New Amiga PSU+ (my own improved variant with Ripple & Noise & Emi filtering & case)

[StingerHU]

For some time now, after the C64 PSU+ (for which I designed everything myself, from the very first circuit to the very last component), I have been working on my Amiga PSU+ power supply, which I have now successfully completed. It is basically built around a Mean Well RT-65B, so I did not design the central switch-mode power section myself; however, I did design a multi-stage ripple/noise/EMI filter circuit for it, into which I also integrated an additional so-called crowbar Zener-diode overcurrent and overvoltage protection — on all three rails.


The reason for this is that, due to their switching operating principle, Mean Well switch-mode power supplies have a very high ripple-noise level, which can cause interference, noise, ripple, and similar issues in sensitive circuits such as the Amiga 1200, affecting video, audio, and other circuit elements. According to the datasheet, this value is typically around 80–120 mVpp depending on the voltage rail, but after extensive testing and design work, I managed to reduce this by approximately 80–85%. The measurements were performed with an oscilloscope, both before and after the modifications, and also under load.

So how does it work?

• The incoming current first passes through a fuse, after which a ferrite bead and a 100 nF ceramic capacitor are connected in series. The ferrite beads attenuate high-frequency noise, while the 100 nF X7R capacitor placed before the ferrite already cuts off very fast spikes at the input, allowing the ferrite to work more effectively.
• The LC filter section (L1–L3 together with C1, C3, and C5): the 33 µH inductors attenuate the main switching-noise band (tens to hundreds of kHz), while the 1000 nF low-ESR electrolytic capacitors absorb the remaining lower-frequency ripple (low series resistance, low ripple).
• The ceramic capacitors connected in parallel filter the mid-to-high frequencies handled by ceramic caps (where electrolytics already become more inductive), ensuring low impedance over a wide frequency range.
• The Zener + clamp circuits and the series resistors next to them are inactive during normal operation, but in the event of an overvoltage spike they quickly clamp the peak, while the series resistors protect the Zener diodes from impulse current.
• The ground planes on both sides and the stitching vias provide short return paths and low parasitic impedance, resulting in less noise, fewer loops, and more stable filtering.
• The toroidal inductors and the shielded layer underneath do not radiate into the environment, and the copper keep-out prevents nearby eddy currents and capacitive coupling, making the solution even more effective.

Together, these form a multi-stage, wideband filtering chain with spike suppression, damping, ripple reduction, and, last but not least, safety overvoltage and overcurrent protection.

As with my C64 PSU+ project, I also designed a completely custom enclosure with a proper layout in which everything has its place. It is safe, made of industrial-grade PETG, resistant to chemicals, heat, and impact, and overall a solid, robust piece. I am attaching a few photos of the finished project.

The best part is that within the Hungarian Amiga community, several people are already happily using this noise filter (among others BSzili, who makes excellent Amiga game ports — special thanks to him for being my first test user ), because I designed it so that it can even fit into the original Amiga power supply housing. It can also be used on its own; this new enclosure and the Mean Well RT-65B are not required. (The new enclosure design for the power supply exists only to make the story complete and to match my earlier C64 PSU+ (and C15X1 PSU+) projects)

ps: the red C logo light is not so bright, just my phone improved it due to HDR.
Attaching a few pictures about the design/final product.
Happy new year for all Amiga enthusiasts!