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Tech Tip -
By Dennis Kambury
The most common reason for amplifier hum is
the ground loop, this is caused when the sound
system has two or more different ground points.
This is very easy to do if, for example, you plug
your guitarist's amp into an onstage socket, and
your mixer into the socket at the back of the
house. These two separate points will have
different electrical potentials, causing electric
current to flow. The result is easy to hear, but
how do you go about fixing the problem?
Your best solution is to make sure that all of
the AC power is supplied from one single circuit
from the power mains. If that's not enough power,
at least make sure that all your circuits come
from the same panel with the same ground.
A ground loop can also be broken with the use of
a ground lift adapter, but it's not a great idea,
as this method is potentially fatalbreaking
the ground means that the signal could possibly
find its way to earth directly through YOU!
Poor or defective cables can also be a source of
problems. Hum can be picked up from light
fixtures, motors, and other common electrical
sources through these bad cables. Try to avoid
cheap molded-head connectors, and take the time
between gigs to check all of your cables for good
solder joints, clean connectors, and undamaged
There is yet another cable-based source of hum
induced from power cabling going into signal
cabling. Briefly, when these two types of cables
are running parallel, the AC 60 cycle signal can
be picked up by the instrument or mic cable,
amplified, and broadcast for everyone to hear!
Keep all your power and signal cables well
separated; and, if they absolutely must cross, be
sure to always cross them at right angles to each
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