Voice amplifying circuit for telephone set - has lockable key setting gain to max. to avoid feedback in noisy rooms

摘要

The voice-amplifying circuit has a microphone and a loudspeaker and a coupler connected to the microphone the amplifier and the voice line. A key (T) disconnects the microphone (M) and sets the gain of the amplifier (V) to a given max. simultaneously. The key has a locking mechanism. The advantage lies in the circuit's producing intelligible signals even in noisy rooms and in avoiding whistles since in a noisy environment the user frequently turns up the gain to a level that results in feedback.