Settings for PS Audio PowerPlant

I can't seem to hear a *x@# - &%$* difference when I switch modes. Except if I go too far down on the voltage.
Then I get a system shutdown, but 100 volts is for Japan, not here. My ML pre. won't take it.

Gerd: the preamp is a 380S and it does not seem to be affected by anything except a drop in voltage. I have a PS300 supplying the preamp and a Meridian 508-24 CDP and the power supply for some Perpetual Technologies stuff I am playing with. The amp (Classe 401) is too big for the 300.