Hypex NC400 - DIY Mods

[boXem]

 

[sq225917]

The resistor delete makes sense in your setup, Bruno didn't do it because super high output level dacs weren't a thing back when the ncores and prior hypex amps were being developed. That's a win.

The capacitors COULD be a win, but only measurement of just that mod alone will prove that beyond doubt. I've done the same in phonostage riaa caps before for a truly tiny improvement in self noise.

I'm less inclined to believe in the inductor.

And your wires still need to be twisted, without any doubt.

 

[Feyire]

The resistor delete makes sense in your setup, Bruno didn't do it because super high output level dacs weren't a thing back when the ncores and prior hypex amps were being developed. That's a win.

Yes indeed, I'm definitely glad that removing the resistor was an easy and quick option for me . Also great for those who have sensitive speakers, and need to get that amplifier gain down.

The capacitors COULD be a win, but only measurement of just that mod alone will prove that beyond doubt. I've done the same in phonostage riaa caps before for a truly tiny improvement in self noise.

As I stated previously, I'm open to measurements, but I simply don't have the appropriate equipment. I don't want to ship my amplifiers oversees to be measured, but if someone living in my country (or nearby) was curious and willing to come by and measure them, I'd welcome that.

I'm less inclined to believe in the inductor.

Care to elaborate further on your thoughts/concerns? EMI/EMC has been brought up previously, and that is a legitimate issue, but I haven't experienced any issue because of it (i.e. the sound from the amplifiers is great).

And your wires still need to be twisted, without any doubt.

I suppose the only answer for this is also - measurements!

 

[Rick Sykora]

This was indeed case for me, as I was using the digital volume control in my DAC and typical listening levels meant attenuating between -20dB to -40dB.

Perhaps, but that is unnecessary in my case, as I already have a DAC with an exceptionally low noise floor. You'd need an equally reference level pre-amp to match the objective performance and I'd rather spend my money elsewhere (such as for mods! ).

While on the topic of mods and for those interested, another quick and easy one is to upgrade any fuses. In the case of the NC400 DIY kit, there is 2 fuses, 1 in the IEC connector and 1 in the power supply. Note that in my case, I replaced the stock IEC connector and the new one does not have a fuse anymore.

In the image below, I replaced the stock ceramic fuse (8A slow blow) in the SMPS600N400 power supplies with an equivalent one from HiFi-Tuning (in my case the Supreme 3 Silver Fuse). Note that this fuse is directional, meaning that the arrow on the body of the fuse needs to point in the direction of conventional current flow as shown below. If you place it the other way around, it just won't sound right (strange eh?).

Safety note: Replacing a fuse can be dangerous if you don't know what you are doing. Always ensure that you disconnect all power from your amplifier (i.e. Don't just use the off switch if there is one), but completely unplug all power cables and let the module rest/cool off if it had been switched on previously, before attempting to do anything. As previously stated for the other mods, attempt at your own risk and be aware that your warranty may be void.


View attachment 140927

While I can appreciate making mods based on solid research, what made you think that removing the mains fuse would have an audible improvement (and so much so that you are willing to forgo the risk of potential shock/electrocution)?

You started this post with stating how much you researched and you stated some references earlier, but appears to get less and less fact based as it goes forward. Can you please share more of the science behind each mod? Thanks!

 

[Feyire]

While I can appreciate making mods based on solid research, what made you think that removing the mains fuse would have an audible improvement (and so much so that you are willing to forgo the risk of potential shock/electrocution)?

I was motivated to try a fuse replacement/upgrade, based on the experience and reports of others who have previously done so on other forums. That's part of the magic of DIY, is to try and experiment with new things and explore different perspectives, even if at first you don't think it will make any difference. You don't know for sure, unless you try it for yourself, and success or failure is part of the journey.

