Hacking the Yamaha DX9 To Turn It Into a DX7

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2025-01-19 22:00:18

In light of reaching the milestone of releasing Version 1.0 of the DX9/7 firmware, I've made a few updates to this article. The most significant update is the addition is about some interesting leftover data found in the Yamaha DX9 ROM. Also, a big thanks to the amazing Olli Niemitalo for correcting an error in how I was calculating the DX7/9's voice update frequency!

Like many vintage synth enthusiasts, I keep a keen eye on the local classified sites for the odd bargain that might pop up. Late last year, amidst the usual sea of second-hand Roland grooveboxes, and Korg Volca synths was something I'd never seen before: A Yamaha DX9.

After my 2021 project creating a detailed technical analysis of the DX7, and my subsequent disassembly of its firmware, I figured there wasn't too much more I needed to know about the inside of the DX7... Seeing the DX9 —advertised at half the price of a DX7, no less— an interesting thought crossed my mind: Could the DX9 firmware be hacked to restore its missing features?

In 1983, Yamaha released the groundbreaking DX7 synthesiser. It featured a revolutionary new sound generation technology which would change the course of popular music, and help define the signature sound of the 80s: Frequency Modulation synthesis. Simultaneously, Yamaha launched the DX9: A more affordable alternative featuring the same FM synth engine, but substantially more limited features than its more popular sibling.