Review and Measurements of Hypex NC400 DIY Amp

[March Audio]

This is a simulation, however these simulations fit very well with real world. Units are as in plots, Volts. 10V/1V is 20dB, as everyone knows.

Bob Cordell has been a big supporter of THD 30kHz measurements to reveal HF non-linearities and other hidden issues. And sorry, though Bob Cordell is an authority in amplifier design for me, @March Audio is not. Similarly Richard Cabot (AP) suggests more distortion test methods including HF THD and 19+20kHz IMD.

Again you are wandering off into the theoretical non real world.

The point is these IMD problems need to show up in band. A 19+20 test is in band not ultrasonic and something I repeatedly advocate. Its products at 38/40 are no where near as important as the direct 1, 18 or 20kHz. A low level of product at 38/40 will not generate further signicant in band imd issues, unless the distortion/non linearity is gross. but if there we can see the easily on an fft.

 

[Julf]

This is a simulation, however these simulations fit very well with real world.

So what non-linearity does that simulation assume?

And sorry, though Bob Cordell is an authority in amplifier design for me, @March Audio is not.

Nice combination of slur and and appeal to authority...

 

[March Audio]

Ok so now it's getting interesting. Reading around the web it would seem that there is not a strict consensus if there are so called hidden distorsions in class d amplifiers like the ncore nc400. I'm very interested in getting to the bottom of it. Thank you.

There are no hidden distortions of class d. These mechanisms apply to all amplifier classes

 

[Julf]

Ok so now it's getting interesting. Reading around the web it would seem that there is not a strict consensus if there are so called hidden distorsions in class d amplifiers like the ncore nc400. I'm very interested in getting to the bottom of it. Thank you.

I suggest a fair bit of care in checking sources of stuff "around the web". Lots of utter BS there, as well as people with hidden agendas. What "hidden distortions" would these be?

 

[March Audio]

This is a class d amp IMD test, the plots on the right. It's extremely good. There are only tiny amounts of imd visible.

 

[DonH56]

All amplifiers exhibit higher distortion at higher frequencies. This is because they have finite bandwidth and feedback loop gain, which reduces distortion, falls at higher frequencies just like the amplifier's output itself. The result is higher distortion, and reduced THD+N (SINAD) numbers as more noise is included in wideband measurement.

This will indeed cause higher levels of IMD, which can in turn generate low-frequency components, but (a) they are generally few if any signals up that high (none from a typical digital source that rolls off sharply above 20 kHz), and (b) the signals that are up there tend to be very, very small resulting from noise and such and so the distortion products are even smaller.

Bottom line: a theoretical but not audible issue the vast majority of the time. And of course marketing preys on FUD by playing the "but it could be a problem in your system, you could be the one in a million" card to sell products that do not really do anything at all for the sound...

 

[audioBliss]

I suggest a fair bit of care in checking sources of stuff "around the web". Lots of utter BS there, as well as people with hidden agendas. What "hidden distortions" would these be?

I have no idea what they would be. I deliberately said around the web..no names mentioned. These people claim the same thing that there are hidden agendas and that class d does not measure well in reality. I have seen no proof at all that this is true but I'm interested in hearing peoples take on it here.

 

[tmtomh]

This is a simulation, however these simulations fit very well with real world. Units are as in plots, Volts. 10V/1V is 20dB, as everyone knows.

Bob Cordell has been a big supporter of THD 30kHz measurements to reveal HF non-linearities and other hidden issues. And sorry, though Bob Cordell is an authority in amplifier design for me, @March Audio is not. Similarly Richard Cabot (AP) suggests more distortion test methods including HF THD and 19+20kHz IMD.

And yet @March Audio also advocated testing above 20kHz - you just don't acknowledge that becuase you consistently adopt a totally ungenerous interpretation and response of what March Audio writes here. And no one should particularly care whether or not you think Bob Cordell is an authority on amp design and March Audio is not. Appeal to Authority argumentation is irrelevant. Cross-tabulating what March Audio, you, and Bob Cordell write to look for areas of agreement/overlap and better identify areas of disagreement is a much better way to start.

