Omega MSX2+ F4-FMPAC v3.2 — FM Sound Module Denjhang Edition

Watch the F4-FMPAC v3.2 in action: Video 1 · Video 2

What is it?

The F4-FMPAC v3.2 is an FM sound expansion board for the Omega MSX2+ home computer, with a PCB originally designed and optimized by Denjhang. It adds FMPAC and MSX-Music (OPLL / YM2413) compatibility to the Omega MSX2+, unlocking FM music playback for MSX software that supports these standards.

What Makes It Special

• Denjhang's original PCB design: Optimized layout and dimensions tailored to the Omega MSX2+, with carefully separated digital and analog signal paths.
• Designed for production: 0603 resistors and capacitors on the back of the PCB help speed up assembly.
• At-a-glance diagnostics: Red and yellow LEDs on the front indicate VCC and A.VCC status for quick power checks.
• Cleaner analog layout: A common-mode choke isolates the digital and analog ground domains. Separate digital and analog signal paths and ground planes are designed to reduce interference and improve FM audio quality.
• Single 5V supply: Unlike v1/v2, v3.2 does not need a separate +12V/-12V supply or an LM7805 voltage regulator, simplifying installation and reducing power consumption.
• Refined FM audio: Drawing on the REBirth RE2-YM2413 sound card's differential amplifier circuit, the NE5532 helps cancel noise between the melody and drum outputs for cleaner FM sound. An LMV358 rail-to-rail preamplifier further refines audio output.
• Adjustable FM volume: An onboard potentiometer lets you tune the FM output level.
• FMPAC & MSX-Music compatible: Supports both FMPAC and MSX-Music (msxmusic) standards.
• Z80 socket installation: Inserts via two pin headers into the Z80 processor socket. Remove the original Z80 from the motherboard and re-seat it on this board.

Power Requirements

F4-FMPAC v3.2 runs on a single 5V supply. No separate +12V/-12V power supply or LM7805 regulator is required for this version.

BIOS / ROM Note

For full software compatibility, the Omega system ROM must be reprogrammed to include the BIOS extension that enables FMPAC/MSX-Music support. Without it, software that detects the FM extension will skip this module and use the primary FM system instead.

Differences from F4-FMPAC v2

• Single 5V power supply instead of requiring ±12V; no LM7805 regulator
• 0603 resistors and capacitors on the PCB back for faster assembly
• Front red and yellow LEDs for VCC and A.VCC status
• Common-mode choke and separated digital/analog signal paths and ground planes
• NE5532 differential audio stage, adjustable FM volume, and LMV358 rail-to-rail preamplifier
• No ROM socket on the PCB
• No cartridge slot signal connections
• Layout and sizing optimized for Omega MSX2+ by Denjhang

Project Credits

• F4 schematic by Kamil Karimov (2011)
• FMPAC Light schematic by Jipe (2010)
• Board and optimizations by RBSC (2016–2018)
• v2 design by MSXmakers
• v3.2 original PCB design and optimizations by Denjhang

Assembly Reference

Assembly instructions for v2 are available on the msxmakers.design.blog F4-FMPAC project page. Note that v3.2 uses 0603 components on the back and has different power requirements.