[sdiy] Yamaha CSY-2 solo synthesizer

[The Old Crow]

     Speaking as asomeone who tore apart some of the NE series modules 
six years ago (see: http://www.cs80.com/ne_proj.html ), I can say that 
the state of Yamaha's combo organ design paradigm was in a state of 
extreme flux in the mid-1970s.  The early (1973-74) synthesizer stuff 
was all potted "for temperature stability" (read: to hide it from Korg) 
as back then there was this mad rush to market for combo synthesizer 
portable gear.  Of course, Yamaha's 1970s stuff was designed at their 
Electone organ facility in Hamamatsu by organ engineers, not 
"synthesizer engineers" like Moog, Oberheim or Buchla.  To this end they 
used the parts they used in designs of Electone models of the day.  The 
GX-1 (according to lead engineer at that time, Mr. Nakamura) was an R&D 
experiment mainly to test all possible aspects of making a polyphonic 
combo instrument using the means they had available.

   Yamaha had what most electronics manufacturers envied at the time: 
their own chip fab.  While this is less of an issue today, back then it 
offered a big advantage in design cost savings as their circuits could 
be done in NMOS, PMOS or bipolar.  Many of their logic engines such as 
key assigners were made this way.  Later DSP engines, too, were made 
this way--from the wavetable engine of the 'PASS' Electones up to the DX 
FM engines of the 1980s Electones and synthesizers.

   Around 1975, they stopped making the cost-inefficient NE potted 
modules in favor of the easier-to- assembly-line discrete boards.  This 
was about when the first part feeders came into use, and fitting TO-5 
cans was not a part feeder friendly package.  Thus, they switched to 
SIL/DIL packages for everything when they could.  The "VCOIII" (NE11500) 
was the only module made in potted form for temperature stable reasons.  
The module contains a sample/hold amplifier made from a complementary 
FET, an op-amp, some polystyrene caps and a low-impedance FET switch to 
open the sample path.  The Oscillator portion is a really vanilla 
sawtooth relaxation type with a FET buffer hung on the timing cap.  I 
recall there was an interesting vibrato CV input that used a little bit 
of piecewise-linear curve fitting to bend the CV into something that 
sounded good along the range of the VCO.  The IG00153 (CS VCO) is 
totally different.  It's closest cousin is the Rhodes Chroma VCO.

   The filters on the later CSY-2 use BA626 and BA627 diode arrays (SIL 
parts) instead of the CA3019s, but the filters are essentially the same 
otherwise.  The GX1 bandpass (NE11000) module uses these as well.

   The EGs would have been a pain to figure out, but the circuits show 
up in the Yamaha patents.  Nothing particularly amazing there, other 
than they crammed all those parts into those boards.

Scott Rider
/**/


On 11/9/2010 9:16 AM, Richard Atkinson wrote:
> This email may be of particular interest to anyone who has studied the 
> first and second generations of Yamaha synthesizer, namely the SY-1 / 
> SY-2 / GX-1 synthesizers with epoxy potted NE series modules in the 
> first generation and the CS series of synthesizers with IG series 
> chips in the second generation.
>
> It turns out there is an intermediate generation of Yamaha synthesizer 
> between these two generations. I found this when looking inside my 
> newly acquired Yamaha CSY-2 organ yesterday. This is a later version 
> of the CSY-1 organ, which has been featured in a few web pages and 
> Matrixsynth articles and which contains the same epoxy potted NE 
> series modules as the GX-1.
>
> I took the lid off my Yamaha CSY-2 yesterday with a friends's help. 
> The insides of my CSY-2 were rather dirty, having played host to a 
> number of spiders and other objects over the years. There was evidence 
> of damp damage on the base of the machine; it has clearly been kept on 
> a damp surface at some point for quite a while.
>
> It turns out the CSY-2 is very, very different internally from the CSY-1.
> Whereas the CSY-1 is a fully discrete design with many circuit boards, 
> some
> of them held vertically in a rack frame, the CSY-2 has the first signs of
> integration.
>
> In particular, the auto bass chord circuit board (ABC CSY-2) has two 
> large
> YM chips on it and there is another board with another large YM chip. The
> function of the auto bass chord system on this organ is quite different
> from the CSY-1, and this would seem to explain why. There is no rack of
> vertically mounted boards; there are much fewer boards and these are all
> mounted horizontally.
>
> Of particular interest is the solo synthesizer section mounted on the
> underside of the top panel of the organ. Like my CSY-1, the solo
> synthesizer boards in my CSY-2 are very clean, much cleaner than the rest
> of the instrument. This no doubt has to do with being mounted upside 
> down,
> gravity being in its favour.
>
> The CSY-2 does not however contain either of the versions of the CSY-1 /
> SY-1 solo synthesizer circuits. It's a completely different, much more
> integrated version of the solo synthesizer. The boards are not named SM1,
> SM2, SK, SP1 and SP2 as in the SY-2. Instead they are named VCO, VCF, 
> VCA,
> FEG, AEG, SK and SP.
>
> VCO is the only board that contains any of the old NE series modules. 
> It has the VCO-III module as seen in later versions of the CSY-1, SY-1 
> and all SY-2s.
>
> The VCF board has four ICs on it, all by Rohm. Two BA626s and two 
> BA627s. I
> have been unable so far to identify what these are but what is most
> peculiar about this is that the organ features neither the older NE 
> module
> based filters, nor the IG chip based filters of the CS synthesizers 
> and the
> later Electone organs, but a generation in between. This is the only
> example of this generation of Yamaha synthesizer filter I have ever seen,
> and as far as I'm aware it's completely undocumented on the internet.
>
> 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
>
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