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Audio Amplifier
Figure 39
The Audio Amplifier is located On the SSM. The output power for the Audio Amplifier is 10 watts per
channel for the Basic and Basic Plus versions. The Core Version has an output of 15 watts per
channel. IC 7700 is the Audio output IC. This is a class D amplifier. Left and Right Audio from the
SSB is fed to Pins 10 and 18 of the IC. The output stages are basically a switch mode supply, which
is driven by a 200 KHz oscillator. The Right Channel pulse width signal is output on Pin 3. The output
is filtered by 5701, 2777, 2776, 2717, 5716, and 2737. The amplified audio is output on connection
1349. In the same manner, Left audio is output on Pin 23. The IC is powered by +19 and -19 volt
supplies. The supplies are protected by fuses 1700 and 1701. The Supply voltage for the Core
version is 4 volts higher than the Basic and Basic plus version. The extra supply voltage is needed to
produce the additional 5 watts per channel output.
Muting and volume control for the audio takes place in the Audio Signal processor on the SSB. The
STBY MUTE line on Pin 6 goes to 2.5 volts to mute the audio when the set is turned On or Off. This
line goes Low to place the amplifier in a Standby mode if a DC voltage is detected on the Audio
Output lines.
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