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Meaurements of Hypex NC252MP in bridge-tied load (BTL)

pma

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Following the discussion in the NCx500 review thread, I was curious how my PMA-NC252MP amplifier based on NC252MP module would perform in a bridged configuration. Original Hypex datasheet allows for this configuration, as we can see in the following part from the datasheet:

1674035123349.png


It declares 400W/1kHz/4ohm at THD 1% peak power. So I have configured my PMA-NC252MP exactly according to the datasheet scheme and started measurements. I would add that my amplifier has huge heatsink and there should be no problem with thermal management.

Let's have a look into my "audio kitchen", this is my measuring place:

NC252MP_bridged_distortion_measurement.JPG


This isolation transformer for the PC breaks possible loop through mains supply:
PC_isolation.JPG


and finally this is my PMA-NC252MP amplifier configured to BTL load:
NC252MP_BTL_load.JPG


My amplifier: https://pmacura.cz/pma_nc252mp.htm

First, I have to say that the amp was doing quite well in the BTL setup. It was able to get 400W/4ohm at much lower distortion than 1% - you will see later. At about 430W/4ohm, the current protection was shutting down the amp, but immediately after lowering the output power it started to work again.

Measurements

I have measured THD and THD+N vs. power and vs. frequency, into 4ohm load, at 1kHz and 6kHz, with 45kHz measuring bandwidth. I use LC filter before the ADC input and this filter has -3dB cut off at 30kHz, and the slope is -40dB/decade.

Filter response
classD_filter_FR.png

First, THD and THD+N vs. power at 1kHz/4ohm and 45kHz measuring BW
NC252MP_bridged_4R_1kHz_BW45kHz.png


A comparison of THD vs. power at 1kHz and 6kHz, 4ohm load, 45kHz BW
NC252MP_bridged_4R_1-6kHz_BW45kHz.png


Comparison of THD+N vs. power at 1kHz and 6kHz, 4ohm load, 45kHz BW
NC252MP_bridged_4R_1-6kHz_BW45kHz_thdn.png


THD vs. frequency at 210W/4ohm, 45kHz BW
NC252MP_bridged_4R_210W_thdfreq_BW45kHz.png


Conclusion

I find the results very good. NC252MP was doing well in my test, also for the reason that it is very well cooled by large heatsinks. 4 ohm BTL operation works, with purely resistive load, however one has to be carefull. Maybe someone of Hypex might comment, @Hypexsales ?
 

Sokel

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Blue traces are the bridged one,right?
 
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pma

pma

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Blue traces are the bridged one,right?
All traces are bridged. There is no measurement in “normal” single ended mode. Orange is for 6kHz. Green in the first distortion plot is THD+N, you can see it in the image legend.

P.S. Normal single ended mode cannot give 400W/4ohm. BTL can do it.
 
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pma

pma

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I have to say that this bridge-mode BTL test of NC252MP was quite a challenge. As you can see, the whole audio chain is involved, except of speakers. And a special XLR-XLR cable must have been made to invert polarity in one channel.

BTL_test_scheme.png
 

Matias

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Nice test, thanks for sharing.
 
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eeMGee

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How about THD and THD+N vs. power at 20 Hz/4ohm?
 
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pma

pma

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How about THD and THD+N vs. power at 20 Hz/4ohm?
I did not measure it. THD and THD+N will be good, however we can predict that the top power would be about 350W. It is the SMPS power supply that limits the performance in the BTL mode. It squeals as a hell when the output power in BTL goes above 200W, and above 300W you can hear "rumble" sound as well.
 
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pma

pma

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Mains frequency. Something is resonating, it is a mechanical sound, not from speakers.
 
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pma

pma

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Would there be any benefit to offering this preconfigured vs just buying a more powerful NC502?
I do not think so. The point of the thread is to show how NC252MP behaves in BTL mode in a real-world audio chain configuration. There have been some questions how Hypex modules behave in the bridged connection.
 

rdenney

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If this translates to the NC502MP, it's a path for Even More Power--a pair of 502MP's would produce nominal kilowatt (probably more like 800 Watts--double PMA's result).

If only I had speakers that could take that much power. And a half mile to the nearest house (make that a mile).

Rick "who can't crank the 502 up to anywhere near its limits without upsetting domestic bliss" Denney
 
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pma

pma

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Hello everyone, I have 2 comparative measurements of "normal" single-ended NC252MP mode vs. bridge-tied BTL mode. One is THD vs. output power at 1kHz/4ohm, the other is THD vs. frequency at 100W/4ohm (SE) and 200W/4ohm (BTL). We can see that distortion slightly rises in the BTL mode, but stays low and we get about twice more power. But, one should be careful, load should not be lower than 4 ohm in the BTL mode.

NC252MP_thdpower_normal_vs_BTL.png


NC252MP_thdfreq_normal_vs_BTL.png
 

Ajax

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Hi,

I recently received my Buckeye build of the NC252MP and for US$550 it is excellent in driving my out door patio system

Source is Sonos Connect with optical out into a Benchmark DAC2 and then onto the amp with inexpensive balanced cables. Speakers are B&W AM1 combined with a 12" Velodyne sub crossing over @ 70Hz.

The clarity and realism of the sound is stunning, which I attribute as much to the electronics as the fact the speakers are dealing with little or no reflections.
 
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pma

pma

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This is a summary of my efforts on distortion measurements of NC252MP, THD vs. power into 4ohm load, various test frequencies from 20Hz to 15kHz, mostly @45kHzBW measurements, NC252MP both normal SE and BTL load, from June 2022 till now. I suppose the results are quite consistent.

NC252MP_thdpower_SE_BTL_multi2.png
 
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pma

pma

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Comparison of THD+N vs. power at 4ohm/1kHz (45kHz measuring BW) of: NC252MP SE mode, NC252MP BTL mode and my class AB A250W4R amplifier (SE).

NC252MP_thdnpower_BTL_SE_vs_A250W4R.png
 

DonH56

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Interesting, pretty clearly shows a~6-8 dB noise hit when bridging, is it correlated? Gain difference?

Also looks like bridged power output isn't hitting the 4x ideal though hard to tell when the bridged output clips (guessing from the uptick at the end of the plot).
 
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pma

pma

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Interesting, pretty clearly shows a~6-8 dB noise hit when bridging, is it correlated? Gain difference?

Also looks like bridged power output isn't hitting the 4x ideal though hard to tell when the bridged output clips (guessing from the uptick at the end of the plot).

Yes, the noise (in all 3 cases) is gain related.
NC252MP SE: Gain = 20x
NC252MP BTL: Gain = 40x
A250W4R: Gain = 53x

NC252MP in the BTL mode is limited by current protection. Every half of BTL sees 2 ohm load (4 ohm BTL total) and NC252MP is rated at 180W/2ohm

1674482103288.png


It was able to give 400W in the BTL mode, in my case, at low distortion. At 430W/4R/BTL, the amp shuts down itself.

Per datasheet, BTL mode (they use narrower measuring BW) :
1674482244432.png
 

Rick Sykora

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From your OP, note the info in italics below the BTL wiring diagram on the data sheet. There is no need to connect the amp's negative terminals.

1680616193790.png


Worth noting that wiring to an actual speaker is much less complex than your test setup.

In any case, is useful testing and thanks for providing it.:)
 
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