Item ref: 952.864UK, 952.867UK
User Manual
Caution: Please read this manual carefully before operating
Damage caused by misuse is not covered by the warranty
This symbol indicates that dangerous voltage constituting a risk of electric shock is
present within this unit
This symbol indicates that there are important operating and maintenance instructions
in the literature accompanying this unit.
Prior to use, read through this manual
Keep the manual in good condition
Pay attention to safety warnings
Observe all operating requirements
Do not use the device near water or wet areas
For cleaning, only use a lint-free, dry cloth
Install according to the specifications
Place away from heat sources or heating appliances
Use mains lead provided and avoid damage to cable or connectors
Unplug power from mains during stormy weather or if unused for long periods
In case of malfunction, water ingress or other damage, consult qualified service personnel
Do not place in damp areas or near liquids or moisture. Do not spill liquids on the housing
Please pay attention to warning symbols during transit and placement
Terminals marked with the symbol are HAZARDOUS LIVE and should only be connected by qualified personnel
Ensure that the apparatus is connected to a mains socket with a protective EARTH connection
Ensure correct operation of the mains switch
To prevent the risk of fire or electric shock, do not expose any components to rain or moisture.
If liquids are spilled on the casing, stop using immediately, allow unit to dry out and have checked by qualified personnel before
further use. Avoid impact, extreme pressure or heavy vibration to the case
No user serviceable parts inside – Do not open the case – refer all servicing to qualified service personnel.
Check for correct mains voltage and condition of IEC lead before connecting to a power outlet
Use insulated loop wire, ensuring the correct gauge for the loop distance required
Do not allow any foreign objects to enter the case or through the ventilation grilles
Use the mounting ears supplied when installing into a 19” rack
For rack-mounting, ensure adequate support for the weight of the amplifier
Ensure adequate air-flow and do not cover cooling vents at the front and rear of the amplifier
Ensure adequate access to controls and connections
Use a soft cloth with a neutral detergent to clean the casing as required
Use a vacuum cleaner to clear ventilation grilles of any dust or debris build-ups
Do not use strong solvents for cleaning the unit
952.864UK, 952.867UK User Manual
Thank you for choosing an Adastra LA series induction loop amplifier for your assisted hearing installation.
This unit is designed to offer high quality hearing assistance for hearing aid users.
Please read this manual fully and follow the instructions to achieve the best results with your new purchase
and to avoid damage through misuse.
Note: All induction loops in the UK should be installed in accordance with BS7594.
Front panel
Channel 1 input level control
Channel 2 input level control
Channel 3 input level control
Bass EQ adjustment
Treble EQ adjustment
Loop current (master level) control
Siren indicator
Loop current level indicator
Power switch and indicator
Unbalanced RCA inputs
Mic/line level, phantom & priority DIP switches
Combined Slave input/output
Metal loss correction adjustment
Rear panel
Mains voltage selector
Combined IEC mains inlet and fuse holder
Loop output terminals
Alarm contact terminals
Balanced combo jack/XLR inputs
952.864UK, 952.867UK User Manual
The LA series loop amplifiers can be operated free-standing or fitted into a standard 19” rack cabinet using
the supplied rack ears. Ensure that the unit is positioned on a stable surface with adequate cooling
There are 3 input channels which can accept inputs via balanced XLR or 6.3mm
jack connection (14) or unbalanced RCA connection(15).
The XLR/jack connectors can be set to accept microphone or line level via the Mic/Line DIP switches (16),
which are also accompanied by switches for activating phantom power (+20V) for use with condenser
Multiple loop amplifiers can be used in master/slave mode using the combined slave input/output jack (17).
Connecting a stereo 6.3mm plug to this socket gives 2 wiring options as shown below.
Connecting a mono 6.3mm plug will function as a slave output. A TRS plug with signal connected to the ring
will be needed for a slave input from another loop amplifier.
Alarm contacts (13) are provided, which will emit a siren on the induction loop when the connection is made.
