Farnell PDA101L Operation Instructions - page 4
Page 4
Doc No. DCP0001751 JC 09/01/03 rev2
Output connections
Loop output
The output is via two Screwless vertical PCB
terminals. Connection is made by way of tails.
To allow cables to be inserted, slide a terminal
screwdriver into the rectangular hole directly
above the cable entry hole to be used, when
cable has been inserted remove the
screwdriver which allows the connector to
close and grip the conductor.
WARNING: The PDA amplifiers are capable of
producing short term peaks of twice their rated
current.
The PDA101 can be wall mounted, using No 8
japanned woodscrews (provided) on 100 mm
centres vertical or 45 mm centres horizontal,
using the holes marked on the diagram below.
Care must be taken when attaching unit to
screw heads to ensure that screw heads do
not damage the printed circuit board.
Wall mounting
Loop cables
Cable selection
Only 0.5mm
2
cable, as supplied, should be
used. If other cable types are used it will be
necessary to adjust the drive current as
appropriate.
Use of a tri-rated cable is recommended. This
is cable with a tougher than usual jacket, the
reason being; damage will occur to the
amplifier if at any point the loop is grounded.
Loop cable should ideally be laid at floor level
but in certain circumstances this may not be
possible. Any large amounts of metal (eg steel
meshed reinforced concrete floors) will absorb
some of the signal strength, in this case the
cable may have to be mounted in the walls.
Aluminium (suspended ceilings) being para-
magnetic should also be avoided, mounting a
loop above an aluminium suspended ceiling
will probably result in almost no coverage,
turning up the output of an amplifier would just
make matters worse as it will just stress the
output stage (and minutely warm the
aluminium) resulting in a definite shortening of
the life-span of the amplifier.
Speaker positioning
If a speaker is placed near or beside a loop
cable the cross-over in the speaker may pick
up the loop signal, so try to keep speakers and
loop cables as far apart as possible. Normally
this does not show up in use because loop
and speaker have the same programme
material, only where the loop has a different
signal to the speakers (e.g. stage talk back
systems)will this become an issue.
Feeder Cables
When connecting an amplifier to a loop some
distance away use a heavy gauge twisted pair
(2.5mm
2
). This will have a negligible
impedance, as such the amplifier will not drive
against it and the power will be fed into the
loop where it can do useful work.
Test loops
We always recommend the laying of a test
loop, there is no such thing as a standard
installation and sometimes only a test loop will
uncover problematic areas.
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Doc No. DCP0001751 JC 09/01/03 rev2
Feedback
Long lengths of unbalanced signal cable may
cause feedback when placed inside the loop.
Keep connecting audio leads as short as pos-
sible.
Problems may occur when using standard
dynamic microphones. The coil inside may act
as a receiver and cause feedback. It is
advisable to use condenser microphones.
These may require phantom powering,
available on both microphone inputs.
Other sources of feedback are coils in other
equipment that is linked to the induction loop
system, for example guitar pickups.
Loop cable class
A loop cable is classed as a 2A cable under
IEEE 16
th
Edition wiring regulations. As such it
must be sited a minimum of 600mm away
from telephone, mains and control cables.
Loop cables