Automatic sound level control for telephone loudspeaker - attenuates signals during pauses and adjusts amplification according to voice level

摘要

The system provides automatic regulation of the sound level produced by the loudspeaker in a telephone system. The amplification is controlled by the voice. The microphone (M1) and receiver (HK) are conventional. There is a microphone amplifier (MF) and receiver preamplifier (FF). These are normally connected via a differential transformer (GA). In parallel with the receiver (HK) is connected a loudspeaker circuit with an attenuator (AT) and a power amplifier (KF) delivering power to a loudspeaker (HO). The attenuator is controlled by the regulator (STY). During pauses in the course of conversation the attenuator ensures maximum attenuation of the signal to prevent self oscillation of the system. When the caller speaks, a control signal is sent via the conductor (T), the regulator and via conductor (S) to establish the required level of amplification. The system avoids self oscillation, and the cutting up of the first words.