Saturday, 19 December 2015

Korg Monotron (Duo) - Buchlarized

I'm resurrecting some of my old Korg Monotron hacks for a new job - adding an extra voice to a Buchla Easel. The easel is a wonderful synth and I'm always looking for ways to expand on it.

The Duo Monotron is very small but is fully analog & has 2 VCOs, Filter & a X-mod circuit
borrowed from the Korg Mono-poly. (VCO cross modulation). The Aux jack allows you to input external audio.

The LP filter is based on the MS10 & MS20 filter design. Sadly there is no HP filter.
The second VCO takes the place of the LFO from the original monotron. 

It should be relatively easy to hack this again. 
The Monotron seems like a prefect candidate for this job. I'm using the Duo Monotron.
If this is successful I will try the same on the Monotron Delay & Original.

The Monotron-Easel BOB (break out box).
The box is a $9 Jaycar job (Australia).
The plan is to be able to plug this into the 208 card slot but still have the slot available for additional
expander cards.

The box was too narrow (by just a few mms) so I had to cut the sides of the card. This makes me cry.
I might in the future etch some smaller 56 slot edge connectors for jobs like this. It's a shame to damage these beautiful expander cards. 

Lots of SMDs. The Red button is for cycling through different scales of the ribbon controller.
the ribbon is quantised to chromatic, major, minor and continuous scales, with chromatic mode the default on power-up.

Both of the Duo's oscillators have square & pulse outs. VCO 1 also has a saw out.

On the back of the PCB are various points labeled gnd, VCC, gate,square 1&2, Saw1&2, PS 1&2, Virb, Vbias, etc

Vrib is the CV input.

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.

It's a bit like the AUX expander.

Now the real fun starts.
For now I'll leave the ribbon alone. Its essentially a linear 10k pot.

Before I start linking the BOB with the monotron, I thought it would be useful to add some additional mods.
The above patch card (from Cobramatic) illustrates some of the cool mods available.

1. CV in (Blue Banana) with an addition on-off-onn switch to gain access to 2 step mode & the
    Seq random No. of steps. 
    You need to add 120k resistors to both of the outputs on the card to properly utilise this feature.

2. Next are the Pulse Outs for each sequencer step (red bananas). 
    For now I've omitted adding the LEDs. I might do this at a later stage.
    Note, these un-attenuated outputs are "hot". I'm reading 15V pulse triggers so do be careful
    when interfacing with external gear. I will prob add some resistors later to cool things down a bit.

3. Now for the Pulse Trigger In’s (yellow bananas) to:
    a. Sequencer,
Random CV generator rate    
    c. Pulser
Envelope Generator.
    This should be extremely useful for syncing with external gear
    You need to add 390k resistors to each jack. 
     I might make some permanent connections between some of these inputs and the monotron.

4. On the right side panel I'm placing the LPG inputs on the top.
    These comprise 2 blue banana jacks with 120k resistors and a switch to add random CVs
    They will step through the different modes : LP Filter, Combination & VCA.

5. Complex Oscillator
    Two CV ins (White Bananas) with 120k resistors & switches to add random CVs
    These connect to the modulation inputs for wave-shapers 1&2.
On the vintage easel card, the complex osc has marked a "key" and two "WS" waveshaper inputs.
The modern BEMI easel cards names them "Key", "t.lev" (timbre level), and "tws" (timbre wave shapes - tri/sq/saw). I understand these are the same so modulation of the left WS input should affect the level of waveshaping, and the WS on the right should morph between tri/sq/saw).

6. Modulation Oscillator
    Two CV ins (Purple in) for modulating the waveshaper &
    the Modulation Mode (FM, AM, none).
    For each input I've also added a simple on-on switch to swap inputs between random CVs and
    banana jack CVs. Again, 120k resistors are needed for each input.

It's a tight squeeze.
Finally, we can add the monotron.

 I'm using just 2 control inputs in this prototype: CV in for the main VCO's pitch & the filter.
The gate and the second VCO inputs didn't respond well to the CVs from the Buchla.
I'm also taking a mix of 5 CV outputs from both of the Duo's oscillators (the red bananas on the front panel).

Some pics of the inside
120k resistors are the magic value for interfacing the buchla
Cvs with the monotron.

I'm using random, sequencer & envelope CVs from the Buchla to modulate the monotron.

++ DIY schematics (original monotron)- Muffs 
++ DinSync (hacking the original monotron)
++ Adafruit
++ Korg's official schematics for the original monotron are here.
++ Duo schematics
++ Muffs - Monotron Duo CV Mod?
++ ElectroMusicDotCom 

Friday, 18 December 2015

Korg Monotron Delay - Build notes for Shock Electronix euro version

These are my build notes for the Shock Electronix Eurorack conversion of the Korg
Monotron Delay.
I remember modifying my monotron back when they were first released. So much fun.

Matt from Rhythm Active has done some great work in producing this kit.
Its very easy to build.
100R x 1
390R x 1
270R x 1
33K x 1


10uF electros

First open up your Monotron Delay.

Lots of surface mounted components. You could hack from this surface to (a future job) but Korg have helpfully placed the patch points on the rear.

I love the people at Korg. They have even made the schematics freely available.
Delay schematics are here.

