Power Vs. Power

By Bob Bornack

WARNING: This article was written in hopes to offer a better understanding of how electricity effects a sound system, not how to alter an existing power source. Do not experiment on your own. Electricity is deadly and can easily kill you. With any electrical device, follow manufacture instructions explicitly because the life you save may be your own.  

If there is one thing I've learned about good sound, it is the the importance of ample and stable electricity.

Over the years, sound systems have become much more dynamic particularly in the low end or sub frequency range thus requiring more electrical power not always available from a typical wall outlet. Contrary to popular belief, your power amplifiers do not "manufacture power", they simply modulate electricity, the same electricity that comes out of the wall outlet. That said, if your supply voltage is poor, expect poor results from your sound system.

When amplifier manufactures test and measure output power at the factory, you can be sure that they have a clean electric supply circuit with a consistent voltage (120 VAC) with ample current or amperage. If they didn't, the specifications that they print would differ dramatically and not in your favor. 

What you can expect to get in terms of performance from your amplifier depends entirely on the integrity of electricity that you are feeding it.

In many cases, overheated amplifiers, audible distortion and low sound pressure levels are the direct result of poor electricity or more specifically line voltage drops or sags. Even though the outlet may initially measure 120 volts, as soon as you put current demand on the circuit (fire up the band) more times than not you will experience voltage sags. To add insult to injury, as voltage drops, current or amperes increase which essentially just creates more heat and begins to eat up any current or ampere headroom that might be left on the circuit.  

A volt meter can go a long way in determining why your system is not performing up to snuff. 

With all due respect to club owners and managers, they are just that. They are not electricians so don't expect them to have to many answers regarding the electrical format and status of their buildings. 

Two areas of real concern with using existing wall outlets are the current capacity of the circuit and any additional loads downstream that may exist on that circuit. While a given circuit may have a 20 ampere breaker, the actual capacity of that circuit is limited by its weakest link. If that same 20 amp circuit is fed by #14 or even #16 guage wire (the higher the number the skinnier the wire) it will really be limited to between 10 and 15 amps, before voltage sag sets in. Even if you have a properly installed (#14 gauge for 15 amp, #12 gauge for 20 amp) circuit, there may be other devices on the line like walls full of neon or dozens of television sets. This can eat up a good deal of the current capacity of the circuit leaving you with far less available electrical headroom than you think you have. 

A quick-and-dirty test of a circuit’s current capacity is to plug in a good-sized static load like 1000W par cans. Two such cans will create a simple 16 or so amp load which will trip a 15A circuit within about 5 minutes. Unfortunately, this does not determine if there are cyclical loads on the line, like a refrigeration unit that can suck up to 20A with the initial start-up. While this may or may not be a big problem for a tiny "PA on a stick" sound system which typically pulls around 400W (3-4 amps), it can create havoc with a decent sized sound system, with multiple power amplifiers, and all the associated outboard.

it is not un-usual for most reputable sound companies to perform what is know as a power tap or ac tap.  In simple terms they are bypassing all of the wall outlets and small gauge wire associated with them by "tapping in" to the electrical panel and taking their electricity right off the buss in the panel where the main feed first shows up in the building. From that point, the electricity if fed into a portable distrabution panel where it is broken off into smaller branch circuits that then feed the entire p.a. system supplying ample power to run the p.a. without otherwise typical sagging a.c. voltage drops. Most importantly, the entire systems shares the same ground which is critical for minimizing hums and buzzes. (Power taps can only be performed by licensed electricians, never attempt to open up or tamper with an electrical panel yourself.)  

In a perfect world, your entire p.a. system would be powered off of one outlet. Those days are pretty much over especially if you are running subs with lots of kick drum and bass.

Here's a few tips on what you can and can't do. 

(1) When the club owner says "we have bands here all the time and they never have power trouble" don't always believe them.

(2) You can also minimize voltage drops in extension cords by using heavy gauge heavy duty wire.

(3) If you have a lighting system, never plug it into  the same circuit that your p.a. is on.

(4) Do the math on your systems current or amperes requirements. The ratings are almost always printed on the back of your equipment. As a general rule, power amplifiers are the biggest culprits for power consumption. Pay particular attention to those.

(5) Never, no matter how tempting, ever "lift" a ground lug or use a cheater plug to eliminate buzz or hums. The shortest path to ground might be you thus making you a human fuse.

(6) keep extension cords as short as possible. The longer the run, the more likely you are to have voltage drops.

(7) If several different circuits are available, distribute your p.a. among them so as to lighten the load of each.

(8) Try to keep the bands personal amplifiers and stage gear off your p.a. circuits to help lighten the load.

(9) Know where the venues circuit breakers are located so if you do trip a breaker you can get back to the show with a minimal of down time.

(10) If you do blow a breaker, after you have reset it, back off a little on the kick drum and bass volume to help conserve current.

(11) Measure the voltage with a volt meter when the p.a. system is on but idol and quiet,  then measure the voltage with the p.a. on and the band playing and note the difference.

(12) Electricity is deadly and can easily kill you. With any electrical device, follow manufacture instructions explicitly because the life you save may be your own.  

(13) Test the outlets you will be using with a  plug in circuit anylizer. You can find these at most hardware stores for about $10.00. These devices check for polarity (hot and neutral) as well as ground.  

(14) Consider purchasing a Furman or similar light bar with a voltmeter on it and monitor the voltage during the performance. I do not ever recommend plugging power amplifiers into one of these devices.

If you have a topic you would like discussed, let us know!

Send your comment to:

bob@tantrasound.com