As I stated previously, what did make an audible difference/improvement for me with the new fuse in place in the SMPS, was its directionality. The sound was better/improved inserted one way (direction of conventional current flow), vs placing it the other way (direction of electron flow). Unfortunately, I don't have any well researched conclusion as to why I perceive this subjective sound difference with the new fuse. Additionally, my better half (she's a natural sceptic whenever I claim to hear any difference with mods) also agreed the sound was different with the fuse switched in direction. Her conclusion agreed with mine, in that the sound was better with the fuse's arrow placed in the direction of conventional current flow.

Below is a brief overview I found from another site offering some insights on the particular replacement fuse I purchased:

Ordinary fuses consist of a glass tube, with on either end small steel caps with a layer of nickel over it. Neither of these parts are ideal. The ideal fuse for audio has to start with a ceramic body, in which should be mounted a silver fuse wire. This wire is connected to end caps made from pure silver, that was covered with copper first, then gold plated. To top things off, all fuses are then demagnetized and cryogen treated for even better conductivity, and less distortion and noise.

Fuses always carry a high current that easily evokes metal fatigue. This causes a degradation of the conducting properties of the fuse wire, thus resulting in a degradation of the equipment in which this fuse was mounted. The HiFi Tuning fuses will have up to 90% less losses than prescribed by the IEC. The HiFi-Tuning fuses are 24 carat gold plated. On one hand, many fuses contain a spiralised fuse wire, that causes a high resistance and inductance. On the other hand, we have the HiFi-Tuning fuses that contain a straight fuse wire made from pure silver. This results in a very low resistance and a negligible inductance.

Is that enough to explain possible audible differences? Probably not, so depending on what you believe and if you are curious, all there is left is to try it for yourself and/or pull out the measuring equipment.

You started this post with stating how much you researched and you stated some references earlier, but appears to get less and less fact based as it goes forward. Can you please share more of the science behind each mod? Thanks!

Is there anything specifically about the original mods that you disagree with?

Perhaps you'll be interested in knowing that Bruno also modded the NC1200 LC filter (amongst other things) for his implementation in the Mola Mola Kaluga amplifier. We know that the stock NC1200 measures exceptional well, so why did he bother using different output capacitors? Maybe, just maybe, these modifications actually make a difference.

The audio circuitry is trimmed to the bare bones and board-to-board connectors are eliminated in favour of soldering star-quad cables directly into the circuit board for the cleanest, lowest impedance connection possible. The input stage is implemented on a separate circuit board that uses the same discrete buffers as those found in the Makua. The output filter sports monolithic capacitors whose dielectric stability is reflected in an impressively neutral and poised rendition.

I have highlighted two statements here.

In the first statement, they state that output cables from the amplifier module are directly soldered to the board, and not using standard connectors as is the case in the stock NC1200. That's interesting, because that is exactly what I do as well with my NC400. If you look the pictures I share from my final mod implementation, notice how I removed the gold plated brass output bridge, and I soldered the output cables directly to the NC400 board.

In the second statement, they state they replaced the original output capacitors in the NC1200 with monolithic ones that have better dielectric stability (i.e. lower dielectric loss). This is also one of the reasons why I replaced the output capacitors on my NC400 with the polypropylene capacitors from WIMA, because polypropylene has a lower dielectric loss than the standard polyester capacitors. It all makes a difference.

 

[Feyire]

Here's another reason to use better output capacitors with lower dielectric loss. Information taken from the NC400 data sheet.

I'm sure some people will jump in saying they can't hear anything above 15kHz anymore, so why should it matter? Well, it matters for those who can.

 

[Honken]

Hm, what do Hypex mean with a "full-power bandwidth" signal? Is it realistic outside of sine sweeps to get content at 15kHz and above at full power?

Personally, I wouldn't mind lowering the gain of my NC400s as I'm usually in the -30 region of my DAC, but I'd rather not do that through soldering.

 

[Feyire]

Personally, I wouldn't mind lowering the gain of my NC400s as I'm usually in the -30 region of my DAC, but I'd rather not do that through soldering.

In the simplest case, all that needs to be done is to remove SMD resistor r141 in order to achieve the lowest gain. Given the amount you are attenuating by, this is the way to go. If you know someone who is experienced with electronics repairs, perhaps ask them and see if they can do it. Visiting a dedicated repair shop or similar is also an option.

