[sdiy] circuit bending a yamaha fm piano question

[Batz Goodfortune]

Y-ellow Peter 'n' all.
         I don't know these boxes at all but I know most of Yamaha's 
programmable FM devices.

What you have to do is find out what synth it's closest to. It sounds like 
a DX9 or something if it's got 2 chips. If each voice is only 64 bytes then 
I'd assume it's 4 op FM. I can't remember off hand if the 6 op synths are 
128, 176 or 256 bytes. It's confusing because there are two types of SySEX 
dumps and neither of them actually have the exact same byte count as what 
is supplied to the chips. Though they're close.

The confusing part comes from the fact that single on/off switch type 
parameters can be shoved 7 at a time into a single MIDI word. Where as they 
can be 8 bits or consume an entire byte each within the machine. However, 
regardless of the MIDI bulk dump format, the voices are all stored machine 
ready in the RAM (Or ROM as the case may be.)

All Yamaha FM machines past MK 1 used a single FM chip. However most of the 
4 op synths were all single chips. The DX9 was the exception because it was 
in essence, a stripped down DX7 using the chips that failed to operate in 6 
Op mode but were adequate for 4 Op.

But there is another possible explanation for why there are only 64 bytes 
of data per voice and not more. Because many of the programmable parameters 
in a DX have probably been hard wired in the piano. Which leaves only the 
basic voice data. That being the case I'd guess that the 64 bytes of the 
voice are equal to the contents of register address 00h - 3Fh in the EG 
chip. Yamaha laid the whole thing out logically so that all the CPU has to 
do is a block load. There are however a number of transient parameters but 
I don't think these would be a problem in this case. If you know what the 
registers do (And that should be in the manual) you know what the contents 
of the patch in ROM are. Sands for transient parameters such as key 
number/velocity and LFO. The latter generated by the CPU.

Your best bet would be to find the synth that has the same chipset. OR. if 
they've renumbered them (And they have been known) then deduce which one it is.

There are a number of sites that might be of assistance in doing that 
without having to own all the service manuals.

http://www.astercity.net/~malf/
http://www.fee.vutbr.cz/~arnost/opl/opl3.html
http://student.cusu.cam.ac.uk/~rga24/computer/music/index.html
http://tenacity.hispeed.com/aomit/oplx/
ftp://byrd.math.uga.edu/pub/html/dx7.html    <--
http://www.motetmusic.co.uk/~synths/yamaha/yamaha.html

If these don't have the NFO you're after, they should have pointers to 
finding it.

Hope this helps.

Be absolutely Icebox.

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