PCB Filtering Board for Amiga 500/600/1200 Power Supply Replacements

A filtering board for home-made replacements of Amiga 500/600/1200 power supplies, designed specifically for Mean Well RT-65B/RT-50B converter modules.

Problem it solves: Mean Well modules provide the required voltages (+5V, +12V, −12V) but generate switching ripple and high-frequency noise, which can impair the stability of the Amiga. The creator emphasizes that the Amiga 1200 is especially demanding regarding the cleanliness of the +5V rail.

Filter architecture (multi-stage):

• 100nF ceramic capacitors for initial filtering of fast high-frequency spikes,
• Ferrite beads (~86Ω @ 100MHz) for damping noise in the MHz range,
• Toroidal coils of 33µH as the main stage of the low-pass filter,
• Low-ESR 1000µF electrolytic output capacitors,
• 0.22µF ceramic bypass capacitors for residual high-frequency noise.

Protections: Each rail has a separate 5×20mm fuse and overvoltage protection (Zener diode + series resistor) to catch transient states.

Test results: On a real Amiga 1200 under load, measured ripple on +5V was approximately 10–15 mVpp with stable voltage around ~5.0V and low component temperatures — meaning the filter effectively works.