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Interview with Bruno Putzey

firedog

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https://darko.audio/2020/07/expert-opinion-bruno-putzeys-purifi-hypex-kii-mola-mola/

Yes, it's by Darko, but Bruno says lots of interesting stuff about measurements of amps.
He says his new Purifi amps are perhaps the best in the world, and that only the Benchmark amp and the Boulder 2150 (only $100k for a pair...) more or less match it in measurements.
He says if you know what to measure ( a more comprehensive set than usually done) you can judge an amp only by measurements - if it is extremely good in all aspects it will sound good. But he says most measurements sets of amps don't measure enough aspects of the performance to find the weaknesses of the amp, and therefore aren't reliably predictive of it's sound.
 
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mikeburns

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I really enjoyed this interview. To be fair I like Darko's stuff alot, though I take most of what he says with a grain of salt. It was clear that some of the things Bruno said in the the interview were challenging to Mr Darko, resulting in some extended breathing and interesting questions. Good on him for chatting to someone who is a true engineer that produces electronics of the finest quality, despite being presented with some aspects that may cause him to pause (and hopefully reflect on his previous assumptions). I know he gets a bit of stick around here (and I can see why most of the time), but he is into music and audio stuff and he is trying to grow interest in this weird hobby of ours in a more modern and engaging way.
 

Vasr

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He says if you know what to measure ( a more comprehensive set than usually done) you can judge an amp only by measurements - if it is extremely good in all aspects it will sound good. But he says most measurements sets of amps don't measure enough aspects of the performance to find the weaknesses of the amp, and therefore aren't reliably predictive of it's sound.

That is a good summary.

This interview was good especially for this site because it is with someone who creates designs that measure well (at least under the usual metrics) and believes in measurements but is realistic about the limitations of measurements. Typically, the latter happens from those who are only looking to discount measurements and so not taken seriously (at least by this group).

Examples include doing IMD measurements with a low frequency along with a high frequency rather than two bunched frequencies as the former might expose some weakness in that particular design of the amp. In Class D, since the design tries to keep the audible range do well and "bugger the rest by design" (his words), it might indicate a high level of distortion at 20khz signal but may not be as important since the higher harmonics are out of audible bandwidth. So, it would be better to test at increasingly lower frequencies to see if any of the harmonics manifest themselves in the audible range.

Those are good points and food for thought as to whether a standard 1khz test for distortion numbers (along with multi-tone) is enough for all amp designs or even sufficient to expose potential issues within a specific amp design. The main takeaway from that interview is that amps that measure "clean" in the limited set of measurements as done here aren't guaranteed to "sound neutral" unless they include measurements that test for the potential weaknesses in that design. Only when they measure well in all of those ways (and he does realize the practical limitations of doing so exhaustively) can one be sure about the amp being "neutral" (or transparent as used synonymously). Another way to look at it is that you can obtain confidence about "transparency" only asymptotically in number of measurements and have to make a cut-off at some point as enough.

The flip side of that thesis is that if you haven't done that exhaustive testing OR an amp doesn't fully ace in the measurements you have done then you have no way to predict how the amp will actually sound.

There are some strong views amongst people I have read here that the measures done here are all one needs to judge an amplifier by. Bruno's views are counter to that.

There is a preference for "standardized tests" here over idiosyncratic ones. For example, linearity for amps is not normally done because there is no standardization of what levels to measure at but that also means it may not expose a potential problem with an amp where that measurement has not been done. Then there is the practical aspect of it. There are only so many tests that can be done within anyone's time and resources. But that does not prove completeness or sufficiency of measurements.

All are good reasons for the limited set of tests used here but I think it is also OK to believe that these tests are not necessarily complete for a given amp design and the final word. Bruno has a persuasive argument for this.
 

amirm

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Examples include doing IMD measurements with a low frequency along with a high frequency rather than two bunched frequencies as the former might expose some weakness in that particular design of the amp.
That is the IMD test I run. It is the SMPTE profile which is a 60 Hz tone plus 7 kHz. I am not a fan of 19+20 kHz tone set that stereophile uses because it is very unrealistic and it doesn't account for low frequency distortion.
 

