Hey, please excuse the other newbie amp question, but this is a quick one: so, when using a head with a speaker cabinet, it's true that the only thing that needs power (like from an outlet) it the head correct? The cabinet does not need it's own power supply, right? or does it? thanks. but so that would mean, at a gig where a band is using three amp heads, each running to cabinets, they only need to plug in the three heads, correct? thanks!