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Monotron Duo.
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MirlitronOne



Joined: Nov 07, 2009
Posts: 77
Location: Surrey, UK
Audio files: 2

PostPosted: Sat Apr 28, 2012 11:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Since the ribbon resistance change is linear, the oscillator response must be exponential otherwise the note spacing would change along the ribbon.
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sneakthief



Joined: Jul 24, 2006
Posts: 531
Location: Berlin

PostPosted: Mon May 21, 2012 10:35 am    Post subject: Reply with quote  Mark this post and the followings unread

MirlitronOne - the microprocessor takes the ribbon voltage and quantizes it. So you can't make any conclusions about the relation of the ribbon's output to what the microprocessor is putting out.

Notice that a pulse from VCO1 is going back into the microprocessor. I believe that this allows the microprocessor to measure the current frequency and compensate for temperature drifts and other things that affect tuning & scaling (cpu-controlled auto-tune).

chorizu - look at pin 4 of the microprocessor to figure out what V/Octave that the vco's are using.

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chorizu



Joined: Apr 28, 2012
Posts: 8
Location: Heidelberg/Germany

PostPosted: Wed May 23, 2012 3:06 am    Post subject: Reply with quote  Mark this post and the followings unread

@sneakthief-i meassured pin 4 against ground,without activating the ribbon it's 2.96 Volt.When playing the ribbon at goes down to 1.5 Volt on high notes and above 3.16 Volt on lownotes,I'd ressume that it's some feed for the OP
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sneakthief



Joined: Jul 24, 2006
Posts: 531
Location: Berlin

PostPosted: Wed May 23, 2012 3:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Well that seems close to 1V/Oct, albeit if you measured it correctly than it's simply inverted.

The ribbon spans roughly 18 notes (1.5 octaves) and you're getting a voltage swing of 1.66V.

However, please measure again using the chromatic scaling mode! Then you'll know for sure what the internal voltage scaling is.

Anyhow, if you look at the schematic, the voltage from pin 4 of the microprocessor gets added to the reference voltage (VD) then goes to a current mirror (Q1 & Q2) before being sent to the 2 VCO's.

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chorizu



Joined: Apr 28, 2012
Posts: 8
Location: Heidelberg/Germany

PostPosted: Wed May 23, 2012 11:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah,thank You,I'll take me some time to make better meassurements.I ordered some micro equipments on conrad.
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chorizu



Joined: Apr 28, 2012
Posts: 8
Location: Heidelberg/Germany

PostPosted: Sat May 26, 2012 3:56 am    Post subject: Reply with quote  Mark this post and the followings unread

@seakthief-You seem to right,but i first explain my more disinct meassurement: Pin 4 to GND toggles around 2,20 Volt and 1,7 Volt(i dont no why). then i hit a high key it goes to 1,54 stable,then i hit 1octave lower it goes to 2,54 Volt.normaly it must have been reverse?
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sneakthief



Joined: Jul 24, 2006
Posts: 531
Location: Berlin

PostPosted: Sat May 26, 2012 4:38 am    Post subject: Reply with quote  Mark this post and the followings unread

As I said, in this case it just means that the VCO is using inverted 1V/Oct scaling.

If you want to control it externally, then invert the CV with an inverting op-amp Smile

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chorizu



Joined: Apr 28, 2012
Posts: 8
Location: Heidelberg/Germany

PostPosted: Sat May 26, 2012 5:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah,alright,Thank You!
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chorizu



Joined: Apr 28, 2012
Posts: 8
Location: Heidelberg/Germany

PostPosted: Sat May 26, 2012 5:43 am    Post subject: Reply with quote  Mark this post and the followings unread

@sneakthief- i'm a little uneperienced in electronics,is this NAND gate good for my purposes
http://www.stm32circle.com/resources/Datasheets/74LX1G04.pdf
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sneakthief



Joined: Jul 24, 2006
Posts: 531
Location: Berlin

PostPosted: Sun May 27, 2012 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

http://sound.westhost.com/dwopa.htm#invert

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chorizu



Joined: Apr 28, 2012
Posts: 8
Location: Heidelberg/Germany

PostPosted: Mon May 28, 2012 4:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank You,very interesting suggestion and Site, too.First, i have to make oprations on how disconnect Pin 4.
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TakeshiAndTheKid



Joined: Feb 27, 2011
Posts: 9
Location: Cork, Ireland

PostPosted: Fri Jun 15, 2012 2:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey there, looking to get one of these things soon. Sad to hear there's no easy way to do a CV Pitch.

