[sdiy] Siel opera6 schematics

[neil.johnson97 at ntlworld.com]

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