если верить блоксхеме и описанию:
The AM and the TAPE inputs are buffered with an
operational amplifier to ensure a high-impedance input
which enables the use of an external resistor divider for
signal reduction. For correct biasing of the first operational
amplifier a resistor must be connected between the input
and pin VREFAD, which acts as a virtual ground (see
Fig.21). The analog input switching circuit is shown in
Fig.3. The input for an analog CD player is explained in
more detail in Section 8.2.3.
если я правильно понял, сигнал надо гасить на землю операционного усилителя. но я не радиоинженер и не знаток английского))))
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