This is a review and measurements of the Nord One MP NC252 SE stereo class D hypex power amplifier. It is on kind loan from a member and costs £554.00 (US $739) as optioned:
This is the upgraded "SE" case which costs an extra £50. It indeed, is a step up from budget cases that these modules tend to come in. Here is the back side, showing another £25 option for trigger support:
There is an option to upgrade the binding posts but I am not sure if these are it or not.
EDIT: company suggested that the input switch may have oxidized causing intermittent performance. This seemed to be the case so review is updated with the new results.
Nord One MP NC252 Amplifier Measurements
I usually end the review with warm up test even though I run it first in my testing. But here, we need to look at it now:
When I first powered up the unit, the right channel performance was 10 dB worse than the left. I looked at everything but could not find a cause. All of a sudden, not only did that difference shrink, but the left channel improved as well. So I started my warm up test. As you in dashed lines, at around 225 seconds, THD+N suddenly took a nose dive, especially in Ch 2 (right). I wiggled every cable, attempted every type of grounding but none had even the tiniest effect, indicating an internal issue. As I was messing around, all of a sudden, performance went back up so I ran the warm up test for twice as long (solid lines) and it stayed good and steady. So I went to run the dashboard:
While not the best performance we have seen from this platform, it is close enough:
Alas, once again, performance degraded with the unit just sitting there:
After much testing, I managed to narrow it down to that peak you see just past 20 kHz. The company spec is 20 kHz and if I limit the bandwidth, we almost eliminate that to get a SINAD of around 88 dB. So I can see how someone may not see this problem if they are going by 20 to 20 KHz response. But the issue is there and is not acceptable.
Now, this kind of noise could be one of instrumentation. To rule that out, I tested one of my reference amplifiers and the results were absolutely clean with none of that noise spectrum. So while I leave the door ever so ajar that this could still be the cause, I am very confident that we have an issue with a supervisory circuit causing that noise.
Note that in addition to above, we have excessive mains noise riding on the right/Ch 2. Again, I could not impact that no matter what I did with grounding so I think it is an internal issue.
At this point, I did not see a point in continuing the testing as the above problem could come and go, corrupting whatever I am measuring.
EDIT: per note in the introduction, I exercised the input switch (RCA to XLR) and it seems to have fixed the variable performance. So I proceeded to run the rest of the tests.
Warm up test up to 10 minutes no longer showed a sudden drop in performance in one channel:
I then re-ran the dashboard and stayed in there a while without the sudden change in Ch 2:
Ch 2 has fair amount of noise which varies with time and hence the difference between first and this run.
EDIT 2: I did some troubleshooting and found out that the switch cabling is picking up power supply noise and in turn, couples to the input flat cable:
Company sent me a new harness for the switch, allowing me to route it away from input cable:
Notice that I twisted the ribbon cable prior to switch re-wiring and it avoided some of the noise as well. Here is the new dashboard:
There is still more noise in Ch 2 which I think is unavoidable given the closeness of the input cable to the power supply and the fact that it is not shielded.
Here is the RCA input:
Don't know why Ch2 improved so much. Perhaps there is still some issue in there biasing toward RCA input.
The noise variability between channels shows up naturally in SNR tests:
Channel separation is extremely good:
And as we expect from Hypex, there is no load dependency:
Distortion is kept quite low, especially for class D:
The amp meets its target power at 4 ohm:
And does nearly as well at 40 Hz:
It does drop a bit more if you keep going to 20 Hz:
My power measurement using the sweep is not very accurate so don't take this number of 8 ohm as gospel:
One channel is noisier on power up/off:
Conclusions
The NC525 module from Hypex is fully integrated with amplifier and power supply. As such, there is less to go wrong with it. Yet, we have an amplifier here which seems to drop its performance by not an insignificant amount of 10 dB. Maybe it is just this sample in which case, I encourage the company to send me another to test. Until then, I can't recommend the Nord One MP NC525 amplifier.
EDIT: exercising input switches seems to have resolved the performance variability. This makes sense as I had toggled the switch on one channel in the first test but not the other. New results show respectable performance but with a bit of excessive power supply noise in the right channel.
