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PMA-NC252MP power amplifier

pma

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PMA-NC252MP

As a manufacturer of electronic equipment I have been granted a web account for Hypex OEM web shop. My newly designed power amplifier based on excellent Hypex NCore modules is PMA-NC252MP. It is an amplifier with rated power 2x250W/4ohm and based on the NC252MP OEM modules.

Hypex NC252MP OEM module

nc252_photo1_s.jpg


The NC252MP amplifier module incorporates a low power standby power supply (meets 2013 ERP Lot 6 0.5W requirements), a highly efficient switch mode power supply and a high-performance Class D amplifier in one compact and easily applicable power brick.

The amplifier used in the NC252MP is a self-contained high-performance class D amplifier intended for a wide range of audio applications, ranging from public address systems to ultrahigh-fidelity replay systems for studio and home use. Chief distinguishing features are flat frequency response irrespective of load impedance, nearly frequency independent distortion behaviour and very low radiated and conducted EMI. Control is based on a phase shift controlled self-oscillating loop taking feedback only at the speaker output.

The main SMPS providing the power for the amplifier is a compact, high power, highly efficient, regulated half bridge converter with synchronous rectification on the main output rails. These properties make this technology ideal for powering Class D audio amplifiers.

PMA-NC252MP power amplifier

is built in a full-size aluminum case with side heatsinks, to allow for maximum continuous sine power without time and temperature limitations. It has large binding posts to allow for insertion of locking banana plugs. Input XLR connectors are standard Neutrik NC3FDM3-L-B-1. The goal is to get the most from the Hypex module, its full potential, especially in continuous sine power.

Class D high efficiency and lower dissipated power (compared to class AB amplifiers) is a temptation for most assemblers to use quite small amplifier case with not much heatsinking capability. This make a benefit of smaller size and weight, however the power capabilities of the Hypex modules are not completely utilized and reliability and life span may suffer. Let me quote from Hypex datasheets:

Class D amplifiers’ known high efficiency often leads to a gross underestimation of the cooling required. Please apply adequate cooling to the module to ensure the module operates within specification. The following graphs provide an indication of the heat (in Watts) generated at different output levels. For more information regarding cooling, please refer to our application note “Thermal Design”, available on our website. Defects caused by overheating due to poor thermal management are not covered by warranty.

So we can see that the proper heatsink and thermal management must not be underestimated. For this reason and to get maximum possible continuous power and maximum reliability of the amplifier, a full-size aluminum case with side heatsinks with fins was chosen. It also fits well to a main home audio system based on 400 - 450mm (19") wide components.

PMA NC252MP uses balanced inputs with Neutrik XLR connectors for optimal performance. The inputs can be connected to an unbalanced source, but the achievable S/N and ground loop immunity would suffer.

Front view of the amplifier

PMA-NC252MP_front_shrps.JPG


Rear view of the amplifier

PMA-NC252MP_rear_shrps.JPG


Technical specifications
  • balanced input impedance | 94 kohm​
  • frequency range | 10 Hz - 50 kHz (+0/-3dB)​
  • power bandwidth | 20 Hz - 35 kHz​
  • output noise voltage | 36uVrms (20Hz-22kHz unweighted)​
  • equivalent input noise voltage | 1.8 uVrms (20Hz-22kHz unweighted)​
  • output power | 2 x 250 W/4ohm​
  • output power, one channel driven | 300W/4ohm/1kHz/THD 1%​
  • S/N at 300W/4ohm | 119.6 dB​
  • THD and THD+N | see the datasheet and measurement below​
  • SINAD | 98.15 dB at 5W/4ohm/1kHz @22kHz BW​
  • CCIF IMD 19+20kHz | 0.0025%/20W/4ohm​
  • gain | 26 dB​
  • dimensions | 430 x 390 x 160 mm​
  • weight | 11 kg​

Measurements

The amplifier meets Hypex electronics specs that can be found in their datasheet

THD vs. output power at 1kHz into 4ohm load, one channel driven
PMA-NC252MP_THDampl%_4ohm_1kHz.png


THD vs. output power at 20Hz into 4ohm load, one channel driven
PMA-NC252MP_THDampl%_4ohm_20Hz.png


THD 5W/4ohm/1kHz (added 12/22/2021)
PMA-NC252MP_THD_5W4R.png


Thermal management

Due to the quite large case with heatsinks with fins, the amplifier runs cool under any output power.