 

[Julf]

I deliberately said around the web..no names mentioned. These people claim the same thing that there are hidden agendas and that class d does not measure well in reality.

Are they people who might have a financial interest in non-class-D amps?

Would love to hear what "hidden distortions" they believe there are. The last time any new "hidden distortions" were found was SID/TIM something like 60 years ago.

 

[March Audio]

I have no idea what they would be. I deliberately said around the web..no names mentioned. These people claim the same thing that there are hidden agendas and that class d does not measure well in reality. I have seen no proof at all that this is true but I'm interested in hearing peoples take on it here.

We can certainly talk further about and play with some real world amps and test signals to demonstrate the results.
But now I need sleep

 

[BobPM]

Reading the original review, it sounds like the test of the NC400 had a disappointing (as compared to hypex spec) 4 ohm power rating due to the builder having split his SMPS600 power supply. I have read the thread and may have missed the answers and have a few questions I hope someone can help me answer.

1) was the low 4 ohm power rating due to the choice to split the SMPS600 power supply in the DIY example tested, and what might the mono's achieve?

2) would the spliced power supply connection result in slightly lower SINAD results than might have been achieved using two separate supplies, or one SMPS1200 with the hypex splitter; and

3) What is the best choice for power both in terms of performance and in terms of longevity?
Two SMPS600's, one SMPS1200 with the hypex module to split the connection, or somehow using two SMPS1200's?

If these questions were addressed somewhere else in this thread, I apologize in advance for having missed it.

 

[BobPM]

I found some of the answers to question 3, best power supply option, in posts 854, 855, 865, 871, and not worth using a single SMPS1200 per NC400, post 809. Consensus leans towards one SMPS600 per NC400 module.

Still wonder if Amir's 4 ohm power rating of 225 watts was limited by using the split SMPS600 power supply, and if using a proper supply would have caused even a slight improvement in SINAD. While the 8 ohm power looked close to spec, the 225 was quite a bit below the 400 watt 4 ohm spec.

 

[JimB]

I found some of the answers to question 3, best power supply option, in posts 854, 855, 865, 871, and not worth using a single SMPS1200 per NC400, post 809. Consensus leans towards one SMPS600 per NC400 module.

Still wonder if Amir's 4 ohm power rating of 225 watts was limited by using the split SMPS600 power supply, and if using a proper supply would have caused even a slight improvement in SINAD. While the 8 ohm power looked close to spec, the 225 was quite a bit below the 400 watt 4 ohm spec.

Well, there is certainly no chance for a higher stereo output with a single SMPS600 - it cannot provide enough power for two NC400s to reach full potential output at the same time. Given that maximum output power was limited by the power supply, SINAD at full potential amp output would likely be a little higher with higher supply output - if the SINAD vs power curve was pushed a bit further to the right. Otherwise, too much speculation. What are you trying to do? How will the possible answers to these questions inform what you will choose?

 

[BobPM]

Well, there is certainly no chance for a higher stereo output with a single SMPS600 - it cannot provide enough power for two NC400s to reach full potential output at the same time. Given that maximum output power was limited by the power supply, SINAD at full potential amp output would likely be a little higher with higher supply output - if the SINAD vs power curve was pushed a bit further to the right. Otherwise, too much speculation. What are you trying to do? How will the possible answers to these questions inform what you will choose?

The simple answer is I want to build a basic Hypex or Purif amp to last for awhile and want the best I can do for the time I want to invest at the time of the build. The cost of the power supplies vs my time is low enough that I want to get the one that will give the most trouble free power possible.

As to the SINAD, basically, I was looking for closer to 400 watts per channel into 4 ohms for my speakers and don't know if I want to wait for someone to come-out with a basic kit for the Purifi build. The Purifi DIY thread got very complicated very fast. My guess is that since the NC400 was only measured with the odd split SMPS600, it was not up to its full potential, and if it had the proper power, it might have improved to closer to the Purifi.

 

[vitalii427]

The simple answer is I want to build a basic Hypex or Purif amp to last for awhile and want the best I can do for the time I want to invest at the time of the build. The cost of the power supplies vs my time is low enough that I want to get the one that will give the most trouble free power possible.

