Wednesday, 29 January 2014

One Evening Project

Easy MIDI Bass Pedals

from your old MIDI keyboard                             

Moog Taurus. Image source Wikimedia Commons.

Organ pedalboards have existed since 13th century. The idea is fantastic! You can use your feet for bass duties while your fingers are busy playing higher registers. Of course you can also use MIDI pedalboards for playing higher sounds or triggering samples and fx or whatever you like.

I was interested to try using bass pedals while playing my electric guitar.
Many rock groups such as The Police and Rush have used bass pedals (in power trio context). 
They used the legendary Moog Taurus - the most famous foot-operated synthesizer.

Taurus 3 is a dream machine but it's like 2000 dollars! And it has only one octave keyboard.

MIDI bass pedals like 12 step by Keith McMillen is more reasonably priced and comes with cool smart sensor keys. It's also has only one octave of keys.

But what if you wan't to try the idea of bass pedals first before buying expensive product.
Maybe you already own something like 12 step but need second machine for triggering samples.

Do you have an old ROMpler keyboard collecting dust? Give a new life to your Casio home keyboard!
You will need a working normal size keyboard (at least 4 octaves) that can output MIDI messages.
I'll show you how to hack it to MIDI bass pedals machine nondestructively!
Yes! Nondestructively. You can reverse this hack if you want to. 

Maybe I'll buy something like 12 step one day but for now I'm perfectly happy with my home made bass pedals hack. I can create cinematic atmospheres with my guitar and play droning bass notes at the same time with my feet like a musical octopus! It's super cool to play some guitar arpeggios with delay fx and try different bass notes - A Happy Accident Generator Extraordinaire!

I hacked my Yamaha SY-35 vector synthesizer. It's a cool synth but not used so often nowadays.  
The other two MIDI capable keyboards I own are E-mu Emax and Roland PC-180A midi controller so SY-35 was the best option. 

Yamaha SY-35 hacked to bass pedals. Yamaha's modulation wheel is also usable as a foot-wheel.

What You Need

Normal size keyboard instrument (at least 49 keys preferably 61 keys) with MIDI output capability

Double sided tape

Normal clear tape

Masking tape

Thin black and white plastic sheets

I like to use polystyrene sheets in my projects

You can also use something like

It should be something thin but quite sturdy material

 I used these cheap containers as a white plastic source

Coloured cardboard (some color other than black or white)

Cutting tools

Marker pen and a ruler


Computer with DAW / VST host / Pure Data / Program that manipulates MIDI messages

Making of Bass Pedals


Clean your poor keyboard from dust and hair. :)

Cut white key sized pieces from coloured cardboard and attach them to following locations with double sided tape. These will work as spacers.

double sided tape 

Spacers in place. You don't have to cover the whole surface of the white key with coloured cardboard.

Make spacers more sturdier by covering them with clear tape

 Clear tape on top of areas where your feet might touch


Use again double sided tape for attachment. Cut white and black plastic to pieces you see in the next picture. You can cut thin plastic with large scissors. 

Attach a piece of coloured cardboard on top of C#3 and D#3 note.

Then make these white plastic pieces and fix them in top of white keys.

If you have 49 key keyboard just ignore the last octave of the instructions. You still get more than an octave of bass pedal keys. 

Now mark the keys with marker pen. Use masking tape on black plastic. 

I made E the lowest note. I didn't want to go as low as C1. It's 32.7 Hz.
E1 is 41.2 Hz. It's the lowest note of double bass and bass guitar. 

Your Bass Pedals are ready!

MIDI message conversion


Red dots on top picture shows original midi notes that needs to be converted to new midi note messages. Only those red dot marked keys are used on conversion and other notes are filtered out.

If you have malfunctioning notes on your keyboard you can change midi notes you use for conversion. For example low F can be C or E instead of D.

Conversion Chart

original midi note --> remapped midi note

37 --> 40
38 --> 41
44 --> 42
45 --> 43
51 --> 44 
52 --> 45
56 --> 46
59 --> 47
65 --> 48
68 --> 49
72 --> 50
75 --> 51
79 --> 52
80 --> 53 
85 --> 54
86 --> 55
92 --> 56
93 --> 57

Here is a picture that shows original midi note and remapped note number

Software options

I tried to find ways to remap MIDI notes that would work in different operating systems. 

