Korg MS-20 Analog User Modifications

Do It Yourself Special:

FREE plans to add MIDI capability

to the Korg MS-20 with the

Synhouse MIDIJACK!

The following plans describe a general method of adding MIDI capability to the Korg MS-20 analog synthesizer for $99 with the Synhouse Original MIDIJACK. Later on, a specific method to install the Synhouse MIDIJACK II: Hertz so good! will be briefly described. You can do this yourself if you have a little experience with electronic repair and the soldering of wires and circuit boards. If not, it is recommended that you send the instrument to Synhouse L.A. for a quick, low-cost Factory Installation. All repairs and modifications made to your instruments will be done at your own risk and Synhouse Multimedia Corporation assumes no liability for personal injury caused or damage to equipment or loss of use caused directly or indirectly by the use of these plans. If in doubt, don't do it!

Instructions for installing the Original MIDIJACK:

1) Proceed with the installation as described for the Korg MS-10 but make the appropriate changes as they relate to the Korg MS-20. The three manuals supplied with the MIDIJACK will provide all necessary information, as they relate to any synthesizer.

2) For the MIDIJACK #3 blue wire and MIDIJACK #4 white wire, connect to the jack circled in blue, and the MIDIJACK #7 brown wire to the jack circled in brown in this photo:

3) Test and calibrate using the procedures described in the Original MIDIJACK Quick Installation Manual.

4) With the Original MIDIJACK, the Korg MS-20 is perfect for computer-controlled live performances with real-time hands-on sound tweaking and patching. The Korg MS-20 is quite a bit different than other analog monosynths and the MIDI control that results from putting an Original MIDIJACK on it is different as well. The Original MIDIJACK is using the Korg's built-in linear-to-exponential converter to get the correct VCO control. To start playing MIDI, you must let the instrument warm up then momentarily press down one note on the Korg keyboard to provide the correct offset voltage. The keyboard intonation can be adjusted with the knob in the FREQUENCY MODULATION section labeled MG/T.EXT. The correct setting will probably be fairly high, between 8 and 10. If the Korg TOTAL input is warmed up and working correctly, the Original MIDIJACK will play MIDI notes perfectly in tune. An advanced user may find it useful to add an extra fine tune trimming potentiometer in series with the MG/T.EXT knob to get finer control and make quick adjustments when temperature changes cause drift. The MS-20 keyboard can be used to transpose the incoming MIDI notes on the fly.

Instructions for installing the MIDIJACK II: Hertz so good!:

1) The method of installation for the MIDIJACK II: Hertz so good! is exactly the same for everything except the connections for the MIDIJACK #3 blue wire and MIDIJACK #4 white wire. Instead of being connected to the volt/octave input, connect these in the same manner to the regular Hz/volt VCO input jack. The pros and cons of using the Original MIDIJACK vs. the MIDIJACK II: Hertz so good! are discussed in question 39 on the Analog User FAQ's page. The MIDIJACK board may be mounted in the lower right corner of the panel as seen here:

With the MIDIJACK II: Hertz so good!, the MIDIJACK #3 blue wire and MIDIJACK #4 white wire, connect to the jack circled in blue, and the MIDIJACK #7 brown wire to the jack circled in brown in this photo:

2) The actual connections may be seen in this photo, which shows Korg MS-20 serial number 144219:

Please note that the MIDIJACK #1 black wire cannot be seen. It may be soldered to any ground point, such as one of the ground tabs hanging from any of the 1/4" jacks. The MIDIJACK #2 red wire can be seen soldered to the trace next to the brown Korg wire above. The MIDIJACK #3 blue wire is soldered to the solder terminal coming through the board from the back of the jack labeled VCO 1+2 CV IN as shown above. The trace coming from that must be cut to break the signal as shown above. The MIDIJACK #4 white wire must be soldered to the other side of the break in that trace, as shown above, where it was most convenient to solder onto the lead of a component coming through the board and trace. The MIDIJACK #5 yellow and the MIDIJACK #6 green wires are not used in the installation and may be taped up. The MIDIJACK #7 brown wire must be connected next. The Korg MS synthesizers use an inverted gate signal similar to Moog synthesizers and the MIDIJACK #7 brown wire (S-trigger wire) works well for this. The MIDIJACK #7 brown wire (S-trigger wire) must then be connnected in parallel with the existing trigger circuit. A small signal diode can be inserted to isolate the signal so the local keyboard will still work when the MIDI is turned off. The correct type of diode is included with the MIDIJACK in the accessory packet, but may also be purchased locally at any electronics store such as Radio Shack as a 1N914 or 1N4148 or equivalent type of switching diode. Locate the factory Korg terminal which connects to the tip of the TRIG IN jack, which is shown in the photo above. This terminal connects to the tip of a plug inserted in the the TRIG IN jack. Solder the anode end of the diode (the end AWAY from the little black band) to this terminal and solder the MIDIJACK #7 brown wire to the cathode end of the diode (the end with the little black band). In summary, the MIDIJACK #7 brown wire goes to the band end of the diode, the other end of the diode goes to the terminal on the trigger jack. The finished connection with the diode can be seen in the photo above.

3) Test and calibrate using the procedures described in the MIDIJACK II Quick Installation Manual.

4) If this installation method is not immediately and completely clear to you, you should refer the installation to Synhouse for Factory Installation.

If an analog synthesizer has the built-in glide function factory wired to be pre-CV/gate jacks, it will not have use of the built-in glide with external CV/gate control. The installation of a MIDIJACK is no different than using external CV/gate control, having no access to the built-in glide. If glide is required for MIDI use, an easy solution for real analog glide is provided in the Advanced Installation Manual, but is beyond the scope of these simple instructions.

Possibilities for customization:

An alternate method of installation that would in the style of the fully patchable Korg MS-series would be to install the MIDIJACK circuit board inside the synth as intended to get the power for the MIDIJACK from the synths' internal power supply, but solder the MIDIJACK CV output wire (MIDIJACK #4 white wire) and S-Trigger output wire (MIDIJACK #7 brown wire) to a pair of new 1/4" jacks on the panel with the rest of the jacks:

When you needed MIDI control, you could patch them any way you like. This configuration would actually make for an easier installation than the intended method which bypasses the keyboard automatically.