| 摘要 |
PROBLEM TO BE SOLVED: To prevent the distortion of an internal power amplifier and to eliminate an unfavorable effect such as distortion on a signal outputted from a pre-out terminal, by providing an amplification varying circuit which reduces the amplification level of a preamplifier at the time of detecting an output that is a prescribed level or more. SOLUTION: An input signal is amplified by a preamplifier 2 and the signal which is further amplified by a voltage amplifier circuit 5 of a power amplifier 4 is inputted to the built-in power amplifier 4. When an input signal of a level that is higher than a fixed level is inputted, it exceeds a power amplifiable signal level in the circuit 5 and exceeds the voltage of power supply voltage±B of the amplifier 4, distortion occurs and noise gets mixed with an output signal of an output terminal 7 because it is amplified by both the preamplifier 2 and the circuit 5. Therefore, an output signal is outputted as a control signal from a comparator 10 which compares a signal attenuated by an attenuator(ATT) 9 with a signal inputted to the amplifier 4, an amplification control circuit provided in the preamplifier 2 is controlled and the amplification is reduced.
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