Hey, I'm from Aus. As such, most of our gear operates at 220-240v, which limits my 2nd hand amp purchasing options.

So the questions is, is it worthwhile using a step down transformer? What are some of the cons, that I could run into?

It's better to use a stepdown or stepup transformer than to fry your equipment. It will be a compromise that may or may not be noticeable. If you were MUCH more specific about what it is you're trying to do, you might get a useful answer.

Looking at 2nd hand headphone amps, since the bulk of them seem to be located in the us and suited for 110v, I'd need a step down transformer. I didn't intent to try using any relevant equipment without the use of one.

I used one here in the US with a 230v CDP that I had (MF xRay v3) and it did not appear to have any impact. Your mileage may vary though when it comes to an amp as I suspect it may be much more sensitive to "dirty" power delivery. I'm sure others with more knowledge will comment.

First of all, what kind of amp are you looking at?

Provided that one selects a step-down transformer capable of providing adequate current I see no reason that it would be at all audible unless the component it's feeding would provide crappy power to the amp regardless of what it's fed.

When you think about it every component uses either a step down or step up trafo in generating B+.

Well, I wasnt looking at anything in particular yet. I may end up going with a Woo, which has a switchable power supply anyway.

But a couple of rsa amps popped up that had me interested. Problem being once I factor in the cost of the transformer, I'm not really saving alot from new.

Heh, if you hang out around here long enough you won't be opting for an RSA amp.

haha, I had no real intention of buying an rsa amp, they seem overpriced for what they are, although I've never heard one. I'll most likely avoid the hassle that comes with a step down transformer.