Siel Opera 6
~ A Synth Re-Engineered ~
Several years ago I was given a non-working
Siel Opera 6 by a very generous guy
synth-diy mailing list.
As befalls many of these particular synths the backup battery had leaked sometime in the past
and attacked the CPU
board resulting in much damage to tracks and components. Considerable work would be
needed to bring this synth back to its original condition.
A fellow Opera 6 owner recently sent me this photograph of the damage that this battery
Disaster!!!! Courtesy of Fabrice Bertaux.
So I have decided to re-engineer it.
This page documents the various changes and modifications I have, am, or planning to make to
this synth. I have made a conscious decision not to modify the
analogue voice board - this will be kept as-is.
So, to begin with, here is my Opera 6 right at the start of this project:
(Note the presence of
Cosmetic condition is not too bad, so nothing much needed there. The most egregious feature are the programmer
buttons - they will be coloured or replaced with some that are a little more in keeping with the colour scheme.
Twenty or so years after this synth was released, we now have blue LEDs.
One of this first things to do is replace all of the red LEDs with
blue ones. As well as replacing the red
LEDs I have also had to change the current limiting resistors from the original 270R up to 33k, otherwise
the blue LEDs are just too bright. It is even possible to change the LEDs
in the switches - you just have to carefully prise off the switch cap to get to the LED underneath.
The pots are standard "commercial" 16mm splined-shaft 10k linear pots. Rapid sell a TruOhm part
that is compatible, order code
The existing knobs looked a bit, well, sad. So I've found a nice replacement, in the form of the MultiComp
CR-MS-5 soft-touch knob, Farnell part
The result of these changes looks more in keeping with the grey/blue colour scheme:
I also hope to replace the 7-segment LED displays with blue ones, but it is
proving a little tricky to find drop-in replacements. I hope to avoid making up little adaptor boards.
In the meantime I have found some green 7-segment displays in
the form of Kingbright SC04-11GWA. They are stocked by
Rapid Electronics, order code
The color is a better match with blue than the old red
ones, and the effect is a brighter display.
After much hunting around, and a stroke of luck, I have found the manufacturer of the round push buttons
used in the programming section. They are made by
Camden Electronics Ltd, type
I have fitted a new set of black buttons, and I think the result looks much cleaner
than the original cream-and-red scheme.
In the UK they are stocked by Rapid, part no.
The photo below shows the new green display, new buttons (all black) and the blue LED on:
Pitch Bend Wheel
I have added a return spring to the pitch bend wheel, so now it springs back to the centre.
Thanks to the most excellent and very generous Gino Wong I now have a second analogue voice board.
And yes, it will be joining the existing voice board, making this a 12-voice Opera6.
That's 24 oscillators. Or two layered voice banks. Or true bitimbral operation.
Or one uber-ffaaatt monosynth.
A quick test proves that there is just enough room in the case to accomodate
the second voice board. One question remaining to answer is whether the existing
power supply is able to power two voice boards.
In the meantime I have sketched out the major blocks of the
Opera 6's voice architecture (PDF, 31kB).
The orange block represents the global controls on the original CPU board, and the
stack of green blocks representing the six voices.
Here is a growing collection of documents (all PDF) related to this project.
Manuals / Schematics
- High Frequency Oscillator
- Quad Current Controlled Amplifier
- 4-Pole Voltage Controlled Filter
- Voltage Controlled Transient Generator
The original processor board of the Opera 6 has two EPROMs marked "E000" and "F000". For posterity
I made a copy of the EPROMs in my Opera 6.
- Siel Synthesizers Website
- A very useful online resource for all Siel synthesizers. Well worth checking out.
- Siel Users Group
- A low-traffic users group for these interesting Italian synths.