Electro Harmonix – Mini Synthesizer

How to midify an Electro Harmonix – Mini Synthesizer. I’ve had a Mini Synthesizer for a long time before I found a way to midi-retrofit. Playing the Mini Synthesizer by hand might be fun but also could be frustrating. It’s got a membrane keyboard which plays awfully but on the other hand; it’s monophonic so who needs good keys anyway. Besides the keys it’s got an internal crystal mic glued on case which makes the synth velocity-sensitive. You can play notes with one hand and tap on the case rhythmicly with the other..very nice.

But! Without any external control inputs the synth can’t be sequenced so that’s a reason to midi-retrofit.

Putting in CV/Gate might look like a straight forward solution, but I and many others, have unsuccessfully tried. The keyboard uses stange voltages and it simply doesn’t react properly. I lack proper technical explanation for this phenomenon. (see Disclaimer).

I managed to mifi-retrofit successfully another method by using two parts:

A DTronics ( Midi to Trigger interface V4 ) has been used but I suppose every standard Midi note – > 5v gate converter board will do. I’ve used the Doepfer MTC64 in other (Solina String and ARP – Omni) units the same way. Buy this one is cheaper, maybe because it has fewer outputs. You don’t need 64 output gates for this little synth.

The DTronics needs 8V – 12V DC. The Mini Synthesizer needs 9V, so you can take power directly from the adapter’s input socket. I chose to solder on the PCB because the input socket already had many wires (batteries and PCB wires) which were wrapped in heat shrink tubing. PCB soldering seemed to be more efficient.

The Midi – Gate converter 5v outputs drives an optocoupler board which holds one optocoupler (and one resistor) for each key. When the Midi – Gate converter receives a midi note, the corresponding +5v gate output will drive (820ohm resitor in series) the optocoupler’s LED-side which causes the other side to shortcut and makes the corresponding Mini-Synthesizer’s key turn on.

Diagram and CNY74-4 and CNY74-2 integrated circuits (ICs) optocouplers pinout:

CNY74-2 and CNY74-4 optocoupler pinout

This has to be done 25 times (once for every key).

Don’t forget to wire ground from Optocoupler-board!

How to wire the Midi – Gate board’s power leads, midi connector(s), learn-switch and gate-output leads I’ll have to refer to the DTronics – Midi to Trigger interface manual since this wiring depends on which interface you choose using.

Have fun!

Gotek – placement

This walkthrough describes how mount your Gotek in your sampler.

Prepare 1:

If your sampler has a working floppy drive, format one or two (spare) floppies so you’ve got a “blanc disk”!

Prepare 2:

If your sampler boots from floppy drive. Make one or two spare boot-disks!

Mounting the Gotek in your sampler:

Remove old floppy drive. Put Gotek in same place.
Power connector probably has 4 leads.
Remove or cut the 12volt lead (yellow on pic). This one won’t be used by the Gotek.
Cutting isn’t necessary, but optional for safety reasons
You don’t want to connect it in the wrong direction while having an active 12v.
This could damage the Gotek.

Connect power lead with according to picture below:

When turning on the sampler the Gotek’s display now should show ‘HXC’.
Turn off sampler, remove (100v/110v/220v/240v) mains and proceed..

Connect floppy flatcable.
Some samplers will work when this cable is connected straight.
Other samplers need to have this cable reverse-connected.
Remember this. When entering “test phase” reversing the cable might be a solution if things don’t work at once.

Jumper settings might differ too depending on which sampler is used.
Often one jumper a position S1 will work fine.
But feel free to experiment if things don’t work.
Jumpers S0, S1 and MO are most used ones (the S-jumpers are for cable select and the MO jumper gives a motor on/off signal if I’m not mistaking).

Buy a USB flash drive. Different sizes will work. Not all USB flash drives will work. I once bought some cheap non-brands which didn’t work at all (I had four of these, none worked).
I’d suggest buying a quality brand.