Alternatively, placing a preamp between the DAC and NC400 is the only other option I can think of. However, you need to be very careful with your selection of preamp, because you want it to have better or at least equal measured performance compared to your DAC and NC400, as otherwise you'd degrade the objective performance of your current system (perhaps even audibly).

 

[Rick Sykora]

I second your and add an !

This thread is a case study of how internet lore is too often used as justification for ignoring known engineering science. It is so alarming and disturbing, that I will simply repeat this…


WARNING: This thread contains information about practices or circumstances that may lead to personal injury or death, property damage, or economic loss. If you are not experienced with electrical safety practices, please do not attempt to modify your equipment.

 

[Feyire]

I second your and add an !

This thread is a case study of how internet lore is too often used as justification for ignoring known engineering science. It is so alarming and disturbing, that I will simply repeat this…

I think you are being overly dramatic. What would happen if you actually visited a dedicated DIY electronics forum. Perhaps call the electronics police in a panic at everything that people are experimenting with? Please be aware that the usual warnings (at your own risk, may void warranty etc..) was one of the first things I noted in my original post and our vigilant moderators then added any additional warning they deemed appropriate.

Back to the topic at hand, please feel free to refute the NC400 modifications I have presented. I see from your signature that you have made various custom Hypex amplifier builds? If there is a NC400 among those builds, why don't you try some of the modifications I mentioned? What better way to prove me wrong, or perhaps you'll be pleasantly surprised with the results? You won't know, until you try . Perhaps you also have precision measuring equipment?

 

[Rick Sykora]

Many ASR members are more than capable of judging the merits each of your claims, so I am not inclined to spend more time validating or refuting them. For the few that are not as technically astute, the posted thread warning addresses that concern.

Am not sure of your credentials, but your claims do not pass good engineering practice for me. Within my engineering experience, we would say “just because you can make a change, does not mean you should”. It may be that the change is a poor return on investment, would take too long to make, or negatively affects quality or safety. Many of your mods are questionable return on investment IMO. However, as you decided to haphazardly removed your case fuse, you do not demonstrate the technical discipline to know when your posts pose safety risks to yourself or others. The moderators asked you to add warnings and when those fell short, felt sufficiently motivated to add their own. If you can be objective, their action is cause for some introspection.

ASR is not about being like other forums as you seem to acknowledge. There is a greater need to demonstrate scientific proof and objectivity here. Several reputable members have questioned your claims and you continue to fail to provide credible proof. The burden is on you to show scientific credibility. DIY experimentation is supported on ASR but scientific scrutiny is part of it. Expect nothing less!

 

[Feyire]

Am not sure of your credentials, but your claims do not pass good engineering practice for me. Within my engineering experience, we would say “just because you can make a change, does not mean you should”. It may be that the change is a poor return on investment, would take too long to make, or negatively affects quality or safety. Many of your mods are questionable return on investment IMO.

The reason why I began my investigation into these modifications, is because I was not fully satisfied with the sound from my NC400s. In the end, it came down to two options, sell them and try something else, or try to modify them. As previously referenced in the thread, the designer of the NCORE modules himself acknowledged and clearly stated that the use of an iron core inductor was the source of an audible flaw - that definitely caught my attention (i.e. was this what was contributing to my displeasure with the sound?). If that is not reason enough to explore options for making changes, then I don't know what is. If an NCORE owner is happy to live with a sonically flawed product, that's fine, but not for me and I'm sure other owners will feel the same. As for the unaware, perhaps ignorance is bliss.

Note that I bought the NC400, because of the technical review on this forum. The measurements provided evidence that this was a near perfect amplifier (relative to amplifiers that were previously measured at the time). Yet this acknowledged sonic flaw, did now show up in any of the current measurements. I wouldn't have bought the NC400 if I had known this previously - would you? To me it seems like nobody here seems to care about this at all? As subjectivists, shouldn't we be all over this, diving deep and trying to figure out how we can measure and quantify this flaw?

