I just bought a used Ketron SD9 Pro, to be delivered on Friday. The store couldn't find the power supply, but the back of the keyboard says DC9V 4A. I don't see any more information in the manual. So I'm trying to find a compatible power supply. Does anyone (maybe someone with an SD9) know whether the Ketron supply is center positive or negative? Does anyone know of a supplier in the US for a power supply? I didn't see any on the ketronamerica.com site.