Format FAT32.
Then put the config file (name of file: HXCSDFE.CFG) in the root BEFORE putting anything else on it!
It’s crucial not putting anything on it before config file has been placed.

When using a Gotek like I descibed here, you should download the “indexed mode” config file from the download area of HXC2001.

Direct download link: HXCFEUSB_HFE_beta_firmware.zip

Download starts.
Here’s the “Indexed mode config file” located: HXCFEUSB_HFE_beta_firmware/Config_Files/Indexed_mode/HXCSDFE.CFG

Place this file in the USB flash drive’s root. Now your USB flash drive is ready to use in a HXC floppy emulator. But your sampler can’t use it yet! (empty) Disk-images must be placed on it to enable the sampler to write and read.

There are different ways to make a suitable disk-image-file for your specific sampler:

  • Create it with HXC software. This option require you to know exactly which paramters have to be set for your sampler.
  • Download pre-made images from the net. A good starting point is the “Quick Install Disk Images” link HXC provides here.
  • Use a physical floppy you used to use and have HXC software convert this to a proper disk image. For this option you’ll need a 32 bit Windows PC with built in floppy drive (USB floppy drives won’t work). For this option you’ll need preperation steps 1 and 2 at the start of this walkthrough. ๐Ÿ˜‰

How to convert physical floppies into HXC images will be the next walkthrough.

Gotek – HXC flash procedure

Hello all,

Quite regularly I’m asked how to flash a Gotek floppy drive emulator with HXC firmware so I wrote this walkthrough. I’ve tried to keep it as short and clear as possible. If any mistakes or shortcoming have occurred, please inform.


  • Gotek USB floppy emulator SFR1M44-U100K or SFR1M44-U100
  • USB-TTL converter
  • HXC firmware licence
  • 32bit windows PC
  • Soldering iron
  • Wire
  • Prepared USB flash drive

Prepare USB flash drive with latest HXC firmware:
Format FAT32
Download latest HXC firmware from HXC download area or use direct download link: HXCFEUSB_HFE_beta_firmware.zip. Unzip and copy the .UPD file onto the USB flash drive. For example: HxCFEUSB_V3_4_11_2a.UPD

Open the Gotek. 3 screw located at arrows:

Pull out PCB: lift backside (connector side) and pull back while gently pushing the LED. Then push display to the right:

Solder a small piece of wire across points shown in pic. This sets Gotek in system bootloader mode:

Buy an USB-TTL adapter. You’ll find these on ebay of whatever electonics webshop cheaply.

Connect USB-TTL converter to Gotek:

Connect USB-TTL to a Windows computer with internet.

Now you have to but a HXC firmware licence here: https://hxc2001.com/store/

Pay by paypal 10,- + VAT and you’ll get one licence to flash one Gotek.

Download the STM32_SerialBridge.zip file, unpack (one .exe and ond readme) and open the SecSerialBridge.exe file. (btw: readme.txt is another walkthrough).

Mind the fact you’ll need a 32 bit Windows PC!

This won’t run in a 64 bit windows machine or Apple.

Use your login credentials, click connect and you’ll see you’ve got one licence (if you bought one) left. Select COM port which carries the USB-TTL converter and click โ€œprogramโ€.

Be patient ..

little more patient…


Now close program.

Remove USB-TTL converter from PC.
Remove green, blue and yellow wires from Gotek.
Insert USB-TTL converter back into PC (so Gotek gets powered).

Gotek Display will show: LDR

Put in the prepared USB flash drive with Firmware and wait until Gotek finished installing the firmware.
Gotek Display will now show: HXC.

Kontakt Instrument – Medieval Organ

While surfing the net I found this beautiful youtube. I liked this sound very much so I sampled it. This organ has been built by: Orgelmakerij van der Putten in the Netherlands.

One sample has been used which is transposed in an EMU E4XT to give it a bit of EMU niceness. After that a 3 sample/octave multi has been made in Kontakt (version 5). On top of that a simple GUI which gives it some synth-based parameters like Filter (+envelope) , Pitch and Amp envelopes. Have fun! Click here to download it