The APSU is designed to power stereo Class AB audio amplifiers of up to 200W per channel and stereo Class A amplifiers of up to 60W per channel. It includes inrush current limiting and mains DC blocking and has been very carefully laid out so that radiated noise is at an absolute minimum. The layout of the supply rail terminals ensures there are no common impedance coupling issues, and for those wishing to use the Hifisonix speaker protection board, the required V+, 0V and AC detect terminals are conveniently grouped together.
The APSU uses a mains-powered relay to provide convenient ON/OFF power control using a 30mA AC mains-rated anti-vandal switch, of which there are many attractive, low-cost options.
The PCB measures 177.5 x 95 mm and accommodates 4 x 22,000 microfarad capacitors and a bottom-side mounted 50A bridge rectifier that mates thermally to the bottom plate of the amplifier chassis.
This power supply removes all of the guesswork with regard to power supply wiring, layout and functionality, offering a complete, very high-performance solution in a compact PCB layout. Just add an appropriately sized low noise toroid, ensure all wiring to and from the APSU to the toroid and the amplifier modules is tightly twisted and cable-tied, and mains noise floor figures as measured at the amplifier output of better than 120 dBr are achievable.
The measurement below was taken on the ax-Amplifier using the APSU. The power supply load current is 4.4A continuous off +-40V rails. The noise floor with respect to 60W RMS output in Class A is below -130 dBr from 100 Hz upwards, an exceptional result, and in part due to the quiet power supply and good wiring practice (note: the ax-Amplifier PSRR is also very high due to the action of the AFEC circuit).
Here is the build document: https://www.hifisonix.com/wp-content/uploads/2026/07/APSU-July-2026-1.pdf
Click here for the BOM: https://www.hifisonix.com/wp-content/uploads/2026/07/APSU-BOM-July-2026-1.csv
If you’d like to buy a PCB for this project, head on over to the shop by clicking on this link: APSU ‘Amplifier PSU’ – hifisonix
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