Given the updated results, I am going to recommend the Nord One NC252 MP (SE).
------------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
This is the upgraded "SE" case which costs an extra £50. It indeed, is a step up from budget cases that these modules tend to come in. Here is the back side, showing another £25 option for trigger support:
There is an option to upgrade the binding posts but I am not sure if these are it or not.
EDIT: company suggested that the input switch may have oxidized causing intermittent performance. This seemed to be the case so review is updated with the new results.
Nord One MP NC252 Amplifier Measurements
I usually end the review with warm up test even though I run it first in my testing. But here, we need to look at it now:
When I first powered up the unit, the right channel performance was 10 dB worse than the left. I looked at everything but could not find a cause. All of a sudden, not only did that difference shrink, but the left channel improved as well. So I started my warm up test. As you in dashed lines, at around 225 seconds, THD+N suddenly took a nose dive, especially in Ch 2 (right). I wiggled every cable, attempted every type of grounding but none had even the tiniest effect, indicating an internal issue. As I was messing around, all of a sudden, performance went back up so I ran the warm up test for twice as long (solid lines) and it stayed good and steady. So I went to run the dashboard:
While not the best performance we have seen from this platform, it is close enough:
Alas, once again, performance degraded with the unit just sitting there:
After much testing, I managed to narrow it down to that peak you see just past 20 kHz. The company spec is 20 kHz and if I limit the bandwidth, we almost eliminate that to get a SINAD of around 88 dB. So I can see how someone may not see this problem if they are going by 20 to 20 KHz response. But the issue is there and is not acceptable.
Now, this kind of noise could be one of instrumentation. To rule that out, I tested one of my reference amplifiers and the results were absolutely clean with none of that noise spectrum. So while I leave the door ever so ajar that this could still be the cause, I am very confident that we have an issue with a supervisory circuit causing that noise.
Note that in addition to above, we have excessive mains noise riding on the right/Ch 2. Again, I could not impact that no matter what I did with grounding so I think it is an internal issue.
At this point, I did not see a point in continuing the testing as the above problem could come and go, corrupting whatever I am measuring.
EDIT: per note in the introduction, I exercised the input switch (RCA to XLR) and it seems to have fixed the variable performance. So I proceeded to run the rest of the tests.
Warm up test up to 10 minutes no longer showed a sudden drop in performance in one channel:
I then re-ran the dashboard and stayed in there a while without the sudden change in Ch 2:
Ch 2 has fair amount of noise which varies with time and hence the difference between first and this run.
EDIT 2: I did some troubleshooting and found out that the switch cabling is picking up power supply noise and in turn, couples to the input flat cable:
Company sent me a new harness for the switch, allowing me to route it away from input cable:
Notice that I twisted the ribbon cable prior to switch re-wiring and it avoided some of the noise as well. Here is the new dashboard:
There is still more noise in Ch 2 which I think is unavoidable given the closeness of the input cable to the power supply and the fact that it is not shielded.
Here is the RCA input:
Don't know why Ch2 improved so much. Perhaps there is still some issue in there biasing toward RCA input.
The noise variability between channels shows up naturally in SNR tests:
Channel separation is extremely good:
And as we expect from Hypex, there is no load dependency:
Distortion is kept quite low, especially for class D:
The amp meets its target power at 4 ohm:
And does nearly as well at 40 Hz:
It does drop a bit more if you keep going to 20 Hz:
My power measurement using the sweep is not very accurate so don't take this number of 8 ohm as gospel:
One channel is noisier on power up/off:
Conclusions
The NC525 module from Hypex is fully integrated with amplifier and power supply. As such, there is less to go wrong with it. Yet, we have an amplifier here which seems to drop its performance by not an insignificant amount of 10 dB. Maybe it is just this sample in which case, I encourage the company to send me another to test. U
EDIT: exercising input switches seems to have resolved the performance variability. This makes sense as I had toggled the switch on one channel in the first test but not the other. New results show respectable performance but with a bit of excessive power supply noise in the right channel.
Given the updated results, I am going to recommend the Nord One NC252 MP (SE).
------------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
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