PDA Range VL1 User manual

VL1
12VMINI AUDIO-FREQUENCY
INDUCTIONLOOPAMPLIFIER
Approved document No. DCM0003479 Rev 1 • Page 1 of 8
The VL1 is a true current mode audio-frequency induction loop amplifier. Its compact
design, 12V d.c. operation and availability in a variety of kit formats make it ideally
suited for use in:-
• Cars, taxis, buses and other private/commercial vehicles (VL1/B1 or VL1/B2 kits)
• Ticket counters and other desktop applications (VL1/C kit)
• Access control applications (VL1/A kit)
In addition to this instruction manual, all of the above kits include Quick Start installation
guides specific to the application(s) for which they are intended. These guides should
always be referenced in conjunction with this manual prior to installation.
Important notes ................................................................................................................................... 2
Safety guidelines .................................................................................................................................. 2
What is an audio frequency induction loop system? ...................................................................... 3
An overview of the VL1 induction loop amplifier ........................................................................... 4
Planning an induction loop system .................................................................................................... 5
Installation, system set-up and testing ........................................................................................... 6/7
Troubleshooting ................................................................................................................................... 8
Technical specification ......................................................................................................................... 8

Approved document No. DCM0003479 Rev 1 • Page 2 of 8
IMPORTANT NOTES
This equipment must be installed by a suitably skilled and technically competent person.
These instructions are general and cannot be considered to cover every aspect of
audio-frequency induction loop system design and installation.
We recommend you also read BS7594 - The Code of Practice for Audio-Frequency
Induction Loop Systems and EN60118-4 - Magnetic field strength in audio frequency
induction loop systems for hearing aid purposes (or any subsequent revisions), both of
which are available from the British Standards Institute, 389 Chiswick High Road,
London W4 4AL. Tel: [phone]. Web: www.bsi-global.com.
Other National standards of design/installation/commissioning should be referenced
where pertinent.
SAFETY PRECAUTIONS
Avoid placing the VL1 amplifier in areas:-
• with poor ventilation • exposed to direct sunlight
• with high ambient temperatures • adjacent to heat generating equipment
• with high humidity or dust levels • susceptible to severe vibration
DO NOT dismantle or attempt to modify the amplifier in any way. No user-serviceable
fuses or parts are included inside the amplifier. For repair, consult your supplier.
Ensure the loop cable and all relevant audio/microphone and power lead(s) are fixed
securely into position before operation. Do not leave any trailing leads or obstructions.
The VL1 amplifier is capable of producing short-term peaks of twice its rated current.

Approved document No. DCM0003479 Rev 1 • Page 3 of 8
WHAT IS AN AUDIO-FREQUENCY INDUCTION LOOP SYSTEM?
An audio-frequency induction loop system allows hearing impaired
people to hear more clearly. Most hearing aids have a ‘T’ or ‘MT’ switch
which allows them to pick up the electromagnetic field generated by an
induction loop system. The hearing aid converts this signal into a sound
suited to its user’s specific hearing requirements. Any hearing impaired
person positioned within or near the loop can hear the loop signal by
switching their hearing aid to the correct position, allowing them to participate more
effectively in general conversation, ordering goods or services, etc.
An induction loop system therefore comprises four main elements:-
The audio source – typically a microphone or a music source (or both).
The induction loop amplifier
The loop – typically a single turn of wire run around the perimeter of the area
requiring coverage or, on smaller systems, a special pre-formed loop fixed to a flat
surface.
The receiver(s) – any behind-the-ear type hearing aid with a ‘T’ or ‘MT’ switch.