These can be connected to an emergency switch or alarm panel contacts to activate the siren for emergency
evacuation, indicated by an LED on the front panel (7)
Alongside the alarm contacts are the screw terminals for the induction loop (12). Connect the 2 ends of the
loop wire to these terminals, ensuring no stray strands or shorted connections. See below for details about
installing the loop wire before connecting mains power to the loop amplifier.
Mains is connected via a rear panel IEC connector (11) with a built-in mains fuse.
Use the supplied lead and ensure that the correct mains voltage is set on the voltage selector (10).
952.864UK, 952.867UK User Manual
Induction loop cable installation
Prior to installation, it is important to check if there will be any equipment in the vicinity that may interfere
with the loop’s magnetic field, such as large transformers, high power cables or substations. It is also
important to ensure that no equipment will be adversely affected by the loop field, such as sensitive data or
signal cables. In these cases, it may not be possible to cover some or any of the required area with an
induction loop.
The cable gauge will depend upon the total length of the induction loop. Usually, the loop will be installed
around the perimeter of the listening area. However, there are various techniques which can be employed to
build arrays to vary the shape and strength of the field. In general, calculations outlined here are based upon
a perimeter installation.
It is recommended to use good quality insulated pure copper cable for the induction loop. The cable gauge
used will need to be determined by the total length of the cable run. The LA-series loop amplifiers are
designed to operate with a load of between 0.2Ω and 2Ω. The following equation can be used to calculate
the total cable resistance, which will show if the gauge is correct.
Cable length (m)
Cable CSA (mm²)
x 0.01786Ω*mm²/m (specific resistance of Copper)
So, for a cable 80m long with a Cross-Sectional Area (CSA) of 1.5mm²…
R = 80/1.5 x 0.01786 = 0.9525Ω
So, this gauge of wire (1.5mm²) would be OK for the 80m run because it is between 0.2Ω and 2Ω
As a quick reference, refer to the table below.
Cable CSA (mm²)
Total Loop Length
60m max.
110m max.
200m max.
Over 200m
The wire may be run in plastic conduit but not in any metal containment so as not to impair the magnetic
flux. The ideal height to install the cable depends upon the width of the loop (i.e. the narrowest dimension
relative to the listener). The optimum output will be achieved if the cable is installed 14% of the loop width
higher or lower than the plane of listening (ear height).
In practical terms, the loop is usually installed onto skirting boards, under flooring or at ceiling height so that
it is unobtrusive. It is recommended to avoid varying height levels as much as possible to avoid anomalies in
field strength.
For irregular shaped areas or larger than the loop amplifier’s capacity, multiple induction loops may be
required for coverage. Connecting further loop amplifiers using the Slave connection will enable multiple
loops to be used together.
952.864UK, 952.867UK User Manual
Cancellation Loops
If there are areas adjacent to the loop where the magnetic field would cause problems, it is possible to avoid
this by use of a “cancellation loop”, which is a narrow loop parallel to the main loop at the problem area.
This loop is the opposite polarity to the main loop and causes the magnetic field to narrow along the
adjacent edge of the main loop to control the spill of the loop field.
Connect any line sources (e.g. CD player, mp3 player) or microphones to one or more of the input channels.
If a microphone is connected, select “MIC” on the DIP switches and connect via 6.3mm jack or XLR input.
If the microphone is a condenser microphone requiring phantom power, select “PHANTOM”.
For standard dynamic and battery powered microphones, set the Phantom switch to “OFF”
For line inputs, select “LINE” on the DIP switches.
For channel 1, there is an option for “PRIORITY” over the other two channels, which will mute the output of
channels 2 and 3 when there is an input to channel 1.
If the loop amplifier is to be used in conjunction with a PA system with loudspeakers, connect the line or aux
output from the PA system to a Line input on the loop amplifier via RCA, jack or XLR connection.
Ensure that this input is set to “LINE” and Phantom is set to “OFF”
Before connecting the induction loop to the amplifier, use a test meter to check the D.C. resistance in the
wire. Ensure that there are no shorted or grounded points in the wire and that the total resistance is not less
than 0.2Ω
Twist the loop wires from where the loop ends to the amplifier terminals to avoid creating an extended loop
to the area where the amplifier is situated.
