DIY Roland 24-pin to DB25-pin Conversion
Features and Specifications:
Use modern, readily available, high quality DB 25 pin cables in place of 25 - 35 year old hard-to-find vintage 24-pin cables
Works with all vintage Roland Guitar and Basses (G-202, G-303, G-505, G-707, G-808, G-33, G-77, G-88).
Works with Roland Guitar Synthesizers: GR-300, GR-33B, GR-700, GR-77B and GM-70.
Download wiring diagram for guitar and synthesizer 24-to-25 pin conversion.
Basic soldering skills required.
GR-300 with DB25 Connector in place of original proprietary 24-pin connector.
Introduction to the "Do It Yourself" Roland 24-pin to DB25-pin Conversion:
Vintage Roland guitar synth players have been replacing the proprietary 24-pin connectors with the more common DB25 hardware for about as long as Roland has been making guitar synthesizers.
For some folks, it did not make sense to keep paying top dollar for the Roland cables, when there is a high-quality, low cost alternative. Now, with the increasing scarcity of the original Roland cables, and the escalating price, it makes more sense than ever to consider moving away from the original Roland hardware.
This page outlines a Roland 24-pin to DB25-pin procedure I developed. I started with a surplus of Roland 24-pin ribbon connectors and locking rings. Basically, I connected 24 wires to the DB25 pin connector, then attached those 24 wires to the Roland ribbons removed from the original 24-pin connectors. By using the Roland ribbons, I did not have to make any permanent changes to either my guitars or synthesizers. To keep wiring organized, I followed the Roland pin-outs, so pin one on my DB25 connector is +15 volts, pin two is -15 volts, etc. the same as on the original Roland 24 pin connector. This also maintained compatibility with the Roland US-2 Turbo and the RC-1324-VR.
How to read the 24-to-25 pin diagram:
Switching over to DB25 hardware is not too difficult, though it is important to keep in mind when wiring the connectors the asymmetric nature of the original Roland hardware. The Roland 24-pin connectors had nine pins on either side, plus six pins in the middle, for a total of 24-pins. The six pins in the middle were not symmetrically distributed, so wiring both sides identically will result in incorrect wiring.
The first page of the diagram outlines creating the connector for the guitar. You will notice the top ribbon, "A1" has twelve solder pads for connecting wires. These are labeled indicating function, original Roland pin assignment, and a color code. For example, the top most pad is labeled as "GND", "Green/Black" and "4". On the original Roland 24-pin connector, pin "4" is one of many pins used for ground. I used a green wire with a black stripe for this connection.
Why does pin "4" come first? If you look at the original 24-pin connector, you will notice that pin "4" is one of the asymmetrically distributed center pins.
The next connection down is labeled as "+15V," "Red" and "1". Pin "1" on the Roland connector is the positive 15 volt power supply. So, on the "guitar" connector, pin "2" on the "A1" ribbon carries the +15 volt supply. If you look at the second page, outlining the connections to the synth, you will notice that the +15 volt supply is now the last connection on the ribbon labeled as "B1."
Follow the pdf diagram, and you will not have any problems. Also, check out the YouTube clip below that I made for a retrofit kit to get an overview of how things were assembled.
I have a limited number of custom machined panels used to mount the DB25 connectors in place of the original Roland 24-pin connectors. The price is $25 (including shipping) for 2 panels. Email me for more details.
Links to more information:
Download wiring diagram for guitar and synthesizer 24-to-25 pin conversion (pdf).
Pin-outs for the original Roland 24-pin connectors.
DB25 pin connector at Mouser.com.
DB25 pin hardware posts at Mouser.com.
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