Northern Airborne Technology PA700 - Manual (Page 28)

PA700 Series High Power Voice Amplifier
SM44 Installation and Operation Manual
Section 3 Rev: 1.00 Issue 4 Page 3-2
ENG-FORM: 806-0112.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
3.3.2 GAIN Control
The GAIN control is a rotary switch used to adjust the gain of the unit. For specific operating information,
see sections 3.3.2.1 and 3.3.2.2 below.
3.3.2.1 Operation with Microphone
For microphone operation the ‘GAIN’ control is adjusted clockwise from OFF. If feedback is a problem it
may be necessary to reduce the input ‘Gain’ control or preferably, improve the sound shielding of the
microphone position.
Loudspeakers will overheat with a continuous signal at full power. Voice operation will generate less heat,
and pauses between words result in a low-duty cycle.
3.3.2.2 Operation with Recorder
When a recorder or other external sound source is to be operated with the amplifier, connection is made
to the recorder (REC) input connector.
The ‘GAIN’ control is rotated counterclockwise from the OFF position to increase the recorder input
signal. Pins B - C will be used for a 600 Ohm source and Pins A - C will be used for a 2000 Ohm source
as shown on the amplifier panel.
If the recorded sound is voice, the correct input level is adjusted in the same manner as for microphone
operation. If the recorded sound is music, it is advisable to operate at a reduced ‘GAIN’ control setting. If
the input signal is siren or trill, the GAIN should be set for maximum volume and the level meter will read
continuously in the red area.
Failure to reduce the gain setting may cause excessive power to be dissipated in the speaker units and
result in failure of the speaker voice coils due to overheating.
Fade operation can easily be performed between microphone and recorder inputs by adjusting the ‘GAIN’
control setting. This operation permits a smooth transition from voice input to tape/playback input and
back again.
CAUTION:
With siren or trill signals, limit full power operation to periods of 15 seconds
ON/OFF to prevent damage to speakers.
3.3.3 Push-to-Test Lamps
These lamps are separately connected to either Section A or Section B of the power amplifier, to provide
independent indications of the status of the separate sections. The lamps should illuminate red when the
POWER switch is selected ON, the voltage and polarity of input power is correct and no protective circuit
has tripped. When pressed with the POWER switch off, the ‘Push-to-Test’ lamps will illuminate to indicate
the presence of DC power at the input power receptacles. Fluctuations in the intensity of either lamp
during operation indicates a high impedance power source or a depleted battery in the relevant section of
the unit.