NAD C370 110V to 230V conversion

Looks like there is a tap at CB707, to change from pins 1&2 120V) to pins 1&3 (240V)
Might be easier to say for sure if you post a pick of that area of the amp. But looks easy enough from the schematic.
Use a DBT with only the PSU connected when you first power on and verify voltages, then add rest of amp and try again to verify no shorts or current draw. Only then run it with that DBT protection.