Trees are dying. Bees are dying. Perhaps, this is due to power line noise?
Martin Glasband, President of Equi=Tech Corporation in Selma, OR, and proponent of balanced power designs for 120-volt AC circuits. has noted:
"The basic problem is that when loaded, all differential mode 120-volt AC circuits create noise in the ground reference. Noise problems occur in audio signal circuits due to an unclean ground. The old Edison circuit (where a 240-volt circuit is split into two 120-volt circuits) is still used today as a standard means of 120-volt power distribution. Standard power is unbalanced."
"...the most damaging form of noise (reactive current in the ground) is left untouched. Low impedance grounding has little effect on reactive current so the problem persists."
"The answer is preventing reactive currents from propagating in the grounding system. This can be accomplished by re-phasing the power source. To get a clearer picture of this theory, one needs to look at the load, the ground reference and the voltage phase in the power wires. For some reason, the simple truth has been overlooked for years."
"The Earth ground now functions only as a reference for electrical safety and for shields as it should be, not as an ineffective sink-hole for reactive current."
Reprinted from the November, 1994 issue
of "MIX Magazine" with permission
from Intertec Publishing Company Inc.
(c) Copyright 1994 all rights reserved
by Martin Glasband
NOISE MAY BE THE MOST MISUNDERSTOOD
PROBLEM in any professional audio or video facility. Today’s recording
technology offers unsurpassed quality and accuracy, yet grounding system
noise still baffles the experts.
Grounding noise is one of
the most common complaints from audio engineers, but it's difficult to
explain noise and grounding problems without addressing power. Grounding
noise is closely linked to AC power under a variety of impedance load conditions.
At first glance, the causes of noise can seem mysterious and perplexing.
Often, dirty power is cited as the reason. But in fairness to the experts,
it is important to remember that conventional power standards were adopted
long before we had sensitive electronics. Eighty years ago, no one predicted
the effects of industrial loads on power integrity.
A brief history
In 1882, Thomas Edison wired
the town of Sunbury, Pennsylvania using a shared-common three-wire DC distribution
system. The cost of copper wire was an important factor, so Edison's engineers
devised a way to distribute two circuits using only three wires. The forerunner
to modern power distribution, DC and AC versions of the “Edison Circuit”
are still widely used.
But this system has one glaring
fault. The level of interference created when a three-phase wye system
is split up and used as three single-phase circuits is truly something
to behold. For example, as much as 20% (or more) of the power used by fluorescent
ballasts is reflected back onto the power grid in the form of reactive
or harmonic currents -- now that’s a lot of distortion. In the late 80’s,
a 40-plus-story office building in Los Angeles actually burst into flames
because of these reactive currents. Incredibly, the origin of the fire
was determined to be from excessive harmonic distortion in fluorescent
lighting circuits which created a high-frequency current overload and literally
a meltdown of the electrical wiring system. The First Interstate Bank fire
in Los Angeles in May of 1988 was the event dubbed by the media as "The
Towering Inferno" a la the Hollywood movie. Codes were adapted to
remedy the fire danger, but the noise problem itself was never completely
Three-phase power nonetheless
remains the bulk power of choice for utilities. When a utility furnishes
single-phase service to an area, the standard procedure is for the utility
to derive single-phase power by using one or two of the distribution grid's
three phase elements. So even single-phase power is linked to the distorted
three-phase grid. Typically, electrical power furnished by utilities contains
3% to 5% harmonic distortion. Single-phase service itself remains "split"
into two 120-volt circuits as per Edison's original wiring design. In one
form or another, these standards have been adopted and put into use around
Focusing on the Problem
It all boils down to eliminating
noise problems. What, for example, needs to be done to completely rid a
production facility of video hum bars. Can the problem of AC noise common
in Class-A tube amps be addressed? How about noisy guitar amps? Many other
examples of stubborn noise problems that have endured the test of time
have failed to yield substantial solutions.
Could it be that the answer
to the problem is in the power itself? Certainly there is room for power
to be cleaned up. Conventionally, this is done in two ways: improving its
level of signal purity, or improving the grounding system's linearity and
lowering its impedance. Unfortunately, even the cleanest power signal available
and the most linear and low impedance grounding system still yield AC noise
in audio and video circuits. How could noise still affect a video production
facility with top-of-the-line active power conditioning and a professionally
engineered linear signal reference? The reason is that power conditioning
systems don't address all aspects of the noise problem. For that matter,
the most damaging form of noise (reactive current in the ground) is left
untouched. Low impedance grounding has little effect on reactive current
so the problem persists. Clearly, a different approach is needed.
The answer is preventing
reactive currents from propagating in the grounding system. This can be
accomplished by re-phasing the power source. To get a clearer picture of
this theory, one needs to look at the load, the ground reference and the
voltage phase in the power wires. For some reason, the simple truth has
been overlooked for years.
