Some 25K log Attack pots with a DPST switch on it were located. These look and feel like the pots used as volume/power on old TV sets. Rather than take up more space on the front panel with a GR disable switch,a little relay changeover module operated by the switches on the pots to providethe SPDT required for GR disable was built.
|GR Disable Circuit (pdf)||GR Disable PCB (pdf)|
An LED output to indicate when the GR was disabled on the front panel was also included.
This module uses some small signal relays and have a 5V coil, so the third PSU rail (which is also used for the VU meter lamps) could be used to power the coils and LEDs when switched on. A series resistor with the relay coil allows the lamp rail voltage to be set to suit the lamps (provided it is 5V or more) and the appropriate resistor selected for the 5V relay coils.