[sdiy] circuit bending a yamaha fm piano question

Batz Goodfortune batzman at all-electric.com
Fri Aug 23 17:59:15 CEST 2002

Y-ellow Theo.

At 05:31 PM 8/23/02 +0200, Theo wrote:
>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?

Not if it's got a 2 chip FM chipset. The 2 OP synths are generally based on 
something like an OPL2 or 3. The latter of which is quite a powerful little 
synth in it's own right if you can find a way of programming them. This is 
sadly neglected on 99% of sound cards that possess them. There is however, 
some third party software that can do this. Some of it's crap and I don't 
know about the others. I will find out in due course as I'm trying to 
accumulate as many of these things as I can. Reading the data sheets they 
seem a doddle to engineer into something else. I'd always wanted to combine 
an OPL3 and a SID. :) But that's a whole other story.

By the time the OPLx came along, they were all tiny SMD chips about as big 
as your little finger. Compared to the behemoths that preceded them. The 
OPLx chips are essentially the same as the chipset in the TX81Z in fact. 
Except that the 81Z does 8 straight up voices while the OPLs running in 4 
op mode, only do 5 plus some drum type sounds. There are a number of 
variations on the flavor. However both they and the 81Z share almost 
identical feature sets.

Now the really early 4 OP tone generators such as the FB01 and the FSG01 
(In the CX5M msx computer.) were single chip FM synths. I can't remember if 
the D-As were inboard or not off hand but there wasn't much analogue to be 
seen in the FSG01. Without dragging down the service manual I can't 
remember off hand. But the FM chip it self was a single 28 pin DIP. The 
other chips involved in that system were simply an I/O processor which 
scanned a dumb keyboard and MIDI, and in the msx it self, yamaha made a 
derivative of the  8910 bleeps and blerps chip that was popular. (Err TI 
wasn't it?) Their mod allowd it to pass the stereo FM synth audio into the 
normal msx channel for people who wanted to listen to their music on a TV. 
(Why bother?)

And since the FSG01 predates even the FB01, I can only assume that this 
piano is very old indeed and has a DX9-like chipset. Which was in fact just 
a DX7 chipset that didn't go fast enough. (IE: Checked working but not 
working well enough.)

To clarify something here though. There are always 2 chips. Even with the 
OPL3s. It's just that we don't include the D-A chip in the equation because 
Yamaha are so good at changing their mind. With the OPL3 you had a choice 
of 2 D-A chips depending on configuration and date. But the choices didn't 
stop there. Some OPL3s conformed to a more-or-less standard 3 wire I2S bus. 
Some didn't. Some had the D-A built in. Most didn't. Some could be 
connected to the digital-in stream of the host chipset. Some couldn't and 
as with the Crystal 8431 card I'm looking at here, the OPL3 system and the 
digital audio system are two separate entities only meeting at the analogue 
mixer stage.

And just to top it all off, Yamaha seem to have a habit of changing the 
part numbers depending on what format the chip comes in. So you never 
really know if it's the same chip or a slightly different one or even a 
completely different one. But there is a base level of backwards 
compatibility with all of them. All of the 4 op synths accept essentially 
the same parameters in the same order. The 6 Op chips are the same as the 4 
op chips except for the 2 ops, extra algorithms and feedback parameters. If 
you look at the algorithms you'll notice some remarkable similarities at 
the base level.

I think I'm very very tired and repeating myself so I'll end it there. 
Except to say that if What Peter has said is correct then this should be 
the case and all that I've said has been based on that. But Peter should be 
able to track down the chip set from those sites and then have more of an 
idea of what the score is.

Hope this helps.

Be absolutely Icebox.

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