The CRC board is a simple dual rail filter stage designed to lower the noise of the standard GSSL, by reducing power supply ripple.
The board can be easily retrofitted into an existing GSSL build. Simply take the secondary wires coming from the input power transformer into this board, then take the output to your GSSL main processing board. Your Hum problems WILL be gone.
A manual for the board can be downloaded from HERE
A video will some more details can be viewed here:
Mouser Bill of Materials is available here for direct ordering