PMA-NC252MP power amplifier

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, amplifier with rated power 2x250W/4ohm and based on the NC252MP OEM modules.

Hypex NC252MP OEM module

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 behavior 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.

Amplifier front view

Amplifier rear view

A brief look inside the prototype ...


Wiring diagram

Technical specifications


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

Frequency response

THD vs. output power at 1kHz into 4ohm load

THD vs. output power at 6kHz into 4ohm load

THD at 102W/4ohm/1kHz

THD at 201W/4ohm/1kHz

Thermal management

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


@Pavel Macura, December 22, 2021. Last edited February 20, 2022.