AUSTRALIAN MONITOR KLA User manual

Australian Monitor
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K snnlns LooP AMPLIFIERS
Introduction
Australian Monitor is proud to introduce to you its range of lnduction Loop amplifiers. Modelled on
the successful K-Series range, these amplifiers utilise our unique impedance and phase sensing
system to provide a constant cunent into a single turn lnduction Loop, resulting in clarity and
detail whilst maintaining total stability.
Hosting most of the features and protection networks of the K-series Audio Amplifiers the KLa
loop amplifiers offer some additional circuitry, controls and lndicators to assist in the conect set-
up of an lnduction loop system.
These include: lntemal limiter with 250mV threshold and front panel indication
10dB into compression indicator
lnput Level Control for adjusting input signal for the ideal operating window
Dual level output cunent indicators
Low frequency output current limiting (and indication)
, Loop disable relay at turn on
Loop open / voltage too high indication
Binding Post and Speakon loop connections
Active Balanced lnputs
Signal Ground "LlFT" switch.
Additional features include: Custom designed - heavy duty chassis, open modular
construction for ease of servicing, well regulating high current power supply, lnput signal
strapping connectors, massive heatsinking, Front to back cooling and a dual speed axial fan.
Protection features include: Mainrs inrush cunent suppression, lnput muting at tum on, lnput
over-voltage protection, RF interference suppression, Short-circuit protection, Mains Circuit
Breaker, lndependent DC supply rail Fuses.
The layout, grounding, decoupling and componentry have been optimised to provide the user with
stability, reliability and longevity.
ltu Austdlan Monitor

KLa Loop Amplifiers 2
Front Panel Controls and Indicators
Your KLa loop amplifier is furnished with simple controls and indicators to assist in the set up of
the amplifier for driving a properly calculated lnduction Loop. The indicators provide visual detail
to show the proper operating levels of input signals and output current.
1 Input Level Control.
A "lnput Level" attenuation control is provided so as to adjust your incoming signal to a level
suitable for processing by the internal limiter. The circuit is based on a fixed gain and thus the
lnput Level Control provides attenuation only. The input of the unit can deal with Gain Levelled
lnput Signals between -10 and +10d8 but OdB (.775v) is preferable.
2 Operating Window Indicator.
This Bi-Colour LED indicates signal level to the unit's limiter circuitry.
Green indicates the threshold of the limiter and is factory preset for 250mV (-10dB). Any
applied signal should be illuminating this LED with the lnput Level control in the appropriate
position.
Red indicates that the signal is 10dB or more into compression. This led should not be
illuminated all the time but should flash with programme peaks. ldeal signal level will cause a
continuous toggle between the LED illuminating green and red.
3 Output Voltage Clip Indicator.
This LED is provided and will illuminate amber when the output voltage of the amplifier is
driven into clipping. ldeally this LED should never illuminate and implies that the output level is
too high, that the loop has gone open circuit and/or the loop impedance is too high.
4 Output Drive Control.
The "Output Drive" level control dictates current drive to the loop. lts position will be dictated by
the peak current level required to properly drive the loop as indicated by the chart on page 8.
/tu Australlan Monitor

KLa Loop Amplifier.s 3
5 Current Level Indicator.
The "Cunent Level" LED is provided as indication to show the peak cunent in the loop.
KLa I - Green = 3Amps, Red =6Amps.
KLa2 - Green = 5 Amps, Red = 10 Amps
see chart for loop calculations.
6 Fault / Current Limit Indicator.
This amber coloured LED will illuminate when load cunent exceeds a safe value. The led
indicates limiting of the cunent into the load and will flash with programme peaks. The
infrequent flashing of this LED on peaks at lower frequencies is quite acceptable. Constant
illuminating of this LED requires the output drive to be reduced.
The LED will also illuminate with other faults such as blown negative rail fuse and short circuits
on the output.
7 On lThermal Indicator
This is a Bi-Colour LED which will normally illuminate green and indicates that the amplifier is
on and receiving mains power.
ln the advent of a Thermal Overload this LED will tum red indicating that the intemal operating
temperature of the amplifier has exceeded a safe level of operation and that the amplifier has
shut down and isolated itself from the loop. The fan will continue to run and once the amplifier
has had a cool down period the unit will restart automatically providing inrush current
suppression, input muting and the loop relay isolation will be bypassed.
8 Power Switch
Press the switch down for ON and up for OFF. Like any other power amplifier in any system it
should be the last piece of equipment you tum on and the first piece of equipment you tum
ofr.
At tum-on a number of events happen during the power-up of the amplifier.
a) Mains inrush cunent suppression is provided,
b) A relay isolates the lnduction Loop until the amplifier has established itself,
c) lnput signal to the main amplifier is muted (>30d8) for approx'2 to 3 seconds.
/tu Aushalian lYonitor

