Commodore Sound Expander

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Commodore Sound Expander
The Commodore Sound Expander cartridge
Type: Cartridge
Producer: Commodore/Music Sales Limited
Price: 125 US$; 99.99 £; 399 DM (ca. 200 €)
Released: 1985
Discontinued: 1986
Processor: Yamaha YM3526 OPL
Info: External Software "F.M. Sound Expander" with C64, SFX or MIDI keyboards

The Commodore Sound Expander or SFX Sound Expander is a sound synthesizer cartridge with 9 voices for the Commodore 64. It was developed by Richard Watts. The synthesizer chip is a Yamaha YM3526 OPL, which can upgraded by a YM3812 OPL2 chip, which is also used by AdLib- and Soundblaster sound cards in PCs. This cartridge was produced by Music Sales Limited in the UK and marketed as "Commodore SFX series" by Commodore world-wide.


Commodore cartridges: SFX Sound Sampler, Magic Voice (Speech Module) and Sound Expander (FM Sound Module).

The cartridge is plugged in into the expansion port of a powerlesss C64. The audio plug can be plugged in into speakers or devices which have a speaker plug in. Also can added the external SFX keyboard with 61 keays and 5 octaves


A manual (user's guide) exists, but provides very little technical information. And also the audio lead book "Start Playing Keyboard - The SFX-Tutor" by Peter Lavender.




  • Used Chips:
  • ROM : ?
  • RAM : ?
  • Dimensions: 53 × 140 × 135 mm
  • Weight: 315? g
  • Power Supply: 5 V= through C64 expansions port
  • Power: ca. ?? W
  • Ports:
    • Expansions port for connection other cartridges
    • Cinch for audio out
    • SFX interface for connection a external SFX keyboard.
  • Extras:
    • Chinch cable
    • Software "F.M. Sound Expander" (aka "Riff Machine") by Music Sales Ltd. on datasette or disk.
    • Manual in Language:english or Language German
    • Songbook by Peter Lavender: "Start Playing Keyboard - The SFX-Tutor" (Music Sales)
    • Keyboard stickers
  • Optional extras:
    • Plastic overlay keyboard for using on C64 keyboard
    • Commodore SFX keyboard with 61 keys and 5 octaves
    • MID interface for other MIDI keyboards
    • Software: "FM Composer and Sound Editor" (2 programs with manual)
    • Other songbooks avaiable

Technical Details[edit]

Reverse engineered schematic (SVG)



Clone without external keyboard connection.

Since 2016 exists a "Sound Expander clone" by Krzysztof Iwanowski, which can bought for 25 Euro.[1]




WP-W11.png Wikipedia: Yamaha_YM3526
WP-W11.png Wikipedia: Yamaha_YM3812