Hearing aid automatic gain control system

Claim 1

A HEARING AID COMPRISING: A TRANSISTORIZED AMPLIFYING SYSTEM HAVING A RELATIVELY LOW OUTPUT IMPEDANCE FOR DEVELOPING, IN RESPONSE TO RECEIVED OCOUSTIC ENERGY OF VARYING LOUDNESS, AN AMPLIFIER AUDIO SIGNAL REPRESENTATIVE OF SAID ACOUSTIC ENERGY AND INCLUDING AT LEAST ONE TRANSISTOR HAVING A COLLECTOR, A BASE AND AN EMITTER AND HAVING A BASEEMITTER CONDUCTION PATH OF RELATIVELY LOW IMPEDANCE; VOLTAGE DEVELOPING MEANS COUPLING TO THE OUTPUT OF SAID TRANSISTORIZED AMPLIFIER SYSTEM AND CONSISTING ONLY OF PASSIVE CIRCUIT COMPONENTS FOR DEVELOPING FROM SAID AMPLIFIER AUDIO SIGNAL AN AUTOMATIC GAIN CONTROL VOLTAGE HAVING A MAGNITUDE DETRMINED BY THE INSTANTANEOUS LOUDNESS OF SAID INCOMING RECEIVED ACOUSTIC ENERGY; MEANS FOR APPLYING SAID AUTOMATIC GAIN CONTROL VOLTAGE AS A VARIABLE BIAS TO SAID BASE-EMITTER CONDUCTION PATH OF SAID TRANSISTOR TO VARY THE INPUT IMPEDANCE THEREOF THEREBY TO VARY THE GAIN OF SAID IMPLIFYING SYSTEM IN A DIRECTION TENDING TO MAINTAIN THE OUTPUT OF SAID SYSTEM AT A CONSTANT AMPLITUDE IN SPITE OF VARIATIONS IN LOUDNESS OF SAID RECEIVED ACOUSTIC ENERGY; A FIRST RESISTIVE-CAPACITIVE NETWORK AT LEAST PARTIALLY INCLUDED IN SAID VOLTAGE DEVELOPING MEANS, AND INCLUDING A PLURALITY OF RESISTIVE AND CAPACITIVE COMPONENTS, FOR ESTABLISHING AN ATTACK TIME OF PREDETERMINED DURATION; AND A SECOND RESISTIVE-CAPACITIVE NETWORK AT LEAST PARTIALLY INCLUDED IN SAID VOLTAGE DEVELOPING MEANS, INCLUDING RESISTIVE AND CAPACITIVE COMPONENTS IN COMMON WITH SAID FIRST NETWORK AND ALSO INCLUDING SAID BASE-EMITTER CONDUCTION PATH OF SAID TRANSISTOR, FOR ESTABLISHING A RECOVERY TIME OF A CERTAIN DURATION, EXCEEDING SAID PREDETERMINED DURATION OF SAID ATTACK TIME.