16 English
6. Adjusting the amplifier
In order to adjust a LOS system, you will require a field strength gauge, e.g. the FSM (A-4291-0).
1. Before you switch on the amplifier, turn all the dials as far to the left as possible. Please note that the amplifier
does not have an ON/OFF button and is switched ON as soon as it is plugged into the wall outlet.
2. Plug in the power cord supplied with the amplifier. The power supply indicator (1) should now light up.
3. Before you adjust the line level, don’t forget to apply a test signal to the corresponding input. We recommend
using our test CD, which comes with the FSM (A-4291).
Use a 1KHz sine signal (track 3 on the CD) and set the volume control (master fader) on the mixing desk or
the audio amplifier as it is normally used at your events.
4. Adjust the input sensitivity regulator (3) of the LINE IN input used so that the control indicator (2) on the front
panel of the device lights up constantly.
5. Turn the master power regulator (8) to the central setting. The control indicator (11) on the front panel should
now light up.
6. Set the FSM to “Norm” and “0dB scale” and hold it vertically to the induction loop level. The ideal height de-
pends on what the induction loop system is being used for; typically, this might be 1.20m (for seated audien-
ces) or 1.70m (for standing audiences).
7. Check the average field strength by running diagonally over the induction loop area and determine the aver-
age of the values indicated. The average value has to measure -12dB (±3dB).
If you do not obtain this value, adjust the corresponding control until this value is reached. Please note that
every time you cross a cable, the field strength will drop briefly. This is normal as long as only one loop is in
operation.
8. Once the master loop is adjusted, unplug the amplifier from the power supply and disconnect the master loop.
Important: Do not alter any of the controls mentioned in the above.
9. Plug the amplifier back into the power supply and repeat Steps 5 to 7 for the slave loop or the slave loop cur-
rent regulator (4).
10. Once the slave loop is adjusted, reconnect the master loop.
11. For the final check, use a normal audio signal, such as music or voice via the microphone and check the field
strength with the FSM. The value should read 0dB (±3dB) in the signal peaks.
If you do not read these values, repeat the measurement process starting from Step 3 and set both controls
higher than for the first test.
12. If the values lie within the stipulated range, the amplifier is set to the ideal levels. Use the headphone jack of
the FSM to evaluate the sound of the signal with a pair of headphones.
