By Dave Rat • March 17, 2011 Although the musicians we work with can tax our patience at times, and occasionally less than pleasant thoughts regarding them cross our minds, I seriously doubt that watching them fry from high voltage is something any of us would want to be responsible for. With that in mind, here are some basic precautions and tests to reduce if not eliminate the possibility of electrocuting our musical friends. Let’s start by stating that it is of the utmost importance that the console with the shortest snake distance to the stage use the same AC (electrical alternating current) ground as the backline power. Microphones are grounded by the “pin 1’s” of the snake, and ultimately, the console(s) that your snake is plugged into. The console closest (and again, by closest I mean “cable length”) to the stage should not be pin 1 lifted. All mics short pin 1 to the casing of the mic itself. This “close” console provides the critical ground to your mics. By “same AC ground,” I mean that the backline power should come from a circuit that shares a common close proximity ground with the “close” console. If there’s a separate stage console, it should be plugged into the same AC distribution as the backline. The same thing applies when using a single console. The majority of buzz, hum and shock problems exist when the people setting up the system use a convenient outlet rather than making sure that backline and consoles all use circuits with close proximity grounds. A list of the absolute minimal number of devices to AC ground starts with the backline gear and console (front-of-house in the cases where just one console is used). I don’t want to get sidetracked into the various system grounding techniques, but keep in mind that AC lifting various pieces of gear can present potential hazards. You want the hum to go away, but you know AC lifting is not the safest thing to do. Yet cutting pin 1 on every loom to a rack is not only impractical, but might not even solve the particular problem. Be careful, “vintage” units in particular can be outfitted with problematic plugs One of the more difficult things to get a handle on is the grounding and safety of the backline gear itself. Unlike a sound system, it’s pretty much something that you often have little or no control over. The affinity over “vintage” gear combined with multiple amp setups can often present an even more unwieldy situation. Though I can’t cover all possible configurations, here are two rules of thumb that help keep musicians safe: 1) Whether there is one or multiple guitar (or bass) amps all connected together, at least one piece of gear in the signal chain must be AC grounded, preferably the one that the guitar (or bass) plugs into or the closest (shortest cable length) one. 2) When presented with a “vintage amp” that has a non-polarized ungrounded plug, pay extra attention to how it is plugged in. At least mark the plug, and actually, it’s best to replace it! These are the AC plugs that don’t have the “fat” and “skinny” flat blades – both blades are “skinny.” On all modern ungrounded plugs the “fat” blade is neutral and the “skinny” blade is hot, therefore making sure the plug cannot be reversed in the outlet. Read the rest of this post 1 2 3 About David Dave Rat President, Rat Sound Systems Dave Rat heads up Rat Sound Systems (www.ratsound.com), a leading sound reinforcement company based in Southern California, and has also been a mix engineer for more than 30 years. Comments Leave a Reply Cancel reply Your email address will not be published. Required fields are marked *Comment Name * Email * Website frank says My apologies. I read, and re-read the first 10 paragraphs of your article before I figured out what you were saying. This is SUCH an important subject for ALL, including roadies and weekend warriers, that this needs to be written so it is crystal clear on the first reading. Sorry, it is not. I’m not an EE but I cared enough to sort out what was being said - many who need to understand will have their eyballs rolled into their head by paragraph 3. When you start in on “...shortest snake distance to the stage use the same AC (electrical alternating current) ground as the backline power.” and then follow up with “... backline power should come from a circuit that shares a common close proximity ground with the “close” console.”. Huh? I’m guessing this is not an issue (generally) in a small club, but in locations where the power distribution is complex and decentralized, that can be a problem. You never mention how one can determine a “close proximity ground”. Hell, most of the time (again, small clubs) one can’t tell if therte is one circuit or many involved. Your message is absolutely on target - I just don’t think too many folks can decipher it, or apply it to their situation. Again, my apologies. oliver says thanks for the info. it help us o lot.. we encounter this problems very often. Mark Phillips says I agree with Frank - good solid stuff but a bit confusingly expressed in parts. One way of achieving that common ground in smallish venues, where there’s a single desk mixing the monitors as well as FOH, is to run a fairly beefy-gauge power cable with the snake in order to power the desk (& its associated gear) from the same stage supply that’s being used by the backline. Using a good heavy gauge of power cable isn’t because the mixer etc needs a lot of power, it’s to keep its grounding conductor resistance low (especially if the cable has to be fairly lengthy) - essential for safety. Alternatively, run a standard power cord and a separate beefy ground-wire with it (but connecting this at the two ends in a suitably safe & reliable way can be quite problematic). Tagged with: Audio Concerts Electronics Engineer Interconnect Live Poll Power Sound Reinforcement Technician · all topics Subscribe to Live Sound International Subscribe to Live Sound International magazine. Stay up-to-date, get the latest pro audio news, products and resources each month with Live Sound.