Can I use an unbalanced signal with a phantom-powered mic input?
No. You can use a balanced dynamic microphone with phantom power switched on, but the only way to connect an unbalanced source to the same system is to feed it through a balancing transformer first. If you were to connect an unbalanced cable, you would short out one side of the phantom power supply, and though a properly designed phantom supply will be protected against damage in this way, it’s not recommended. More seriously, some or all of the phantom power voltage will be applied to the pins of the unbalanced device and this may cause damage to some studio units.