Today's facilities are fed
typically with three-phase service. Common three-phase power systems lack
an inverse phase relationship between power wires. Power wires are phased
120 degrees apart so there is never a point in time where the system is
completely off (common zero crossing voltage) as in single-phase systems.
Consequently, reactive currents instead of nulling begin to "stack up"
in manner of speaking, end to end at very well-ordered intervals on both
the neutral and ground wires. After each phase peaks, a pulse of reactive
current is released onto the common wire or neutral. This occurs at a rate
of 60 times per second per phase. All three phases sum together in this
way on the neutral equaling 180Hz, the third harmonic. On line video facilities
powered by a three-phase (120/208V) grid are typically beset with noise
problems. When three-phase based, 120-volt power is used directly for audio
or video electronics, one can be assured of more interference than with
all other types of 120-volt systems.
One issue remains. What is
wrong with grounding? The answer is simple. As a rule, the grounding circuit
is not meant to carry any type of current except for rare occasions when
there is a short circuit, and then only momentarily. However, Underwriters'
Laboratories standards are somewhat lax in this respect. “Objectionable
ground current" is loosely defined in every area except for hospital operating
rooms. Outside of hospitals, “objectionable ground current” is gauged more
closely to shock hazard levels (about 3.5 milliamps). It seems that this
standard has backfired. Data corruption, disk crashes and simple hum noise
cost time and money -- sometimes a lot. Clearly, UL standards that define
"objectionable ground current" are inadequate by today's standards. On
the other hand, UL is not responsible for re-engineering audio equipment
and AC systems. Normally, performance standards are left up to manufacturers
and the marketplace.
The basic problem is that
when loaded, all differential mode 120-volt AC circuits create noise in
the ground reference. Noise problems occur in audio signal circuits due
to an unclean ground. The old Edison circuit (where a 240-volt circuit
is split into two 120-volt circuits) is still used today as a standard
means of 120-volt power distribution. Standard power is unbalanced. Even
when a high quality 120-volt isolation transformer is installed, one side
is grounded (made neutral) which is really not much different at all. The
way the AC voltage phase is referenced and carried by the circuit has everything
to do with electrical interference in a grounding system. If any aspect
of the circuit is applied or loaded in an unbalanced manner, noise will
appear in the ground.
Success, at last
Understandably, such a simple
explanation of noise problems can invoke a kind of knee jerk skepticism
or denial. But, requiring proof is not an unreasonable demand. In locations
using balanced 120-volt power systems, the results speak for themselves.
When balanced power is applied systemwide, the results are often quite
dramatic. On the average, 16dB improvement in background noise has been
noted. Where audio and video components are properly installed and maintained,
in no known case has balanced AC failed to substantially lower the noise
floor. In high-end systems utilizing 24-bit digital equipment, peripheral
gear needs balanced power to approach the noise floor capabilities of the
When symmetrical AC power
is used, grounding also tends to be more forgiving. Recently, a studio
owner needed some consultation and assistance installing a 120-volt symmetrical
power system for his home studio, a 24-bit digital facility that also included
a fair amount of class-A tube gear. Despite careful planning, there was
a miscommunication over some of the particulars regarding radial (star)
grounding for the outlets. Consequently, the electrician, unfamiliar with
studio AC wiring systems, looped entire strings of outlets together using
only one #12 gauge ground wire. In spite of the mishap, the system performed
perfectly -- quietly. This episode would indicate that unbalanced power
is the true cause of noise, not a poor AC grounding design. .
The system was built full
of ground loops, but grounding currents and chassis potentials were nowhere
to be found. This is how it should be. Star grounding and linear signal
reference grids are nothing more than "Band-aids" that, at best, can only
marginally mask over some of the noise. To be free of noise problems, grounding
circuits must remain clean -- that's all there is to it. If they're not,
a hundred ground rods won't help.
The symmetrical 120-volt
system is unique in that it deals specifically with balancing all power
and load elements with respect to a single point grounding reference. This
is the only prescription for maintaining a clean ground regardless of how
big the facility or what sort of gear is used. A specially wound isolation
transformer with a center tapped 120-volt output shown in Figure
4 and again in Figure
7 and Figure 8
is basically the heart of the system. Both the load and the power signal
are balanced with respect to the common output terminal (center tap) on
the transformer. Here is the true single point grounding reference for
a recording studio. The Earth ground now functions only as a reference
for electrical safety and for shields as it should be, not as an ineffective
sink-hole for reactive current.
Martin Glasband is the PresidentRead more at www.equitech.com
of Equi=Tech Corporation in Selma, Oregon. Formerly as an electrical contractor
and consultant has designed electrical systems for KCET-TV, The Post Complex,
Warner Brothers, Oz Audio and Post, ABC Radio Network, Baby'O Recorders
and New World Pictures