ABOUT THE VL1 INDUCTION LOOP AMPLIFIER
Below is a brief overview of the VL1’s connectors, controls, indicators and operation.
Two inputs are provided on the amplifier:-
MIC (microphone): a 3.5mm jack input supplied with 9V phantom power for use with
electret microphones. Dynamic microphones are NOT compatible with this input.
LINE: a 3.5mm jack input for the connection of an audio source such as a CD player.
The sensitivity of each input can be adjusted using the amplifier’s LINE LEVEL and MIC
LEVEL controls.
General operation:-
The amplifier mixes and amplifies the input signal(s) and feeds them through its
sophisticated automatic gain control (AGC) circuitry before outputting them to the
induction loop.
The induction loop connects to the amplifier via the two screw terminal connectors at
the terminal marked LOOP.
The strength of the magnetic field generated by the induction loop can be adjusted
using the amplifier’s DRIVE control.
In applications with high metal content (i.e. loops fitted in vehicles), the amplifier’s
metal compensation control (METAL COMP) can be used to help combat the frequency
response problems caused by metal ‘absorbing’ the magnetic field.
Three indicators are provided on the amplifier:-
The Peak indicator illuminates red in line with peaks in the input signal.
The Limit indicator confirms the AGC circuit is functioning. The rate at which it illumi-
nates will depend on the signal being fed into the amplifier. If the signal is speech
based, it will only light when someone is talking into the microphone. If the system is
used to amplify music, it will normally be lit more constantly.
The Power indicator illuminates green when the amplifier is powered up.
The amplifier operates at 12V dc. Dependent on the application and VL1 kit pur-
chased, this can be derived from a plugtop mains adaptor, a fused cigarette lighter
adaptor or a local 12V power source and connection lead, all of which connect to the
amplifier’s 2.5mm 12V DC socket.
Approved document No. DCM0003479 Rev 1 • Page 4 of 8
DRIVE
MET AL
COMP
LINE
LE VEL
LEVEL
MIC
LO OP
12V DC
P ower P eak Limit LINE MIC
P DA V L-1

PLANNING AN INDUCTION LOOP SYSTEM - HINTS & TIPS
Induction loop system design and installation can be simple provided that a few basic
facts are understood. To help avoid poor performance and the need to re-position the
amplifier or loop cable at a later stage, we strongly recommend you refer to the infor-
mation below and the example layout diagram(s) provided in our seperate kit specific
Quick Start installation guides.
Maximum area coverage
The approximate coverage provided by the VL1 amplifier using the TX2 pre-formed
loop (as supplied in all VL1 range kits) is 1.2m2to 1.5m2.
Loop cable position
The TX2 loop can be positioned either horizontally or vertically. In all instances, the
exact position of the loop will depend on the application and the area requiring cover-
age - refer to the Quick Start installation guide supplied with your VL1 kit for further
information.
Always run a trial loop and test to evaluate performance and coverage by listening to
the signal with either a hearing aid or a dedicated loop test receiver.When you are
happy with the quality and coverage of the loop field, the loop should be secured into
position using a fixing method appropriate to the application.
Overspill and ‘cross-talk’
The signal generated by the loop will radiate outside as well as inside the loop. If
there are any other loop systems in close proximity, overspill such as this may lead to
‘cross-talk’ (signals from different loops merging into one). If this is likely to be an
issue, special designs of loop can be implemented to help reduce the overspill field -
contact your supplier for details.
Applications with high metal content
Large amounts of metal can affect the strength of the loop field and result in a
“muffled” sound being generated. The VL1 includes a metal compensation control
that can help combat such problems - see page 7 for further details.
Mounting the amplifier
The amplifier is designed to be permanently mounted using the mounting holes pro-
vided and 2 x No. 8 japanned woodscrews. Fix the amplifier securely to the chosen
surface taking note of the Safety Precautions on page 2 of this manual. The stated
screws will be suitable for most applications. However, always assess the condition and
construction of the mounting surface prior to installation and use an alternative screw
fixing if necessary.
Microphone position
Position the AMT microphone (as supplied in VL1/C,VL1/B1 and VL1/B2 kits) as close as
possible to mouth height using the self-adhesive pad supplied. For optimum perform-
ance it should be located no nearer than 300mm and no further than 1.2m away from
the operator’s mouth. If an alternative microphone is used, it must be an ‘electret’ and
not a ‘dynamic’ microphone.
Approved document No. DCM0003479 Rev 1 • Page 5 of 8