As to the SINAD, basically, I was looking for closer to 400 watts per channel into 4 ohms for my speakers and don't know if I want to wait for someone to come-out with a basic kit for the Purifi build. The Purifi DIY thread got very complicated very fast. My guess is that since the NC400 was only measured with the odd split SMPS600, it was not up to its full potential, and if it had the proper power, it might have improved to closer to the Purifi.

I’m also considering NC400 DIY kits or Purifi.

Actually somewhere in this thread Amir posted measurements of only one NC400 module driven by SMPS600 and he got 335W at the knee and a bit less than 400W at 1% if I remember correctly. As I understand to get 400W from NC400 with SMPS600 you need to live in Europe or somewhere else with 230V outlet.

 

[JimB]

The simple answer is I want to build a basic Hypex or Purif amp to last for awhile and want the best I can do for the time I want to invest at the time of the build. The cost of the power supplies vs my time is low enough that I want to get the one that will give the most trouble free power possible.

As to the SINAD, basically, I was looking for closer to 400 watts per channel into 4 ohms for my speakers and don't know if I want to wait for someone to come-out with a basic kit for the Purifi build. The Purifi DIY thread got very complicated very fast. My guess is that since the NC400 was only measured with the odd split SMPS600, it was not up to its full potential, and if it had the proper power, it might have improved to closer to the Purifi.

Amir did a boat load of comparisons to the NC400 for people in his review of the Purifi evaluation stereo amp. See especially posts #54 - 107. I think the general conclusion was that the Purifi 1ET400A had lower distortion than the NC400, but that was not realizable at lower power, because then noise dominated, and they were very close to each other there. There has also been a lot hand wringing about the susceptibility of the NC400 to moderate levels of RF on its inputs. So, I think the newer 1ET400A IS technically superior, but not by much, and maybe not enough for you to care. Regardless of the modules you choose, you must provide them with sufficient power if you want them to reach their full output potential. That is at least 600W for a single channel, and 1200W (or 2 x 600W) for two. On the other hand, the NC400s are bridgeable, and the 1ET400As are not.

 

[JimB]

I’m also considering NC400 DIY kits or Purifi.

Actually somewhere in this thread Amir posted measurements of only one NC400 module driven by SMPS600 and he got 335W at the knee and a bit less than 400W at 1% if I remember correctly. As I understand to get 400W from NC400 with SMPS600 you need to live in Europe or somewhere else with 230V outlet.

This issue of mains dependent amp output has to due with the voltage swing available. These Hypex SMPS have outputs that track input voltage, within their ranges. It is not a factor when current limited. From the SMPS600 datasheet:

 

[audioBliss]

I don’t understand why people are trying to figure out their own way of building their own nc400 or from third parties?? Just go to the Hypex website diyclassd.com and buy the original DIY nc400 monoblocks where Bruno has made sure they are the ultimate.

No offence intended

 

[BobPM]

The start of this thread, or maybe other threads I've read, raised some doubt about the quality or long term viability of the SMPS600. Other posts I've come across suggest that either, or both, the SMPS600 or 1200 may have been upgraded recently. So is one "better" than the other in terms of long term viability? Also, is there a post or thread on just how to bridge the NC400's?

Then again, maybe I should just take audioBliss's advice and stop sweating it and just build the mono's from hypex (although I prefer the stereo kits from Ghent as it would work better with my system and would only require one power cord).

 

[tmtomh]

I don’t understand why people are trying to figure out their own way of building their own nc400 or from third parties?? Just go to the Hypex website diyclassd.com and buy the original DIY nc400 monoblocks where Bruno has made sure they are the ultimate.

No offence intended

Very good point. I think people like to tinker and investigate the possibility of building something even better for less money (or perhaps something a lot better for modestly more money). And I think that's an important part of the spirit of this forum.

But personally I do agree with you - I prefer the option of buying something that looks to have had the kinks worked out and has been designed and rigorously tested to ensure that the sum of the parts performs as well as one would expect based on the individual components' capabilities.