Extending the range of Minimoog Model D

[grembin]

Hi Guys,

I'm thinking of adding a bigger keyboard to a Minimoog Model D. Does any one know if that's possible?

I was looking here http://www.keyparts.co.uk/project-keyboard-controller at the keyboard controller and It can output in CV they say.

I'm wondering could I add e.g. an 88 key keyboard that has CV out from the keyboard controller would the range extend far enough? Would the Minimoog make the required sound throughout the full range of the keyboard, or is there some limitation to 44 keys?

Also, I had been thinking that Minimoog Model d's used 1v per octave but someone told me today that they actually use something like 0.96v per octave, does anyone know what exact voltage per octave they should get.

Thanks for any help,

Grem.

[torinkrell]

2nd question first. AFAIK the Minimoog Model D is 1 volt per octave. It's the Mulimoog that has a nonstandard volt per octave issue. If you just wish to play the Minimoog with the full frequency range already available it could work provided you make some mods for interfacing a very well made full length analog key and mod assembly. The C V interface in the back of the Minimoog does not take the original keyboard and Mod wheel out of circuit so custom mods would need to be made. Of course the Mini could be MIDIfied with the Lightner designed MIDI kit which would enable a variety of MIDI controller options. I haven't tried any of these suggestions and I am not a tech so perhaps others here can inform you further.

[thealien666]

Yes, the Minimoog D is 1V/Oct.

As far as using a bigger keyboard, you can already use the the external Oscillator Control (CV) input and EXT S-trigger input (using the proper connectors) to control it from a CV keyboard (provided that the lowest note is played first on the original keyboard, since its pitch CV is added to the external Osc CV internally). Either from a CV generating keyboard (like the one used on the Moog Modular System) or by using a MIDI-to-CV to generate de analog signals to drive it from a bigger MIDI keyboard controller.

Or you could take a chainsaw and butcher your Mini into a frankenstein keyboard with an 88 keybed and the control panel nailed to the casing...

[MC]

Yes, the Minimoog D is 1V/Oct.

The external CV input is 1v/oct. The keyboard CV is 1.02v/oct. Check the ua726 schematic...

(Don't ask me why they chose that scaling...)

Or you could take a chainsaw and butcher your Mini into a frankenstein keyboard with an 88 keybed and the control panel nailed to the casing...

Nah - use duct tape for the control panel

[MC]

Also the VCO board is pitched with low F at zero volts. If you use a keyboard with a low key other than F (IE low C at zero volts), the VCOs will need a slight modification. The trimpot may not have enough range to get you there.

[MC]

FWIW, my Minimoog has the Lintronics MIDI retrofit and it responds to a MIDI note range of 60+ notes.

[thealien666]

My Mini doesn't have ua726 chips in it. (although in the service manual it states that this "new" oscillator board, with these Fairchild differential pair temperature compensated ICs, also operates on a 1.00 Volt per octave basis, on page 2.3)

It's a CA3046 machine, and my keyboard, as well as the external pitch CV input, is also 1.00 V/Oct (as also confirmed to me by the late Kevin Lightner, back when we had discussed his Opto-Key system design and why he had decided to go the extra mile and put a 16 bit high quality D/A converter onboard for a "no compromise approach" on the precision of those pitch CV values ).

BTW, the Opto-Key MIDI implementation only allows the 44 notes of the original keyboard to be played via MIDI. (MIDI was only an afterthought in the Opto-Key project and added late in the design. The main goal was only to replace the buss bars and springs contacts with optical sensors)

[MC]

Doesn't matter whether you have ua726 or 3046 or discrete VCO board. The CV summers use different gain for external CV input and for keyboard CV. The ua726 schematic says "1.02 v/oct". The input resistors are different on the opamp summers on all VCO versions.

Sure you can scale the keyboard CV to 1.00 v/oct, but the external CV will not be 1.00 v/oct anymore...

[MC]

I was just helping Scott "Old Crow" Rider with a minimoog clone. He ran into this problem, that's how we discovered the difference between keyboard and external CV scaling...

[CZ Rider]

The input resistors are different on the opamp summers on all VCO versions.

That's an interesting difference on those latter version oscillator boards. But the other two oscillator versions have the same value input resistors on the three 1V/oct. inputs. 6A the keyboard, 7A mod input and 8A external input all have the same values with 51.1K 1% resistors on the 2nd revision oscillator board. Checked both the schematics and an actual board here with all three having 1% resistors marked 5112F. Same with the original discrete R.A.Moog oscillator board with all three inputs 6A,7A,8A matching resistor values.
The last version board shows input 6A with a 102K input resistor , while input 7A and 8A have 100K resistors. Strange? Might be a slightly different keyboard circuit on those later Minis with an output of 1.02V/oct. Easy fix for a clone using a standard MIDI 1v/oct input by using all 100K resistors for those inputs.
My one Mini here has an 88 key controller using a MOTM-650 MIDI to CV converter. Tracks very well and 88 keys is pushing the useable range as the lows are almost sub audio. Really fun to play and I have the oscillator inputs split so it can play three note polyphonic.