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In many of the email messages I receive people express an interest in eliminating noise they hear when playing electric guitar. Noise and the elimination of noise is the topic of this article.
In many of the email messages I receive people express an interest in eliminating noise
they hear when playing electric guitar. Noise and the elimination of noise is the topic of
this article.
In this newsletter my intent is to provide useful information about the source of noise and
methods that can be used to reduce or eliminate it. Heres my disclaimer: the information
presented here is based on my personal experience and what I have learned from others
over the years. Please let me know if you disagree with any technical aspect presented
here or if you have found any alternative methods for reducing noise- I would like to hear
from you!
One more disclaimer: I use the term eliminate in this article; in my use of this word I
intend to describe the reduction of noise to such a low level that the noise is no longer an
annoyance. It is unlikely one would ever eliminate 100% of the noise signal.
Back to the issue of noise
The noise I am focused on in this article can sound like an old electric shaver and is very
annoying.
Pickups and the tone & volume control circuits in a conventional electric guitar such as a
strat, tele or Les Paul are very good at picking up electromagnetic radiation from
nearby devices that utilize alternating current (AC) electric power. Passive (un-powered)
pickups can have 5,000, 10,000 or more turns of wire in the coil. Such a coil can function
very effectively as an antenna to receive noise from sources in the environment. Sources
of AC interference include florescent lights, power transformers and dimmer switches.
The fundamental frequency of this noise is 60 Hertz (abbreviated HZ and represents
cycles per second). Noise from devices powered by AC electricity may also contain
higher frequencies that are multiples of 60 Hz (120 Hz, 240 Hz and so on).
Over the years very clever folks have put significant effort into minimizing noise.
There are typically three approaches:
1. Reducing noise at the source
2. Shielding from the noise source
3. Reducing noise at the receiving end
January 2007 To get the lowest noise possible one must think of the whole system: the electromagnetic
environment (noise sources), guitar, guitar cable, amplifier and the AC power supply.
Lets take a look at each of these approaches separately.
1. Reducing noise from external sources
Devices operated with AC electric power such as florescent lights, track lighting (which
use transformers), electric motors and other items radiate electromagnetic energy in all
directions. This radiated electromagnetic energy is easily received by the pickups and the
wiring circuit in an electric guitar. Eliminating these sources of AC induced noise can
go a long way towards reducing hum heard through an amplifier. Recently my wife asked
me to install ceiling mounted low-voltage track lighting in the room where I practice; the
first time I played my guitar through a Fender Hot Rod Deville with this track lighting on
I noticed a significant amount of hum. Turning off these lights made the hum go away.
After thinking about it I concluded that the powered track may be an excellent antenna
for broadcasting electromagnetic radiation from the transformer that powers the lighting
system. I now use a standard incandescent lamp in this room and experience very little
noise when playing my electric guitars. Magnetic fields can also induce noise in electric
guitars, but the good news is that magnetic fields tend to fall off in intensity in short
distances. Another potential source of noise is from static electricity. In the winter during
periods of low humidity is when the presence of static electricity is most obvious.
Another important thing to check is the electric power outlet the amplifier is plugged
into. If the outlet is improperly grounded or has other wiring issues noise will be a
problem. I use an outlet tester as shown in the photo below. This type of outlet tester is available in many hardware stores and costs ~ $8 to $10.
When plugged into a properly wired outlet the tester will indicate the circuit is good as
shown below:
During the winter I spray the carpet where I practice with an anti-static spray such as
Static Guard; this virtually eliminates the pop and hiss that can be caused by static
electricity generated when my shoes move across the carpet. Static guard costs ~ $3.50 a can and is available in many stores including Walgreens.
2. Shielding from noise
Use of an undamaged high quality coaxial shielded guitar cable to send the signal from
an electric guitar to an amplifier is essential to eliminating noise. Wireless systems
introduce yet another possibility for the introduction of noise and will not be discussed in
this review. It is also a good idea to check that the amplifier itself is free of unwanted
noise. To test for this, insert a guitar cable into the amp with the other end of the cable
not plugged into an instrument. Turn on the amp and listen for noise as the volume and
gain are increased. Please note that the free end of the guitar cable should not be in
contact with any conducting or partially-conducting surface (such as your hand) during
this test. If your amplifier makes noise during this test no amount of work on the guitar or
other components of the system will eliminate the noise. A noisy amplifier should be
serviced by a qualified amplifier technician to eliminate the cause of the noise and to
ensure there are no safety issues.
Proper grounded shielding in the circuit of an electric guitar can be very effective in
eliminating unwanted hum caused by external AC electric fields.
The history of grounded shielding dates back to the 1800s and is attributed to Michael
Faraday
1 Michael Faraday, (1791 1867) was an English chemist and physicist who contributed
significantly to the fields of electromagnetism and electrochemistry. It was largely due to
his efforts that electricity became viable for use in technology. The SI unit of capacitance,
the farad, is named after him.
In his work on static electricity, Faraday demonstrated that the charge only resided on the
exterior of a charged conductor, and exterior charge had no influence on anything
enclosed within a conductor. This is because the exterior charges redistribute such that
the interior fields due to them cancel. This shielding effect is used in what is now known
as a Faraday cage.
A Faraday cage or Faraday shield is an enclosure formed by an electrically-conducting
material. The electrical charges in the Faraday shield repel each other and will therefore
always reside on the outside surface of the shield. Any external static electrical field will
cause the charges to rearrange so as to completely cancel the field's effects in the cage's
interior. This effect is used to protect electronic equipment from lightning strikes and
other electrostatic discharges.
To a large degree, Faraday cages also shield the interior of the enclosure from external
AC electromagnetic radiation from noisy sources such as florescent lights, transformers
and electric motors. The faraday cage must be connected to a good electrical ground to
function.
In an electric guitar it is common to line the inside surfaces of the controls cavity and
even the pickup cavities with copper tape. Each panel of copper tape must be in good
electrical contact with the ground connection of the output jack of the instrument. Unless
otherwise requested, I put grounded shielding in the pickups I make. When the pickups
are properly shielded no additional shielding is required in the pickup cavities. Shielding
does add capacitance to the guitar circuit. The effect of this added capacitance can affect
the tone of an instrument. When a significant surface area of shielding (more than 10 square inches of surface area) is added to an instrument the treble frequencies will be
affected in the same way a tone pot removes treble.
Be aware that it is possible to wire the output jack of an electric guitar backwards; if this
is done the grounded shielding will not function and a potentially dangerous situation
may be present.
Output jack used commonly used in an electric guitar
3.
Eliminating noise
Several approaches have been developed to eliminate noise in electric guitars:
humbucking (or hum-canceling) pickups, active pickup systems and noise gates.
Seth Lover's famous humbucker design (U.S. Patent 2,896,491

) was the P.A.F. (Patent
Applied For) which he designed while working for Gibson Musical Instruments in 1955.
Humbucking pickups are comprised of two coils connected electrically in series that are
reverse polarity, reverse wound (RWRP) with respect to each other..If one coil is wound
clockwise and has a magnetic field polarity that is north up, the other coil would be
wound counter clockwise and its magnetic field would be south up. The signal induced in
one coil from the vibrating strings of a guitar has a waveform with a specific