KLa Loop Amplifters 4
Rear Panel
I Balanced Input & Strapping Connection
A female 3-pin XLR connector is provided as input connection. A male XLR connector is
provided as a strapping connector wired in parallel with the input XLR allowing
strapping/looping between multiple amplifiers.
Pin allocation is: Pin-l = Signal Ground, Pin-2 = Cold (reverse phase), Pin-3 = Hot (in phase).
2 Signal Ground Lift Switch
When this switch is engaged it disconnects signal ground from the amplifier. lt is intended to
be used when "HUM" is caused by earth loops or stray magnetic fields.
The amplifier should be tumed off before engaging this switch.
Loop Outputs.
Your Kla Loop Amplifier is provided with 2 options for output termination of the loop. Heavy
cunent Binding Post outputs are provided as well as a Neutrik "Speakon" connector.
The Speakon connector is wired 1+ = positive & 1- = negative.
Mains Lead
Your amplifier is supplied with a heavy duty mains lead (power cord) appropriately rated for the
mains supply voltage marked on the rear panel of your amplifier. The wires in the mains lead
are coloured in accordance with the following code.
Brown = Active, Blue = Neutral, Green/yellow = Earth.
Your unit must always be earthed!
Mains Circuit Breaker
A "push to reset" thermal circuit breaker is supplied to provide overall protection of
amplifiers power supply. lt will isolate the "active" mains conductor in the event of a
current internal fault or in continued overload conditions,
D.C. Rail Fuses
3AG "fast bloy/' type fuses are provided and are in series with the positive and negative supply
rails for your amplifiers output stage. These fuses provide overall protection of the output
stage.
The fuses must be replaced with the same type fuse.
KLal = 8 Amps, l(La2 ='10 Amps.
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KLa Lpop Amplifiers 5
To set up your KLa Loop Amplifier:
Once all connections have been made:
I Make sure all the controls are down before you tum the amplifier ON.
2 npply signal (applied signal should be gain levelled and be around odB - 0.775 volts )
3 Turn up'INPUT LEVEL'knob until 'OPERATING WINDOW" LED is flashing between green
and red illuminations.
NOTE: The red LED should not be on constantly, but should flash with programme peaks.
4 Tum up 'OUTPUT DRIVE" control to the desired cunent level.
KLa 1 Green = 3Amps, Red = 6 Amps.
KLa2 Green = 5 Amps, Red = 10 Amps.
NOTE: These LEDS are to illuminate on peaks only.
5 Use a field strength meter or loop listening device to monitor level and coverage in the loop.
The do's and don'ts
There are a few precautions you need to consider when installing your lnduction Loop System.
As there is a strong field radiating from the cable it can interfere with other electronic equipment
thus your loop should be restricted (as far as possible) to a defined listening area.
Do:
Always ensure the installation of your Loop is in accordance with wiring regulations.
As far as possible have your loop at the same elevation as the listening position, 1 to 2 metres
above or below this is acceptable but more cunent drive may be required.
Run balanced signals / cables wherever possible.
Do Not:
Do not install the loop with other cable runs - never run the loop cable in parallel with other cables
- and always cross other cables at right angles.
Do not run your Loop cable in conduit or in / or near shielded trays as this may effect its
performance.
I
Do not have dynamic type microphones, which may be a part of the signal source, inside or near
- the loop. The coil may pick up the radiated field from the loop and cause feedback to occur in
the system.
' Do not run unbalanced signals / cables as they may be affected by the Loop and cause
feedback.
/tu Ausbdan Monitor

