ET120 & ET60 Installation & Maintenance Manual
Speaker Line Input
The Speaker Line input is presented on a two-way two-part screw terminal connection, and is designed
to accept speaker audio directly. The speaker line input can accept signals from 20dBV (30W 8
Ω
speaker connection) to 40dB (standard 100V line input).
For most purposes the amplifier can be considered as a speaker and wired as such.
Loop Connection
The area covered by the ET60 & ET120 can be determined from the chart below, if the area to be
covered (ET120 light grey, ET60 dark grey) has a high quantity of metal or the loop is placed at a higher
level than 2.4M then a larger current will be required (approximately 20% additional current per metre in
height)
2
10
20
30
40
50
60
70
4
6
8
10
12
Loop Length (metres)
Valid Area Coverage for A Floor
Floor Loop or Ceiling Loop (2.4 metres height)
Lo
op W
idt
h (
m
et
re
s)
The amplifiers are designed to drive a single turn loop around the perimeter of the area to be covered,
the loop cable should be chosen from the table below, the maximum impedance of the loop cable
should be 3
Ω
when measured using an impedance or LCR meter at 1KHz.
Maximum length (m) Vs Cable Size (mm
2
)
Amplifier
1
1.5
2.5
4.0
ETCF
*
ET60
70 80 90 100 90
ET120
90 105 120 140 140
*ETCF copper foil tape is equivalent to 1.8mm
2
cable but has a lower inductance per metre
Commissioning
Before powering up the amplifier, check all mains wiring and signal wiring, and turn all four controls fully
anticlockwise.
Initial setting
An audio signal should be sent to the loop amplifier, either by placing a speaker and sound source of
65dBA near the microphones or by playing calibrated pink noise through the system.
Using a screwdriver adjust the input level for the audio source until the limit LED blinks, repeat the
above for each input.
The peak current required for a room with the cable at floor can be obtained from the formula:
Ι
=4*A/9
Where
I
= peak current required and A is the length of the shortest side of the loop.
Using a screwdriver adjust the drive control on the loop amplifier until the LED representing the value of
I
lights. (This gives a good first approximation for the required current).
Document DCC ET12 7001-03 Rev 1 Aug 2005
Page 7 of 8
