Universal MIDI interface for keyboard matrix type synthesizers and more

Description | Machines and manuals | Configurator | Order online


uniMatrix is a universal MIDI interface suitable for many synthesizers, drum machines and other gear *. It can interface existing keyboard matrixes directly and provides MIDI input and output. Additionally it offers multiple inputs and outputs to control or read additional parameters both analog and digital.
These features allow it to control many aspects of a synthesizer, not just the keyboard. Often, sound or patch settings, filter cutoff, or similar can be controlled as well.

uniMatrix is freely configurable by using our configurator tool, but we also provide installation instructions for various gear.

* maybe create a midi controlled calculator or a midi controller from a calculator.


  • Midi input and (in some cases) output
  • Freely configurable universal midi interface
  • Can interface existing keyboard matrixes of any size up to 14×8, each contact freely configurable
  • Supports Notes, CC, program change, and more
  • Up to 22 I/O pins can be configured as digital inputs and outputs
  • Outputs multiple MIDI clocks with adjustable divider and MIDI start/stop signals
  • 2 additional CV-outputs
  • 6 pins configurable as CV-inputs
  • Short-push mode to simulate short button presses
  • Optional learn button to change the MIDI channel quickly
  • Small size fits into almost any gear
  • 3-5V supply voltage
  • All I/Os with over-voltage protection
  • DIN or TRS Midi sockets available

Matrix interface

Many electronic devices utilize a circuit called keyboard matrix, sometimes also referred to as diode matrix to read buttons and switches. Here, buttons are arranged in a grid defined by a number of output pins and input pins. Each output is turned on one-by one and the inputs read. This allows it to read many buttons with a relatively small amount of pins.

uniMatrix can interface this type of configuration by ‘listening’ to the outputs and injecting the correct stimulus signal into the devices inputs at the right time. uniMatrix supports both kinds of polarities as well as a special high-impedance injection method that is sometimes preferable.
At the same time, uniMatrix also reads the buttons or keys connected to the keyboard matrix, debounces and sends out corresponding midi messages.

Each button in a matrix can be freely configured to react to MIDI notes, CC or program change messages. Furthermore, uniMatix can simulate short button presses automatically.

Additional I/Os

I/O pins not used by the matrix interface can be used for other purposes. Each of these I/Os can be used to generate digital signals and react to MIDI Notes or CC.
Each pin can also output its own MIDI clock with adjustable clock divider as well as start/stop signals. Up to 22 different clocks can be used at the same time.

Pins can also be configured as inputs to read digital states and send them out as MIDI Notes or CC.

An analog input is available on 6 of the pins, reading the voltage and sending out MIDI CC messages.


Two CV-outputs are available. The are suited to control parameters like filter cutoff or other sound parameters. Due to their low resolution they are less suited for pitch-CV though.
CV-outputs can be linked to note velocity, aftertouch, channel pressure. Or they can output values received via MIDI-CC messages.

The board

With its small size of only 37x28mm (1.5×1.1 in) and a height of ??, the uniMatrix board fits in even the smallest devices.
There are two ways wires can be connected to the board:
The small 1mm pitch connectors are perfect as they do not add any additional height. We supply crimped wire assemblies with pre-tinned wires with the kit. Various lengths are available.
Alternatively, 2.54mm pitch pin headers can be soldered onto the underside of the board. Here, dupont style connectors can be used. These wires are typically thicker and available in lengths up to 50cm.
Two mounting holes are provided to fix the board inside a device. Alternatively, double sided tape can be used easily, as there are no components on the underside.

uniMatrix works with a supply voltage of 3V – 12V. The voltage on its outputs does never exceed 5V though. All pins are protected against over voltage.
It is possible to interface keyboard matrixes that run on a voltage larger then 5V, as long as the device accepts a 5V signal as valid key press. In such a case, 100k series resistors are recommended at the uniMatrix inputs.

List of machines and Installation manuals

Click on a Link to get to the specific installation manual. If there is no link, we think uniMatrix will work with this machine, but were not able to try it yet.
Generally, uniMatrix works with keyboard matrixes running at 3-5V. In some cases, voltages slightly above that might be fine, too. Another important factor is timing. uniMatrix has a very low latency of 1µS, but in some cases this is not sufficient (SX-210 for example).
If uniMatrix does not work because of tight timing or high voltage, our organDonor interface can be used instead.

