AUTOMATIC GAIN CONTROL CIRCUIT OF MAGNETIC RECORDING AND REPRODUCING DEVICE

摘要

PURPOSE:To decrease greatly the amplitude change of a video signal produced in a switching mode and to eliminate the generation of buzz noises, by supplying the output of an automatic gain control wave detecting circuit in a recording mode and then a signal of a fixed level of voltage in a reproducing mode respectively. CONSTITUTION:In a recording mode the output 20 of an AGC wave detecting circuit 19 is selected by a switch circuit 28 and supplied to an AGC amplifying circuit 2 in a conventional way to ensure a normal AGC action. While in a reproducing mode a reference voltage source 29 is selected by the circuit 28 and supplied to the circuit 2. The voltage of the source 29 is set at about the mean value of the voltage delivered from the circuit 19 in a recording mode. Therefore the change of the AGC control voltage is reduced greatly compared with the conventional level despite a switch from a reproducing mode to a recording mode. As a result, the amplitude change is also reduced during a switch mode for the video signal to be supplied to an RF converter 23.