ys! Downunder is correct. I collect Trace Elliot preamps....I have 7 GP12, 4 GP12XV, 3 GP12SMX and one MP11 and one Vintage Preamp.
You don't want to overdrive the gain (input control) too high because you may shut down the preamp for a few seconds. So play the hardest you can with your right habd and adjust the gain to see only green and yellow lights, a few red lights are ok, but if you see red lights for every note, then you are playing too hard, and the knob needs to come down. Once you have that you can control how much volume you send to your power amp with the output knob (on the right of the preamp); then after that you can still increase the volume in your power amp as well...very intelligent design. These guys know what they are doing, I swear by their preams, it's all I use.