This guide explains how to install a MIDI input in a Casio SK-1 keyboard. We use uniMatrix to interface the keyboard matrix and simulate key presses.
The default configuration plays notes from C3 (Midi note 36), but this can be changed.

It is also possible to change instruments via MIDI program change messages.
ProgCh 0: Piano
ProgCh 1: Jazz Organ
ProgCh 2: Pipe Organ
ProgCh 3: Flute
ProgCh 4: Trumpet
ProgCh 5: Synth drums
ProgCh 6: Trumpet
ProgCh 7: Brass
ProgCh 8: Sampling sound
ProgCh 9: Harmonic Sound

The following CC control is also implemented:
CC 5: Portamento ON/OFF
CC 6: Harm Synth
CC 7: Env select
CC 8: Vibrato ON/OFF

Installing uniMatrix

Use double sided tape to mount the uniMatrix board to the big IC on the SK-1 board. Then, solder the wires to the points shown in the picture below. The numbers are the uniMatrix I/O numbers. Do not rely on the wire colors in the picture, these might be different in your version of uniMatrix.
Solder the two power wires Vin and GND to the points shown.

Overview

Solder points for uniMatrix I/Os

Solder points for uniMatrix power

Finally, drill a hole in the back using the drilling stencil provided in the kit, mount the MIDI socket using the two M3 bolts and plug it into the MIDI in connector of uniMatrix.

Using the uniMatrix configurator, load the configuration for SK-1 (right click, save-as) and send it to uniMatrix.

Congratulations, you can now play your MT-90 via MIDI !

WARNING!!!

Notes played via MIDI will sound ca 50ct lower than when played on the keyboard. You can compensate for this easily with the tuning knob of the synthesizer, but you of course can`t play the synthesizer via Midi and by hand at the same time.

Overview

The M-500 version of OrganDonor offers the following features:

• Midi input
• Optional learn button to set midi channel.

Installation

The installation is relatively simple, but does require basic soldering skills. You will need to drill a hole for the midi socket.
Installation instructions can be found in this PDF.

User guide

Setting midi channel and keyboard offset

If the optional learn button is installed, it can be used to quickly change the midi receive channel of organDonor.

Connect midi out of a computer or keyboard to midi in of organDonor. Make sure not to send any notes.
Press the learn button and while it is pressed send a midi note on any midi channel. organDonor will set this note as the lowest note of the synthesizer and use its midi channel. These settings are saved.

Playing notes

Send midi notes on the configured midi channel (see above)

More configuration

Alternatively you may configure a lot of parameters using our organDonor configurator.
We recommend using the M-500 config file as starting point
1.) Save the file on your hard drive via right click -> save as
2.) in the configurator press “Load configuration” and select the file

There are several sample packs on Brainstep’s SD card already, however you can also create your own.
You will need up to 12 different samples with a maximum total length of 2.7s
You can use a lower number of samples and just duplicate them to use all keyboard keys. If duplicated, samples will only be saved once to save space.

Brainstep’s samples are rather LO-FI: 8-bit mu-law encoded with a samplerate of 24kHz.

To convert your samples into Brainstep’s sample pack format, you can use the web-based converter tool. If you want to be able to do this without an internet connection, just right click on the link, press “save as”. The html file works without being online.

Here are some investigations and improvements on the Juno-6 and Juno-60 noise performance. We looked at both, the original CPU as well as our Juno-66 upgrade

Both, the original CPU and Juno-66 create noise on the output. You can hear that by not playing anything on the keyboard, select SAW as input waveform (as this seems to reduce the VCA bleeding) and pull the gain all the way up.
The noise performance can be improved by adding additional filtering to the 5V supply. In case of the SH-101 for example which has a similar problem, an additional 10µF ceramic cap close to the CPU worked very well.

Now, at least in the case of my Juno, the original CPU has actually a much louder noise ( I assume because it draws more current), as compared to Juno-66.
However, the noise is not focused on one frequency, but a broader spectrum. This is due to jitter in the original CPU processing.

Juno-66 on the other hand, produces noise with a dominant frequency content and hence might be more audible – even though actually quieter.

To rectify this, I have created a firmware update that introduces additional jitter to broaden the spectrum a bit. Note, however that a good solution would of course eliminate the noise via supply rail filtering.

Noise of the original CPU, while a key is pressed the frequency is a bit different.

With the same settings: Juno-66 firmware 1.29. I press keys and change the portamento switch. Note, that this is already quieter than the original CPU

Same setting: Juno-66 firmware 1.3 – jitter is introduced

Soldering an additional 10uF capacitor between GND and 5V on the bottom of the board across the CPU supply pins, improved the noise even further.

You can find the 1.30 firmware on the updater site.

