Some of these problems
directly impact the audio and/or picture quality. Let's examine
each type of powerline disturbance below. Please understand that
a full discussion of each of these issues would require a large
chapter in a book -- these definitions merely scratch the surface.
In order to fix
a problem, it helps to define the problem. Some of the problems
are electrical only, but manifest themselves in the audio or video
circuitry. Sometimes a problem actually originates in the audio
Some percentage, perhaps 5% to
25% above of the "stated", "nominal", or "specified
Brownouts are the
opposite of the overvoltage condition, above. The original issue
of brownouts was when in large cities, heavy current demand for
air conditioners in the summer put such a strain on the power
grid that the voltage sagged, or went down. Sometimes this happens
TO the power companies, and sometimes this is caused BY the power
companies. (i.e. controlled or rolling brownouts) The end result
is the same: less current is available and lower voltage is available.
caused by the powerline source being too high an impedance to
supply the necessary current demand; could be milliseconds (such
as from a motor start capacitor drawing inrush current ) or many
seconds (any continual appliance, such as an electric iron, clothes
dryer, heater, etc. This is more often than not caused by too
small a wire used in an installation or by Aluminum wire used
in place of copper.
The sine wave simply
stops for a few milliseconds, or perhaps as long as a few cycles.
This might be caused by a lightning protection changeover relay
device somewhere upstream in the power grid, or, it could even
be caused by an intermittent connection, and although that would
be a rather rare condition, it does happen.
occurences which ride on top of the sinewave; perhaps up to 750V
or so. A spike might be considered the shortest duration, perhaps
a few microseconds to a few milliseconds. A surge might be from
a few milliseconds to a few seconds. And a peak condition might
last from a few seconds to a few minutes.
Perhaps 500 to
5000V lasting from hundreds of nanoseconds to hundreds of microseconds.
It is these higher voltage spikes which burn out equipment, often
in mysterious ways. Typically these high voltage spikes are caused
by lightning somewhere on the grid, from a few feet to a few miles
The opposite of peaks: V-shaped
cutouts in the sine wave as seen on an oscilloscope
Power Factor is
the phase relationship between the VOLTAGE condition of the line
and the CURRENT condition of the line. A totally resistive load
(i.e. a lightbulb) has "unity" power factor. A load
that has a CAPACITIVE or INDUCTIVE component REACTS with the sinewave;
therefore this is said to be a "reactive" load. This
causes a harmonic imbalance of the sinewave, resulting in Harmonic
Distortion, explained below. One goal of load balancing for example
on a 240 Volt circuit is to even out the different power factors
so as to NOT introduce either a voltage imbalance or a harmonic
imbalance on the power line.
Odd and/or even
order distortion of the 60 Hz sinewave causes mechanical humming
in transformers. The waveform, instead of being a 'pure' 60 Hz
sinewave, contains some combination of even (120, 240, 360, 480
Hz) or odd (180, 300, 420, 540 Hz) harmonics.
Noise (in a transformer)
'humming' sound emanating from a transformer: the transformer
windings are magnetically saturated, often because the voltage
is too high. This saturation starts turning the sine waves into
square waves. Square waves, by nature, are composed of a train
of odd harmonics. These harmonics mechanically vibrate the transformer
and its mounting apparatus, and that is what you hear 'mechanically'.
In the instance of a subwoofer, you might think the subwoofer
[speaker] is making the noise, but actually it's the transformer
inside that is making the noise and you are hearing this transformer
noise through the paper or cone material of the speaker.
This noise is often a mix of both 60 Hz and 120 Hz, and some of
both of their odd harmonics.
(radio frequencies, i.e. from an AM radio station, TV station,
CB radio, Ham/ Taxi / Police / industrial walkie-talkie radio,
etc etc) amplitude modulating the sine wave envelope. This is
commonly referred to as "picking up RF". See also rectification,
Noise common to BOTH sides of the
line (sometimes a problem when operating from 240 Volts)
Noise showing up
on one side of the line measured to ground. Therefore in the case
of a 240 V line the noise would be only or mostly on ONE side
or leg, i.e one of the 120 V "legs".
