Well all, I'm calling off the dogs on this one. I discovered an odd thing tonight. I have two amp setups, both using the same head. One is a GK MB210 combo, a 500W 2x10. The second is a stand alone GK MB500 head paired with a Bergantino CN212 which goes to bigger venues. The test you hear is with the 210 combo, input pad on for the active system, and at a fairly low volume. Tonight with the head/cab I run that with the input pad off. No particular reason, I just prefer it that way. Pretty quickly I noticed that I seemed to have a normal volume control response. Surprised, I tested a bit more and sure enough it's working fine. I'll check tomorrow but it seems the issue is with the input threshold of the amp and NOT the control. Wrong cause and effect I guess! Feeling a bit stoopid but happy there's no real isssue with teh preamp or components. Thanks all.
Wow..amp interphase error!