This is a review and detailed measurements of a DIY power amplifier based on Hypex NC400 amplifier modules. It was built and is on kind loan from a member. I asked him to list the parts and this is what he supplied:
So putting aside labor, it is about USD $1,100. From outside, the unit looks very professional, sans branding:
The unit came with balanced inputs and speaker outputs and that is how I tested it.
The amplifier as noted is based on Hypex NC400 modules. If you don't know much about it, the chief designer Bruno Putzeys was the person that put high performance class-D amplifiers on the map, producing amplifiers that not only matched performance of classic AB amplifiers but bested them. I have been meaning to measure one for a long time and this is the first time I have had the opportunity.
Class-D amplifiers have the advantage of high-efficiency as the transistors are operated in switching mode: either full on or full off. They don't use power when fully off and when fully on, have the least resistance and hence lowest power consumption. The audio signal is used to modulated these pulses. Before outputting the signal though, the pulses need to be filtered as the thing will act like a little FM or TV station spitting out tons of high energy and high frequency noise. The filtering must be passive (e.g. like the one in your speakers). This can make class-D amplifiers load dependent.
Class-D amplifiers are quite a bit more complex than traditional amplifiers due to operating at high speeds (well above audio band). Creating a reliable one is also challenging. This is the motivation behind creating modules around them so that the design can be done once and reused without chance of screwing things up. Countless audio companies as a result buy these modules and use them in their products. These modules are also available to DIY people in both kit and individual form as is the case here.
I opened the unit and was pleasantly surprised by the clean layout and nice work the owner had done to put it together (click on image for larger size):
View attachment 19461
The two round PC boards are the NC 400 modules which as the name produces, is able to generate 400 watts of power. They are powered by a switching power supply also from Hypex (SMPS600). As you will see later, the power supply limits the amount of power these two hungry amps can generate.
I was so pleased to see proper and safe grounding lug in green and sanding off the anodizing finish on top right and bottom of the chassis and likewise the mating position on the lid to make sure it is grounded. Both of these are
missed in some products such as created by Schiit.
Personally I would have given up the aesthetics and put the speaker plugs close to their modules to make a symmetrical system. The wiring colors for the speakers follow mains voltage convention in US with black being "hot" and "white" not (neutral). In DC wiring though, we like to use red for positive and white/black for negative. Alternatively white can be positive and black negative. Fortunately that is a visual nuisance as they are wired correctly to the amp and the terminal.
The only major concern I have is not regarding the assembly but the design of the switchmode power supply by Hypex. A number of power transistors are mounted to the bottom clear aluminum heatsink which is nothing but bent piece of metal. It gets quite warm and is sitting within a millimeter or two of the large electrolytic capacitors below it. The two caps were getting quite warm even in limited use and will surely result in them drying out prematurely and failing. This case is plenty large so personally I would attempt to straighten the bent aluminum so that it is more vertical.
Just casually feeling the heat generated by the amps and power supply, the later was much warmer. The case on the other hand, has vents for the amp modules and not the power supply. If the lid can be reversed, that may be something I would do to keep the power supply cooler.
Let's get into measurements and see if we finally have a performant power amplifier as our previous units have failed us and failed us badly.
Measurements
As usual, let's start with our dashboard with 4 ohm load and 5 watts of power with AES-17 40 kHz filter:
View attachment 19464
Wow! Finally we have a power amplifier that matches the performance of mid-tier DACs and outperforming previously tested amplifiers by tens of dBs. The third harmonic is actually well below -110 dB. And if I turn one channel off, we get near perfect performance:
View attachment 19465
The second harmonic is now down to -130 dB!!! Pretty remarkable.
Of course that is at 5 watts. Let's sweep the input level and see the performance across the range:
View attachment 19466
Performance actually improves up to about 30 to 50 watts and then starts to climb some. At near full clipping, we get healthy amount of power (225 watts both channels driven) with 0.004% distortion. It completely blows out of water the previously tested amps in both power and distortion/noise.
Using near max power, we get very nice signal to noise ratio:
View attachment 19467
Frequency response is also far better than digital amps we have tested:
View attachment 19468
I need to develop more complex loads to better determine the response into real speakers.
Broadband FFT shows what exists above audio band (post AES-17 filtering):
View attachment 19469
We clearly see the switching frequency of the amplifier (around 460 kHz) despite the filtering in the amplifier and the AES-17. We can see the same in our waveform at very, very low power levels:
View attachment 19470
Harmonic distortion versus frequency is exceptionally well behaved and good:
View attachment 19471
Notice the NC400 (in blue) relative to the abomination that was Behringer A500 (in dashed red). Note that this is a wideband test so THD+N is higher than the dashboard (it would not otherwise include all the harmonic distortions at 20 kHz).
Conclusions
Folks, welcome to adult amplifier world!
Previous amplifiers that we tested were awful in measured performance and I was starting to think good amps are a thing of past. Fortunately Hypex NC400 amplifier modules show that very well engineered amplifiers exist in class-D configuration no less! Not only we have stellar performance here, but also get to have high efficiency and cool running amplification to boot. With nearly quarter of kilowatt of power available, there should be no issue driving even inefficient speakers to very loud levels.
For better longevity I would use a different and possibly more powerful power supply to get even more performance.
As it is,
I can wholeheartedly recommend hypex NC 400 modules for power amplification. Yes, the pink panther is happy!
This seems to be a very easy DIY project although I caution you to NOT engage in it if you are not comfortable and knowledgeable about mains wiring and voltages. You can easily get yourself shocked or killed. So buy an already made one if you are not able to build one safely.
I am pleased to have a reference for testing a few more power amplifiers that have been piling up in my lab.
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