Condenser microphones contain internal circuitry and capsule which require a power supply. Phantom power uses the same wires of the mic balanced output signal to carry that energy from the mixer console to the microphone. Phantom power is required by condenser mics but not by dynamic (moving coil). Professional mixers give you the option to switch the the phantom power on or off for each input channel. Semi-pro and consumer mixers enable or disable the phantom voltage globally or in groups of input channels. In general, connecting a dynamic mic to a phantom powered input is not a problem as both ends of the coil (or transformer) will be at the same voltage and no current will flow through them. This holds true as long as the connection is a correctly wired balanced cable. There are many other situations under which phantom power can cause damage to connected devices. This simple circuit blocks the phantom voltage to safely connect any device to a 48v powered input channel.