Since this is about hum as well, another consideration is the layout.  The magentic field from the power transformer and reachout and inject a signal into sensitive circuits.  Physics, you know.  A loop of wire produces a voltage according to the change in field strength.  So one needs to distance high current signals from sensitive circuits, and make the areas in the circuit loops small, even if a bit inconvenient.  There are a couple of ways of keeping loops small.  If it is in wire, there is twisting them.  Each half twist helps cancel the one next to it.  In circuit layouts, there is the possibility of a figure 8 loop between the signal and ground...  That also helps to not pick up other stray signals.

Have a great day, Eric