Remember that setting your gain on your preamp, effects box and/or amp is not the same as setting your volume. With gain you are adjusting the amount of power in your signal — not the volume leaving the system through the speakers (that’s adjusted with your channel fader and mains fader) A good rule of thumb is to sing one of your more powerful passages and watch the meter (some preamps have a single red “clip light”). Turn the gain up until your signal clips and then turn the knob to the left a bit.

-The Ultimate Guide to Singing