StepUp & StepDown Votlage Transformers?

I can only think of two variations on the same technology:

Auto-transformers.......primary and secondary share windings.

"Regular" transformers....primary and secondary use independent windings.

Don't advise auto-transformers for what I suspect you have in mind.

As for core construction.......toroids won't have the hum field that a stacked iron core will. But it will let more crud through, due to its higher bandwidth.

As for size......I would have stated it differently, but that is a good starting point.

Without an idea what you are cooking up, anything more specific would be a guess. I think I know...but I'll hold off for now.

I may be moving to Europe for a couple of years .... debating whether I should get my equipment re-tapped for 200-240VAC or use a step down. Digital front ends and pre-amps don't pull a lot of current but its my power amplifiers & integrateds that I'm worried about (Sim Audio W5LE, Bryston 9BST & 100BSST & a Rowland Concentra Mk2).

A lot of those have internal switches for 120/240. Pretty sure the Rowland does, as most of his work is for export.

Transformers are heavy to schlep back and forth. Sending stuff back and forth to the factory is not fun.

Check to see which ones are user selectable. Come up with a list of those that aren't and write down their current consumption. We can then look at transformers, and get an idea what they will run. You will have to change the plugs on any that you buy here.

(When you come back..........change the ends back, and use them for isolation transformers. Get more for your money that way.)