A pair of stereo headphones with a 3.5mm jack plug connection is also useful
to monitor the loop signal.
System Requirements:
The induction loop cable itself should be already installed according to the
“Designing Induction loops” handbook, or as per specific design instructions
provided by Ampetronic. As a result, a target peak current should be known,
based on achieving acceptable field strength across the area to be covered.
Connection and Set-up:
It is advised that the loop system is initially set up using a local audio source
such as CD player, which is not connected into any other system. This avoids
the complication of ground loops and feedback etc, whilst the unit is set up.
The following procedure describes the installation of a stand alone ILD122,
and does not incorporate connection of other ancillary units such as
microphone pre-amps or signal processing units.
1. Turn all controls fully anti-clockwise.
2. Connect the loop cable into the Loop connector supplied. Where using a
perimeter loop (floor/ceiling level), the feed cable should be tightly twisted
and less than 20m in length. Total resistance of loop and feed must be
between 0.2
W
and 1.8
W (
at DC). The “Designing Induction Loops” handbook
contains more details on loop and feed cables. The correct design and
positioning of the actual loop is vital for satisfactory system performance. If in
doubt consult Ampetronic for advice.
3. Connect the signal input(s) appropriately:
a) Suitable dynamic or condenser microphone with balanced cable feed.
Select phantom power as required, depending on the type of microphone
you are using. Connect to MIC input using a 3-pole XLR plug wired as
per
Connections
drawing.
b) Line level input from other audio equipment such as PA system,
mixing desk or CD player to the LINE INPUT.
You may use either or both inputs.
Do not run the input and output cables close together.
The SLAVE I/O must
NEVER
be used as a separate input. It must only be
used with Ampetronic signal processing equipment, or for obtaining a signal
for recording. See
Connections
section for details.
4.Connect AC power to the ILD122. See points 6 and 7 in
Safety
section.
5. Switch ON. The POWER LED will flash for a few seconds while an internal
self test is performed and the loop resistance is tested. If both tests are
successful, the POWER LED will illuminate continuously and the unit will be
in an operational mode. If the POWER LED continues to flash, or the ‘Loop
Error’ LED illuminates, consult the
Troubleshooting
section.
6. Select one input and apply a suitable, audio signal (ideally a CD player with
music or continuous speech applied to the LINE INPUT, with no connection to
the MIC input). Turn the associated input control clockwise until 2
COMPRESSION LEDs are illuminated on the peaks of the signal.
7. Turn the LOOP CURRENT control clockwise until the target current is
achieved – as indicated by the CURRENT LEDs. Note that consecutive LEDs
illuminate at 3dB intervals. Headphones can be used with the LOOP MONITOR
socket to listen directly to the loop current. If high frequency oscillation of low
frequency hum is experienced, consult the
Troubleshooting
section.
8. The loop system should now be providing a magnetic field inside the area of
the loop – use the ILR3 or field strength meter (FSM) to examine its
performance with respect to:
a) Magnetic field strength. This will vary across the coverage area, due to
layout, metal loss and LOOP CURRENT.
b) Frequency response. Metal losses tend to increase with frequency, and
may require the adjustment of the METAL LOSS CORRECTION.
As a result of this analysis, adjust the LOOP CURRENT and set the METAL
LOSS CORRECTION (on the rear of the unit) to achieve best sound quality.
This should result in an adequate magnetic field strength and level frequency
response in order to satisfy IEC 60118-4. Note: Do
not
adjust the METAL
LOSS CORRECTION whilst listening via the LOOP MONITOR socket.
Once the LOOP CURRENT AND METAL LOSS CORRECTION have been
adjusted to the correct level they should
not
need re-adjusting.
9. If not already done so, steps can now be taken to integrate the ILD122 into a
PA / mixer arrangement following standard audio techniques. If any unusual
effects are experienced refer to the troubleshooting section.
Note: Ideally, each input signal level should be set up to achieve 6dB (one
LED) of COMPRESSION with the quietest level of input that is likely to be
used. This will maximise the dynamic range of the system and ensure
satisfactory performance.
10.Repeat above procedure for other signal input if used. When adjusting each
input, make sure that the signal(s) are removed from the other inputs. This
ensures that all signals are set to equivalent loudness and drive the
compressor properly.
