I would always turn the source components on first, then the preamp, then the power amplifier last. Everything before the power amplifier should stabilize (or the output be kept muted) before the power amplifier is turned on to avoid any pops or buzzing. If the preamp has a MUTE function, it should be kept muted while turning on or turning off the amplifier.

All Audio Research preamps have a 50-second delay when they are turned on. The output stays muted (grounded) during that time and you can only turn the MUTE off after the 50 seconds is up; that is a good system.

The power amplifier should be turned off first, and 30 seconds or so should be alowed for its power supply caps to discharge before the other components are turned off.

for a happy and prosperous new year!