... why is a 20 amp circuit recommended over a 15 amp out of curiosity?
My understanding is that 15 amp circuits are often wired with 14 gauge conductors, although they can be wired with 12 gauge, while 20 amp circuits must be wired with 12 gauge or larger. For a given amount of current 12 gauge will of course produce less voltage drop in the conductors than 14 gauge, resulting in a slightly higher voltage being supplied to the components. (Although if the line voltage that is supplied to the particular location is near the high end of its +/- tolerance less voltage drop in the conductors could conceivably not be preferable, depending on the design of the specific components). Also, of course, with a 20 amp circuit and breaker there is less chance of overloading the circuit and causing the breaker to trip, for instance if the power amp and/or the sub draw large amounts of current for significant amounts of time, during high volume musical passages.
@lowrider57
... correct me if I’m wrong, one of the receptacles needs to be grounded to the service panel, not self grounded. If there are two separate runs of Romex, then both need to be grounded to the panel to help prevent a ground-loop. This may also lower the noise floor.
I think your words "not self grounded" are referring to the fact that it is preferable for the safety ground wire to not be connected to metal conduit at the outlet, and that is correct per my understanding. Regarding that also see page 191 of the reference I linked to earlier, which discusses "isolated ground" receptacles. Note that using Romex to connect to a non-isolated ground receptacle accomplishes that by its nature, since there is no conduit.
And of course neutral and safety ground for all runs must be connected together at the main service panel, and they should be and hopefully will be connected from there to a nearby earth ground.
Best regards,
-- Al
