I thought I’d share with you that I successfully built a Guitar ¼ inch Adapter Cable for Roland GK 13-Pin connections! This is a cable that allows you to connect a guitar or other instrument with a ¼ inch output (bass, ukulele, etc.) to the Roland GR-55 guitar synthesizer. If you are on a gig using the Roland GR-55 the usefulness of this is that if you don’t have another amplifier and effects, you can access the Roland COSM effects and amp models within the GR-55 and use the same sound reinforcement system that the GR is connected to.
Below is a copy of my wiring diagram that was adapted from a similar diagram posted on Vguitarforums.com by “Elantric”. As the diagram indicates, the normal guitar (or other instrument) signal is transmitted to the GR-55 via pin 7 in the 13 pin plug. A voltage divider has been added to reduce the GR-55’s +7 vdc to +5 vdc to feed pin 8 which signals the GR-55 that a GK pickup’s volume control is set to 10. I tested it and, yes, it works!
I hope this information is helpful to you.