Review and Measurements of Hypex NC400 DIY Amp

[anphex]

As I stated, the second article (This Thing We Have About Hysteresis Distortion) goes into the technical details of hysteresis and outlines measurements for showing the effect of it. Is that not objective evidence for you?

Do you disagree with Bruno's research and conclusion regarding hysteresis distortion? If so, I look forward to you presenting your counter argument and appropriate objective evidence to the contrary.

If believe you, and I don't think you want to ruin the NC400 for us, just stating an interesting piece of information. But unless I have a clear lead that switching to Purifi would mean a great audible upgrade I'll stick to my NC400 for a while. The market release of the NC400 is about 10 years ago if I remember correctly, so I wouldn't be surprised if Purifi with it's much more recent design by the person who made nc400 would reside a few floors higher on the performance ladder. But if it means getting from the 150th floor to the 160th I don't care, specially since the market average is about the 75th floor.

Maybe, only maybe, if there'd be a noob friendly DIY Kit of Purify I would be inclided to try it out. I don't really understand why Purifi doesn't go through the effort to make a dedicated case for EVAL1 and EVAL2 and sell the as a kit. Considering the success for NC400 since Amir measured those stellar results.

 

[Feyire]

"very much audible" and "nasty" is not a very accurate representation of this problem.

For myself, and other owners who complained of this issue - it absolutely is. There is nothing worse than being unsatisfied with the sound of your system.

Quoting Bruno once again:

Left to its own, hysteresis produces a recognisable grainy texture in the sound, a blanket of fuzz that always stays just this side of audible, taunting and infuriating like an itch you can’t scratch.

Not sure how you interpret this, but that sounds nasty to me - not something I want in my system.

In general nCore sounds great, and no one comparing either of these three amplifier modules blind would be able to say "oh, there's the nasty one" when listening to the ncore.

Note that this issue bothered me so much, that I went ahead and modded my NC400 in order to resolve it - the alternative was to sell them and try something else (e.g. Purifi).

I'm sure there are lots of owners out there who do not hear this issue and I'm certainly happy for them, but in my case, it was audible and very annoying. I wouldn't be surprised if the transparency/quality of your overall audio system is important here. I have very good speakers and an objectively near-perfect DAC. Perhaps a less transparent/quality system will not reveal this flaw as clearly audible, but this is just conjecture on my part.

 

[Julf]

For myself, and other owners who complained of this issue - it absolutely is. There is nothing worse than being unsatisfied with the sound of your system.

That dissatisfaction might be because of a real audible shortcoming, or just a belief/knowledge that something else is possibly better...

Note that this issue bothered me so much, that I went ahead and modded my NC400 in order to resolve it

In what way did you modify your NC400?

I wouldn't be surprised if the transparency/quality of your overall audio system is important here. I have very good speakers and an objectively near-perfect DAC. Perhaps a less transparent/quality system will not reveal this flaw as clearly audible, but this is just conjecture on my part.

Ah, the classic "maybe your system is not resolving enough"....

 

[Colonel7]

For myself, and other owners who complained of this issue - it absolutely is. There is nothing worse than being unsatisfied with the sound of your system.

Quoting Bruno once again:
Not sure how you interpret this, but that sounds nasty to me - not something I want in my system.

Note that this issue bothered me so much, that I went ahead and modded my NC400 in order to resolve it - the alternative was to sell them and try something else (e.g. Purifi).

I'm sure there are lots of owners out there who do not hear this issue and I'm certainly happy for them, but in my case, it was audible and very annoying. I wouldn't be surprised if the transparency/quality of your overall audio system is important here. I have very good speakers and an objectively near-perfect DAC. Perhaps a less transparent/quality system will not reveal this flaw as clearly audible, but this is just conjecture on my part.

Sorry but that's not what you wrote to lead off your thread on it. You never measured before or after, you're making an appeal to authority from the designer who is on the PR trail for the successor product, and you are using the whole meme of your incredible ears and resolving system. Audible "Granularity? Your proof is "people say". Below is what you wrote.

"have recently spent a lot of time researching various possible NC400 DIY modifications, for the purpose of improving the listening experience with my amplifiers, but also having some classic DIY fun."

 

[boXem]

Seems we have different definitions of "objective evidence". I think the right description of what you are presenting is "appeal to authority".

Not even. Just "inability to read more than 10 lines in a raw".
BP states that hysteresis distortion is solved by post filter feedback and that as a consequence all class d amplifiers with post filter feedback solve it.
@Feyire has his own thread about his NC400 mods (among them directional fuses...) where he repeats the same kind of bs. Good luck with this, I stopped trying.

