20
Hum
The exceptional audio performances
of your PL–L will give you hours of
listening pleasure. However, you can
only benefit from the total quality of
your PL–L if it has been correctly
installed.
Any error in the connection of the
system is likely to create hum caused
by AC ground loops. The first step is
to be sure that all the various units in
the system (DVD, PL–L, amplifier,
CD–player, etc...) are powered
correctly.
As a preamble, we will explain the
hurdle. Any wire has an electrical
resistance, and all currents passing
through a resistance create a drop in
voltage. Depending upon where the
voltage drop occurs, you will be
confronted with more or less AC hum.
Normally, the AC network that powers
your equipment is made up of three
separate conductors, these being the
ground/earth, the neutral and the
phase, the latter two allow the
passage of energy to the device being
powered. The latter two wires are not
floating; the phase wire, which should
not be touched for risk of electric
shocks, carries a high alternating
potential (110V or 220V), whereas the
neutral wire is very close to the
ground/earth and can normally be
touched (in principle!) without any
risk. Normally these two wires carry
an identical current, one being the
return of the other.
The third wire, the ground/earth,
allows all the chassis’ of all the
equipment in the installation to be
linked together. It constitutes a
security in the event that one of the
pieces of equipment has a break in
the isolation of the phase.
In principle, this wire carries no
current, and therefore according to
the theory above, there should not be
any difference in potential between
different points along its length.
Unfortunately, this is not always the
case.
In fact, the demands of modern
regulatory standards regarding high
frequency protection create a
significant circulating current along
the length of this wire.
In addition, it is possible that various
pieces of equipment connected to
your AC network, without being
defective, present an earth problem,
which in itself causes a loop current
within this precious earth wire. Finally
there is the most frequent case,
where the neutral and the earth wires
are one, and cause these currents to
be carried throughout your
installation, causing in most cases
terrible AC hum.
If you find yourself confronted with a
situation similar to that shown below,
you have every chance that you will
be listening to the mains hum rather
than your favorite piece of music!