My 2.1 speaker's transformer is consuming active power even when the PC is off. I know it because it is always warm. Thus, I want that only when my PC is operating the transformer will get the AC power from the gird. So I need to put a relay between the L1 from the grid to the correct pin in the transformer. I have managed to configure in my BIOS that when the PC is off the USB will not have output voltage, so I am planing to use a USB port (5V) as control pin for the relay.
I saw that there are relays which have a second level of isolation by using a LED. Is it too dangerous to use only 1 level of isolation between my PC (USB port) to the grid? I mean that the 5V from USB will output the current for the relay's coil.