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The main takeaway from that interview is that amps that measure "clean" in the limited set of measurements as done here aren't guaranteed to "sound neutral" unless they include measurements that test for the potential weaknesses in that design.
The weakness in the design is immaterial unless it is an audible one that also escapes the battery of other tests I run.
 

Vasr

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The weakness in the design is immaterial unless it is an audible one that also escapes the battery of other tests I run.

This isn't inconsistent with the takeaway.

His thesis is that even though a unit may have come clean in that set (or any limited set) of standard tests (clean defined as no audible artifacts detected within those tests), we cannot be confident that the amp will be completely transparent (i.e., not have audible artifacts) unless we also measure using tests that are specifically designed for that class of design which may show behavior resulting in audible artifacts that are not manifested in the standard tests or in other amp designs. He was specifically asked what such a test might be for Class D.

If you want to ask what such other tests may be, Amir meet Bruno, Bruno meet Amir. :)
 

Vasr

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It was my understanding that the original reason for 60 hz plus 7 khz is to uncover amps that have poor power supplies. The 60 hz at high level will uncover those problems. Obviously that is pretty much not a thing for class D design in the sense it will not uncover PS issues with those frequencies.

That is exactly the point. If that particular test is necessary for linear power supply amps (or whatever suffers from it), then that test must be done for such amps. But that test done for Class D may be useless. There might be a separate combination that excites the Class D switching design (I am just hypothesizing here to make a point) which a Class AB may have no problems with. So just using one for both isn't sufficient.

The difficulty, of course, is deciding which test suites are necessary and sufficient for each type of design. It is like deciding which tests suites are necessary and sufficient for a piece of a software to fully test it. That is a hard problem even though there are a lot less variations in amp designs.
 

amirm

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If you want to ask what such other tests may be, Amir meet Bruno, Bruno meet Amir. :)
I have met him. How he talks to me is not the same has how he talks to subjectivists. :) He has to straddle that fence, I don't have to.
 

Vasr

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I have met him. How he talks to me is not the same has how he talks to subjectivists. :) He has to straddle that fence, I don't have to.

:) I get that. But is there anything incorrect in what he says to a subjectivist or anything there in that interview that he does not believe in? If not, those points still hold.
 

Blumlein 88

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I have met him. How he talks to me is not the same has how he talks to subjectivists. :) He has to straddle that fence, I don't have to.
Yes, it has gotten almost to the Dr. Jekyll/Mr. Hyde range with Bruno these days. I preferred back when he didn't straddle the fence. It was straightforward and you didn't have to decode some of what he says.
 

Blumlein 88

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:) I get that. But is there anything incorrect in what he says to a subjectivist or anything there in that interview that he does not believe in? If not, those points still hold.
He leaves room for subjectivist to wonder about some unmeasured distortion or some such when I don't think in his own mind there is anything to worry about. He even says in the interview there isn't any new information about amp behaviour he needs to consider with Purifi vs the earlier Hypex designs.
 

Vasr

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He leaves room for subjectivist to wonder about some unmeasured distortion or some such when I don't think in his own mind there is anything to worry about.
I can't really know what he thinks in his mind or assume something unless he has said something different elsewhere. But then people also evolve over time to more finessed viewpoints that aren't necessarily wrong just not as black and white in the earlier ideologue days. Getting into business is a fast way to that transformation. ;)
He even says in the interview there isn't any new information about amp behaviour he needs to consider with Purifi vs the earlier Hypex designs.
For the measurements design, it wasn't the contrast with different Class D designs but between Class D and Class A/AB.
 

Blumlein 88

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I can't really know what he thinks in his mind or assume something unless he has said something different elsewhere. But then people also evolve over time to more finessed viewpoints that aren't necessarily wrong just not as black and white in the earlier ideologue days. Getting into business is a fast way to that transformation. ;)

For the measurements design, it wasn't the contrast with different Class D designs but between Class D and Class A/AB.
The business wisdom he has learned is playing up a little to the subjectivists crowd keeps the market open to him as that is where the money is. His evolving thought on the performance electronics side.......not much change in my opinion.
 