Pavel Macura, December 21, 2021
 
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LEGCRAMP

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Are you going to be building and selling these? Looking to build/buy these for myself but the modules are so hard to find nowadays.
 

Matias

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Wow with all this heatsinks the cost is going to quite high, both product + shipping.

How long does it last running full power?
 
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pma

pma

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Are you going to be building and selling these? Looking to build/buy these for myself but the modules are so hard to find nowadays.

I am not sure yet. This is a prototype and I want to test it and run it in everyday operation for 6 - 12 months. I have no personal experience with class D modules reliability and want to gain some. Definitely it is not intended to be sold soon.
BTW, even in this casework with large heatsinks the weight is half of the weight if the class AB amplifier of similar output power and with linear PSU is inside. Big toroidal transformers + capacitor bank missing make the weight difference.
 
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MakeMineVinyl

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I do not know, yet. There seems to be no problem with long - term continuous power. My test load (6R8 // 10R 200W resistors built on heatsink) gets too hot earlier than the amp starts to be even mildly warm.
In my experience with Hypex modules like this, and using heatsinks, the run time with continuous high power is basically forever.
 
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pma

pma

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Some more IMD and multitone measurements

PMA-NC252MP_SMPTEIMD_5W_4R.png


PMA-NC252MP_DINIMD_5W_4R.png


PMA-NC252MP_TDFDIMD_5W_4R.png


PMA-NC252MP_multitone_2.5W_4R.png


P.S.: the small spectrum peak at 8kHz that is present in all measurements does not come from the amplifier, but it is a bug from my measuring system. Haven't fixed it, yet :(.
 
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pma

pma

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Add audio sense and some VU meters and i’m sold!

Thanks, but as said, this is a prototype for me to evaluate the Hypex NC252MP OEM module. I have made no decision on production, yet. The production is a lot of stress then, you know, been there. In my age and situation, I have no urgent need to make money. Rather it is a pleasure of investigating of new design solutions, better than to repeat statements that amplifiers were better 40 years ago (which is not true) :).
 

Madjalapeno

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pma

pma

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Another source. Not sure if it would be any cheaper for you though.


Interesting! Probably yes. Even if there would be shipment costs, duty and VAT above it. It would need a proper calculation. Anyway thanks for the link!

Correction: ..... probably not - the shipment cost would be $105.97 .....
 
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Larry B. Larabee

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Good Luck if you decide to go ahead. This is what a 'Class' D amplifier should look and perform like.
Do you think you can get it to under $2000 Usd?
 
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Prana Ferox

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I was wondering if you were going to mount the module directly to the heatsink.

I still think this case is overkill for the application. Outside of pumping sine waves for forum measurements, I don't see a home audio application with continuous power draw / heat generation that remotely requires it. Yes, the datasheet says it can put out 110w of heat, but that's at 100% duty cycle; even a constant 1/8 duty cycle is <14w and that's not hard to passively dissipate. In a professional application (which Hypex designed this for) you would forced air cool these. Right now that right-side heatsink is just wasted weight and cost. At the least, if I were to use this case, I'd put two NC500MPs in to justify it.

The interior craftsmanship is nice work, pma.
 
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pma

pma

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Good Luck if you decide to go ahead. This is what a 'Class' D amplifier should look and perform like.
Do you think you can get it to under $2000 Usd?

Thank you! You have made a good guess, regarding price, if this would be produced :).
 
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