Bit of a strange problem, although now resolved - thought I’d share to gather other people’s thoughts.
Since adding a HiCap DR to my SN3 I’ve noticed that switching on the connected Sony CD player will cause the tuner button to flash for about a second before the amp returns to previous setting. This happens even if the input selected is not “cd” and regardless of the amp being muted or not.
Without the HiCap connected, switching on the CD player makes a small “crack” sound through the speakers which suggests an arc in the power switch of the Sony (well, it is about 35 years old!) but the amp does not trip overcurrent.
I’ve flipped the figure of 8 power cable on the Sony 180 degrees and now there’s no noise from the speakers and with the HiCap back in circuit, no tripping of the amp.
Problem solved, but the engineer in me needs to know why! Voltage spike from the CD player? Induced current in the Snaics to/from the HiCap? All ideas welcomed…