YamahaSynths
Four-operator FM synth
The DX9 is a four-operator FM synthesizer made by Yamaha in 1983 as a lower- cost relative of the six-operator DX7. It has 16-note polyphony, eight FM algorithms and 20 preset voices, and user voices can be saved to cassette tape. It has no analog filter, since the sound comes entirely from FM synthesis.
The replacement ROM needs the DX9's mask ROM swapped for an EPROM. Per the project FAQ, early DX9s used two 2764-series EPROMs and later ones a single 27128, so a single-chip socket will likely be required. The first install of any version fills the synth's parameters with random data until reset by holding FUNCTION at boot; back up patches first.