Well, I wouldn't do it for the purpose of archiving my LP's, but I note that Electronics World has one of their little circuit snippets with an RIAA amp with power derived from the USB port -- it's not a bad idea, they use a Maxim regulator to "remove the noise" from the 5V USB power line. This is kinda (that's my neologism for the day) like using a bandaid where a tourniquet is required. Seems to me that a pair of double-A's would have been more than satisfactory.