Blumlein 88

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@Bruno Putzeys

He has posted here at times. Maybe he can tell us what measurements Amir could add to more thoroughly characterize if Purifi or other amps are wholly transparent. He says the Boulder 2150 is, but it is eclipsed by a few other A/B designs in specs. Maybe he could address that too.
 

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The business wisdom he has learned is playing up a little to the subjectivists crowd keeps the market open to him as that is where the money is. His evolving thought on the performance electronics side.......not much change in my opinion.
It's of course that , it helps market and indeed brand him and all the things he's involved in.

If a brand is too technical, nasty and digital, it can't be organic ! It can't be natural and we all know organic and natural sound best. Also audiophiles are quite narcissistic, it has to be all about them and all about their way if thinking , so you leave a bit of ambiguity so they can indulge their imagination.

Fair enough, Bruno is behind some great designs , we all want them to succeed as it's in the interest of high fidelity playback.
 
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firedog

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He also says a few other interesting things in the interview:

a) that various forms of electrical/RF noise coming over a network source (streamer) or from a PC CAN influence the sound output of the DAC or even a speaker. He doesn't go into detail, but does say that switching supposedly bit perfect digital sources can make a difference....

b)That even though he's a believer in measurements, he understands manufacturers who don't publish them. He says that no matter what you publish you are criticized, often by readers who don't understand what they are looking at;

c) a similar reaction to forum participation: he apparently doesn't enjoy the interaction with many (implies most) posters who aren't able to actually understand what he writes and then tell him why he's wrong. He mentions reaction to his use of negative feedback in products as one example, if I remember correctly.
 

March Audio

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He also says a few other interesting things in the interview:

a) that various forms of electrical/RF noise coming over a network source (streamer) or from a PC CAN influence the sound output of the DAC or even a speaker. He doesn't go into detail, but does say that switching supposedly bit perfect digital sources can make a difference....

b)That even though he's a believer in measurements, he understands manufacturers who don't publish them. He says that no matter what you publish you are criticized, often by readers who don't understand what they are looking at;

c) a similar reaction to forum participation: he apparently doesn't enjoy the interaction with many (implies most) posters who aren't able to actually understand what he writes and then tell him why he's wrong. He mentions reaction to his use of negative feedback in products as one example, if I remember correctly.

Well we already know this; the modern take on the ground loop is that "I hear computer noises, especially when I move my mouse......."

However that is mostly caused by the use of single ended RCA.

RF ingress can cause problems, but as usual the largest cause of these sort of allegedly audible differences is not the equipment of RF/electrical noise, its the listener.
 

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It's of course that , it helps market and indeed brand him and all the things he's involved in.

If a brand is too technical, nasty and digital, it can't be organic ! It can't be natural and we all know organic and natural sound best. Also audiophiles are quite narcissistic, it has to be all about them and all about their way if thinking , so you leave a bit of ambiguity so they can indulge their imagination.

Fair enough, Bruno is behind some great designs , we all want them to succeed as it's in the interest of high fidelity playback.

Exactly, BP is in the hi-fi business and I think that many forget that these are products that need to be sold. As long as they are SOTA I couldn't care less if Purifi add to technical sound arguments a bit of marketing sauce to sweeten the pill for subjectivists that believe in the secret sauce that can't be measured. At the end of the day the subjectivists crowd is 90% of the market, or maybe 99%, you can't plainly tell your customers that they are a bunch of idiots.
 

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He leaves room for subjectivist to wonder about some unmeasured distortion or some such when I don't think in his own mind there is anything to worry about. He even says in the interview there isn't any new information about amp behaviour he needs to consider with Purifi vs the earlier Hypex designs.

I am increasingly convinced that the abyss which separates objectivists and subjectivists stems from the fact that the former are unwilling to entertain the possibility that many people enjoy particular types of euphonic distortion and that the latter are unwilling to accept that the equipment they prefer doesn't measure well even though it sounds better to their ears. The mute talking to the deaf...

Then there's equipment interaction. Hi-fi playback is called a system for a reason.
 
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