| 摘要 |
An audio frequency amplifier particularly for an induction loop system (19) wherein the input to said amplifier, consisting of stages (17, 18), includes a variable cut-off low pass filter (13). This filter controls the bandwidth of the amplifier in response to the detection of conditions approaching overloading of the amplifier by high amplitude high frequency signal components in such a manner as to reduce the high frequency response of the amplifier during periods when said high amplitude high frequency signal components might otherwise overload the amplifier. The filter (13) is controlled by a signal derived from the output of the amplifier (18), and fed via overload sensor (21) and time constant (22). The arrangement avoids resultant distortion of the amplifier output signal and also avoids the generation of radio frequency interference signals in the induction loop (19) connected to the amplifier output. The amplifier may be a current-driving amplifier or a voltage-driving amplifier. |