Overview

The Kawai SX-210 version of OrganDonor offers the following features:

• Fully polyphonic midi input for all 61 Notes
• Optional learn button to set midi channel.

Installation

The installation is relatively simple, but does require basic soldering skills. You will need to drill a hole for the midi socket.
Installation instructions can be found in this PDF.

User guide

Setting midi channel and keyboard offset

If the optional learn button is installed, it can be used to quickly change the midi receive channel of organDonor.

Connect midi out of a computer or keyboard to midi in of organDonor. Make sure not to send any notes.
Press the learn button and while it is pressed send a midi note on any midi channel. organDonor will set this note as the lowest note of the synthesizer and use its midi channel. These settings are saved.

Playing notes

Send midi notes on the configured midi channel (see above)

More configuration

Alternatively you may configure a lot of parameters using our organDonor configurator.
We recommend using the Kawai SX-210 config file as starting point
1.) Save the file on your hard drive via right click -> save as
2.) in the configurator press “Load configuration” and select the file

This manual describes how to install our OrganDonor midi interface in Oberheim 4 voice and 8 voice synthesizers.

You can purchase the kit here: Shop: Organ Donor

Picture derivative work:
Robert Brook, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

The installation guide can be downloaded as PDF here

The config file for OrganDonor is here

Overview

The Roland RS-09 version of OrganDonor offers the following features:

• Fully polyphonic midi input for all 44 Notes
• Optional learn button to set midi channel.

Installation

The installation is relatively simple, but does require basic soldering skills. You will need to drill a hole for the midi socket.
Installation instructions can be found in this PDF.

User guide

Setting midi channel and keyboard offset

If the optional learn button is installed, it can be used to quickly change the midi receive channel of organDonor.

Connect midi out of a computer or keyboard to midi in of organDonor. Make sure not to send any notes.
Press the learn button and while it is pressed send a midi note on any midi channel. organDonor will set this note as the lowest note of the synthesizer and use its midi channel. These settings are saved.

Playing notes

Send midi notes on the configured midi channel (see above)

More configuration

Alternatively you may configure a lot of parameters using our organDonor configurator.
We recommend using the Roland RS-09 config file as starting point
1.) Save the file on your hard drive via right click -> save as
2.) in the configurator press “Load configuration” and select the file

Overview

The Crumar Performer version of OrganDonor offers the following features:

• Fully polyphonic midi input for all 49 Notes
• Optional learn button to set midi channel.

Installation

The installation is relatively simple, but does require basic soldering skills. You will need to drill a hole for the midi socket.
Installation instructions can be found in this PDF.

User guide

Setting midi channel and keyboard offset

If the optional learn button is installed, it can be used to quickly change the midi receive channel of organDonor.

Connect midi out of a computer or keyboard to midi in of organDonor. Make sure not to send any notes.
Press the learn button and while it is pressed send a midi note on any midi channel. organDonor will set this note as the lowest note of the synthesizer and use its midi channel. These settings are saved.

Playing notes

Send midi notes on the configured midi channel (see above)

More configuration

Alternatively you may configure a lot of parameters using our organDonor configurator.
We recommend using the Crumar Performer config file as starting point
1.) Save the file on your hard drive via right click -> save as
2.) in the configurator press “Load configuration” and select the file

We have not had the chance yet to build our OrganDonor midi interface into a RS-101. However, we did install one in a RS-202 and – according to the schematics and a single picture found on the web – they seem to be identical when it comes to the tone generator/gate board.

This means it should be relatively straight forward to use the RS-202 installation manual and apply it to the RS-101.

If you want to try, we will of course assist. You can also contact us and send some pictures of the inside of your RS-101. We’ll be happy to help.

Overview

The Yamaha SS-30 version of organDonor offers the following features:

• Fully polyphonic midi input for all 49 Notes
• Optional learn button to set midi channel.

Installation

The installation is relatively simple, but does require basic soldering skills. You will need to drill a hole for the midi socket.
Installation instructions can be found in this PDF.

User guide

Setting midi channel and keyboard offset

If the optional learn button is installed, it can be used to quickly change the midi receive channel of organDonor.

Connect midi out of a computer or keyboard to midi in of organDonor. Make sure not to send any notes.
Press the learn button and while it is pressed send a midi note on any midi channel. organDonor will set this note as the lowest note of the synthesizer and use its midi channel. These settings are saved.

Playing notes

Send midi notes on the configured midi channel (see above)

More configuration

Alternatively you may configure a lot of parameters using our organDonor configurator.
We recommend using the Yamaha SS-30 config file as starting point
1.) Save the file on your hard drive via right click -> save as
2.) in the configurator press “Load configuration” and select the file