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Review and Measurements of Purifi 1ET400A Amplifier

audioBliss

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So what I'm wondering is how this will sound compared to the nc400. When is performance so good that it doesn't matter anymore?
 

maty

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Because they are two very important values, which are usually hidden by manufacturers, especially the Hi-Fi or High-End.

In the audio forums there is an old controversy about the power cords and whether they affect or not. As usual on the Internet, everyone knows everything. It turns out that a PSRR > 90 dB guarantees that, if you have a terrible electrical supply like in my house, the amplifier will be immune to a large part of these problems.

If you also use a good and, unfortunately, expensive SMPS I can forget about the DC that swarms my grid.

That is why I am very interested in this module, because it promises a lot a priori.

It remains to be seen if these great specifications imply excellent sound. I already have it in my second system but I would like it to be much better and that it went beyond the deficiencies detected and that I do not think it can improve any more because of the design of the amplifier itself. 3D sound and, above all, sound planes when listening in the far field.

Now the music fills the room thanks to the great dispersion of my small coaxes but I lack the above. When you first listen to the sound plans, you do not forget it in your life! And I want it with SS and not with tubes.

- The End -
 

March Audio

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Purifi 1ET400A is the evolution of those two modules, the DIY and the OEM. It is logical to make the comparison to know what they have improved.

And I was not the first to compare with NC400.
Yes it's a logical comparison but you need to understand the particular specification and the implications of the numbers.

If PSRR was a problem you would see evidence in the output measurements. Both the units Amir has tested were powered by hypex smps and neither show issues in the measurements. The psu regulation and noise levels are very relevant to whether improved PSRR is required.

The final CMRR would have to be measured with the input buffer. The buffer would set the CMRR
 
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maty

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At the beginning of the nineties, when I lived in Barcelona (where I went to study and... ). Acoustically conditioned room, Avalon column speakers and tube amplifier (I did not notice).

In the Style Sound store, where I was treated incredibly well despite my youth. I guess now there are other people attending. https://stylesound.com/

The new generations of Spaniards are much less kind and solicitous. I guess it does not just happen here.
 

March Audio

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Because they are two very important values, which are usually hidden by manufacturers, especially the Hi-Fi or High-End.

In the audio forums there is an old controversy about the power cords and whether they affect or not. As usual on the Internet, everyone knows everything. It turns out that a PSRR > 90 dB guarantees that, if you have a terrible electrical supply like in my house, the amplifier will be immune to a large part of these problems.

If you also use a good and, unfortunately, expensive SMPS I can forget about the DC that swarms my grid.

That is why I am very interested in this module, because it promises a lot a priori.

It remains to be seen if these great specifications imply excellent sound. I already have it in my second system but I would like it to be much better and that it went beyond the deficiencies detected and that I do not think it can improve any more because of the design of the amplifier itself. 3D sound and, above all, sound planes when listening in the far field.

Now the music fills the room thanks to the great dispersion of my small coaxes but I lack the above. When you first listen to the sound plans, you do not forget it in your life! And I want it with SS and not with tubes.

- The End -

The power cord topic isn't really a controversy, it's just an audiophile delusion.

The psu regulation, noise levels and the amp PSRR will dictate immunity to external mains fluctuations.
 
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maty

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Off topic

orangejello and the presence/sound plans

https://www.audiosciencereview.com/...ements-of-benchmark-ahb2-amp.7628/post-190338

You can hear three distinct depths. There is the main orchestra and soloist at the first level. Then there is a small group of strings at the next level- maybe 20-30 feet back. The echo chamber instruments were placed at the third level WAY in the back of the church (which has a lot of reverberant energy). The effect is really interesting, and the engineers captured it very well. You hear the main orchestra and when they are silent or only the violin soloist is playing, you sometimes here this island of strings much further back at the second level. And when Vivaldi whats the full echo, you hear the third layer very far away. Subjectively it sound like they are almost one hundred feet back. They may well have been...


