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.
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 circuitry itself.
Some percentage, perhaps
5% to 25% above of the "stated", "nominal",
or "specified voltage".
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 voltage is available and THEREFORE lower current
condition 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. (Aluminum wire is cheaper, but has
higher resistance than copper.)
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.
voltage 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.
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 away
The opposite of peaks:
V-shaped cutouts in the sine wave as seen on an oscilloscope
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.
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
Noise (in a transformer)
mechanical '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 and definition, are composed of a series 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, below.
Noise common to BOTH sides
of the line (sometimes a problem when operating from 240
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".
noise or currents caused by bad, loose, or high impedance
ground connections; can also be caused by rectification
in the grounding wiring, where corrosion forms between
copper and aluminum connections.
caused 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.
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.
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.
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 plate.
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 metal mating surfaces.
circuits use relays filled with nitrogen which will not
allow an oxidizing arc to form... since there's no oxygen
inside the relay.
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'.
Noise: Hum at 60 Hz
A true ground loop! A true
ground loop is ONLY a 60 Hz sine wave component !
Noise: Hum at 120 Hz
a power supply filter problem; however most people "think"
that 120 Hz hum is a ground loop. It isn't!
a bad capacitor, noisy transistor junction, or IC / OpAmp
going bad or latching up.
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 different
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.
Noise: Common Mode Noise
that seems ike a combination of a buzz and noise, typically
caused by "office" fluorescent lights and their
Noise: Transverse Mode Noise
the noise you hear from "dimmers" where the
buzzing changes pitch as the dimmer knob is rotated; you
are hearing the on/off duty cycle of the dimmer change.
Noise: 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.
Noise: Video Interval Beating
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
white papers / application notes on the Jensen Transformers
treatise, originally courtesy Middle Atlantic morphed
into Legrand company's white papers section... HERE
(superb, and a clickable table of contents)
has morphed into ESP (Electronic Systems Protection) which
has morphed into AMETEK, and their technical library is