Minimoog now has a working keyboard

[Jacob Hunt]

Hey everybody,
I just got a new to me Minimoog, and this thing is amazing, but it has no keyboard. It was a studio electronics rack mounted original Minimoog I believe, and has a case still to go with it, and I intend to make it back to original form.

I have a pratt read keyboard from an old organ that is the right size, and I'm wondering if it could be made to work with it. Would it be easily possible to convert the keyboard to be compatible with a minimoog, or is there a better solution available? Would an optokey system easily interface with any old pratt read? Any help/ideas would be greatly appreciated.
Thanks!

[sequentialsoftshock]

I mean... Just getting a MIDI keyboard would save you a lot of time and effort. If you're deadset on restoring it, I think there's more to it than just being the proper number of keys. IE is the voltage it sends per note going to correspond to what the moog plays..?

[Hybrid88]

Pictures would help a lot.

Is it in a rack at the moment? Because if it's saveable as a MIDIMINI I'd go that route.

To me the most annoying thing about a minimoog is its keyboard. Great when it works properly, but that's hardly ever. The contacts get dirty, you need to constantly play it to keep it working and any dust between the keys and you're in squirrel city.

If it has MIDI already from being racked up, I'd just get a bog standard MIDI keyboard for cheap, whack it in the case with guts and hook up the MIDI. Far easier and better than the original keyboard.

[db0451]

I wish almost all of my keyboards had already been racked! Once I had one or two proper keybeds of different types, there would be no reason to get extra keys in my opinion. But when they aren’t available in rack form, I have to… Currently I have all synth-action keybeds of a couple of types, and I would ultimately like also to get an 88-key weighted and/or polyphonic aftertouch mechanism, but those will have to wait a long time. Racks are where it’s at for me, whenever possible. I wouldn’t be complaining here!

[madtheory]

Yes he said a Studio Electronics rack, so it sounds like a MIDIMINI. Seems like owner retained the woodwork?

Yes, I agree, forget the original keyboard. Not just because it's easier. Play it with a weighted keyboard, it's great and you get velocity and aftertouch as mod options, and a much better pitch bend control. Much more musical than the original.

So sell the woodwork and use it to buy a nice controller!

No doubt AG will be along to explain why the original keyboard is better...

[Jacob Hunt]

Well... It doesn't have MIDI built in, but rather alot of extra CV jacks and controls, and extra osc. for LFO. I don't really know alot about the mods, but I'm definitely deadset on getting a keyboard put back in it, I just like for all my stuff to have keyboards in them

Right now the boards are in the original encasement and I have the original wood body as well. I'm really liking the thought of getting the optokey put in the pratt read from the organ if it'll work out. It'd also add MIDI as a nice bonus.

[Jacob Hunt]

Come to find out the PR keyboard I have won't work with the optokey, it doesn't have the exact same system.. Plan B.

[madtheory]

A picture's worth a thousand words Interesting mods. Casework looks great. Keyboard is a bit of an omission alright! How many CV inputs does it have? Would you consider building in a MIDI keyboard with a good MIDI CV to handle it all?

[Jacob Hunt]

I may end up being able to source one.. In the meantime though I'm wondering that if that doesn't work out I may be able to get a cv controller built in (plugged inside rather than out). And if that doesn't work out then I may just get a little midi controller with a MIDI converter. I'm also really missing the glide The glide knob was reassigned to extra LFO depth, and I don't seem to be able to modulate with the 3rd oscillator, a feature I was really looking forward to. It was modded to accept v-trig and has a couple extra inputs I think, forgot to get a pic.

I really do love the look, the previous owner chose a real nice color. I've been playing it with the polymoog because that's my only compatible synth, and it doesn't always work just right, it sometimes plays flat, but man it still sounds great

[madtheory]

WHAT?!?!? No glide? That's one of the best things on a Mini Moog! IIRC the Kenton Pro Solo does Mini Moog style glide very well. So maybe go with one of their boxes? I've no idea how to restore the glide control, but it should be pretty simple it's just an RC circuit AFAIK.

Playing flat sounds like a CV calibration issue- either with the Polymoog or the Mini. My guess would be the Poly, those things are full of dodgy (by now) caps and are a pain to work on, from what I've seen.

[Jacob Hunt]

I'm hoping it's as simple as routing some old wires back where they belong Haven't opened it up yet, so not sure what to expect yet.
The odd thing about not being able to modulate with osc. 3 is that it mentions osc 3 control on the mod labels, but it appears as if it was left off, no amount of switch flipping or anything allows for it, but mod. by noise was retained, so maybe the mod isn't completely working.

Here's some pics of the extras up top

[Jacob Hunt]

Well after weighing all the options, I've decided to use the pratt read keyboard. I'm connecting a second board to its electronics/contact assembly for use as the trigger contacts. It looks to me like for the pitch bar contacts a resistor needs to be wired in between each of them. Can anybody confirm that this correct? I'm thinking I need to to wire the appropriate resistors to the base of each contact, essentially connecting them together by resistors, as far as I can tell by the schematics. Then the only challenge will be getting both contacts to move with each key, but I've got a few ideas

[Jacob Hunt]

And it works!!
The keyboard is sending the correct pitch! I just need to get the trigger buss working now.
Here's a pic of my crazy setup. Those are boards from an old Kimball, and I have three buss bars from it and a 44 note keyboard. I stacked the boards and stuck the second contact into the guide with the soldering iron. Can anybody tell me the correct way to wire the trigger buss? Is that third bar used or not? Sometimes the schematics seem to say no, but other times it seems to go to board 2 20B. It's also very possible that some of the wires inside aren't routed correctly I suppose.

[Jacob Hunt]

And the trigger buss is working now!! My last problem to overcome is that whenever I let go of a key, the Mini reverts to playing the lowest F note.. It tracks pitch correctly across the keyboard and triggers notes pretty well (albeit a bit squirelly ) but it just doesn't hold on to the note that was last played when the key is released. It did when I played it with the polymoog's keyboard though. Perhaps the pitch buss isn't wired correctly?

[Jacob Hunt]

Still scratching my head on this.. I noticed that my polymoog's keyboard behaves the same way at the output of it's pitch bar, so I imagine something is holding the last given pitch, and that something must have been bypassed on the Minimoog with the mods. I have the pitch buss output running into the proper input on the keyboard circuit but no luck, it doesn't even respond to pitch changes this way. Does anybody have any info as to what all was modded by studio electronics? It seems as if mine is a bit of an oddball though, as far as the mods go.

It seems as if something is keeping the keyboard circuit from operating properly. Maybe the glide switch and pot not being present? That seems worth a try anyways. I don't know how the Mini's circuit should behave technically, so I'm not sure what should be happening. Is it some kind of sample and hold? Would the absence of the glide switch and pot make a problem?

Edit:
I've found a technical description of the circuit and there is in fact a "track and hold" system in the circuit. I just need to find why the keyboard circuit isn't responding to pitch cv (the cv input jack is wired into the oscillators I believe, which does allow it to respond to cv when using the jack, but no track and hold).

Here's the schematic I'm going by


I'm so close, just gotta get past this and I'll have a cool custom Mini with an even weirder keyboard