You also make it sound like I have some nefarious motive, as if I wish for people to unnecessarily damage their amplifiers or something, nothing could be further from the truth. I offer an alternative solution to a known flaw, along with a few other extra modifications, for those interested in pursuing further enhancements. I'm very happy with the modifications to my amplifier, it sounds fantastic. All I want to do is share that same happiness with others who are interested in going that extra step.

ASR is not about being like other forums as you seem to acknowledge. There is a greater need to demonstrate scientific proof and objectivity here. Several reputable members have questioned your claims and you continue to fail to provide credible proof. The burden is on you to show scientific credibility. DIY experimentation is supported on ASR but scientific scrutiny is part of it. Expect nothing less!

I apologise for not being able to afford an APx555B.

 

[boXem]

The reason why I began my investigation into these modifications, is because I was not fully satisfied with the sound from my NC400s. In the end, it came down to two options, sell them and try something else, or try to modify them. As previously referenced in the thread, the designer of the NCORE modules himself acknowledged and clearly stated that the use of an iron core inductor was the source of an audible flaw - that definitely caught my attention (i.e. was this what was contributing to my displeasure with the sound?). If that is not reason enough to explore options for making changes, then I don't know what is. If an NCORE owner is happy to live with a sonically flawed product, that's fine, but not for me and I'm sure other owners will feel the same. As for the unaware, perhaps ignorance is bliss.

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. Describing Ncore as a "sonically flawed product" is an interesting affirmation.
I still didn't get the technical flaw that you corrected with a "directional" fuse.

 

[Feyire]

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.

Here is the quote from the audioxpress article referenced in my original post:

His NCore amplifiers were touted to be more linear than any other amplifier in any other class, but some recent products challenged that statement, so it was time for a next leap forward. Sporadic reports of a sort of “granularity” in the sound reproduction also prompted an investigation into whether this indeed happens, and if so, what would be the cause.

The flaw can be heard, as stated in the article. It was the complaints from the listeners that lead to the investigation, with the conclusion being that the iron core inductor was the source. Why are you insisting on contradicting the statements from the article?

Describing Ncore as a "sonically flawed product" is an interesting affirmation.

It is a fair conclusion, given what is stated in the article. It is part of the reason why the Purifi was developed.

 

[boXem]

Here is the quote from the audioxpress article referenced in my original post:

The flaw can be heard, as stated in the article. It was the complaints from the listeners that lead to the investigation, with the conclusion being that the iron core inductor was the source. Why are you insisting on contradicting the statements from the article?

It is a fair conclusion, given what is stated in the article. It is part of the reason why the Purifi was developed.

I am not used to change the conclusions from a reflexion based on logic and education because I read whatever article on the internet. Can you find an interview or a paper from BP with such a statement?
What are the technical differences between a Ncore and an Eigentakt that make the Ncore be that bad and the Eigentakt be that good?

 

[Rick Sykora]

@Feyire you might have good intentions, but even if you have the skills to make mods, you are not able to objectively show how they improve the sound. If you have spent as much time seeking experienced input before making mods to allegedly improve the NC400, you would know why your posts have been questioned.

Ask a few less loaded questions and you might get a better understanding of ASR members. Here are a few examples…

1. Are there existing threads on fuses already posted on ASR?
2. Are there other members that are unhappy with their NC400s? Am a big advocate of defining the problem before trying to solve it btw.
3. Do I need an expensive audio analyzer to check my mods? Hint: I have something quite reasonably priced

 

[Feyire]

I am not used to change the conclusions from a reflexion based on logic and education because I read whatever article on the internet. Can you find an interview or a paper from BP with such a statement?

Purifi has a nice technical breakdown and examples of hysteresis distortion here: Purifi - This Thing We Have About Hysteresis Distortion

Quick summary for those who don't want to read the whole article:

Hysteresis distortion isn’t something that we simply decided to big up in search of a USP. It’s very real, very different from what you’d expect and not at all subtle. It takes the form of popping or crackling noises that go off at almost but not entirely random moments. You can’t rely on masking to render it inaudible because cause and effect are not coupled in time and the distortion level tracks the signal level.

