The tone control circuit for the higher audio frequencies is connected to the l.f. amplifier input. It contains a capacitor in series with a resistor connected to the reference potential. The amplifier (5) has a negative feed-back circuit (R1, R2). The tone control circuit (15) resistor (R3) is a part of a positive feed-back voltage divider (R3, R4). The reciprocal of the voltage divider division ratio is about equal to the gain of amplifier (5) with negative feed-back. The other end of the voltage divider is connected to the wiper (17) of a potentiometer (18) between the amplifier's output (11) and reference potential.
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