[Spanish] https://es.wikipedia.org/wiki/Plano_de_presencia_(sonido)

to English:

* https://translate.google.com/translate?hl=&sl=es&tl=en&u=https://es.wikipedia.org/wiki/Plano_de_presencia_(sonido)

* https://www.translatetheweb.com/?from=&to=en&dl=en&a=https://es.wikipedia.org/wiki/Plano_de_presencia_(sonido)#

- End off topic -
 

kn0ppers

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Hello. I would just like to suggest the following:

In no way do I want to tell anybody how to use this forum (in fact it's my first post here), but PLEASE CONSIDER USING SPOILERS for pictures not directly related to the tested product. This doesn't seem to be popular here, but in most forums I frequently use (which are at least 5 or so), using spoilers is a common thing and it makes for easier reading and a more convenient user-experience for everyone. (Edit: To clarify, I think it's great having pictures of the PCBs, but apart from that the main focus should be the graphs, not other amps...?!)

Regarding power cables for amps: I can see why you would want a cable with quality connectors and maybe even some nice sleeving for the looks or the wife-acceptance-factor, but apart from that I don't see why a power cord should cost any more than a couple bucks. Everything 3-figures-US/€ and above is just crazy to me.

My main question:

I think I recall the Interview with the Purifi guys stating that the modules will become available in this exact configuration tested here, a.k.a the Evaluation board for OEMs? I would like to see this confirmed or denied. If Bruno won't join us here, which I could totally understand, hopefully Amir can ask him about that.

Idea: Take the Purifi-Kit as shown here, desolder the XLR Inputs. Build the Putzey Volume Control from the G-Word paper (only the parts that I actually need, with some more sophisticated replacement for the dual-pot), then frankenstein it all together in a large case with plenty space and organize the resulting mess of cables. Would this work or am I totally missing something? I like volume control on my amps somehow, preferably in the same unit.
 
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audioBliss

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I have this with the nc400. 3D imaging is, imo, more to do with room acoustics, speakers, speaker placement and of course a very good recording. The most important is almost the recording because most of the time it's just not there. They just mix a wall of sound with low dynamics. But once you find a good recording with depth then everything else in my list there makes or breaks it. With a very good room these planes are very distinct. I've been in an insane room where you could get a 3D image that went from floor to ceiling and front and back with a psytrance track. It was very cool.

Edit: What do you hear in these recordings? ( warning for strange music :p)

Laurie Anderson - My Compensation
Pixel - Brown Shirt
Monolake - Ghosts
Pixel - Lion
Penta - Here We Come

In a good room with good speakers these should sound pretty interesting..
 
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FrantzM

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So what I'm wondering is how this will sound compared to the nc400. When is performance so good that it doesn't matter anymore?

I think we are near this. I remain on the fences when it comes to amplifiers and the way they may interact with the varying and difficult load that some speakers present.
The kind of performance provided by these modules however, could render the differences nil even in those loads. This won't stop audiophiles from hearing "vast" differences or the "planes of sound" to be .... whatever... and some background to be black-er etc ;)
 

PierreV

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Pixel - Brown Shirt

Ouch. That one will be a mandatory listen for all my friends when they visit me. Will let you know if they sue me for emotional damage.
 

audioBliss

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Ouch. That one will be a mandatory listen for all my friends when they visit me. Will let you know if they sue me for emotional damage.

Haha :D

Sorry if I'm way off topic here but there are also some interesting tracks from CoH and Hecq with out of phase noises and strong bass. "Ilpo Väisänen - Autioitu 1" and "Bazar Blå - Home" is also pretty fun for the bass.
 

Armand

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I would like so see a CMRR test too. The test is really easy to do on the APx555 as it has built in automatic switching of 10 ohm resistance on pin 2 and pin 3. This video shows how to do it on the APx555.
https://www.ap.com/technical-library/quick-tip-155-cmrr-iec/

Also, can you run a test at 20Hz with full power with only one channel to see if it is stable? Class D amplifiers have problems with "bus pumping" that will drive the rails up to too high levels and make the amp go into shutdown.
 

maty

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Laurie Anderson - My Compensation
Pixel - Brown Shirt
Monolake - Ghosts
Pixel - Lion
Penta - Here We Come

In a good room with good speakers these should sound pretty interesting..

