In general, I don't think it's a good idea. there was a post about someone powering their PMD-661 with 9V (it wants 5), and thought it was fine throughout a whole show. at the end of the night, the deck was wicked hot. too hot to pick up or touch. all that extra voltage will get converted to heat, and I think he had to send the deck back to oade for repairs because something had fried on the inside. I'm sorry I can't find the exact post now, but it's somewhere in the PMD-661 threads (either in the team boards or the two long threads in the recording gear section). so, to sum up, while it may work for some gear, I wouldn't risk sending any other voltage to a piece of gear other than what is specified. it's easy to enough to find a power solution that meets the specs exactly, so why bother?