7. With the audio input source(s) active, increase the appropriate Level
control(s) until the red Limit indicator is just flashing occasionally.
TIP: If you are using the microphone and line input at the same time,
adjust both level controls to achieve an acceptable balance.
8. Adjust the Drive control until the red Peak indicator just lights during
periods of high signal level (i.e. when the red limit indicator just lights).
Warning: If the system is set up so the Peak indicator is permanently lit,
the audio sound quality will be distorted and the amplifier may shutdown
to protect it against overheating.
9. Using an induction loop test receiver, listen to the loop signal in
all areas where coverage is required. If the signal level is not
acceptable, adjust the Drive control in small increments until it is.
Note that when testing the installation, you may hear a slight
‘humming’ noise in the background. This IS NOT a fault with the
induction loop system but a common occurrence caused by mains
wiring. This hum will normally NOT be heard by hearing aid users
as most modern hearing aids have filters which cancel this noise
out.
10. If a large amount of metal is present in or near the induction loop, you
may find the sound you hear through the loop listening device is ‘woolly’
or ‘dull’. This is caused by the metal in the room absorbing the magnetic
field at a rate that increases with frequency, i.e. high notes are absorbed
morethan low notes resulting in a ‘muffled’ sound. If this is a problem, try
turning the amplifier’s METAL COMP control clockwise in small increments
until a natural balance is achieved. Please note however that due to the metal absorb-
ing power from the amplifier,its area of coverage will be reduced and further reduced
as the METAL COMPENSATION control is turned clockwise.
11. For compliance with BS7594 (the code of practice for audio-frequency induction
loop systems), we recommend you test the system using our PDA RANGE FPROK1
induction loop test kit. Please contact your distributor for details.
Approved document No. DCM0003479 Rev 1• Page 7 of 8

TROUBLESHOOTING
If no sound is being picked up by the hearing aid or induction loop test receiver, first
check that the amplifier’s green Power indicator is lit.
If the Power indicator IS NOT lit:-
Check that the power lead is correctly plugged into the mains supply and the amplifier.
If the power indicator is still not lit, the power lead or the amplifier could be faulty.
Check the amplifier with another power lead. If the problem persists, return the
amplifier to your distributor/supplier for repair.
If the Power indicator IS lit:-
Check that the amplifier’s Limit indicator is lit and that an audio signal is active.
If the Limit indicator IS NOT lit, make sure all microphone and audio connection leads
are correctly plugged in and at least one audio source is active.
Adjust the amplifier’s Limit control until the Limit indicator just flickers.
If there is still no sound being picked up by the hearing aid or induction loop test
receiver, check that the loop cable is not broken or misconnected.
Tip: The loop strength meter WILL NOT illuminate if there is a break in the loop cable
or if it is misconnected.
TECHNICAL SPECIFICATION
Rated supply voltage and current: 12V DC
Rated power consumption: 500mA
Maximum RMS output current: 1A
Maximum peak output current: 2A
Maximum RMS load voltage: 4V
Total harmonic distortion: <0.5%
Max. area of a square loop, or of a rectangular loop of stated aspect ratio in m2: 25m2
Recommended loop conductor size:
0.5mm2@<15m loop length or 1.0mm2 @ >15m to <30m loop length (inc.tails)
Recommended number of turns: 1
Frequency response –1dB: 120Hz – 16kHz
Frequency response –3dB: 120Hz to 5kHz as per IEC 60118-4
Rated Input voltage: Mic: -60dB, Line: -27dB stereo unbalanced
Rated Input Impedance: Mic: 1k Ohm , Line: 100k Ohm
Signal to noise ratio, A weighted (reference maximum RMS current, maximum gain): -60dB
AGC range (3dB change in output current), reference rated input voltage: 10dB
Control and indicator labels and functions: Power LED, Limit LED, Peak LED, Mic Level
control, Line Level Control, Metal Compensation Control, Drive current control.
Special features: Compact, 12V DC Powered.
Connections: Power - 12VDC 1A, Loop Output - 2 Way Screw Terminal, Line - 3.5mm stereo
jack socket, Microphone - 3.5mm mono jack socket.
Fixings: 2x No.8 Japanned Woodscrew (supplied)
Dimensions (H x W x D): 31mm x 120mm x 60mm (Including controls)
Mass: 220 grams
© 2012. Errors and omissions excepted. The manufacturer of this equipment operates a
policy of continuous improvement and reserves the right to alter product specifications at its
discretion and without prior notice.
Approved document No. DCM0003479 Rev 1 • Page 8 of 8