 

[JohnYang1997]

For myself, and other owners who complained of this issue - it absolutely is. There is nothing worse than being unsatisfied with the sound of your system.

Quoting Bruno once again:
Not sure how you interpret this, but that sounds nasty to me - not something I want in my system.

Note that this issue bothered me so much, that I went ahead and modded my NC400 in order to resolve it - the alternative was to sell them and try something else (e.g. Purifi).

I'm sure there are lots of owners out there who do not hear this issue and I'm certainly happy for them, but in my case, it was audible and very annoying. I wouldn't be surprised if the transparency/quality of your overall audio system is important here. I have very good speakers and an objectively near-perfect DAC. Perhaps a less transparent/quality system will not reveal this flaw as clearly audible, but this is just conjecture on my part.

The effect itself can be nasty potentially. However it's easily proven to not be the case in practice in these amplifiers.

There's no feedback technology can correct distortion more than the loop gain. As stated 1et400a has more than 70dB loop gain at all 20-20khz range. In output impedance test, it shows the loop gain is not much higher in lower frequencies.

nCore and UcD use essentially the same technology as purifi which is phase shift self oscillating with full post filter feedback. As some of us have simulated and shown by Bruno himself the loop gain is 60-65dB in the audio band. So Purifi does not provide much higher loop gain hence correction is in the difference of 10dB. The effect wouldn't be so different in Purifi, nCore and UcD.

If this doesn't prove it, if the effect is so nasty that 60dB loop gain does not corrects it, all non post filter feedback class D will become straight up unlistenable. This is however not true. With a good quality inductor the distortion can be in the range of 0.0002-0.0005% depending on current.

Also to address the elephant in the room. Any effect that's audible will show up in the measurements. As simply demonstrated by all the measurements performed, there's no audible issue with any of them. A nasty effect will show up as distortion higher than 1%.

 

[EB1000]

Sorry, but maybe I'm missing the point here (I have the DIY NC400 monoblocks driving Focal Aria 936), what hysteresis distortion?

THD+N remains below 0.01% up to 200W @4 Ohms for the stereo pair. With the monobloks using separate PSUs, the amp can reach 180W @ 8 Ohms w/o crossing the 0.05% THD threshold. No speaker can have <0.01% distortion, and no human can hear anything below 0.1% distortion, so I don't see the hysteresis distortion an issue for any scenario. The way I see it, there is really no need for the Purifi, at least not at it's current revision. I'd consider upgrading Hypex to Purifi, only if it will come as a full bridge topology instead of an half bridge, and the max switching frequency will be increased to at least 750kHz...

 

[Feyire]

You never measured before or after

That's correct, because I don't have the appropriate measuring equipment, which I also clearly stated in that previous thread. I am also open to having my unit measured (but don't want to ship overseas).

You're making an appeal to authority from the designer

So you don't think it is relevant to listen to the designer of these amplifiers, and what he has to say about them? So who/what do we fall back on then? Who could possibly be more credentialed to talk about this kind of issue affecting the amplifier?

who is on the PR trail for the successor product

Are you insinuating that Bruno is overstating the relevance and audibility of this issue in regards to the NCOREs, in order to sell more Purifi amplifiers? That is quite the accusation if so.

and you are using the whole meme of your incredible ears and resolving system. Audible "Granularity? Your proof is "people say".

I stated that was simply conjecture. Doesn't change the fact that I had an audible issue, found an explanation and reasoning for it from the designer himself and then proceeded to resolve it in my own way. Hysteresis is a problem, it's real, and in my system it was audible.

 

[Julf]

So you don't think it is relevant to listen to the designer of these amplifiers, and what he has to say about them? So who/what do we fall back on then? Who could possibly be more credentialed to talk about this kind of issue affecting the amplifier?

It is relevant, but not objective. Something doesn't become truth just because Bruno says so.

Are you insinuating that Bruno is overstating the relevance and audibility of this issue in regards to the NCOREs, in order to sell more Purifi amplifiers? That is quite the accusation if so.

I hold Bruno in very high regard as a designer and engineer, and also respect his integrity - but we often fall in the trap of hearing an improvement just because we believe there should be one.

One of my favorite quotes comes from Oliver Cromwell of all people: "I beseech you, in the bowels of Christ, think it possible you may be mistaken."

That is (or should be) the guiding principle of every scientist and engineer - "Is what I think I see or hear really what is going on, or am I deceiving myself? How can I verify the result objectively?".

Hysteresis is a problem, it's real, and in my system it was audible.

That is what you say, but without detailed double-blind ABX logs, there is no way to tell.

 

[Feyire]

Also to address the elephant in the room. Any effect that's audible will show up in the measurements. As simply demonstrated by all the measurements performed, there's no audible issue with any of them. A nasty effect will show up as distortion higher than 1%.