VST plugins

If you like to use VST midi plugins there is a really nice collection of plugins called Piz MIDI. It's made by Insert Piz Here and it's should work on Windows, Mac OS X and Linux. You can download the collection from here

In the site there is a list of DAWs that will work with those plugins

You will need midiNoteMap and midiTranspose plugins from the collection 

I use Windows computer and Reaper DAW. 
I have only tested midiNoteMap with Windows computer but there is a strange bug at least in the Windows version. To work properly you need to put midiTranspose plugin before midiNoteMap and set transpose value to +6. For some reason midiNoteMap sees incoming notes -6 semitones off. But using midiTranspose to correct this is a quite an easy workaroud.  
If you find that midiNoteMap is working correctly in your system please let me know!

Here is a screenshot from Cockos Reaper. There is no GUI in midiNoteMap so every DAW shows it differently.

There is a slider for every MIDI note. You can set remapped notes with sliders.
Simply turn unneeded midi notes to far left. Then the value is '-' and the plugin filters out that midi note.

Pure Data


If you don't want to use VST plugins you can use Pure Data to manipulate midi messages.
You can download patch I made from here

PD bass pedals

Screenshot of Pure Data Patch

I use Midi Yoke in Windows to route midi between applications. There are instructions in the web how to do it on OS X. I don't know how Linux handles MIDI.

In Pure Data's MIDI Settings I set my hardware MIDI input as input device and MIDI Yoke as output device. I disable any input and output device in Audio Settings. It's important that you set Delay (msec) value to 0 in Audio Settings. If delay value is something else than zero there is latency in MIDI messages.

You can now route your manipulated MIDI messages to DAW or hardware synths. 

Happy playing!

Playing tip!

In some keyboards the keys are pretty high. If you play standing up it might help your playing if you use something to lift yourself a little higher from the floor.

Demo video of Bass Pedals in action

I used AAS Ultra Analog for bass sounds. The white keys are not yet covered with white plastic in this video. I made a setup that uses modulation wheel to crossface between two synth presets. Mod wheel also acts as a volume control for Valhalla Shimmer reverb (in guitar fx chain) that is set to octave pitch shift feedback effect.

The track I play is called One Hour Backwards.


I made also an Instructables-version of this project

Tuesday, 14 January 2014

How to build MonotrOndes Part 4

The Expression Controller  

Finally I will show you how that volume and filter cutoff controller works. 

Lever is spring loaded. I used potentiometer's shaft as an axle and used this kind of torsion spring for the resetting mechanism.

The Torsion Spring


The potentiometer serving as an axle for the expression lever. Sheet metal is used for the lever system's base.


The Lever and the Torsion Spring. There is a hole in the knob that keeps the spring in place. I used aluminium knob. Aluminium is easier to drill than harder metals.


 The Lever System. The paint is worn out because of heavy playing. :)

The whole synthesizer and expression system is shielded. I wanted to make my MonotrOndes an usable musical instrument so any unwanted noise is minized with shielding. As you can see from the pictures I used sheet metal for the lever system's base.
If you don't know anything about shielding and grounding I suggest you google about shielding and guitar stompboxes. DIY guitar FX websites are very good places to learn basic audio electronics.  

Here is a picture from time when I was building the expression system.

 The Other Side 

You can see that the pot's metal housing is removed. I extended axle with a piece of glued acrylic tubing. There is a large hole in the wood for the axle. Pieces of aluminium tape are used for shielding. 
All the electronics are inside this metal box that I found from my local shopping mall. Even better if you can find a box with a lid that isn't painted at all.

As you can see the lid is on the lever side. There is a drilled hole in the lid for the axle to come through.

White paint is scrached off where the aluminium tape and lid makes an electrical contact. That black thing glued to the acrylic tubing is a shutter. I made it from polystyrene. Thin polystyrene is a wonderful material for a maker. You can cut it with scissors! Though I must say it's not environmental friendly. You can also use cardboard.

The Optical Potentiometer System

I wanted to make a scratch-free volume controller. I got the idea for an optical system from optical volume pedals. My first design was using only one LDR (Light-dependent resistor). In my first youtube video the MonotrOndes was still equipped with that design. There was problems. Sound was leaking a little when the lever was in the rest position. I also had to amplify the sound with preamp. Then I got the idea of using two LDRs as a voltage divider. That idea made possible also to use lever system for voltage control. Here is an animated GIF that shows how the shutter works.