KLa Loop Amplifiers 6
Why An Induction Loop system.
Usually, an lnduction Loop system is installed as an aid to provide audio for the hearing impaired.
The system is driven by an amplifier which can provide a constant cunent into a wire loop
encompassing the listening area. A field is radiated from the cunent flowing in the loop, and this
radiated field induces cunent to flow (more often than not) in a "T-Coil" in the hearing aid device
of the hearing impaired.
Because a length of wire is used as the load from which the signal is radiated, it makes special
demands on the amplifier driving it.
The wire will exhibit a very low impedance at low frequencies and exhibit a higher impedance as
the frequency rises. To maintain a constant radiation from the piece of wire (through the audio
bandwidth) you must maintain a constant cunent into the load. Normally encountered amplifiers
are a constant voltage type and will not drive an lnduction Loop System properly as their voltage
output is constant (regardless of load variations) and fidelity will be lost in the system as radiation
will reduce as the frequency rises.
The graphs below show the transfer characteristic of a Klal into 50 metres of 2.00 mm2 cable.
This Loop exhibits an impedance of 0.5 ohm at 200H2 and an impedance of 4 ohms at lokHz.
Power into the loop @ 2O0Hz = 12.5 VA but @ 10kHz the power = 1O0 VA. A constant voltage
type amplifier diving the same loop at 5 amps @ 200H2 would be down 1$dB @ 10kHz.
Also the amplifier is driving a virtual short circuit for the lower frequency spectrum and thus would
invoke protection circuitry to continuously operate in constant voltage type amplifiers.
Two traces are shown above. The KLa Loop Amplifiers have an internal adjustment (RV-1)
which allows for the higher frequency response to be extended. The upper trace on the graphs
show a fully- compensated high frequency response. This adjustment would normally be left at the
factory pres'et (no compensation), but could become useful in circumstances where the loop was
not properly calculated.
The hearing impaired can detect more detail in the programme if dynamic range is reduced. For
this reason lnduction Loop Systems should be fed with gain levelled signal. The KLa amplifiers
have a built in limiter to further reduce transients in the applied programme source.
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OutDut Voltase Vs Freouencv Current OutDut Vs Freouencv
The above graph (lowest trace) shows the output
voltage variation of e KLal required to maintein e
constant current of 5 amDs into the lnduction LooD.
The above graph (lowest trace) shows the
Frequency Response relative to cunent output of the
KLal. odB reference = 5amps @ 200H2.
/tu Ausbalian Monitor

KLa Loop Amplifiers 7
Calculating the Induction Loop.
The following information is provided as a guide for the proper calculation of your lnductive Loop
installation. You will need to know the size of your loop to ascertain the peak drive cunent
reguired and to select the appropriate gauge of the wire for the loop.
LOOP
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H|GH cuRRENr TERMTNA-floN ",o"" I
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OUTPUT TFRMINAI S : LENGT H
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PARALLELING LINKS
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First we need to calculate the Peak cunent required in the loop. The lnduction Loop Peak Cunent
Chart (page 8) shows the relative cunent required for different size loops - Pick the closest
cunent (Ampere) curve. lf your loop is a circle, simply approximate it to a square.
Then we need to determine the length of cable required (length + breadth) x 2. this will give us
the perimeter of the loop. To this add the loop feed distance, for a total wire length.
Now we need to calculate the gauge of the wire. lt is recommended that the total D.C. resistance
of the loop is between 0.5ohm and 1.0 ohm. We also recommend that you ensure the cunent
rating of the cable is well above the peak cunent required into the loop (>2 times) and that the
insulation is of a heavy duty type with a good dielectric strength and high thermal capacity.
To help reduce the variation in wire gauges needed to satisfy every loop we suggest running a
heavy duty figure-8 cable with a termination block (as shown in the above diagram) which will
allow you to parallel the conductors if the resistance of the loop is too high.
Stranded copper conductors to 836360 - 1991
For example: A loop that is 15 metres by 40 metres requires a peak cunent of 8 amps. lts
perimeter = 110 metres and the loop feed is 10 metres long, thus 120 metres of cable is required.
To achieve a D.C. resistance of between 0.5 and 1.0 ohms we would need to use 12 AWG wire
which will give us 0.72 ohms total D.C. resistance and a cunent rating 2.5 times the peak cunent
required (20 amps). Paralleling 16 AWG wire would give us a similar result @ 0.756 ohms for 18
amps.
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