Elka Concorde 802 restoration
Yeah this was a huge project that took a full year to somewhat finish. 50 year old electronics don't do well when they're moist for a decade~
YouTube video series can be found here.
Here's the Service Manual for the 802. Since the file is so big I had to use Google Drive, go figure.
About the Elka Concorde and X-705 organs
Elka was founded in 1987 in Italy and primarily made organs until they were bought (together with Orla) by GEM... Which then was bought by GeneralMusic to mainly make amps. Of course Elka is most known for the Elka Synthex synthesizer, but they made so many more great things.
Elka had previously introduced their Rhapsody 490 and 610 string machines, the monophonic Solist 505 and the Wilgamat series of backing/drum machines. And then they got the wonderful idea of smooshing these all together into a couple of their organ models. This is where the X-705 and later the Concorde organs were born.
Comparing the schematics of these organs to the previously mentioned products indeed reveals barely any changes to the circuitry, they literally did just straight up put them into one big package.
Whereas the X-705 (left picture) came with two full size keyboards, the Concorde models instead had all sorts of variations in how you played them (see pictures below).
They mainly came with an accordion style chord keyboard for the left hand and either a normal keyboard or an accordion button keyboard for the right hand.
On top of that Elka just did great with the designs of these organs which led many people to lovingly call them "The Cockpit" as a nod to it's retro-sci-fi look and many big buttons and switches.
And yes, they are very satisfying :)
Pondering my Elka Concorde 802, the one with the button keyboards.
The Elka Concorde 902, it's the same as the 802 but has a normal keyboard for the right hand.
Another difference between the X-705 and the Concordes is that the former had two Rhapsody 610 string machines whereas the latter only had one. Further more the later Concorde models made the transition into digital circuitry and I believe sample based synthesis. But don't quote me on that one.
The Crazy Insides and the Restoration
To the left you can see the face of a man questioning his life choices... Luckily that didn't last long after the initial shock when I opened this thing.
So, a quick tally from the top of my head:
- Roughly 280 circuit boards;
- Too many old capacitors per board, hundreds in total;
- Various unobtanium AY-1 and other expensive analog IC's that I did not have the money for to replace;
- Several meters of wiring that goes all over the place, the color coding barely helps;
- PCB connectors were made of plastic that had gotten very brittle with age, which made (un)plugging boards rather scary;
- Dodgy solder joints everywhere, not sure if it's from the factory or other people have been into the guts too much.
Oh, and to top it all off:
- The only sounds it made were the demonic, tortured screeches or a synthesizer in horrendous pain.
...
Yep... But at least it was free! Right? :)
Luckily once you start diving into the thing you quickly realize it's actually designed in a very "modular" fashion. Every part of the organ has its own dedicated mother- and daughter boards, with a big bar of metal to keep it all in place as you can see in above picture.
There's a separate section for the oscillators, string synth, drawbar organ mixer, drawbar organ filters, solo synth, backing track and drum machine and finally the effects and output boards.
To the left is where the magic begins for most of the organ: the master oscillator, octave dividers and then the string synth and organ magic.
The string synth is rather straightforward: for each key of the treble keyboard there is two envelopes and waveshapers. These generate the two string "(violon)cello" and "strings" and the "piano". There's also connections that connect to the Sustain slider controls for the strings and piano on the front panel.
You can see the switch of the keyboard key at the bottom of the circuit.
The envelopes are simple release envelopes with instant attack for the string synth, and a simple decay envelope with instant attack for the piano.
The drawbar organ gets a little more complicated, although the circuitry itself is many (MANY) repeats of the same simple circuit.
The keyboard keys are all connected to ground in their resting state, but when a key is pressed it connects over to -27V. This signal goes to a very simple gate and envelope circuit, the first row of boards on the schematic, using capacitor in combination with the sustain slider to create a simple RC release envelope ("release" is always called "sustain" on the organ). Since it's an organ the attack is instant and there's no decay. Well, it would get horrendously complicated too if they were to add those envelope stages!
The second row (which repeats with even more rows outside of the image) is where the envelope signal mixes in with the square wave signals coming from the oscillators board. They do some clever tricks with diodes to create a very simplistic VCA that basically sets the maximum voltage of the square wave signal to whatever voltage the envelope has.
Various footages are then generated by mixing the appropriate signals together before they are send to the drawbars, which set the volume of each footage.
After that each individual footage is filtered by simple RC low pass filters to create close approximations of sine waves, which are then finally get mixed together to the output signal of the organ. Gosh, that's a lot of circuitry to get a rather nice Hammond tonewheel organ clone. Transistor style!
REST OF THIS PAGE IS TODO! Coming soon :)