I have to confess that I do not know who they are. I am very disconnected from the current productions of almost any type of music, I focus on recordings from old analog masters. The same thing happens to me with modern literary production, which for decades has ceased to interest me in general.

Obviously the room, its conditioning and the speakers matter a lot but the amplifier is very important too. I refer to those in which you can very easily appreciate the sound plans to which I referred and not only depth.

Recordings of that type do not abound, let alone today. Acoustic instrumentation, that is, small jazz groups or orchestras.

If I change the amplifier is to make a qualitative leap in quality, I say. As I usually listen in the near field, I have assumed the absence of depth and planes. But when I get excited about the recording I usually get up and go around the room, turning off the lights and usually directing the orchestra or singing with the choir. For me, sound must not only be spectacular, it must also excite me. And that rarely happens to me with the current recordings.
 
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Frank Dernie

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When is performance so good that it doesn't matter anymore?
Good question.
When I started in hifi we had very coloured light paper coned speakers which were quite efficient and 15 watt amps, if we were lucky. Then we got heavier plastic coned speakers with better damping, far less colouration but awful efficiency and a 30 watt amp was powerful, and the mega powerful 80 watts, the first Krell was 50 watts iirc.
Now we have amps which will be only using a small amount of their available power most of the time but able to deliver the peaks we missed back then. I have efficient speakers and 1000 watt amps, so the full dynamics of an orchestral recording are theoretically available to me at home.
What I find difficult to believe here is that the Purifi is in any meaningful way better than the ncore as an audio amp. The point where it starts being better than the earlier ncore is at such a high power it will, in my estimation, only be running there on the occasional peak. The ncore is already orders of magnitude lower in distortion than any speaker it will drive so I would be gobsmacked if there would be any audible difference, admirable though the engineering may well be.
A bit like DACs.
 

Bruno Putzeys

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Hi all,

Just checking in!

First off, mega thanks Amir for doing this review. And more generally for running this forum. It is enormously heartening to see someone working to collect actual data for a substantive technical discussion and comparison between products. It's even more heartening to see that indeed, substantive discussion ensues.

Amir mentioned I'd be saying something about the high-frequency IMD results. Let's start by explaining why I prefer to measure distortion strictly inside the audio band. There is an ongoing controversy about whether signals above 20kHz might or might not be audible, but what is not controversial is that signals below 20kHz are much, much more audible than signals above 20kHz. So if you are in a situation where you have to choose between optimizing performance below 20kHz or above 20kHz, you go for optimizing the bit that we are most likely to hear. Even high-res enthusiasts seem to have tacitly accepted this a long time ago. Remember DSD? A DSD AD/DA converter that, when measured over 20kHz, would easily clock a SINAD of 120dB would "degrade" to 50dB as soon as you upped the measurement bandwidth to 40kHz. But what you heard was of course 120dB, the rest was for the bats. Note the delicious irony. DSD was hawked on the grounds that you needed >20kHz bandwidth for high fidelity, while its skyrocketing supersonic noise floor was excused on the grounds that it was inaudible. As it is, DSD is perfectly listenable. I can find no more eloquent argument that the ear is not very sensitive above 20kHz than DSD...

Anyhow, this is why I like to test amplifiers with test signals that in themselves would be audible (i.e. fit below 20kHz) and also read the distortion and noise only in the band below 20kHz. Of course, I know perfectly well that if you then do a THD versus frequency sweep, any readings above 10kHz are meaningless because even the second harmonic will be outside the audio band. But as our sensitivity to those harmonics drops off rather quickly around 20kHz (as does the ability of most speakers to reproduce them), it's fair to conclude that they do not say much about sound. On the other hand, we can't just go ignoring any underlying non-linearity. We still need to test for misbehaviour at high frequencies. If you choose to limit measurement bandwidth to 20kHz you have to include something like the 19kHz + 20kHz test. I didn't invent that procedure btw, I got that from Bruce Hofer at AP who recommends it. In fact his version is even neater, he uses 19.5kHz and 18.5kHz, making sure that even order products sit at even multiples of 500Hz (from 1kHz upward) while odd products sit at odd multiples of 500Hz, from 17.5kHz down, potentially fitting 37 distinct IMD products inside the band. This refinement doesn't make much difference with the 1ET400 amp of course since there aren't that many IMD products poking up over the noise floor.

