PHASING: If you wire multiple piezos into one Cortado MkII circuit, pay attention to the phase of the piezos. By convention, always solder the white wire to the white ceramic center, and solder the red wire to the copper disc. If you are mounting the to the same side of a vibrating surface, keep them in-phase: at the PCB wire all the reds together, and wire all the whites together. If you are mounting the piezos to opposite sides of the same vibrating surface, then wire them out-of-phase: at the PCB, simply reverse the reds and whites for the piezos mounted to the rear surface. In other words, all of the front-side piezos must be wired identically to each other, and all of the rear-side piezos must be wired the opposite way.