increasing significantly at 130 watts (8 ohms), 260 watts (4 ohms), and over 500 watts (2 ohms--500 watts is where they stopped the graph). Once the effects of clipping reach -45 dB SINAD, limiting kicks in for 4 and 8 ohms (500 watts isn't high enough to show this point at 2 ohms). Power levels at that point are about 185 watts into 8 ohms and 370 watts into 4 ohms.

Taking the noise limit, at 8 ohms the amp is moving 3.5 amps, 7 amps at 4 ohms, and a little over 8.5 amps at 2 ohms. Taking the knee of the curve, the current at 8 ohms is 4 amps, 8 amps at 4 ohms, and 16 amps at 2 ohms. Not much load effect up to that point. Distortion+noise at all of these points is less than -115 dB FS, which is astoundingly good.

At "hard clipping" (which is still less than 1% THD+N), the current is a bit less than 5 amps at 8 ohms, a bit less than 10 amps at 4 ohms. From my read of their data, all these points are voltage-constrained. Current constraint comes in a 2 ohms, and if I'm reading their charts correctly, it happens at 47 volts RMS, or 23.5 amps. Their spec states the amp will go into overcurrent protection at 25 amps, so my read of their charts is in the ballpark. That point is also better than 1% THD. 23.5 amps at 47 volts is...a lot of power.

This is the final amp, of course, and not the buffer. The amp provides 12.8 dB of voltage gain, but will happily amplify whatever voltage upstream gain stages present to it. That won't be a function of its own current capability, though.

Rick "suggesting close study of the datasheets for the Purify and Hypex modules--they are well-documented and I don't have 40 years of experience designing amps" Denney
 

rdenney

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But several milliohms in cables, as you mentioned the output network, then crossover. Likely several 100 before you get to the diver. Point is, in the real world, a DF of 20 or 20,000 is irrelevant. I am more concerned with the PS ability to remain stiff under dynamic peaks.
That wasn't the question, and go back to the article DonH56 wrote that I linked. The question was what was the damping factor, and I answered that. The real question is whether the amp can be pushed around by the speakers, especially compared to conventional designs, and I think we know the answer to that.

Yes to the power supply. And their specs for the module assume a power supply that can provide 70-volt rail voltages under all operating conditions. The power supply usually used is the Hypex SMPS1200A400, which is rated to provide 1200 watts for a brief period, and 400 watts continuously. But, of course, you can use whatever power supply you want, and some have done so. ATI use Hypex modules in one of their amps with a linear power supply, for example. The efficiency of Class D, however, makes providing a sufficiently stiff power supply a lot easier, it seems to me.

Rick "not disagreeing with you" Denney
 
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Jim Matthews

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I am more concerned with the PS ability to remain stiff under dynamic peaks.
Hence my pleasant surprise at the integral amps in my speakers. Only a decade ago, they were awful. Now? Better than the finest analog gear I could ever afford.
 

BrokenEnglishGuy

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Purifi provides this in their data sheet: 0.07 milliohms at 1KHz, and <0.65 milliohms across the band, at 1 amp of output.

I'm seeing a minimum damping value of 8/0.00066=>12K. That's only at 16 KHz--most of the damping values will be much higher. Essentially, the output impedance is effectively zero--that's about as load-invariant as it gets, as long as a low-impedance load does not draw more current than the amp's power supply can provide.

The older Hypex amps have a peak output impedance of 3 milliohms (for the NC502MP), for a damping factor of 2.7K or greater.

These are measured at the module, of course, and the wiring to the speaker terminals along with the terminals themselves will dominate the value measured there.

Rick "far higher than needed to make these amps load-invariant" Denney
Well, 16000 was a lot higher than i thinked. lol.
Ty.
 

pablolie

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It amazes me sometimes what people think they can hear... :-D And justify it with charts of measurements that have a built-in margin of error/variance that literally makes many of these "perfect" amps indistinguishable.

I gave up after trying to establish a preference between the Benchmark AHB and the NAD M22. It was the least fun music listening I had done for a while because I obsessed trying to hear a difference that IMO wasn't there. I did pick the M22 by the way, but just because I preferred the looks. I tried to convince myself it sounded a "bit more fun" but it was probably nonsense caused by fatigue.

If there is one thing the measurements prove is that these things don't have a "sound signature", they are linear as heck for pretty much any load. The difference will be somewhere else in your system, and in most cases you'll be left with over 200W of power reserve you'll never use - not that that's a bad thing. I am often far more worried how things sound at moderate and even low sound levels, but no reason to worry about that here either, these Hypex and Purifi architectures stay consistent.

It is my complete and total conviction these days that we're in an era where setup and environment is the limiting factor, and the latest generation of equipment is basically pretty darn perfect - except for speakers of course. That's where you'll get a difference and can tailor stuff to your preference... but you're wasting your time and $ and testing time unless you truly invest in setting things up right. You can NOT overcome environment problems with better equipment, it is a losing game: you'll just get marginally better compromised sound...

