This modification is for GK-1 users to enable the String Select function.
GK-1 operation is not affected in any way
One jumper wire is soldered on the GK-1 circuit board
Jumper is wired from Pin Number One (+15 volts) to Pin Fifteen (Mode 3)
VIEW OF UNDER SIDE OF GK-1 MAIN PCB
GK-1 owners do not have access to the String Select feature of the GR-300. String Select refers to the bank of six switches that turn the synth tone on or off for each string. A check of the schematic shows that String Select is tied to the Mode switch. The GK-1 does not have a Mode switch. In fact, the GK-1 is hard wired in Mode II. My simple modification changes the GK-1 from Mode II to Mode III. GK-1 owners will find that their system operates exactly as before, except you can now use the String Select feature! Plugging a simple foot switch into the String Select jack on the back of the GR-300 will disable the String Select feature, activating all the strings again! And the good news is, this is a simple modification!
ANOTHER MODIFICATION OF A GK-1
Installing a Mode Switch: Harry Bissell Modification
GR User Harry Bissell has a great suggestion for adding a mode switch to the GK-1: install a switch in place of the miniature input jack for the guitar. All that is needed is a SPDT switch, with a middle off position. Run the output of Pin 1 (+15) to the center pin of the switch, and connect Pin 16 (Mode 1) and Pin 15 (Mode 3) to the other pins. In addition, solder a 10K resistor from Pin 15 and Pin 16 to ground. This will duplicate the existing Mode switch on a GR-series guitar.
MODE SWITCH
Special thanks to Michael Bacich whose insights, suggestions, and GR-300 schematics made this possible!