Given the choice between a sinewave test at 20kHz which only produces inaudible products and a two-tone test that produces all kinds of in-band distortion I go for the latter. By implication, we should be designing a control loop that maximises loop gain all the way up to 20kHz, but not beyond. Any control system obeys a law called the Bode Inequality. This is the closest we control theorists have to mass-energy conservation. In the case of a class D amplifier it implies that if you maximise loop gain over a largeish fraction of the switching frequency you'll have to take it down really fast afterwards. So that's why the wideband THD vs frequency plot goes up somewhat suddenly at the end. It's a compromise I'm knowingly making. Consider the alternative: I could instead pander to the bat-eared crowd and choose to minimise harmonic distortion components up to 40kHz, say. That would mean accepting a lot less loop gain below 20kHz and hence higher distortion in the audible frequency range. It's not a good tradeoff.

Anyhow, this should explain why the high-frequency IMD spectrum is so much cleaner than a wideband THD test would lead you to expect. But as I see it, the former is the one that is most likely to have a meaningful correlation to sound.

(While I'm at it I ought to point out that the idle noise is noise shaped. This is visible on the broadband noise plots where you can clearly see the rise after 20kHz. The extra outband noise is caused by the comparator and driver chips and ends up being noise shaped by the control loop. I only wanted to mention that because the wideband THD vs F plots are mostly swamped by this HF noise which bore some explaining.)

In vindication of that POV we've now seen more than one enthousiastic "subjective" reviews of the 1ET400A go up expressing delight that we have both great measurements and great sound (as if that were a contradiction). I'd like to state here that in our company, as listeners we are fanatic about sound and as engineers we are fanatic about measured results. The trick is to pick a set of measurements that have a modicum of relevance to psychoacoustics (in the case of amplifiers, accepting that hearing goes south beyond 20kHz and that music is more than sinewaves). Once we get the lab result that we expected, we go and listen carefully to make sure we're not missing anything. That's rarely the case so the next stage (playing great music and breaking open beers) tends to follow quickly afterwards.

Oops that's another page long post. I was wondering if I could ask for a favour. I have a proclivity to spending lots of time on very detailed answers but there's other work on my plate too. So what I'd like to do is sign off for something like a week and then sift through any items that come in during that period. So let's have all your questions and round about next weekend the two of us here will go through them.

Cheers,

B.
 

phoenixdogfan

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Hi all,

Just checking in!

First off, mega thanks Amir for doing this review. And more generally for running this forum. It is enormously heartening to see someone working to collect actual data for a substantive technical discussion and comparison between products. It's even more heartening to see that indeed, substantive discussion ensues.

Amir mentioned I'd be saying something about the high-frequency IMD results. Let's start by explaining why I prefer to measure distortion strictly inside the audio band. There is an ongoing controversy about whether signals above 20kHz might or might not be audible, but what is not controversial is that signals below 20kHz are much, much more audible than signals above 20kHz. So if you are in a situation where you have to choose between optimizing performance below 20kHz or above 20kHz, you go for optimizing the bit that we are most likely to hear. Even high-res enthusiasts seem to have tacitly accepted this a long time ago. Remember DSD? A DSD AD/DA converter that, when measured over 20kHz, would easily clock a SINAD of 120dB would "degrade" to 50dB as soon as you upped the measurement bandwidth to 40kHz. But what you heard was of course 120dB, the rest was for the bats. Note the delicious irony. DSD was hawked on the grounds that you needed >20kHz bandwidth for high fidelity, while its skyrocketing supersonic noise floor was excused on the grounds that it was inaudible. As it is, DSD is perfectly listenable. I can find no more eloquent argument that the ear is not very sensitive above 20kHz than DSD...

