The Roland GR-300 synthesizer was released on the early 1980´s and still an unique device for guitar players since then. The original japanese connector used on it is not produced anymore, when I had a chance to buy a GR-300, I decided to make a new connector for the cable I had from my old GM-70 midi converter and use it on the GR-300.

It´s impossible to write this Instructable without mentioning Wayne Jones and his page with lots of information about the GR-300 and many other guitar synthesizers, without his page I coudn´t fix the cable and connector.

Step 1: Preparing the PCB - 1

The first step is to prepare the printed circuit board that will later be populated by the 24 signal pins plus the guide pin. Cut a piece of single sided fiberglass PCB  42mm x 14mm ( I know, I made mine a little short). Use a 0.8 mm drill to make the 24 smaller holes on the PCB and a 1.8mm drill to the guide pin. Follow precisely the dimensions on the attached image to avoid fitting problems later, I used a coordinate table of a mini-mill to do that, fortunately my mill has dimensions in milimeters.

Step 2: Preparing the PCB - 2

The image shows the evolution of the PCB, bare  board, board drilled (there´s one hole missing for the bolt), the board coated with resist paint and board ready.
Next step is coat the board with an ink that will resist to the chemical corrosion with ferric perclorate on the next step. I use a Colorgin Alumen ink spray  for aluminum that dries very fast. Before the corrosion you´ll need to erase the resistive paint to allow the  corrosion isolate electricaly each pin from their neighbour ones. Use a metal stick with a small tip and scratch between the rows and lines to expose the cooper (the third PCB on the image shows one row done). The fourth PCB shows it after the paint was removed with a thinner bath. Check that all contact points are insulated from the other - you don´t want a short circuit  on your GR-300 !

Step 3: Soldering the Pins

On this step you´ll have to solder the 24 pins. Remove 24 of the long pins from that kind of bar easely found on the stores that sells electronic items.  The pins will enter the  0.8mm holes with a small pressure, leave 5mm of the pins out of the connector. The solder side of the PCB, of course, must be inside the connector case.  Check the coupling with the female connector on the GR-300 before soldering the cables.

Step 4: The Connector Case

Initialy I made the case from a piece of  white Delrin, my idea was to take the model to a foundry and make it in aluminum. In the end I use the original Delrin model to make the connector I use. The block has 14 x 45 x 41mm, I made a cut that  turn the  rectangular block into a "U", see the dimensions on the image below. There´s a hole in the base of the "U" (nor seen) where the F3D111-50 cable recommended by Wayne will get in, This hole shall be made a little more to the side that have more space to spread the wires. The two small holes are to fix the lateral plates that conceals the wiring inside.

Step 5: Solder the Wiring

The last step is  to solder the individual cables to the correct  pin inside the case, use the table on Wayne´s page as guide, use thermo-contractile to avoid shorts.  This is the hard part it´s very easy to make a mistake as there are so many cables in a so short space.
The white plastic on the picture is a lock that avoids damages to the cable if someone stumbles on the cable.

Double check after done before turn on. See also the video :

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