Thanks Jo22 -- schematics don't seem to help. I wonder how long 2 4.5 v would last? Or one 9V?? I need 2 hours. None of my portable power bricks have 9v outputs, only 5, but according to the scope it's pretty good quality.

I have a need to run my MT-32 where there is no mains supply. I'm wondering if anyone has tried running it on 5V (USB)? I can't test right now, unfortunately. Thanks!