There's only one mod I really want to do though, I'm getting one because it seems really awesome for videogamey sounds. To me, having 2 square waves seems kind of redundant so I'd like to change the second square to a pulse, maybe.

Would this be hard to do?
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vonkhades



Joined: Jun 17, 2012
Posts: 1
Location: madrid

PostPosted: Sun Jun 17, 2012 9:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey guys!

Im tryin to mod my DUO so I can control it externallly... I've read the whole thread but couldnt find info on it ... i've googled a lot but still unsuccesfull to find any info or schematics. The last thing Ive tried was dinsync.info/2010/06/how-to-modify-korg-monotron.html which is for the regular monotron.. but doesnt seem to work... as you said on the last messages the CV wont be easy...

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Anyway there a couple youtube users that made some advancements on this.:

http://www.youtube.com/watch?v=ae6t6bN8Pyg
http://www.youtube.com/watch?v=--UNbu23DSY

I've tryied to contact them too, but no answer yet Sad

do you have any suggestions? what pads you solder or a schemmatic/resitor values?? Im sequencing it with a baby10, with both CV and Gate set max outputs to 5v.

cheers!!
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andeje0



Joined: Jun 11, 2012
Posts: 5
Location: Florida

PostPosted: Tue Jun 26, 2012 9:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Anyone have any updates on figuring this out?
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Cynosure
Site Admin


Joined: Dec 11, 2010
Posts: 713
Location: Toronto, Ontario - Canada
Audio files: 42

PostPosted: Tue Jun 26, 2012 5:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I saw someone posted this - http://www.youtube.com/watch?v=1-E7qPsI4Cw
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andeje0



Joined: Jun 11, 2012
Posts: 5
Location: Florida

PostPosted: Thu Jun 28, 2012 9:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Hard to tell if he's really sequencing the pitch there or just the gate and the fiddling with the pitch knobs...will give it a go in the next few days and see...
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andeje0



Joined: Jun 11, 2012
Posts: 5
Location: Florida

PostPosted: Thu Jun 28, 2012 12:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Chorizu have you had any luck testing the inverted op-amp to pin 4 of the micro-controller to control the pitch?
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TakeshiAndTheKid



Joined: Feb 27, 2011
Posts: 9
Location: Cork, Ireland

PostPosted: Fri Jul 06, 2012 11:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Is there any way to stop that annoying popping noise you get when you disengage the ribbon controller on the Duo? It kills my ears when using headphones. It's not as noticeable with the filter up but with it down it's unbearable.
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andeje0



Joined: Jun 11, 2012
Posts: 5
Location: Florida

PostPosted: Fri Jul 06, 2012 12:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Try reading some of the links of this thread on Muffwiggler -

http://www.muffwiggler.com/forum/topic-47195.html&highlight=monotron+noise
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TakeshiAndTheKid



Joined: Feb 27, 2011
Posts: 9
Location: Cork, Ireland

PostPosted: Fri Jul 06, 2012 12:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

andeje0 wrote:
Try reading some of the links of this thread on Muffwiggler -

http://www.muffwiggler.com/forum/topic-47195.html&highlight=monotron+noise


404
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TakeshiAndTheKid



Joined: Feb 27, 2011
Posts: 9
Location: Cork, Ireland

PostPosted: Fri Jul 06, 2012 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah got it now. I think this is talking more about the background hiss though, and the solution looks very awkward. I get a "tapping" noise when the ribbon controller is disengaged.
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Bozzy



Joined: Dec 18, 2012
Posts: 1
Location: Italy

PostPosted: Tue Dec 18, 2012 4:30 pm    Post subject: Re: Monotron Duo Reply with quote  Mark this post and the followings unread

joe wrote:
Just a quick summary:

- Vbias is the +3.36 "middle" voltage between GND and VCC.


