Summary: the amount of mythology that surrounds Phantom Power is staggering. mostly the problem is that people don't have to understand anything about electronics making lots of the information the stuff of magic. there are claims that say it's bad to mix mics, that having Phantom Power on will hurt a mic that doesn't need power and that you can "hear" the 48v. this subject is confusing enough and should not be glossed over with a blanket statement... don't do that. Phantom Power is a DC voltage used to power a capacitive plate that sits behind a diaphragm. when the mic is spoken into the plate discharges making small electrical changes which become an audio signal. this is different the passive signal generated by a diaphragm moving a magnet inside of a coil. the spec for Phantom Power is that it's 48v DC at 10 milliamps. this is the maximum amount of power an mic needs to work. if the power is off the mic will not work. while 48v is the defined spec less voltage can be used. a balanced Microphone cable uses a "differential" signal to ensure that there is no "noise" introduced to the line over the distance of the cable. any noise that is picked up is automatically canceled out when the audio is recombined. pins 2 and 3 carry the audio signals. pin 1 is ground. Phantom Power put power on pins 2 and 3. if a mic is dynamic there is no connection to ground (pin 1) required to complete a circuit. if you measure voltage on pin 2 to pin 3 there will be +0v or nothing. measuring between pin 1 and pin 2 or pin 1 and pin 3 will reveal 48V DC. what kind of mics need Phantom Power? Dynamics do not need power. they generate their own signal power. mics like the Shure SM58, the Heil PR40 and the Electro Voice RE20 are dynamic mics. condensers require Phantom Power. mics like the Perception 01, the Neuman M and the raft of cheap chinese mics all require power. there are other mics that also require power. like ribbon mics. but these have different power requirements and are beyond this discussion. (http://knowtech.tv/wp-content/uploads/2010/06/sm58_schematic.png) so here are the myths and questions that come up. will phantom power hurt my dynamic mic? No. all modern mics follow a design that simply ignores power if it is present. if you look a the schematic for a dynamic mic you can see that even though power is present on pin 2 and 3 of the mic because neither line is connected to ground there is not a complete circuit. so a bad cable can ruin my mic if Phantom Power is turned on? yes or maybe or no. YMMV. depends on the mic. if you are in the habit of making your own cables and don't do a very good job of making them you could easily damage your mic. you should ALWAYS test your cables with a multimeter or a cable tester to make sure it's good. if you are setting up and tearing down on a regular basis always test your cables before you connect your mics. how do I know if I need Phantom Power? if your mic isn't working at all that's a good sign it needs power. if the mic is big and heavy and the box that it came is says "condenser" on it somewhere then it needs power. you should always check the specs before you plug your mic. what about a mic that has a battery? some mics contain their own power. lav mics (Lavaliere), wireless mics, and shotgun are all types of mics that may have a different source of power. there is no need to use Phantom Power with this type of mic. in face the presence of Phantom Power might ruin this mic. I have a vintage mic. what happens to my mic if it's not compatible. too bad, so sad. seriously. if you have something very old chances are you need to care and feed it. don't just plug it into your board without knowing exactly what it needs. lots of these old mics required a pre-amplifire in order to work. and just because it has a 1/4" jack doesn't automatically mean you can just plug it into your modern board. can I hear if Phantom Power is on? no. you cannot hear DC voltage.