Back to the build.
Resistors first.

Wednesday, 16 December 2015

Buchla Easel - Program card map for BEMI, Vintage & Rev II 208s

Some maps to help navigate the Buchla Easel program/patch card.
These first 2 pics are for vintage & rev2 versions (not the Rev 1).

1. +15V                                          15. sequencer (out) B ?? (different to tab13F ??)
2. Gnd  (Quiet)                                16. Random out
3. ?  ("rng" on the BEMI card)           17. Envelope trig in
4. ?                                                18. Pulser out A
5. ?                                                19. Env Duration (sustain on the BEMI card) in
6. ?                                                20. Pulser out B
7. Voltage Level - Step 1 (in)             21. Env (in) decay
8. Voltage Level - Step 3 (in)             22. Level (Gate) 1 in
9. Volatge Level - Step 4 (in)             23. MOD osc waveshaper
10. Voltage Level - Step 5 (in)           24. Keyboard in for mod & complex osc
11. n  - sequencer no of steps (in)     25. Level (Gate) 2 in
12. Pulse sequence in.                    26. Envelope Det (CV B)
13. Sequencer CV levels (out)           27. Gate Mode 2?
14. Random (trigger) in.                    28. Inv (Buffer)

On the vintage easel card, the complex osc has marked a "key" and two "WS" waveshaper inputs.
The modern BEMI easel cards names them "Key", "t.lev" (timbre level), and "tws" (timbre wave shapes - tri/sq/saw).

1. -15V                                 15. key Volt B
2. ?                                       16. pulser trig in
3. ?                                       17. timbre
4. ?                                       18. attack (envelope)
5. ?                                       19. Pressure (Env ??? B)
6. ?                                       20. Envelope Gen (CV B)
7. Voltage Level - Step 2 (in)    21. Seq out (Pulse B)
8. random                              22. Mod osc (Mode) in
9. Period in                            23. Inv  (CV) in
10.index (in)                           24. Complex Osc (WS in) 1
11.frequency (in)                     25. Complex Osc (WS in) 2
12.Sequencer - *Trig in*           26. Gate Mode 1 ?
13.pitch in                              27. SR (Gate out) Offset (EN B)
14.keyboard (pulse B) out        28. SR Gate in (Gate 2 ??)

Modern BEMI cards are 99% the same. They don't have the upper prototyping section
and there is an additional RNG patch point for the mod osc.

The inputs to the "rng" on the BEMI card are 3rd tab, front.
The outputs from the "rng" are tab 27 on the rear of the card (the second last tab).

On the vintage easel card, the complex osc has marked a "key" and two "WS" waveshaper inputs.
The modern BEMI easel cards names them "Key", "t.lev" (timbre level), and "tws" (timbre wave shapes - tri/sq/saw).

Amendment. 07 Jan 2018.
Front row, pin 6 is Modulation Oscillator out on the newer BEMI Easels.
Many thanks to Sascha H. of Northern Light Modular for this info.
I haven't checked this on any my easels yet. I have a vintage, a early Roman 208 Rev 2 and a early BEMI.
++ The trigger point for the sequencer can be either of the bottom two connections
 (below the K or P).
  It corresponds to Tab 12 on the rear card edge connector.
  Looks like the 208 works well with 5V triggers --as tested with my littlebits sequencer.

++ Muffs- Easel Mega BOB - Cobramatic

++  Muffs 2 - Easel extension card thing

++ Todd Barton - Easel exploration II
If there are any errors, omissions or BS, please let me know.
I'll update this page as I sus out all the connections.

Sunday, 13 December 2015

Buchla easel vs Korg Littlebits (and some patch card magic)

I'm surprised at how good the Korg LittleBits sound through a Buchla 208.

This setup involves a BEMI easel with the Cobramatic breakout box (BOB) and two of my easel patch cards (the main & satellite).

The satellite one lying on the table with the little bits on top is powered from the vintage easel.
The trigger point for the sequencer can be either of the bottom two connections (below the K or P).
It corresponds to Tab 12 on the rear card edge connector.

Everything is clocked from the Littlebits sequencer even the two easels. We were really surprised how easy this was to do.

Thanks to Adam S for the idea & inspiration to use the LittleBits

Saturday, 5 December 2015

bUCHLA 100 - exploring the 195 filter

I started with the intention of only using one VCO (a 144) and the 195 , ten channel (Octave Format) comb filter to see how many sounds I could get from a minimal setup.

 It seems quite a bit.
 Over the course of the night I decided to add 3 more VCOs - two 158s & a second 144.

 The 285 frequency shifter was used for the sound triggered on key no.1
Signal 158, mod 144. Control mod ... CV from a 281

Stereosonic 2015 - Sydney Australia

The festival has been marred this year with 2 deaths so far - Sydney & Adelaide.
Please everyone be careful & don't do drugs. The Music is all you need to have a great time.

The final fireworks. !!!

Duke Dumont - one of my highlights.


View from the grandstand - Armin van Buuren

I thought the misspelling of Voltage Controller Oscillator 1 & 2 was funny. Should be Voltage Controlled Oscillator.


And what on earth is a "Long Jab Prebuffering module" ?????? I have never seen one of those.