Ray 240 Active Speaker Circuit Description - Raymarine RAY 240 Manual

RAY 240 Active Speaker Circuit Description

The RAY240 Active speaker amplifies the audio signal from the RAY240 base unit to the handsets to
allow operators to listen to incoming traffic without the need to listen to the handset. A volume
control is accessible from the front of the unit to adjust the volume of the speaker from off to a
maximum of 5W output power. Additionally, two extra control lines are controlled by the RAY240
base station. One control allows the output of the speaker to be muted, whilst still allowing the audio
signal to be routed on to the handset. This is especially useful when intercom mode is selected to
prevent 'howl-round' of the audio signals in this full-duplex mode. The second control overrides the
volume control setting, even when the unit is switched to the off position, to output an alarm sound
when DSC distress calls are received on the RAY240 radio. The unit will produce an alarm output in
excess of 80 dB spl at 1m. Turning the volume fully anti-clockwise will set the unit into standby
mode, and current consumption of the unit is then less than 10mA.
Power Supply
Power is supplied to the active speaker from the main radio via an extension lead and waterproof
connector. There is no provision for reverse supply protection, as this is impossible if the connectors
are fitted correctly. Provision for reverse polarity protection is provided inside the main radio. As
such, the polarity of the voltage to the active speaker should always be correct.
The power supply can range from 9V to 25V, accounting for the wide range of voltages that can be
obtained from a discharged, or fully charged nominal 12V lead-acid battery, up to inadvertently
connecting the unit to a 24V system.
The amplifier used in the Active Speaker is thermally protected from overload and output short
circuit protected for supply voltages up to 18V. The amplifier can tolerate supplies up to 25V, but at
supply voltages above 18V it should be ensured that the audio to the input of the amplifier is off to
ensure that damaging current do not circulate in the output stages of the amplifier.
A COMS 4066 analogue switch is incorporated in the amplifier. Its supply is zener limited to 15V to
ensure it will not be damaged when the amplifier supply exceeds 18V All the other devices in the
amplifier are tolerant to 25V.
The amplifier is capable of pulling peak currents of 2A from the supply. With an 830mV rms 1kHz
sine wave applied to the input of the active speaker, the current consumption of the unit should be
just less than 1A. Current consumption in standby mode is less than 10mA.
Audio Amplifier
The amplifier is a Philips 8943SF single channel bridge tied load audio amplifier with an output
power of 6W into an 8ohm load with a 12V supply. The outputs are protected by an internal thermal
shutdown protection mechanism and short circuit protection. A mode selection pin allows the
amplifier to enter 3 separate states by applying the proper DC voltage to it. These three modes are:
Standby, Mute and Operating.
In STANDBY mode the current consumption is very low and the outputs are floating. The device is
in standby mode when the mode pin of the amplifier is between (VCC   0 .5 V) and VCC. The power
consumption of theTDA8943SF will be reduced to <0.18 mW.
In the MUTE mode the amplifier is internally powered but the audio output circuits are disabled. The
DC level of the input and output pins remain on half the supply voltage. The device is in mute mode
when the mode pin is at a voltage greater than 3V and less than (VCC   1 .5 V).
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