[sdiy] Siel opera6 schematics

[Scott Nordlund]

I have similarly repaired mine (a DK 600, and also the Expander module), though there are still some problems.  Until it "warms up" it sometimes doesn't produce a sound, and some parameters can be mysteriously changed by tapping on the case.  This may be partly due to those awful DIP connectors... Also voices 5 and 6 have some sort of interference that comes in somewhere (a CV I guess) and distorts the sound somewhat.  I imagine both of those would be a pain to figure out.

I have considered modifying the voice board, though the actual construction would probably be a real headache.  Still I wonder what it would sound like to "cross modulate" the oscillators by mixing the saw reset pulses (the Roland JX3P and JX8P seem to do something along these lines, though I don't know what else is going on simultaneously)... also saw to tri converters, sub oscillators, xor "ring modulation", independent speed/depth controls for LFO 2, another LFO for PWM, filter FM... well maybe not...

> Date: Wed, 17 Dec 2008 14:37:19 +0000
> From: neil.johnson97 at ntlworld.com
> To: damsagain at free.fr; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Siel opera6 schematics
> CC: 
> 
> Hi there,
> 
> Interesting topic - I'm re-engineering a Siel Opera 6 that I picked up some time ago (*waves* - hello Julian!).
> 
> A first stop is the Siel site here:
> 
>    http://home-1.worldonline.nl/~smeyer/siel/
> 
> On the Opera 6 page you can find a link to the service manual, which includes full schematics.
> 
> There is also a group on yahoo for Siel synthesizers in general:
> 
>    http://launch.groups.yahoo.com/group/siel/
> 
> You can get a rough idea of the chip lineup from the VintagePlanet website:
> 
>    http://www.vintageplanet.nl/
> 
> According to that site the following would be my 'difficult-to-obtain' chip list:
> 
> SSM2024        Quad VCA . . . . . . . . . . . . . . . NOS    16.50
> SSM2031        VCO  . . . . . . . . . . . . . . . . . NOS    24.99
> SSM2044        4-Pole VCF . . . . . . . . . . . . . . NOS    19.50
> SSM2056        ADSR . . . . . . . . . . . . . . . . . NOS    35.00
> TMS3631AN2L    8-Channel Tone Generator . . . . . . . OR     48.50
> TMS7002NL-2    8-Bit Monolithic CPU . . . . . . . . . OR     32.50
> DAC0831LCN     8-Bit DAC  . . . . . . . . . . . . . . NOS     8.50
> M5517APL       SRAM 2K x 8  . . . . . . . . . . . . . NOS    14.90
> MC68B50P       Asynchronous Comm Interface Adapter  . NOS    27.50
> MM5837N        Noise Generator  . . . . . . . . . . . Out of stock
> 
> (Prices are including Dutch VAT)
> 
> The one VERY important point is to check if the memory backup battery has leaked.  If it has - and eaten into the PCB and surrounding components - it is going to be a right pain to fix.  Bob has some useful comments:
> 
>    http://sounddoctorin.com/synthtec/siel/siel.htm
> and
>    http://sounddoctorin.com/synthtec/siel/dk600.htm
> 
> The oscillators have an interesting architecture.  The two core oscillators are analogue high-frequency VCOs (SSM2031).  These then drive dividers to give 4', 8' and 16'.  Then follows two 8-channel (although only 6 are used) programmable tone generators - TMS3631.  These output pulses that are used to reset simple analogue sawtooth circuits.  The rest is pure analogue.
> 
> Pitch modulation (pitch bend and LFOs) is applied to the high-frequency VCOs.  So I'd say this is a hybrid VCO/DCO system - the only stable crystal oscillator in the entire synth is that used to provide the clock to the CPU.
> 
> Notes of my on-going project are here:
> 
>    http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=4&subsubmenu=4
> 
> Cheers,
> Neil
> --
> http://www.njohnson.co.uk
> 
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