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Stopping Hums, Buzzes And Shocks On Stage — Part 1: Volts
The first in a multi-part series on based upon our ProSoundWeb electrical safety survey.
Aug. 27, 2010, by Mike Sokol
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  Audio Basics, Audio, Church Sound, Worship Sound, Safety, Stopping Hums Buzzes And Shocks On Stage, Electricity

If you’ve read the survey that’s been running here on ProSoundWeb (Haven’t taken it? Please do!), you’ll discover that 71% of the musicians and sound technicians surveyed have been shocked by their mics, instruments and sound systems. 

What follows is the first in a 12-part series about basic electricity for performers and technicians and how to safely stop hums, buzzes and shocks from your amps and equipment.

This series of articles is provided as a helpful educational assist with sound system setup and musical performance, and is not intended to have you circumvent an electrician or qualified audio technician.

The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles.

If you feel you have a dangerous electrical condition in your PA system or instruments, make sure to contact a qualified, licensed electrician or audio installer.

Amp Safety
Guitar amps and mixing boards as wired from the factory are inherently safe, but they can become silent-but-deadly killers if plugged into an extension cord or wall outlet that’s improperly grounded.

This is because guitars are held in your moist hands while your wet lips are touching another electrical circuit, the microphone. It’s up to you, the musician or sound tech, to make sure your guitar or microphone is never electrified due to poor maintenance, bad connections or a broken-off ground plug.

Click to enlarge.

This so-called Hot-Chassis problem is what causes a tingle or shock when you touch the mic with one hand or your lips while holding a guitar with your other hand.

Just the Basics
Most musicians really don’t want to learn about electrical engineering, or even how basic electricity works.

Everyone, however, should learn how to test for and avoid electric shocks on stage.

With that in mind, there are some novel ways to think about and teach basic electricity to the musician and technician.

Click to enlarge.

This series promises little or no math, no fancy schematic reading and certainly no memorization of formulas.

It’s my privilege to teach you basic electrical safety as long as you do one thing for us — let us know if the information is making sense and is helpful to you.

So after reading this post, give us some feedback — good or bad.

The failure of the student to learn is the failure of the teacher to teach, and I take my teaching job seriously. So, comments are encouraged.


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Comments (2) Most recent displayed first
Posted by Jonathan Johnson  on  08/30/10  at  04:25 PM
Do you recommend installing GFI (Ground Fault Interrupter) breakers on stage & PA circuits?
Posted by John E. Lawton  on  08/27/10  at  05:16 PM
A hot chassis is--contrary to the way you've loosely defined it above--a chassis (or metal framework for mounting electrical- or electronic-components) where the metal chassis is purposely connected to a power-supply positive- or negative-voltage, rather than being connected to (0 volts) ground (or "earth" if you speak "British English" rather than the Americanized version). Hot chassis are regularly, commonly--and primarily, inexpensively!--used to make TVs and other equipment and are reasonably safe when properly maintained and operated.

What you're most likely talking about--as a former electronics technician--is a situation whereby a chassis has become "hot" through a wiring-fault.

While most factory equipment should be safe (one shouldn't trust it, but, should test it!), a lot of amplifiers and other sound-equipment get modified, often by people who are not trained to do so. Thus, they have wiring faults.

Modern 110-120 VAC equipment that uses a two-blade, polarized plug, is reasonably safe--without a ground-wire--provided it is used properly. The same should be true--but isn't always--for three-wire, grounded AC equipment. The ground-wire is there primarily to short circuit abnormal voltages to ground, i.e., if a hot-wire to a motor breaks, the ground-wire provides a short-circuit, low-resistance path to ground for the circuit, lessening the chance of accident by shock.

It is relatively simple, using a VOM with one lead with a clip, to check to see if an abnormal voltage exists between two pieces of equipment. Placing the meter on its highest AC range, attach the lead with the clip, using one hand with the other one in your back pocket, to the chassis of one piece of equipment, to a shiny screw, grounding post, etc. Then, while still keeping your other hand in your back pocket (while not standing on a wet-carpet on wet-cement, in a damp basement; staying out of puddles, bathtubs, etc.) touch the other lead to a shiny screw, metal edge, etc. on the other piece of equipment. If you read even the slightest voltage, remove the last lead, reset the meter to a lower range (with one hand in your back pocket unless you disconnect the other lead first!), and repeat to get a better idea of exactly how many volts difference exist between the two chassis (between amp chassis and mike, etc.). Any indication of more than a very small voltage (0.01v to 0.1v) should be checked out further, preferably by someone certified by the manufacturer to do repairs on those pieces of equipment.

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