The NXA20L now has the entire input driver stage power supplies on board, so all that is needed is a small power transformer to run it. The remaining power supply for the output stage is provided by an external power board like the PSU One or the PSU Two power board.
Typically this would be one of the PSU Two boards or a suitable hand wired power supply.
The Class A module also has a much more complex and accurate bias control circuitry.

The new Class A module has electronic voltage regulation for the Input-VAS stages, DC Servo for less than 1mv DC offset, Baker clamps for perfect high frequency clipping behavior and 4 position DIP switch selection for 9dB of gain adjustment starting at around 27dB down to 18dB of Global Gain.

The PCB has been designed around the NXV500L form factor and the 4 main output devices have the same positions as the NXV500L module, so for those that already have the 500L or R2 module and want to try out the Class A module, the new Class A module is a practical drop in replacement, with exception to a power supply replacement or reconfigure to suit the Class A module requirements.

With 4 single die lateral MOSFETs on board this module can deliver just over 20 watts in Pure Class A into 8 and 4 ohm loads.
The Input-VAS stage supply requires +-30 volts to +-35 volts DC input from a raw DC supply to feed the on board power voltage regulators which the regulate this down to a very smooth and quiet +-26 VDC.
The Output stage just requires +-23VDC from a 160VA raw DC supply.
DC supply filtering for the output stage is recommended at 20,000uf per voltage rail as a starting point.
Input-VAS DC raw filtering is much less demanding at 4700uf per voltage rails as a good starting point.

The Class A module has been designed as a Mono Block amplifier in mind, so two separate power supplies as described above would be highly recommended for the best performance.

Total Harmonic Distortion for 1 watt is 0.003% 1khz and 10khz at 0.005% into 8 ohms loads
15 watts it is almost the same at 0.0035% 1khz and 0.0047% 10khz.
Signal to Noise Ratio is -103dB at 27dB Gain.
The PCB dimensions are 220mm x 65mm

For more information please contact me via info@holtonprecisionaudio.com or visit the HPA Facebook page for additional comments and notes about this module.

HPA-NXA20L Specifications

• 20 Watts RMS sine wave into 8 Ohms Per Channel with 1.7 amps bias
• 40 Watts RMS sine wave into 4 Ohms Per Channel in Class AB
• Biased into Pure Class A
• Power Bandwidth 3.5hz to 350khz -3dB
• THD+N 0.003% 1khz, 10khz 0.005% @ 1 watt - 8 ohms
• THD+N 0.0035% 1khz, 10khz 0.0047% @ 15 watts - 8 ohms
• THD+N 0.0055% 1khz, 10khz 0.008% @ 22 watts - 8 ohms
• Dampening Factor At 100hz 8 Ohms = 800
• RCA Single ended Input impedance 22k Ohms
• Single Ended Input Gain = 27.0dB Position One.
• Single Ended Input Gain = 24.0dB Position Two.
• Single Ended Input Gain = 21.0dB Position Three
• Single Ended Input Gain = 18.0dB Position Four
• Signal to Noise Ratio -103dB @ 27dB Gain Setting
• Recommended Linear Voltage Supply for Output stage +-22 Volts DC
• Recommended Linear Voltage Supply for Input stage +-35 Volts DC
• 35 volt raw supply is regulated down to +-26 volts DC
• One x 160VA power transformer with 2 x 18VAC secondary windings.
• One x   50VA power transformer with 2 x 25VAC secondary windings.
• Printed Circuit Board Dimensions 220mm x 65mm
• Minimum Heat Sink Conrad MF35-100 or MF35-151.5 per channel.
• Amplifier can be switched into low power dissipation or standby mode

Recommended parts to build a Mono Block NXA20L Amplifier.

• 1 x HPA-NXA20L Mono Amplifier Module
• 1 x HPA-Power One R3 AC Mains Controller
• 1 x 160VA power transformer with 2 x 18VAC secondary winding's.
• 1 x 50VA power transformer with 2 x 25VAC secondary winding's.
• 1 x Conrad MF35-100 heat sink 350mm x 100mm x 48mm
• 1 x Chassis Two R2 Case with built in Conrad MF35-100 heat sinks

Recommended parts to build a Stereo NXA20L Amplifier.

• 2 x HPA-NXA20L Mono Amplifier Module
• 1 x HPA-Power One R3 AC Mains Controller
• 1 x 300VA power transformer with 2 x 18VAC secondary winding's.
• 1 x 50VA power transformer with 2 x 25VAC secondary winding's.
• 1 x PSU Two power supply board for the output stage supply
• 1 x Conrad MF35-100 heat sink 350mm x 100mm x 48mm
• 1 x Chassis Two R2 Case with built in Conrad MF35-100 heat sinks