I've got a Studer amp to keep my Stax menagerie under control via the SRD-7 Spritzer. It has always had quite marked mechanical hum when run at 240V (Australia's mains voltage). I have a 240 -> 110V transformer and the Studer is able to be configured to almost any possible mains voltage via a rotary switch and with a change of fuse. Did that. NO FREAKIN' HUM! $2.50 for 2 new fuses! Love it.