Sorry to resume a quite old thread. I'm just interested in this topic and found this googling around... but this info was (is) incorrect.

In the Monotron DUO the +3.36V is labeled VD and serve as Digital power source (Vcc), it's not the value of Vbias.

Vbias is the +1.35V "middle" (or virtual ground) voltage between GND and VCC used in the analog section.

Cheers,
Bozzy
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alfa66



Joined: Mar 03, 2014
Posts: 3
Location: Bay Area, California USA

PostPosted: Mon Mar 03, 2014 8:41 pm    Post subject: Making sense of the Monotron DUo Reply with quote  Mark this post and the followings unread

I would like to share some thoughts, after beginning modding my monotron DUO.

I just want to capture these thoughts, so they don't get lost and I can share more with the community as we go.
In fact, I have read this thread and proved very inspiring to me, so hopefully somebody else will find my comments/findings useful.
Also, please be kind if I make any mistake Smile

Ultimately I want to MIDI-fy my Monotron DUO: so far I replaced the VCF knobs with a digital potentiometer controlled (via MIDI) by a teensy 3.1 - this works great.

I wanted to use the DAC of the teensy 3.1 to control the pitch, here is where things "seem" complicated, but I now have a plan (the plan consists ultimately in desoldering completely the TI uP and substitute a few of its pins with teensy 3.1 ports.... but let's take one step at the time).

According to my calculations, V bias is 1.35V. VD is 3.36V.
So Vbias seem more like a mid point, a sort of ground for signals that vary between 0V and 3.36V.

In this post i want to start pointing out that IC3B is a non-inverting low pass filter, its topology is well described here:
http://www.interfacebus.com/opamp-low-pass-active-filter-design.html

The purpose of this filter is to turn the frequency generated by the MSP430 (pin 4, aka "PITCH", which is likely PWM) into a steadier value (CUTOFF), which is used to provide the pitch (linear voltage) of the main VCO.
The configuration of Q1 and Q2 is, in fact, another well known topology that uses logarithmic voltage (controlled with the MASTER PITCH KNOB, I think of this more as an octave selection) and linear voltage (our CUTOFF point) to control the frequency of the VCO.

All i am saying (and I have yet to try it) is that we don't need to tap on the PITCH node to change the pitch. I bet that if we put an oscilloscope probe there we will find a PWM signal (the depth of the PWM signal controlled by SW2A, which changes our scale from major to minor, etc..... again, speculation here, haven't made any measurement - I just studied briefly the MSP430).

What I am suggesting is that to control the pitch of the main VCO we should just tap onto CUTOFF.
CUTOFF is the same voltage that goes to the VCF. I thought about this, it makes sense as my old Poly 61 had a "keyboard tracking" filter, so the cutoff frequency of the filter was the same frequency of the key pressed.

Please let me know what you think of the above, I won't have time to try that myself for a least a couple of weekends.
If I have time I will start writing some equations for this filter, before digging on how the VCO topology (Q1 and Q2) work....

Have a great week !
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jingkon



Joined: Aug 21, 2009
Posts: 4
Location: Michigan

PostPosted: Sun Mar 16, 2014 5:50 am    Post subject: Re: Making sense of the Monotron DUo Reply with quote  Mark this post and the followings unread

@alfa66

This is exciting news, though I can't really comment on any of your theories. I hope to hear that you've cracked the code on controlling the duo's pitch. Between here and Muffwiggler I keep thinking someone will figurd it out.

John
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KalleWhoever



Joined: Mar 15, 2014
Posts: 1
Location: Bremen

PostPosted: Thu Mar 27, 2014 9:43 am    Post subject: Programm your Duo with Energia and the TI Launchpad
Subject description: New discovery
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Hi guys,
I discovered that the MSP430 within the Monotron Duo is quite easy to program.