LDR-pair is controlled with a shutter mechanism. Shutter in the middle gives same amount of light to both LDRs. Shutter in the another extreme shuts another LDR from light entirely and fully lights another LDR. Smooth and crackle-free potentiometer!

There are 2 pairs of LDRs. First pair controls volume and second pair controls cutoff CV. Cutoff control is a voltage divider that changes VCC and then goes to cutoff terminal in the PCB.


 I used LEDs from broken solar garden lights. They were 3V LEDs. Perfect! :)

Here are the schematics

 The Volume Control Part of the Circuit. 

The Filter Cutoff Controller Part of the Circuit.

There are extra trimmers in the filter cutoff circuit. Filter CV should be trimmed to usable voltage values. I added extra potentiometer to metal chassis for adjusting cutoff control depth. That way I can change between violin and brass type sounds. 

That's it! Feel free to contact me if you wan't more information about building your own MonotrOndes. 

Saturday, 4 January 2014



Happy New Year 2014!

This instrumental song is my tribute to Old School Synthesizer Heroes.

Especially to Jean-Michel Jarre, Vangelis, OMD and Kraftwerk

And this song is, of course, also a tribute to all the athletes of the world. :)

Other influences are

Thomas Dolby
Depeche Mode
Jan Hammer
Tangerine Dream
Klaus Doldinger
Thompson Twins
Sports games of Epyx


E-mu Emax
MonotrOndes (layered strings and fx)
Bass guitar
Alesis SamplePad
Homemade Hi-Hat pad

Boss and Behringer Chorus stompboxes
Symetrix Compressor

Soft Synths

NI Battery 3
MuTools Mux
Korg M1 Le

and various effect plugins

thanks to and OCAL for sport pictograms

I created those motion graphics with Processing 2.1 and Wax 2.0

Friday, 13 September 2013

My new youtube video 

Fanfare intro to a forthcoming instrumental song called Athlete.
All melodic sounds are played with MonotrOndes. Expression control of the filter cutoff makes beautiful brass sounds!

It's shocking how similar my playing looks in those different windows. But if you look carefully you notice that every window is a different performance.
Those subtle differences in pitch and timing makes that beautiful ensemble sound.

Here is a link to an audio track on SoundCloud

Monday, 19 August 2013

How to build MonotrOndes Part 3


Sorry, It's been a while since my last post! It was a warm summer here in Finland and I didn't have a summer holiday. So I enjoyed sunny evenings and weekends. But I have also improved the design of MonotrOndes.
Now the expression lever also controls the filter cutoff!

The Pulley System

Mitsushi Abe's Ondes Martenot MIDI Controller was the first design I came across that uses horizontal pulley system. This site gave me inspiration to build MonotrOndes that way too.
I don't understand japanese but the pictures were very informative. :)

Horizontal version simplifies construction a lot.
Check out Mark Steiner's awesome Artemis that also uses horizontal system.

The Pulley System. Top left pulley is connected to the multiturn pot. The other pulleys have ball bearings to ensure fast action. The tension spring is very important part. 

I'm not going to tell every possible detail about the mechanical construction. There are many ways to build this kind of system. The basic idea is quite simple. It's more fun when people add their own personal touches. I bought my pulleys from finnish online hobby shop. I had to enlarge holes. I don't own a drill press so holes are not perfectly centered but it doesn't affect performance. In the near future I will resin cast my custom pulleys - topic for future blog post. :)
The string is fake leather cord - same type that jewellery hobbyist are using. The ring is keychain ring that fits to my finger. I knitted a little "padding" for the ring. I covered ugly knots with aluminum tape. :)
Dana Countryman used piece of pipe and velcro for the ring. I think it's a much better idea.

The Ring.

You need a tension spring. I have an assorted spring set which I found from hardware store. I'm sure you'll find similar sets in your country.
When the Ring is in the middle of the keyboard the Tension Spring should also be in the middle.
Attach the Tension Spring first. It's a little challenging to tie the Ring - there should be a little tension in the spring when the Ring is in place.

The Ring and the Tension Spring in the middle of the keyboard.

