Its amazing how this simple subject always gets bogged down in complexity and code and comments, usually from people who've never done and so don't know what they're talking about. I've actually had the standard normal house wiring, and then run a dedicated circuit, and then run an even better dedicated 240v to a step down transformer. Say again, I've actually done the wiring and listened and compared.
Your best cost option is to put everything on one single circuit, conservatively rated. i.e. use 20A even if you could get by code with 15. Do not run two circuits. If you do then put all your audio on one, all non-audio (record cleaner, lights, etc) on the other. As someone correctly noted it takes only a very tiny difference in ground potential to produce hum. Again, I know for a fact and from experience you can and will get hum when different components connected to different circuits are connected together. Different manufacturers follow different construction so that what looks the same is not. i.e. just because you see a ground plug does not mean the manufacturer connected those pins with a wire! So you may sometimes get away with it. Or you may just give yourself a headache.
One circuit. KISS. Capiche?
Your best cost option is to put everything on one single circuit, conservatively rated. i.e. use 20A even if you could get by code with 15. Do not run two circuits. If you do then put all your audio on one, all non-audio (record cleaner, lights, etc) on the other. As someone correctly noted it takes only a very tiny difference in ground potential to produce hum. Again, I know for a fact and from experience you can and will get hum when different components connected to different circuits are connected together. Different manufacturers follow different construction so that what looks the same is not. i.e. just because you see a ground plug does not mean the manufacturer connected those pins with a wire! So you may sometimes get away with it. Or you may just give yourself a headache.
One circuit. KISS. Capiche?