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Review and Measurements of Hypex NC400 DIY Amp
- Thread starter amirm
- Start date
No it wont burn, and it doesnt as I have owned one of these units in the past.
It doesnt dissipate 400 watts of heat. Thats one of the major benefits of class D and switching power supplies.
Circa 90% efficient, so worst case 40 watts to dissipate as heat. However its better than that because music RMS power content is only about 1/5th the peak so it will never get any where near having to deliver a continuous 400 watts in real world use.
Idle losses around 15 watts for psu and amp.
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Your agenda looks somewhat suspicious too.
I don't see where the IEC is grounded, be very careful, I'd take it to a guy who knows what he's doing and make very sure it's safe--unless, of course, you own a home defibrilator and have a loved one who's trained in how to use it.
audioBliss
Active Member
Can someone clarify the significance of the 90kHz bandwidth measurement to the left vs the 22.5kHz measurement to the right here. Why would the measurement to the left not point to significant issues with the amp?
Are you sure you posted the right pictures? The one at left is distortion as function of frequency at different power levels, the one at right is distortion as function of power. What issues do you think they show?
audioBliss
Active Member
It was posted previously in the thread - I couldn't find an apples to apples comparison. I was just thinking mainly about the rise of distorsion in the higher frequencies when more power is used(the pic to the left). So wouldn't this mean that the amp has a lot of distorsion in the higher frequencies whenever you use more than a few watts of the amp?
No. What makes you think it would? According to that graph, THD + N stays below 0.1% in all situations. Distortion above 10 kHz is not audible anyway. Also keep in mind this is THD+N, not THD - as noted, noise tends to dominate.
audioBliss
Active Member
Well I don't know why it would. I'm just asking because I'm interested in understanding the graph. What do you mean distortion above 10kHz is not audible?
Can someone clarify the significance of the 90kHz bandwidth measurement to the left vs the 22.5kHz measurement to the right here. Why would the measurement to the left not point to significant issues with the amp?
Ok so our hearing, as I'm sure you know, extends to about 20kHz when we are young. So the question to ask is what is more important for audio quality? Sound which resides below 20kHz, or above 20kHz? The obvious answer is the correct one, below 20kHz.
So why test harmonic distortion to 90kHz? It's a good question. Well if we hear to 20Khz some argue that we want to test what happens when we put a 20kHz signal into an amp. If we do this, unless we have a perfect amp, harmonic distortion will be created at multiples of 20kHz, ie 40kHz, 60, 80 etc. It's important to look just to see if there is anything truly odd going on, however don't confuse this with any relation to audio quality. You simply can't hear those harmonics at 40, 60 and 80kHz, and even if you could your speakers almost certainly wouldn't reproduce them.
So, imo, this is why we should be careful with the parameters of thd tests. Quoting numbers to 90kHz bandwidth is misleading if you want to relate it to audio quality. Seeing low levels of thd above 20kHz is totally irrelevant from an audio quality perspective.
However again I would stress yes we do want to look above 20kHz. An FFT is far more helpful and informative than thd in doing so.
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The first harmonic of 10 kHz is 20 kHz. Most of us don't hear that, and those who do, only hear it if it at a pretty strong level.
audioBliss
Active Member
Great answers, thank you. But then my next question is why does it look like the stuff >20kHz is affecting the audible band 10kHz-20kHz in this case? Or am I not interpreting this correctly?
Edit: So while 0.05% THD at 15kHz or whatever probably would not be of concern. doesn't that mean that the performance might not be as good as you might think reading the initial review of the amp?
Edit: So while 0.05% THD at 15kHz or whatever probably would not be of concern. doesn't that mean that the performance might not be as good as you might think reading the initial review of the amp?
Tomrrow I will post some REW plots that will help explain.
It's the way it's plotted, it is misleading. I will show this tomorrow.
audioBliss
Active Member
Thank you, that would be greatly appreciated!
@March Audio says "totally irrelevant" ......, or maybe he only does not know that high 20kHz distortion reflects in high HF IMD distortion with difference tones and their multiples and also the skirts in the audio band. See below the 20kHz THD and related 19+20kHz IMD.
Pavel, can you stop this going out of your way to contradict me or trying to imply I don't understand things like IMD?
I was specifically talking about low levels of thd and its measurement above 20kHz.
Imd is a different subject in manifestation even though thd and imd are mathematically rekated
Imd is the product of mixing 2 signals. If you have a 50khZ signal and a 51 kHz signal, obviously inaudible in themselves but in a non linear amplifier they can create a signals at their sum, subtraction and at the difference. 49khz, 52 kHz 101khz and importantly 1 kHz.
1 kHz is obviously audible.
Two things to note here. Unless the signals at 50 and 51 kHz are high level, or the amplifier is grossly non linear and distorting, the signal at 1 kHz simply won't be high level.
Second thing is that if there is something at 1 kHz we will measure it as part of the in band (below 20 kHz) noise measurement. Again more helpful to look at an an fft as opposed to a rather limited overall thd number.
I was specifically talking about low levels of thd and its measurement above 20kHz.
Imd is a different subject in manifestation even though thd and imd are mathematically rekated
Imd is the product of mixing 2 signals. If you have a 50khZ signal and a 51 kHz signal, obviously inaudible in themselves but in a non linear amplifier they can create a signals at their sum, subtraction and at the difference. 49khz, 52 kHz 101khz and importantly 1 kHz.
1 kHz is obviously audible.
Two things to note here. Unless the signals at 50 and 51 kHz are high level, or the amplifier is grossly non linear and distorting, the signal at 1 kHz simply won't be high level.
Second thing is that if there is something at 1 kHz we will measure it as part of the in band (below 20 kHz) noise measurement. Again more helpful to look at an an fft as opposed to a rather limited overall thd number.
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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.
audioBliss
Active Member
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.
What measurements are need to say an amplifier without a doubt has no detectable distorsion of any kind? I guess it's the introduction of the SMPS power supplies as well as class D that has sparked this confusion? I have not read about similar discussions when it comes to class AB.
What measurements are need to say an amplifier without a doubt has no detectable distorsion of any kind? I guess it's the introduction of the SMPS power supplies as well as class D that has sparked this confusion? I have not read about similar discussions when it comes to class AB.
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