The Keyboard

Technically it's not a keyboard. It's only a reference for finding a correct pitch. But let's call it keyboard anyways. :)
Many people have wondered why the keys gets narrower in the higher octaves. Monotron has linear to exponential conversion. But it’s not perfect 1 volt/octave. It's not designed to have pitch range of many octaves. If you want to make keyboard more even you will need extra circuitry.  I haven't tried this but I think you can use an anti-log trick.
I'm also a guitarist and I like the fact that the keyboard gets thinner in the higher octaves like frets in stringed instrument. I get more violin like vibrato and larger note range that way.  

When adjusting the pitch range and intonation use Monotron's own intonation trimmer and that trimmer pot I introduced in part 2. 
I have four and half octaves in my keyboard.
Lowest octave in my keyboard is 20 centimeters wide from C to C. fourth octave is less than 9 cm wide.
Multiturn pot is adjusted to be in the end of it's travel when the Ring is in the highest point of the keyboard. 

Here is how I did the keyboard overlay:
I adjusted pitch range first. Then I attached paper strip under the string and listened reference pitches from other instruments. I marked painstakingly every note. The paper strip as a reference I drawed stylised keyboard with Inkscape and printed it with a laser printer. I laminated both sides with clear contact paper. For those tactile pitch points I used scrapbooking stickers.

I wanted to keep keyboard overlay changeable. For example I might want to experiment with micro tonal scales. I used a piece of a picture frame and Velcro stickers as a way to keep keyboard in place.

Wednesday, 19 June 2013

How to build MonotrOndes Part 2


Check out also the updated first part!

I'm using 3-pin DIN Connectors for connecting the Pitch Controller-module to Synth+expression-module of the MonotrOndes. I'm only using 2 pins and a ground point in this connector. You can choose a different type of connector. Or you can choose to make a non-modular version of MonotrOndes where everything is in fixed place without connectors and cables. But I have a point! The left-handed player can put the synth+expression-module on the right side of the pitch controller-module so he/she can play expression lever with his/her right hand. It's also nice to have a possibility to position the modules in a way that suits to your playing style.

 3-pin DIN Connector

 Here is an aluminum box that contains the multiturn pot. DIN connector at the top. 
Multiturn pot is connected to a pulley.

Here is the wiring inside the aluminum box. 

And here is the pitch control wiring inside the Synth+expression-module!

Stay tuned! :)

Thursday, 6 June 2013

How to build MonotrOndes part 1

This post is updated!  

At first I have to give credit to my twin brother Kalle. He came up with the name MonotrOndes.
My video has been very popular. I thank you all for your nice comments!
Someone even asked if I could build and sell these things. Maybe if there is enough people willing to buy them. I don't even know if it's legal to sell modified synthesizers without permission from manufacturer like Korg.

Pitch Control Electronics 


I assume you know a little bit about electronics and components. You should also understand that if you mod your Monotron, you loose all warranty! So please be careful and don't blame me if something goes wrong.

MonotrOndes is not using the original ribbon controller. There is a connector from the ribbon controller to Monotron board. You can disconnect the ribbon from there.

I removed one SMD resistor from Monotron's PCB. Instructions for removal and the location of that resistor are in this site:

Here is a new picture!

After removal of the ribbon and that SMD resistor I found out that monotron was playing continuously - exactly what I wanted. I don't know if it's necessary to remove that resistor. There might be an easier way to mod Monotron to play continuous sound.

For controlling pitch you will need two potentiometers - a trimmer (at least 47k) and a multiturn pot (100k). Of course you can use a normal potentiometer instead of a trimmer.
In the circuit the trimmer behaves as a variable resistor that sets the range of the pitch control. When you have found the right value for the pitch range you don't have to adjust it anymore. That's why we are using a trimmer type pot.

The multiturn pot's value changes when playing. Together the trimmer and the multiturn pot forms a voltage divider circuit. Monotron uses 3 volts to operate but there is internal circuit that magically (not really!) outputs 5 volts. The point in the Monotron PCB that outputs 5 volts is called VCC. That 5 volts is feeded to voltage divider that changes voltage value to smaller values. That divided voltage output is connected to pitch CV point in the Monotron PCB.

Now we have voltage controlled pitch!

I have to borrow unmodded Monotron for pictures. In the meantime check out this post from Din Sync blog.

There you can find picture of unmodded Monotron PCB. The important solder points are Pitch, VCC, Ground terminal and positive terminal.

You can see the important solder points in this new picture! Check out also a secret audio output point that bypasses Monotron's own volume pot. :)

Here is a schematic

Here is a picture of I/O connections