Hi, I'm an Italian keyboardist (excuse me for my english please) I've purchased a couple of Shure Beta87A. I have also 2 voice preamp (DBX286A) with phantom power. My question is: why my microphones shure beta87a plugged on preamps works the same if phantom power is off? I notice only that if phantom is on, the high frequency is sligthly presence but no more. Please help me!