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MIDIbox of the Week (MIDIfied Korg Polysynth by Francois)


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The easiest and most secure way to MIDIfy a vintage poly synth is the use of reed relays.

This has been proven today by Francois and me :)

View with removed frontpanel - each key has a seperate pin, which is connected to -15V when the key is pressed.

In parallel to these key->gate board connections, Francois has led through the inputs via ribbon cables:


The backside of the synth with a nice view to the voice boards (sorry for the bad picture quality!)


Core Module + 6 DOUTs stuffed with reed relays. Schematic can be found here: http://www.ucapps.de/mbhp/mbhp_doutx1_reed_relays.pdf


The bottom of the vero board:


After two hours all cables were soldered and tested. First checks with a MIDI keyboard and with MBSEQ V3 were very successfull! :)


Hard to believe, but this was only the first of three Polysynths which should be MIDIfied! ;-)


Best Regards, Thorsten.

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How does a person aquire TWO PS-3100's? Is just the keyboard MIDI'd or do you have the SHX8 module on there as well to control individual parameters? I'm assuming it's just the keyboard that's MIDIfied. Still I've been scared of doing that to my MaxiKorg. I couldn't imagine doing it to a PS-3100. I can't wait 'til the SHX8 module gets firmware written for it so I can MIDI up a bunch of stuff.

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oh its true, I haven't seen the second one. 2 identical sweet korgs, imagine, you have replacement parts so at least one is going to work for a long time...

sorry for my ignorance but, isn't it better to make an external CV to midi converter? or none of these Korgs have CV input?  or there's a disadvantage I ignore? ???

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You didn't see the second one as well the third one.  ;)

I got the one which is midified in 88 for 80 euro. It is my first analogic synth. After this, I found one in Paris in 1998 or 1999 which I trade against a Korg Monopoly around 400 Euro at this time. Again, a friend of mine proposed his for around 800 Euro, the one which has some wood scratched. But, it is not a big problem. I wanted to obtain a Korg PS3300 sound.

With 3 Korg PS3100 I even get better.  :D But It takes more place. All of the 3 work perfectly and I don't have to canabilise one to repair the other.

I know fine that synthesizer. And it is a really strong one.

Yesterday evening, I did connect the output of the midified one to the audio input of a kobol..

And I modulated it via a midibox CV. Was really cool too!  8)

I really don't care about a full midification on it.. I waited around 20 years to get it midi..  ;)

I also tried to patch the few jacks inputs via the midibox Cv but without any success.. The input signals should be beetween -5volts and + 5 volts..

But, I am thinking to connect all the 3 Korg PS3100 together thru the same relay set, using SCSI 1 flat cables.. The cheapest solution to get a PS3300 sound in live.

I will order that to Reichelt and will let you know the result!


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Francois: maybe you remember, that we modified the AOUT module for your polykobol to a voltage range between -5V..+5V - you could use it for the PS3100 now, just upload the MIDIbox CV firmware to the core module, which is currently in the IBM box ;-)

Sooner or later, we could modify the firmware, so that it can control the DOUT + AOUT module - only one core would be required anymore, and the second core is free for some other MIDIfication stuff ;)

Best Regards, Thorsten.

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Ok.. I will take the IBM one.. ;D

But, I wanted to list the connectors I have to order to repair another Polykobol.

I want to repair 2 polykobols this week and after this, if I have to wait to some components

to do the mod you proposed.

Also, I would like to do a DOUT module to midify a Polykobol.

Or, is there already an aplication doing a coding which could be adapted to the keyboard plug connector?



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2 korgs are too much, 3 its an outrageous number  :o

I wish synths would appeared like daisys in my country as it happens in France... but that will never happen :-\

BTW, je sais français, j'ai allé au lycée français de Montevideo presque tout les annés du lycée. Je un peut oublié le français mais bon... je peut lire parfaitement et j'ecoute musique trés souvant. ;)

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  • 15 years later...

i tryd to midify a old home organ (where every key was wired to  lots of voices - without any logic...) at least there i had a lot off noice from the microcontroller, and bleeding.... but it worked - except from the noise - it worked - maybe ti would helped to use a lot of capictors to LPFilter the shiftregister outputs....

i gues the Relays terminate the digital-noise/transistor bleeding - so you get a clean solution.


Edited by Phatline
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