Monotron++

monotron++ front panel
monotron++ front panel (Click to enlarge the picture)
Photo by OZAWA (C)2010

Monotron++ is modified version of Monotron that come from Korg. 'MIDI-IF', 'VCA' and some other things are added onto it.
'MIDI-IF' allows you to be able to control Monotron++ by keyboard. VCA works as noise gate. But you can use it by external cv to control its expressions (option). The schematic of VCA is also based on MS-20. It's getting to be almost MS-20 clone now.
All the information for modifying is opened for anyone else of the world.

I add 4 parameter to Monotron++

  • Glide
  • VCO Wave form selector Switch(SQR / SAW )
  • Pulse width for SQR Wave
  • EG/LFO switch
  • Output Volume (for recording out)

monotron++ back panel
monotron++ back panel (Click to enlarge the picture)

Glide is also called as 'portamento'. when you use ribbon to make sounds, there is no need this parameter. But if you drive monotron through MIDI, you may want to need this like me.
VCO Wave form selector Switch can change its VCO's source wave form. You can switch square wave and saw-tooth wave.
Pulse width knowb can change its pulse width from 50% for almost 0%. It works only when you switch wave selector to square wave. When you set it 0%, there is no VOC wave. And you can use VCF oscillation for the sound making.
EG/LFO switch can change LFO to EG. LFO is re-trigered when the gate comes in from control that is ribbon or something. So one note that you play is short enough than one cycle of LFO then it seems to work as EG. EG swith will stop the re-trigering by its cycle. It's simple but effective.
This switch allow you to use LFO as decay only EG.
And there is output volume. Monotron++ has VCA inside. So there is no noise when you stop the sound from monotron.
There is MIDI input (DIN 5p) and recording output (mono)
3.5mm jack is for output. You can use it as line-out. I want you to use it as recording output.
It have AUX input and headphone output and volume for headphone still. you can use AUX input when you hit your MIDI keyboards.
I remove ribbon controller and speaker. Just only MIDI input can drive Monotron++.

Now let's get inside of Monotron++.
Monotron++ receive MIDI note on / off, pitch bend, modulation wheel and some control changes.
MIDI channel is fixed to 1 ch. There is option to change it from 1 to 8. You need to add switch to monotoron++. Default channel is fixed to channel 1. It recognize over 24 as note number. Less than that should sound same tune as the lowest note.
Pitch bend renge is also fixed to 1 full note.
Modulation wheel message can control vibrato. Its speed can change via control change message 4C (76 in decimal).
There is also option to control vibrato rate by knob. When you choose it, it can't change its speed via MIDI. Anyway you need add knob to the case.
And Monotron will get all reset message from another Legacy MIDI equipments.

Monotron++Demo (G's Blues)

There is tuning support function (option). It's not automatic. When you push the button, then you can here the 220Hz tone for tune. turn pitch knob and set Monotron++'s tune your self. You can use it for another musical instruments.

Korg's orignal Monotron have DC/DC converter inside and it's very sensitive for power source. I don't recommend another power source than battery. Orignal Monotron is designed for battery only. You can use AC adapter . But it's not easy to use it in safe. Monotron++ had been changed from MU4X2 to MU3x2.(AA type Alkaline battery is recommended)

Its size is 130mm×30mm×90mm. It made from aluminium and it is 1mm thick
I put my original sticker on it. you can remove them and put another one you like.
There is template for sticker. You can re-design them for yourself.

Monotron++ can receive not only MIDI but also CV+GATE for external ribbon controller. This is one of options. This input can be tuned into 1V/1Oct same as MOOG SYSTEMS. Gate is 0V->5V.

The pitch of Korg's monotron is drifted along changing of temperature yet. And Monotron++ have also drift. Use it at indoor only. And re-tune it yourself for each seasons just like as piano or something. For information about tuning Monotron is here.

Any way it's also charm of analog stuff. Enjoy drifting!

Demo video or something will comming soon. check them out!

Information

There is information to build your own Monotron++ by yourself. Try them and let me hear your sweet music!

Adding VCF input
To add wave shape converter, we need add VCF input. So we remove capacitor that couppling with VCO and VCF.　Any way couppling capacitor is needed for Monotron. So I add it on wave shape convertor. VCO output can get from solder side of "monotron" named "VCO". VCF input can get from the foot print of VCF side of coupling capacitor.
SMD foot print is so small week for the force. Attach the wire another components on the board to avoid be teared off by grue.
  • The couppling capacitor with VCO and VCF
  • The foot print of Removed capacitor
  • Adding wire to get VCF input
    • The kit that I'm providing as "MIDI-IF of monotron" don't need this mods.
    Enable The "Gate"
    The GATE pad on the solder side of monotron PCB connect with Ribbon CV input its inside. And this couses some trouble using CV+GATE input. For making it work be sure, we must remove one chip registor from monotron's PCB.
    Just remove it only, no adding. This process is needed for using MIDI IF.
  • The chip register to enable GATE INPUT pad
  • The foot print of Removed register
    • this mod will kill the Ribbon of monotron. you can drive monotron by CV+GATE only.And you need this mod for using "MIDI-IF for monotron" that I'm providing.
    if you want to keep Ribbon, then try this mod. KORG monotron CV/GATE input adding I do that in my video. Check also this.
    Schematics
    Analog part(2011-01-23)
    MIDI part(2010-12-23)
    PCB Design
    Analog part and MIDI part
    Farmware for MIDI part
    AVR Studio format(2011-01-12)
    Case Design
    case design(in PDF FORMAT)
    Sticker template
    first variation
    another variation(Designed by Rafael living in Switzerland! Thanks a lot!)
    Yet another variation(MS-20 Type)(Designed by Radek living in Czech republic. Thanks a lot!)
    Yet another variation(MS-20 Type Printable Version)

    All the software are written in C. I compile it by WinAVR (20100110 version) using 'AVR Studio 4.14(589)' You can download newest WinAVR from here.

    All the infomation are 'AS IS'. There is no guarantee and it may be changed with no previous notice.

    Kits

    MIDI-IF for monotron++ PCB
    MIDI-IF for monotron++ PCB (Click to enlarge)
    Old version is here

    I distribute PCB now. It's MIDI part only. But it should make easy to build Monotron++ yourself.
    there is no OCB of Analog part for Monotron++. Because it need some critical tunings to get good sound around Wave shapper.
    it's almost compatible with gakken's SX-150's MIDI-IF. Here is the documentations

    it's price is just 1200YEN (w/o shipping fee. Let me know where you live).And I have pre-programd CPU and parts set also. I can accept Paypal only for oversea. Please check next page out!.

    Feel free to send me a mail for more inforamtion.

    Ready-Made Monotron++

    Monotron++ is DIY project. You must do it yourself if you want to get Monotron++. But if you are not familiar with elecrlic DIY, I can build it for you. Now it's 2nd LOT. the difference with 1st LOT and 2nd LOT is ..

    • Output jack changes to standard(1/6 inch) phone jack instead of 3.5mm MINI jack.
    • I outsourced digging holes of enclosure. they do it by N.C. machine
    there is no - changings of sounds. but it looks nice more. Please check next page out!. it's all handmade item. I can't have so much stock at a time in my hand. Anyway Feel free to send me a mail for more inforamtion.