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]

FM-YAM sound expansion with OPL2

Xentax released FM-YAM [2] in March 2018. FM-YAM is a Sound Expander compatible with ym3812 (OPL2), audio in (to mix SID audio) and audio out (with FM and SID mixed). Over 200 cartridges have been sold to date. See MsMadLemon's review here: It also featured in the Zzap!64 Annual 2019.



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