Here are a couple of questions we get about the use of 48-volt phantom power switches on many mixers.
A: It is possible to use BALANCED dynamic microphones when 48-volt phantom power is on. The microphone coil ‘floats” up with the voltage, preventing damage to the mic by ensuring “zero” volts across the microphone coil.
However, if the dynamic microphone is configured UNBALANCED (where pins 1 & 3 are connected together), then the dynamic microphone will be damaged. This is because one side of the microphone coil is connected to ground, with the other side connected to 48 volts. Thus, the voltage will be across the microphone coil, causing it to burn out.
Q: “When phantom power is on, do the Line inputs have 48 volts on them?”
A: No. It is perfectly OK for line level audio sources to be connected to a console when the phantom supply is active on the XLR inputs. However, you should be careful not to connect XLR line outputs of things like bass or guitar amps to these XLR mic inputs. The phantom power can, in some cases, burn out components in the amp’s output section.
Q “I’ve heard that you shouldn’t use phantom power with ribbon mics because it will damage them?”
A: This can be true with regard to vintage ribbon mics, but modern mics are designed to be immune to this type of problem.