I'd agree with you that if it is audible, it should show up in measurements. However, for me, the elephant in the room is why doesn't this effect show up in the measurements, but does get audibly noticed by some? This is what I'd really like to understand. We know that every NCORE amplifier has the same inductor, so what other variable is causing the issue to be audible (or not) for some people?

I have experienced it within my system and the designer of the amplifiers confirms it is audible. So, how does it go unnoticed in the measurements done here at ASR? Perhaps the set of measurements currently done here, cannot convey the true nature of this particular problem?

 

[Julf]

I'd agree with you that if it is audible, it should show up in measurements. However, for me, the elephant in the room is why doesn't this effect show up in the measurements, but does get audibly noticed by some?

The real elephant in the room is that we all believe we hear differences even when there are none. Can you believe your ears?

 

[Colonel7]

That's correct, because I don't have the appropriate measuring equipment, which I also clearly stated in that previous thread.

Get some. You don't need very expensive equipment to do it. Rick Sykora offered to help you out. Something tells me a year from now you still won't have it.

And your rhetorical appeal to authority questions are just hearsay as to proven audibility. You can't even prove your tweaks don't measure worse, nevermind whether they're audible. Purifi does measure better than Ncore but as to audibility I don't believe Bruno's PR and journalist paraphrases anymore than I believe Revel's PR that the Beryllium speaker line is far superior to the F line or Salons.

 

[Feyire]

It is relevant, but not objective. Something doesn't become truth just because Bruno says so.

I hold Bruno in very high regard as a designer and engineer, and also respect his integrity - but we often fall in the trap of hearing an improvement just because we believe there should be one.

So you believe that Bruno started his investigation into the reported "granularity" of the sound from the amplifiers on a false premise, and came to wrong conclusion that the cause was an audible issue due to hysteresis?

Bruno did his research, documented it in various articles and provided objective evidence in the form of measurements, showing the effect of hysteresis. Since you continue to disagree with the conclusions, it is now on you to provide your own research and objective evidence to refute this.

 

[JohnYang1997]

So you believe that Bruno started his investigation into the reported "granularity" of the sound from the amplifiers on a false premise, and came to wrong conclusion that the cause was an audible issue due to hysteresis?

Bruno did his research, documented it in various articles and provided objective evidence in the form of measurements, showing the effect of hysteresis. Since you continue to disagree with the conclusions, it is now on you to provide your own research and objective evidence to refute this.

His comments includes all of his amplifiers, from UcD to Purifi. Read the two paper he put in the page. They are from 2005 and 2009.
Don't put his name in front all of your statements. It's solely your incapability of understanding what he actually said.

 

[Feyire]

His comments includes all of his amplifiers, from UcD to Purifi. Read the two paper he put in the page. They are from 2009.
Don't put his name in front all of your statements. It's solely your incapability of understanding what he actually said.

Can you please provide me with a link to the specific paper(s) you are referring to?

 

[JohnYang1997]

Can you please provide me with a link to the specific paper(s) you are referring to?

You provided the link. Do you even read what you post?

 

[Feyire]

You provided the link. Do you even read what you post?

I want to be sure we're talking about the same document, in order to avoid any confusion.

So are you referring to the "Globally Modulated Self-Oscillating Amplifier with Improved Linearity" paper from 2009?

 

[Honken]

@Feyire Do you have any material where the granularity is easier to pick up?

 

[Feyire]

His comments includes all of his amplifiers, from UcD to Purifi. Read the two paper he put in the page. They are from 2005 and 2009.
Don't put his name in front all of your statements. It's solely your incapability of understanding what he actually said.

Ok, so please help and guide me then. What exactly is it that I'm not understanding, that is so obvious to you?

Here's a previous quote from @boXem | audio, from another thread on the same topic. Is this the same point that you are trying to make @JohnYang1997?

The flaws from iron core inductors are corrected by post filter feedback, not by replacing them by EM antennas. This is valid for UcD, Ncore, Eigentakt and a few others. So these flaws cannot be heard since they are already corrected with these amplifers.

My understanding from the audioexpress article and Purifi articles was that this issue was only resolved in the updated Purifi (i.e. Eigentakt) feedback design, and that UcD and NCORE remained flawed.

Note that the investigation into this issue began based on complaints from NCORE owners. So if the current NCORE feedback design from 10 years ago already solves this issue as claimed above, then why did these people make these complaints and why was the conclusion from the designer that it was due to audible hysteresis distortion?

 

[boXem]

the conclusion from the designer that it was due to audible hysteresis distortion?

Again. Where and when did BP himself make such a statement?