[sdiy] Yamaha CSY-2 solo synthesizer

[Scott Nordlund]

> VCA, FEG and AEG contain standard parts, CA3080 OTAs in metal can packaging
> and so on. The VCA board is self explanatory, the FEG board is for the
> filter envelope and the AEG board is for the amplifier envelope. No NE
> modules here, in particular no VCF-EG or VCA-EG modules. This is the only
> example of these Yamaha envelope generators I have seen, again completely
> undocumented on the internet as far as I know.
>
> The remaining boards, SK and SP, seem to be the same as in the older
> machines. They are for the gate and trigger pulse recovery and for the
> presets.
>
> Sound-wise, it behaves much like a cross between the two generations. The
> oscillator definitely has the same timbral qualities as an SY-2, but the
> filters are much, much cleaner. I wouldn't go so far as to say they sound
> like CS series IG chip filters, but they are certainly more well behaved
> than the highly distorting diode bridge filters in the NE series epoxy
> filled modules.
>
> Richard

I won't try to speculate too much, but those potted NE modules don't 
contain anything especially exotic.  Korg used similar modules in their 700,
700S and 800DV synths, but the 770 uses the same circuits without encasing
them in epoxy; they're described in the schematics also.  It may have been 
decided that the secrecy wasn't worth the trouble.  So it may be early 
versions of what was later integrated into the IG series chips (I think you 
can similarly follow the evolution of Roland VCFs from the BA662 ones to 
the IR3109), and/or the NE module contents laid out on a new circuit board.
Certainly of interest to anyone who wants to make replacement parts.

Organs can be strange beasts; higher end models sometimes used very exotic
synthesis techniques that never made it into synthesizers, and I think 
there are some interesting drum machine circuits that are still "unknown"
to the rest of the electronic music world. But there's very little interest
now, and given the opaque interface and lack of documentation, there's no
good way to know what's really going on in there.