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Faultfinding Your System
Cause and
Elimination
of Hum
Hum is a particularly annoying form of noise in any high fidelity system and a
t
some time has been experienced by many of us.
Hum may result from a number of different situations and to make matters
worse maybe caused by a seemingly illogical combination of circumstances.
One or more of three specific causes creates hum in the system.
Induced Hum
Hum can be induced into the system from one or more sources and is generall
y
associated with the radiation of noise from one system into another.
Hum and noise can be radiated from any object or system involving AC voltag
e
and current such as power supplies in amplifiers, motors, switching equipmen
t
etc. All of these may be found in your hi-fi system or within your own home.
Hum may be induced into any part of the system, so there are no specifi
c
instructions that can be given which will offer a guaranteed cure. A goo
d
practice to adopt is to keep low-level signal equipment such as phono systems,
tuners etc. well away from high-level signal equipment such as powe
r
amplifiers. Alternatively, careful designs must be employed to negate thes
e
effects on low-level signal equipment. Another good practice to adopt is to keep
all signal leads away from power leads.
The practice of neatly tying excess leads together for a tidy looking installatio
n
should be resisted, as this could be the cause of induced hum in the system.
Earth Loops
Earth loops are a particularly annoying cause of hum in the system. Earth loops
are created by mains frequency current flowing in the screen of signal leads an
d
becomes apparent with the lack of adequate earthing between the various pieces
of equipment making up the hi-fi system. This is further compounded by th
e
fact that the equipment earthing considerations vary between differen
t
manufacturers and countries.
Perreaux products used with equipment manufactured by other manufacturers
may cause an earth loop situation, but Perreaux products used with othe
r
Perreaux products will not cause an earth loop situation provided the followin
g
precautions are observed:
àThe entire hi-fi system must be connected to the same mains/line power
outlet. This will ensure that each piece of the system shares the same earth
or ground. This rule applies to all installations of all brands of equipment.
A preamplifier or power amplifier may be operated from an extension cord
plugged into the same mains/line outlet.