Anyhow, this is why I like to test amplifiers with test signals that in themselves would be audible (i.e. fit below 20kHz) and also read the distortion and noise only in the band below 20kHz. Of course, I know perfectly well that if you then do a THD versus frequency sweep, any readings above 10kHz are meaningless because even the second harmonic will be outside the audio band. But as our sensitivity to those harmonics drops off rather quickly around 20kHz (as does the ability of most speakers to reproduce them), it's fair to conclude that they do not say much about sound. On the other hand, we can't just go ignoring any underlying non-linearity. We still need to test for misbehaviour at high frequencies. If you choose to limit measurement bandwidth to 20kHz you have to include something like the 19kHz + 20kHz test. I didn't invent that procedure btw, I got that from Bruce Hofer at AP who recommends it. In fact his version is even neater, he uses 19.5kHz and 18.5kHz, making sure that even order products sit at even multiples of 500Hz (from 1kHz upward) while odd products sit at odd multiples of 500Hz, from 17.5kHz down, potentially fitting 37 distinct IMD products inside the band. This refinement doesn't make much difference with the 1ET400 amp of course since there aren't that many IMD products poking up over the noise floor.

Given the choice between a sinewave test at 20kHz which only produces inaudible products and a two-tone test that produces all kinds of in-band distortion I go for the latter. By implication, we should be designing a control loop that maximises loop gain all the way up to 20kHz, but not beyond. Any control system obeys a law called the Bode Inequality. This is the closest we control theorists have to mass-energy conservation. In the case of a class D amplifier it implies that if you maximise loop gain over a largeish fraction of the switching frequency you'll have to take it down really fast afterwards. So that's why the wideband THD vs frequency plot goes up somewhat suddenly at the end. It's a compromise I'm knowingly making. Consider the alternative: I could instead pander to the bat-eared crowd and choose to minimise harmonic distortion components up to 40kHz, say. That would mean accepting a lot less loop gain below 20kHz and hence higher distortion in the audible frequency range. It's not a good tradeoff.

Anyhow, this should explain why the high-frequency IMD spectrum is so much cleaner than a wideband THD test would lead you to expect. But as I see it, the former is the one that is most likely to have a meaningful correlation to sound.

(While I'm at it I ought to point out that the idle noise is noise shaped. This is visible on the broadband noise plots where you can clearly see the rise after 20kHz. The extra outband noise is caused by the comparator and driver chips and ends up being noise shaped by the control loop. I only wanted to mention that because the wideband THD vs F plots are mostly swamped by this HF noise which bore some explaining.)

In vindication of that POV we've now seen more than one enthousiastic "subjective" reviews of the 1ET400A go up expressing delight that we have both great measurements and great sound (as if that were a contradiction). I'd like to state here that in our company, as listeners we are fanatic about sound and as engineers we are fanatic about measured results. The trick is to pick a set of measurements that have a modicum of relevance to psychoacoustics (in the case of amplifiers, accepting that hearing goes south beyond 20kHz and that music is more than sinewaves). Once we get the lab result that we expected, we go and listen carefully to make sure we're not missing anything. That's rarely the case so the next stage (playing great music and breaking open beers) tends to follow quickly afterwards.

Oops that's another page long post. I was wondering if I could ask for a favour. I have a proclivity to spending lots of time on very detailed answers but there's other work on my plate too. So what I'd like to do is sign off for something like a week and then sift through any items that come in during that period. So let's have all your questions and round about next weekend the two of us here will go through them.

Cheers,

B.
Bruno. I currently have an SMPS1200 and two Ncore 400 modules on order to go into a Ghent case. When the Purifi modules become available, is there any way you could include instruction and a wiring harness to connect it to that SMPS1200 if I just want to swap out your modules for my NC400s.
 
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boXem | audio

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... in the case of amplifiers, accepting that hearing goes south beyond 20kHz and that music is more than sinewaves...
About correlation between sinewaves and music, we see more and more the 32 tones test (32 sines equally spaced on log scale from 20Hz to 20 kHz).
From an instinctive standpoint, it looks like being closer to a musical signal than 1 or 2 sines. Is the instinct not to be trusted in this case?
 
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