Sound Check You Complete Me (and the Circuit)
posted by March 20 at 15:30 PMon
The Croc’s Jim Anderson talks about electricity and grounding and how to safely check a mic to see if there is current running through it.
Ever get the shit shocked out of you when you touch the mic?
Something’s not grounded. When you touch a microphone plugged into a PA that’s not properly grounded, you complete the circuit. Voltage passes through you. It’s unpleasant and can wipe your mind. It can make you wish you were in diapers. It can also be lethal.
Electrical current can come through the wall, through the plug, into your amp, through the metal quarter inch cable, and into your guitar or bass with its metal strings. Then it goes through you, until you touch something else metal, like the microphone. The human body is made up of lots of water and salt and therefore is highly conductive.
The term “ground” refers to a connection to the earth, which serves as a reservoir of charge. A ground wire provides a conducting path to the earth which is independent of the normal current-carrying path. This protects against electric shock. Electricity is always trying to find that ground. Sometimes you become the path of least resistance.
Older guitar amps with two-prong plugs like the Airline are notorious. That missing third prong is the ground. The Airline also doesn’t have a polarity switch. There you are at the club, excited to use your vintage Airline which is pulling 120 volts. The chorus pedal you’re playing is pulling 110 volts and everything is plugged into the same ungrounded circuit. Can you say unstable? It’s mic check time:
Testing, testing, Z-BAM! A shock is delivered to those gentle lips. Shock the monkey. Flash of white. Surge of current. You jump back, can’t remember any of your songs, and sing the Kermy version of “Somewhere Over the Rainbow” over and over for the rest of the night.
Jim Anderson says:
The ground is there to dispose of, relieve, and neutralize any excess current in case there’s a fault. You want the current to ground so it will blow a breaker or a fuse, before it blows through you. In Europe the 220 volts will knock you on your ass. Here, the lower voltage is sometimes even worse, because people can become stuck there and defibrillate. I’ve seen people put their wet full cocktail on top of an outlet. That’s a frustrating thing to see.
Is there any safe way to check the mic to see if there’s any current running through it?
Jim: Yes. Set the guitar down, hold guitar chord between your thumb and forefinger, wrap the cable through your other fingers, and touch the back of that hand to the mic. The skin on the back of the hand is more sensitive. Also if there is current running through that mic, the natural muscle contractions of the hand and arm will pull you away if there’s a big shock.