I just picked up an MF Trem. On the label above the external power jack is written +9V which I think means center pin positive. However there is a sticker over the external power jack that says to use a 9V Center pin negative power adapter! Which is it center positive or center negative?
Hey!
You’re right, the “+9V” is not mmaking it obvious. I’ve just tried my MF Drive with both polarities: 9V negative center is the right one 
Thx. Wonder why they did that!?
Well, no sure myself. But I had never bothered about it, to be honest 