©1994 ~1999 by Eddie Ciletti
After years of service, the power strips in my equipment racks are getting tired. Some of the outlets are dead or intermittent, causing occasional clicks and pops. Yeah, I bought the cheapest things available. Iíve never felt the urge to spend money on surge and spike protectors, the only real path to power conditioning IMHO (in my humble opinion) is an un-interruptible power supply (UPS), which I donít have, yet!
I found the ultimate replacement while thumbing through the Hosfelt Electronics surplus catalog (800-264-6464). They carry several models of SL Waber Trimline-Series outlet strips. Part # UL7415-6 is a particular favorite. At four feet long, it features fifteen snug-fitting grounded outlets on 2-7/8 inch centers. Thatís right, thereís enough space to plug in a wall-wart without sacrificing a neighboring outlet. Photo One shows a road-ready wart secured to the strip with a tie-wrap. The quality is infinitely better than the typical ten- or fifteen-dollar strip and, at $58.95, is only slightly more expensive.
Photo One: Waber Power Strip has room for Wall-Warts
|Trying to minimize power-related noises in a recording
environment can be a major challenge. No matter how much you try ó with
hospital-grade outlets, separate ground wires, a spike in the ground or
whatever ó sometimes itís NOT your lack of skill, finances or preparation.
It may be the gear that's at fault. Click
here for an example, or...
If your audio gear can detect subtle changes in neighborhood power consumption, consider hiring your system out to the FBI! Nobody likes noise, especially when you're trying to be creative. Eliminating hum and buzz is not Voodoo. It is about taking a systematic approach to troubleshooting. So, in your spare time, put down that creative hat and try this new gee kmodel on for size.
WHY POWER RELATED NOISES VARY
Copyright 1994 by Eddie Ciletti
Figure One: At left is what "the juice" should look like when it comes from the outlet.
Power at the outlet is supposed to be pure hum, or more precisely, a sixty-hertz sine wave. Buzzes are the harmonic contribution of power-hungry appliances such as air conditioners, electric heaters, computers and light dimmers. Any device that can make your lights dim when powered also creates spikes and mangles the waveform. These are distortions that can be reflected back into the power line. Susceptible gear will receive these "transmissions" either directly through the power cable or radiated into the air.
Electric guitar pickups, for example, are susceptible to all sorts of radiated noises, a fact not lost on guitarists who intuitively position their axes for minimum noise. (Hopefully they can still face the audience!) By wiring two standard pickups out-of-phase, most of the noise will cancel. This is the principle behind the humbucking pickup; two coils wired back-to-back into one assembly. Only one set of coils faces the strings, so the music comes through relatively unscathed. Some dynamic mics also include a humbucking coil.
Itís not so easy with audio gear. As your system grows,
so too does its susceptibility to power related noises. Specifically, gear
can be grounded by an audio cable, the third prong of the power plug, contact
with the rack rail and via computer interfaces such as the SCSI port. Each
additional connection causes a ground loop that can bring out the demons
in certain pieces of gear.
A BRIEF DIVERSION...
In the typical home, youíll find a single phase of 220
volts in the breaker box. This power is reserved for large air conditioning
systems or electric ranges. From each phase-to-neutral is 120 volts, the
sauce that feeds standard appliance outlets. The electricianís goal is
to balance the loads on each phase. The analogy is tug-of-war, where you
get to be the rope, A.K.A. Neutral. Both the "A" and "B" phases are
pulling, but so long as the load of each phase is equal, you (Neutral)
When the load becomes unbalanced your system is likely to pick up bizarre intermittent noises. This is especially true when more than one outlet source is used. When possible, avoid potential problems by plugging everything into one dedicated outlet. Before doing so, determine the total power consumption in either of two ways: One: read the specs either in the documentation or on the rear panel of the unit. Unfortunately, adding up power specs may be difficult because power consumption can be specified as Watta, Amps and VA (Volt-Amperes). Two: use an "Amprobe" clip-on ammeter to measure the current being drawn. Be sure to add a 30% to 50% safety margin. For example, if the total load is 10 amps, the typical 15 amp breaker will be happy. (Running too close to maximum will make the breaker run hot or it may blow if everything is powered up at once.)