PS: Here's also a word of advice to anyone that takes these one-time measurements as the ultimate truth... while the measuring equipment stays consistent, we have no insight into other environment variables. How isolated from environment variables is the measuring setup? Did a dog bark a block down? Did someone slam the refrigerator room in the next door? Did a mouse fart under the listening couch? etc... I have learned to take these limited run measurements with a grain of salt. I don't at all doubt they provide very valuable data to establish the fundamental competence of a design, but when within a certain margin, and especially when they are single run events in semi-controlled environments, they don't represent that ultimate universal truth many take them to be...
 
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MasterApex

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Until recently I did not have the opportunity to have multiple amps and speakers.
With my older speakers, I could not tell the sound quality / presentation differences with these amplifiers.

However, with current 802D3 speakers , the amps under comparison are audibly distinguishable (amps were not driven to clipping, just engaging SPL level varies from 80-97dB SPL at 10ft distance).

It makes me wonder whether we have standard for highly resolving speakers ?
So when someone says he/she could not hear the difference, does he/she have resolving speakers to resolve the sonic differences?
 

pablolie

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So when someone says he/she could not hear the difference, does he/she have resolving speakers to resolve the sonic differences?
They may.

My comment was very specific and compared two amps using Hypex and Benchmark technology, respectively. Their published measurements make it rather improbable that anyone can hear a difference. :) I am sure with other amps there might well be an audible difference.
 
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Mnyb

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Did you test double blind with near instant change over and levels matched within 0.2 dB?
we may never figure where the method errors in this comparison is ? but they are sure much more likely than that there is a general cause that markets best amps are "audibly distinguishable" from each other when used inside their specs .

When you find something improbable first suspect method errors even if you cant fathom how .

Bias hints:
"highly resolving speakers" . slightly better than wife heard it from the kitchen :)
Making a general case of a small home trial ?
 

Pdxwayne

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I have a thread about online blind timing tests.

Different kind of headphones gave me different kind of clues. I would say he400se is more resolving than k371 based on success rate of passing timing tests.

More details here:

If headphones can give different clues....I would expect certain speakers can provide better clues than others.
 

Lord Victor

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Until recently I did not have the opportunity to have multiple amps and speakers.
With my older speakers, I could not tell the sound quality / presentation differences with these amplifiers.

However, with current 802D3 speakers , the amps under comparison are audibly distinguishable (amps were not driven to clipping, just engaging SPL level varies from 80-97dB SPL at 10ft distance).

It makes me wonder whether we have standard for highly resolving speakers ?
So when someone says he/she could not hear the difference, does he/she have resolving speakers to resolve the sonic differences?
There is not standard, as the is no objective measure for it, so a standard is effectively impossible outside of just deciding a specific speaker is the only accepted reference.
Often differences with amp (if any) are rather than by ‘resolving speakers’, likely to be shown by speakers with particularly odd or uneven crossovers/impedance, or with unusual frequency responses, such as with the B&W which are well known for that. Wether they’d retain that, for now, subjectively perceived measure of resolution, if they were EQ’ed or otherwise corrected to measure more evenly/flat, I can’t say fx.
1644948764765.jpeg

1644948824171.jpeg
 

JohnM-73

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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.

My exact (subjective) findings too. I found it an utterly perplexing listen, perhaps the most frustrating componemt I’ve yet owned. Because there was nothing obviously wrong, yet music failed to hold my attention. That’s never happened before on music I love. I wanted to keep this amp, as I adored the smaller form factor (Ghent cased EVAL1) and - having still got issues with my back after a slipped disc 6 years back - the ability to move the amp around easily without needing a JCB or a mountain of pain killers afterwards was a big win! It was non-bling, which I also appreciated. Yet my attention was constantly wandering. In the end, I decided life is too short to own a piece of hifi that is turning you away from the music - despute the objectivists findings that it should be, for all intents and purposes, perfect. I sold it on here after giving it three months, at a loss of about £300. Went back to my Quad 606 and music just felt ‘right’ to me again, my attention stopped wandering etc. I’d love to know what’s going on here… reverse confirmation bias?! I *wanted* to love the Purifi. Or do I simply prefer the sound of the 606s imperfections? Perfectly happy to accept that, if this is indeed the case. I almost want to try one again now a year has passed, but can’t afford to take another financial hit if I want to sell it on again after a few months. I’d love an efficient, compact, and reasonably light-weight amp, but can’t stretch to an AHB2 alas.
 

