There has recently been a proliferation of old Bryston equipment selling at outrageously low prices on Ebay - well under $1000 for a 4B-ST. I've been mildly tempted, but obviously Bryston models have different power supplies depending on whether they are intended for the US or UK market. (This is not true of all brands. Lexicon processors, for example, have universal power supplies, IIRC). This leads to me wonder about the general case: where processors and amplifiers are concerned, how much of an issue is mains voltage and frequency? I'm not suggesting one should just plug a device intended for a 110V supply into a British mains socket and hope but obviously one can buy step-down transformers, which should at least supply the correct voltage. But do these add noise to the mains signal? Do they allow as much current through as you might expect to come out of an actual american mains socket? Is the 50Hz/60Hz frequency difference an issue? And how much does one have to pay for a step-down transformer that really does the job?