[sdiy] circuit bending a yamaha fm piano question

Theo t.hogers at home.nl
Fri Aug 23 17:31:27 CEST 2002


The 64 bytes for each voice sounded fishy to me too, even 4 op FM voice
should need more.
But there where PSR? "home"(toy?) keyboards that where in fact programmable
2 operator FM synths.
My thought was could this piano module be in the 2 op category as well?

Theo


From: Batz Goodfortune <batzman at all-electric.com>

> 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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