SIY

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My exact (subjective) findings too. I found it an utterly perplexing listen, perhaps the most frustrating componemt I’ve yet owned. Because there was nothing obviously wrong, yet music failed to hold my attention. That’s never happened before on music I love. I wanted to keep this amp, as I adored the smaller form factor (Ghent cased EVAL1) and - having still got issues with my back after a slipped disc 6 years back - the ability to move the amp around easily without needing a JCB or a mountain of pain killers afterwards was a big win! It was non-bling, which I also appreciated. Yet my attention was constantly wandering. In the end, I decided life is too short to own a piece of hifi that is turning you away from the music - despute the objectivists findings that it should be, for all intents and purposes, perfect. I sold it on here after giving it three months, at a loss of about £300. Went back to my Quad 606 and music just felt ‘right’ to me again, my attention stopped wandering etc. I’d love to know what’s going on here… reverse confirmation bias?! I *wanted* to love the Purifi. Or do I simply prefer the sound of the 606s imperfections? Perfectly happy to accept that, if this is indeed the case. I almost want to try one again now a year has passed, but can’t afford to take another financial hit if I want to sell it on again after a few months. I’d love an efficient, compact, and reasonably light-weight amp, but can’t stretch to an AHB2 alas.
Or perhaps it's a non-audible thing. Human brains are funny that way.
 

Lord Victor

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My exact (subjective) findings too. I found it an utterly perplexing listen, perhaps the most frustrating componemt I’ve yet owned. Because there was nothing obviously wrong, yet music failed to hold my attention. That’s never happened before on music I love. I wanted to keep this amp, as I adored the smaller form factor (Ghent cased EVAL1) and - having still got issues with my back after a slipped disc 6 years back - the ability to move the amp around easily without needing a JCB or a mountain of pain killers afterwards was a big win! It was non-bling, which I also appreciated. Yet my attention was constantly wandering. In the end, I decided life is too short to own a piece of hifi that is turning you away from the music - despute the objectivists findings that it should be, for all intents and purposes, perfect. I sold it on here after giving it three months, at a loss of about £300. Went back to my Quad 606 and music just felt ‘right’ to me again, my attention stopped wandering etc. I’d love to know what’s going on here… reverse confirmation bias?! I *wanted* to love the Purifi. Or do I simply prefer the sound of the 606s imperfections? Perfectly happy to accept that, if this is indeed the case. I almost want to try one again now a year has passed, but can’t afford to take another financial hit if I want to sell it on again after a few months. I’d love an efficient, compact, and reasonably light-weight amp, but can’t stretch to an AHB2 alas.
The only way to really know is doing a blind properly voltage matched AB test - I deliberately pick AB over ABX here since this is not some empirical study, but rather trying to find any actual tiny difference there might be.
I’ve just gotten the Class D amp I compared it to as well as another one. I haven’t done matched blind testing with it yet, so take it as you will; but it seems to have the exact same character I experienced last time when I borrows it: precise and exciting to the point where it can be fatiguing with some speakers/music, but stunning with the right stuff. And I have more normal/neutral sounding class D amp next to it when I don’t want that, which I suspect sounds closer to the Purifi and my class AB amps.

I intend to eventually get a Purifi amp as well (ideally one of the new high powered ones), probably. At the end of the day I’d say just use what you like and don’t care about the rest of you can help it. If you do want class D and want to try something non Purifi/Bruno based, then I’d recommend giving Gato audio a look - they use the same brand of amp boards that I’m currently experimenting with. Plus they look gorgeous.
 

SIY

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No, I don't think it's a mental disorder by any means. Normal human brains, and most people aren't really aware of how powerful a liar is that hunk of goosh in our crania.
 

JohnM-73

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Or perhaps it's a non-audible thing. Human brains are funny that way.
That's likely a distinct possibility. Or there's something else present that the average human can't hear per-se, but can detect. It really bugged me - still does - as I wanted to keep the Purifi and retire the Quad 606. Wish I had the funds to buy another, and get somebody to help set up a true DBT, AND a longer listening test too as an extra data point. I remain convinced that some 'traits' only manifest themselves after listening for a while. As you say, human brains are funny.
 

JohnM-73

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At the end of the day I’d say just use what you like and don’t care about the rest of you can help it. If you do want class D and want to try something non Purifi/Bruno based, then I’d recommend giving Gato audio a look - they use the same brand of amp boards that I’m currently experimenting with. Plus they look gorgeous.

True. It just bugs me as by every metric this should have had me enjoying music into the early hours daily. But I had to make an effort to enjoy the music. Perhaps I've grown so used (conditioned) to the 'additions' by more conventional amplifiers that when one hears a 'perfect' amplifier then by comparison, the brain 'detects' something is missing - flags that as confusion/disappointment - except it's the added extras by lesser amp designs. I'm tempted to order another EVAL1 board at some point this year and give it another go. I do love the Quad 606, but really want something smaller and lighter to move about due to back issues etc. Cheers for the Gato recommendation - with get a Googling!
 

MaxBuck

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My exact (subjective) findings too. I found it an utterly perplexing listen, perhaps the most frustrating componemt I’ve yet owned. Because there was nothing obviously wrong, yet music failed to hold my attention.
You need to quit drinking decaf, obviously, and return to high test.
 
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