The second PCB was to house the Arduino, the FX loop and the gain pot optoisolators. I decided to mount it directly underneath the main PCB, 20mm apart using spacers. Any connections between the two would be made using 0.1" spaced double ended headers. After arrival from China, the population of the second PCB began and the two PCB boards were mated together.

The three empty optosolator component spaces can be seen at the top of the PCB. They were now relocated to the lower PCB resulting in a much lower noise floor.