Phantom Power Question

Bob Storti · Post by **Bob Storti** » 24 Jun 2005 11:43 am

Alot of PA mixers have a single switch for phantom power and when turned on will apply the voltage (let's say 48 volts) to all the mixer's channels. My question is if I have a condensor mic in channel 1 (phantom power ON) and a Shure SM58 in channel 2, is the phantom power voltage going to damage the SM58? Thanks.

Bob

Will Holtz · Post by **Will Holtz** » 24 Jun 2005 12:14 pm

Dynamic microphones (such as an SM-58 or SM-57) will not be damaged by having phantom power applied to them. With ribbon microphones (very uncommon in live sound, but show up in studios a bit), an improperly wired PA can harm the microphone if phantom power is applied.

Dave Grafe · Post by **Dave Grafe** » 24 Jun 2005 3:44 pm

"Phantom Power" refers to the to the practice of applying an equal and positive DC voltage (anywhere from +9v to +52v) to BOTH pins 2 and 3 (the balanced signal lines). With the circuit closed by pin 1 (the circuit ground), there is equal voltage - and thus no current - across the pickup coil of a dynamic mic, while a condensor mic or an active D.I. box can tap this "phantom" voltage to power its preamplier.

What you DON'T want is to plug an XLR to 1/4" adapter or an unbalanced dynamic mic into a phantom powered XLR jack. Nothing good can possibly come of that.<font size="1" color="#8e236b"><p align="center">[This message was edited by Dave Grafe on 24 June 2005 at 04:47 PM.]</p></FONT>

Bob Storti · Post by **Bob Storti** » 24 Jun 2005 4:06 pm

Good information - thanks a bunch guys!

Bob

Michael Garnett · Post by **Michael Garnett** » 27 Jun 2005 11:38 pm

Also, to add to what Dave said, the condenser mic needs phantom power to work on a fundamental level, not just for a preamp. A condenser mic works by charging up the faces of the diaphragm, which act as a capacitor. As the diaphragm moves, it changes the overall capacitance of the system. Since capacitance and voltage are inversely proportional, you get a voltage change, leading to a sound signal that goes into your wire. And since the diaprhagm is so large and not connected to a heavy wire coil, condenser mics tend to be much more sensitive, meaning you can gather sound from an entire ensemble with only one mic. But watch out for feedback from the monitors!

So, to reiterate, you only need phantom power if you're running a DI box without its own batteries, or if you have a condenser mic. Ribbon mics, being very fragile and expensive, are not used frequently in live sound situations. If you accidentally leave it on, it won't hurt any dynamic mics, because they create their signal through different means.

Thank you, Audio Engineering I class!

-MG