Divide down based tone generation. Able to mix 4 different sections; Brass, Piano, Reed, Strings. Updated Orchestra 1. Near identical to OR-400 apparently as well as the SCI Prelude. My prelude I see varies in that it has "organ" instead of "Reed". Of course there *are* 'reed organ' instruments but maybe they actually voiced this a little different? Never heard one so not sure. THe organ section's controls read "Pipe, organ 1, organ 2) on the SCI rendition, while on the Siel marketed machine "Church organ, Accordian, Musette". So I'm kind of guessing it's just a label variation.
The string section is identical. The Piano section varies only in the labelling again probably with the SCI unit reading "Decay, Piano 1, Clav, Piano 2" and the Siel "Decay, Piano, Clavi Chord, Honkey Tonk". Attack, cutoff preceedes both Brass selections but the SCI says "Brass 1, Brass 1, Swell, Resonance" afterward. The Siel "Trombone, Trumpet, Crescendo, Resonance". Siel also adds the helpful word "Decay" before footswitch on the back :-). Everything else on the EQ and modulation is identical it appears.
Anyway I haven't seen an actual schematic on these yet. May comment more later when/if I do. HOWEVER in working on my first OR400 here..I see that the power supply board is the same part number as in the Siel Mono for which schematics are available online in nice pdf. It's fairly simple to modify to use standard 7800 series regulators in place of the old uA78MG/UA79MG devices. Also note that there are 10 ohm fuse resistors off ceramic standoffs that can blow if an op amp shorts out etc. on all the back boards and bottom board. A power supply problem caused a lot of deaths and some burned traces also in the unit I'm working on now. op amp on right under keyboard took out raw signals. Bad 13700 took out brass. Someone had already replaced a bunch of stuff and I've done half a dozen chips now and more to go! Luckily they're all socketed or this would have been a scrapper for sure.
I have the SCI Prelude and it's capacitors have drifted so that decay times vary quite a bit. I may just sell it because I have so many similar types of machines and don't need another job like that.
I have several scraps from Siel units and lots of the discrete parts.
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