Ground noise or
currents caused by bad, loose, or high impedance ground connections;
can also be caused by rectification in the grounding wiring.
by dissimilar metals such as aluminum / copper junctions which
then rectify the RF in the air and add the resulting modulation
voltage to the power line.
Where some digital
"audio" or "power supply" circuit feeds its
switching noise back into the power line and the noise then shows
up in another piece of equipment.
Sonic or ultrasonic
"whine" from a poorly designed switching power supply
leaking back into the power line. Expect a whole new generation
of problems with so-called "switching" audio amplifiers
- especially as they get old.
Caused by loose
or dirty mechanical connection; even caused by such seemingly
innocent devices as pushing a wire into a captive wire slot in
a switch instead of properly screwing the wire down securely under
the connection screw. May also come from relays or motor brushes.
If a switch was opened or closed at EXACTLY the zero crossing
point of a sine wave, since there is no voltage present there
is no current flowing. Since this is not a very likely occurrence,
most of the time when either a relay opens or a person opens a
switch the waveform is at some other spot than zero, and therefore
there IS current flowing. The current attempts to continue to
flow across the airgap, causing arcing. Arcing then oxidizes,
pits, and eventually wears out the mating surfaces. Some [better]
circuits use relays filled with nitrogen which will not allow
an oxidizing arc to form... since there's no oxygen inside the
noise from the previous circuit; this often implies improper gain
staging or matching, but may be a defective component as well,
acting as a noise 'generator'.
Hum at 60 Hz
A true ground loop! A true ground
loop is ONLY a 60 Hz component !
Hum at 120 Hz
Quite likely a
power supply filter problem; however most people "think"
that 120 Hz hum is a ground loop.
Perhaps a bad capacitor,
noisy transistor junction, or IC / OpAmp going bad or latching
Buzzing is typically
120 hz that is clipped, (or where the filtering circuitry in the
power supply has faulted) generating a series of ODD harmonics,
i.e. a mix of 120, 360, 600, 840, 1080 Hz, distinctly measureable
by specific test equipment, such as a spectrum analyzer. Since
it is clipped, it has turned into square waves; square waves by
definition are odd-order harmonics. So a true buzz has a very
recognizable sound. Please note that Hum and Buzz are completely
Hearing the demodulated
audio from AM, FM, TV, ham, shortwave, Marine, Taxi, CB, etc etc.
This is NOT the same as leakage, where one signal leaks into another
undesired area usually because solid state "switches"
are used rather than mechanical ones.
Common Mode Noise
A sound that seems
ike a combination of a buzz and noise, typically caused by "office"
fluorescent lights and their starter circuitry.
Transverse Mode Noise
This is the noise
you hear from "dimmers" where the buzzing changes pitch
as the dimmer knob is rotated; you are hearing the duty cycle
of the dimmer change.
Ticks and Pops
condition such as a spike will usually produce a tick in an audio
circuit. Only the very best power supplies will really filter
this out, and even they have no control of this if the tick is
riding on an audio signal which is properly going through an amplifier.
This could also be caused by a refrigerator motor or washing machine
motor (on the same circuit) starting up. The higher impedance
the entire chain of wiring is, the more likely this will happen
and be noticed.
Video Interval Beating
59.94 hz beating
against 60 Hz; often caused by ground differentials between a
feed from a "TV cable company" and the local house or
studio ground; perhaps as high as 65 volts differential. This
manifests itself as a buzzing sound, cyclical in nature, sort
of repeating every 14 seconds. Once this sound is heard and memorized
it is VERY recognizable.
Fabulous white papers / application
notes on the Jensen Transformers site:
originally courtesy Middle Atlantic morphed into Legrand company's
white papers section... HERE
(superb, and a clickable table of contents)
Surgex has morphed
into ESP (Electronic Systems Protection) which has morphed into
AMETEK, and their technical library is here: https://www.ametekesp.com/resources/white-papers