It is not like normal distortion that the ear just files away as colouration, or can otherwise get used to. 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.

This is why we put so much effort into removing it from our amplifiers and speaker drivers.

Well that description goes in the direction of what I had been disliking in regards to the sound from my NC400s. So coming back to your previous statement, it is actually UcD and NCORE that have this audible flaw. Bruno claims to have resolved it with the Purifi using an improved feedback design.

Additionally, here's another article regarding hysteresis from Purifi: Combating Hysteresis Distortion (part 1: Amplifiers).

Here's a brief excerpt from that article, which you may find of interest:

You might fix hysteresis distortion by putting in a chunky air coil (thus failing EMC and needing extra filtering to pass).

This brings back up the concern you raised previously, that using an air core inductor may cause issues with EMC. In my own case, I have not experienced (audible or otherwise), any issue in regards to EMC/EMI with the air core inductor in place. But that is not to say that it can't be an issue - everyone's environment is different.

So put simply, if you are a UcD and/or NCORE owner and you are looking for an upgrade, you can consider these modifications, or save yourself any risk and effort and simply purchase the Purifi knowing that it resolves a previously well defined and known audible issue.

 

[boXem]

Purifi has a nice technical breakdown and examples of hysteresis distortion here: Purifi - This Thing We Have About Hysteresis Distortion

Quick summary for those who don't want to read the whole article:
Well that description goes in the direction of what I had been disliking in regards to the sound from my NC400s. So coming back to your previous statement, it is actually UcD and NCORE that have this audible flaw. Bruno claims to have resolved it with the Purifi using an improved feedback design.

Additionally, here's another article regarding hysteresis from Purifi: Combating Hysteresis Distortion (part 1: Amplifiers).

Here's a brief excerpt from that article, which you may find of interest:
This brings back up the concern you raised previously, that using an air core inductor may cause issues with EMC. In my own case, I have not experienced (audible or otherwise), any issue in regards to EMC/EMI with the air core inductor in place. But that is not to say that it can't be an issue - everyone's environment is different.

So put simply, if you are a UcD and/or NCORE owner and you are looking for an upgrade, you can consider these modifications, or save yourself any risk and effort and simply purchase the Purifi knowing that it resolves a previously well defined and known audible issue.

The second article is entirely about post filter feedback as a solution and very briefly explains that air core inductors are NOT a good solution.
You are happy with your mods? Good for you. But please, stop advocating them as panacea for correcting a supposedly bad sounding Ncore. That's utter bs.
That said, I will stop here. I have a company to run and some actual engineering to do. Have fun.

 

[Feyire]

The second article is entirely about post filter feedback as a solution and very briefly explains that air core inductors are NOT a good solution.

The air core inductor is a valid DIY solution, with its own caveats as noted. From a large scale commercial company perspective however, I can understand that the air core solution would not be ideal, due to a much higher material cost, larger physical size and having to deal with EMC regulations, which are all valid reasons why Bruno would not take such an approach.

But please, stop advocating them as panacea for correcting a supposedly bad sounding Ncore. That's utter bs.

It is not bs at all. I'm sorry, but you are clearly in denial now. NCORE is audibly flawed, as outlined in the article regarding Bruno's technical presentation on the issue of hysteresis and all the technical articles they wrote about it at Purifi. I understand that the truth can hurt, but it is what it is. So accept it, move on, and perhaps like I suggested previously, let's figure out how we can measure and quantify such audible flaws on this forum, so we can avoid products with this problem in the future.

That said, I will stop here. I have a company to run and some actual engineering to do. Have fun.

I appreciate you having taken the time to discuss this here with me.

 

[littlepotato_as]

For those interested, an excerpt from the NC400 schematic showing the LC filter circuit with the appropriate inductor and capacitors highlighted:

View attachment 124770

Nice! where can I find this schematic? That's way better for me to do modifications on the nc400 board, could you please share this if possible?