With the power switched off (9), connect the loop cable to the loop terminals (12) on the rear panel of the
loop amplifier.
952.864UK, 952.867UK User Manual
The front panel controls on the loop amplifier are recessed and can be adjusted using a flat blade
screwdriver. This is to avoid tampering or mal-adjustment after the correct settings have been applied.
Where new or unsupervised operators are making adjustments to equipment in the venue, they may not be
aware if they have adjusted the induction loop settings unless they themselves are a hearing aid user.
Set the Ch.1, Ch.2, Ch.3 and Loop Current controls (1, 2, 3, 6) to minimum and keep the Bass and Treble
controls (4, 5) in the mid position (12 o’clock)
Power up the loop amplifier and increase the Loop Current control (6) part way.
Whilst playing a signal into one of the input channels, gradually increase the level (1, 2 or 3) until the peak
current indicator (8) shows movement.
The optimum operating level is achieved if the channel level controls are set so that if all connected signals
are at maximum level, the Peak Current indicator does not show overloading.
It is recommended to use an induction loop receiver (952.855UK) to check the audio from the induction loop.
Adjust the Loop Current control to set the main audio level from the induction loop.
The Metal Loss Correction control (18) enhances higher audio frequencies which may be absorbed by metal
architectural features and appliances within the induction loop area. If the building has a lot of metal
structure or reinforced concrete in the vicinity of the loop, use this control to adjust the audio quality of the
loop signal.
Adjust Bass and Treble controls (4, 5) to set the tonal characteristics of the audio from the induction loop.
The mid-point (12 o’clock) is the zero position. Turning to the left of the mid-point will cut Bass or Treble and
to the right of the mid-point will boost Bass or Treble.
When the induction loop is not required, ensure that no hearing aid users are remaining within the loop area
and switch off the loop amplifier (leaving the settings in position will ensure that the induction loop is set up
correctly for the next usage)
952.864UK, 952.867UK User Manual
LA-300 mkII (952.864UK)
Power supply
Area coverage
Frequency response
Input sensitivity : line
Input sensitivity : mic
Signal to noise ratio
Rack height
110/240Vac, 50/60Hz (IEC)
T1A 250V
300m² max.
50Hz - 5kHz (±3dB)
-6dBu/6k Ohms
-56dBu/2k Ohms
75dB (line), 60dB (mic)
483 x 235 x 44mm
LA-600 mkII (952.867UK)
T2A 250V
600m² max.
483 x 235 x 88mm
No power indicator when
switched on
Peak current indicators are
not showing any signal
Dead spots within
induction loop field
Loop field interfering with
other audio equipment
Siren activated
Peak indicators mainly
showing overload (red)
Loop current is very low
Poor quality audio from
the loop
Check mains is connected and switched on at the socket
Check that the mains fuse is not blown – refer to qualified service personnel
If the fuse is blown, check that the loop contacts were not shorted out
Check input connections are OK and that a signal is present on the input
Check that the loop is intact and connected to the amplifier properly
Increase channel level controls and Loop current if necessary
Check for large metal structures within the architecture close to the loop
Avoid changes in height of the loop cable (running over door frames etc.)
Ensure that the loop cable is twisted between the loop and the loop amplifier
If necessary, form a cancellation loop to avoid affecting other equipment
Ensure that the alarm contacts are not accidentally shorted out.
Loop current or input levels may be too high, decrease the relevant controls
Check that the loop is not shorted or grounded at any point
Increase input signal, channel levels and loop current controls as needed
If there are metal structures nearby, increase metal loss correction level
Use Bass and Treble controls to help improve intelligibility
Disposal: The “Crossed Wheelie Bin” symbol on the product means that the product is classed as Electrical or
Electronic equipment and should not be disposed with other household or commercial waste at the end of its useful life.
The goods must be disposed of according to your local council guidelines.
Errors and omissions excepted.
Copyright© 2016. AVSL Group Ltd.
952.864UK, 952.867UK User Manual
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