Your synth is not on the list at all? Contact us!

Casiotone 601
Casiotone 701
SK-1 (confirmed working)

CS-01 (maybe, we need to test this)
VSS 200


Kawai / Teisco
SX-210 Timing issues, use organDonor instead.

PPG Wavecomputer 360 (confirmed working)

Texas Instruments
Speak & Spell




Polysex now open source hardware


Tubbutec Polysex is discontinued but we decided to make all the design files available to the public as open hardware. You can still purchase the PCBs in our shop.

The files include front panel mechanical drawings and print data, schematics and PCB layout, the mechanical stencil design and manuals.

If you use or modify this, please be so kind and leave a comment below. We also like pictures and videos 🙂

You can download the files as .ZIP here: Tubbutec Polysex design files.

Files are licensed under the CERN OHL v. 1.2.

Juno-66 update – now features custom scales


Juno-66 firmware version 1.24 is released. Apart from the seven built in scales,  is now possible to upload a four custom scales using a program like Scala. Of course micro tuning is supported and you can have any number of notes per octave. Have a look at the user manual (chapter 10) for details.

In case you missed previous firmware updates, here are a few of the new features since the initial 1.00 release:

  • New school chord memory modes
  • Optional auto portamento in MONO B mode
  • Three voice mode
  • Looping mode, delay and polarity for ADSR

More infos about the Juno-66 upgrade on the Juno-66 product page.



SH-101 noise reduction mod


The Roland SH-101 while an awesome sounding synthesizer, unfortunately suffers from digital noise on its output. The main source of this noise is the current flowing through its DAC combined with bad grounding. The Tubbutec SH-1oh1 mod reduces the noise floor below that of the original (amongst a lot of other features), but noise is sometimes still an issue especially with bass sounds.
This is the instruction of an easy to perform – and reversible – modification that reduces the noise substantially, by about 10dB.

Update: We added an additional, also very simple procedure to reduce noise further. Is is also a simple addition with a lot of beneficial impact on noise performance. See section “Filter cap for 5V supply” below.

Continue reading

Unison mode for Korg Poly-61


While the older brother of the Korg Poly-61, the Polysix, features a monophonic ‘Unison’ mode, the Poly-61 does not. The reason is most likely the fact, that the Poly-61 is DCO based, making the voice spread technology used in the Polysix Unison mode not possible.

It is however nevertheless desirable to add a monophonic mode to the Poly-61. Playing a monophonic synth is quite a different experience compared to a polyphonic one and if you have extended features such as not retriggering the envelope when playing legato, a whole new world of sound opens up.

If you install the Modysix mod you will have this feature build in, the only problem is: There is no ‘Unison’ button. You can select the unison mode using Midi, but it is actually quite simple to install an extra button and led.


You only need four parts and a little bit of wire: A push button, an led, a diode and a resistor. The push button can be any kind of button, the one I chose is what I had lying around, but you can probably find one that looks more like the original buttons.  The diode is a general purpose one, such as 1N4148. For the resistor choose a value of your liking. I found that the value of 470 Ohms used for the other leds in the Poly-61 gives too much brightness with modern leds (led technology has vastly improved in the last 30 years), so you might use a larger value such as 1k Ohms.


After installing the switch and led in the front panel, you can connect them to the panel board labelled KLM-482 – it is the one the ‘poly’,’chord’,.. buttons are mounted on. Pin3 and Pin9 in the schematic above refers to the pins on the connector on that panel. You can find +5V where I connected the resistor in the picture above. As you can see, I soldered the diode and resistor directly on the back of the PCB.


The last connection goes from the LED to Pin6 of IC3. It can be found on the processor board (the one with the battery).

When finished you can now use the unison mode on your Poly-61. Have fun!

Polysex example

A beautiful example of a Polysix modded with the Tubbutec Polysex mod:


The author of this blog not only had a walnut chasis manufactured for his Polysix but also created a completly new overlay for the front panel which includes the Polysex mod.

I am sure Imploded View will have some new tracks soon and we will be able to listen to his Polysix 🙂