Fuses and circuit breakers are always specified in amperes (AKA "amps"). The information on the back of the unit or in the operatorís manual will be specified in watts (W) or volt-amperes (VA). The Power Formula is: Power = Volts times Amps ( P = V I ). Since "I" is the current in Amperes, "VA" is volt-amperes, which should be the same as Watts except that the "power vector" must be considered (this detail is not yet fully developed on this page). Since the current is "alternating" and not "direct," we can not simply multiply volts and amps to get watts. Expect to make a few phone calls to the manufacturer.
Meanwhile, here are a few tips to keep the beasts at bay.
Is it worth the added expense?
Consider the following
An Isolated Ground (IG) can be worth the added expense, but ONLY when approached in a very specific and consistent way. Otherwise the benefits will be nominal at best. Almost all new systems are sonically clean, so don't kid yourself into thinking you got what you paid for (IG) or got away with not paying for (IG).
Assuming a New Installation
If everything is connected to the same noise source there will be no noise. The problem with most systems is that, over time, connections become loose. Inconsistent noises are the result of changes in temperature, moisture and current demand over TIME.
It is also important to consider the habit of electricians. Most do house and commercial wiring, few have the sensitivity to do audio installtions. It is quite common, for example, for outlet boxes to be run in series RATHER THAN running a fresh wire back to the breaker box. Consider strings of "holiday" lights where, if one bulb is pulled, the others go out.
In power distribution, daisy-chaining outlet boxes puts a potential noise-maker at every juntion: hot, neutral and ground. Again, the tightness of each connection is important, because the lack of same generates heat, causing expansion (and contraction), which, over time, generates intermittent noises into the system wiring. Power hungry appliances and audio gear could potentially heat up every weak junction.
An Isolated Ground system requires the following:
1.) three wires: hot, neutral and insulated ground to the IG outlet.
2.) To be legal, a metal jacketed cable securely connected to a metal outlet box (if used). When metal studs and metal boxes are used, there will be multiple ground connections. The isolated and INSULATED ground wire can not be used for, nor can it touch, the metal box or metal stud.
Using the spike-in-the-ground approach, there is still the problem tht results when all of the wires are in the same jacket. Consider that even audio gear generates noise. The proximity of the ground wire -- isolated or not -- to the hot and neutral means that gear noise will be induced from the power lines into the ground wire.
To legally take full advantage of an true IG system, balanced power distribution (BPD) is required. Yet another expense, BPD requires a power transformer with 120 volt windings, precision center-tapped at the mid-point to yield 60 volts (60-0-60) to both the former NEUTRAL and the somewhat less HOT. With balanced power, minimal, if any. noise will be generated into the ground wire, isolated or not.
IG sans BPD
To keep the ground wire clean, it should be run away from -- and not parallel to -- the power lines. This is not "to code," but for the moment, consider this:
In additon to the legal requirement of the standard hot-neutral-ground cable to the outlet box, run a separate ground wire -- that is not paralllel to any of the power lines -- to the isolated-ground outlets. ALL of the ground wires -- legal and clean -- will go back to the same ground bar in the breaker box. Assuming the same clean, tight connection for every wire, the system should remain clean.
NOISE will occur if you join a clean system to a noisy system as might occur when connecting to a guitar or bas amp via direct box. Of course, ALL potential audio outlets should have their own ground wire and a straight return to the breaker box.
Glossary of terms
Hertz (abbreviated Hz) is the frequency, in cycles per second, of an alternating current (AC). When specifying voltage, the RMS (root mean square) value is used so that the effective power is equivalent to that of direct current (DC). For example, the voltage at the power outlet is 120 volts RMS which is actually about 340 volts peak-to-peak.