You know the free space on the right hand of the PCB?
Well, the five holes over there form a programming header, which will allow you to programm the MCU with your Launchpad.

If you take a look at the schematics you'll find these header next to the MCU. I soldered these pins right to the J4 Header on my TI Launchpad, but you'll find some tutorials on the web on How-To-Use-the-ti-launchpad-as-isp, so I won't explain any futher.
Code:

_________________________________________
|   Launchpad J4   |   Monotron Duo     |
|--------------------+------------------|
|   2 (VCC)         |   4 (VCC)         |
|   3 (SBWTCK)      |   1 (CLK)         |
|   4 (SBWTDIO      |   2 (I/O)         |
|   5 (GND)         |   3 (GND)         |
–––––––––––––––––––––––––––––––––––––––––


My next step was to take a raw dump, hexout and disassemble everything via mspdebug. I also did a disassembly with nakem_asm but since I don't know assembly this does not really help me. Maybe some of you can do better, I'll attach everything.

The last and most interestig step to me was to programm the MCU via Energia in a Arduino-like language. If you fire Energia up, make sure you remove the programming headers on the launchpad ( you know.. those tiny plastic bits) so you are only connecting to the MSP430G2331 in your Monotron. Then go to Tools -> Boards and select "Launchpad w/ msp430g2331 (1MHz)".

To program your Monotron Duo in a way that you can use it in a musical way (I define making noise as musical), you need to understand what the different pins are doing.
Code:
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
|   Pin Number  |   Testpoint   |   What I assume it does.                                      |
|---------------+---------------+---------------------------------------------------------------|
|   P1.0        |   Vrib        |   Reads the value of the Ribbon for Gate and Pitch.           |
|---------------+---------------+---------------------------------------------------------------|
|   P1.1        |   knob        |   Reads the value of VCO1 Pitch for coarse tuning.            |
|---------------+---------------+---------------------------------------------------------------|
|   P1.2        |   pitch       |   Controls Pitch via PWM. (-> @alfa66 )                       |
|---------------+---------------+---------------------------------------------------------------|
|   P1.3        |   gate        |   I bet you know what it does ;-)                             |
|---------------+---------------+---------------------------------------------------------------|
|   P2.6        |   SW2A        |   Changes interval of the Pitch played on the Ribbon.         |
|---------------+---------------+---------------------------------------------------------------|
|   P2.7        |   VCO1        |   Takes the output of VCO1 Pulse. Propably used for tuning.   |
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––


I don't know if I got everything right, but I attached a sketch that I will use for experimentation. Since there are 3 unused Pins on the MSP430 and a spare opamp on the PCB I see many possibilitys for extending the Synth.

In the next days I will try to create a sketch that allows normal Monotron use (without pitch quantization). Afterwards I could imagine to add a two more potis and use the opamp as LPF for CV control (-> @alfa66) of the VCF ( or maybe VCO2) and adding a digital AR-Generator, LFO, S&H or even a sequencer. I won't promise but there is also a chance of "native" MIDI control Wink

I'm looking forward to see what you will do with this,
Lars Christian



Resources:
Korg Monotron Duo Schematics:
http://www.korg-datastorage.jp/Manual/monotron%20DUO_sch.pdf
Energia IDE:
http://energia.nu/
MSP430G2231 Data:
http://www.ti.com/product/msp430g2231
Schematics of the TI Launchpad:
http://www.ti.com/lit/ug/slau318e/slau318e.pdf


IMG_20140327_141532.jpg
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Image of the programming header on the Monotron Duo.
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IMG_20140327_141532.jpg



IMG_20140327_141610.jpg
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Launchpad side with a nice coffee stain.
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The whole setup.
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monotronduo.hex
 Description:
Output of mspdebug hexout.

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MonotronDuo.tar.gz
 Description:
Framework for programming the KORG Monotron Duo with Energia IDE.

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