Automatic gain control for magnetic sound recorders

Claim 1

IN A MAGNETIC SOUND RECORDER HAVING MULTISTAGE INPUT SIGNAL AMPLIFIER MEANS FEEDING A RECORDING HEAD, AN AUTOMATIC GAIN CONTROL ARRANGEMENT COMPRISING, IN COMBINATION, SAMPLING MEANS FOR DERIVING FROM THE OUTPUT OF SAID MULTISTAGE AMPLIFIER MEANS A VARIABLE VOLTAGE PROPORTIONAL TO THE AMPLITUDE OF THE CURRENT PASSING FROM SAID AMPLIFIER MEANS TO SAID RECORDING HEAD; COMPARATOR MEANS FOR COMPARING SAID VARIABLE VOLTAGE WITH A SUBSTANTIALLY CONSTANT PREDETERMINED REFERENCE VOLTAGE AND FOR FURNISHING A CONTROL VOLTAGE DEPENDING UPON ANY EXISTING VOLTAGE DIFFERENCE BETWEEN SAID VARIABLE VOLTAGE AND SAID REFERENCE VOLTAGE; AND RETROACTIVE REGULATING MEANS CONTROLLED BY SAID CONTROL VOLTAGE AND TENDING TO REDUCE SAID VOLTAGE DIFFERENCE TO ZERO BY REGULATING THE GAIN OF THAT PORTION OF SAID MULTISTAGE AMPLIFIER MEANS WHICH CARRIES OUT AN PARTIAL AMPLIFICATION OF THE INPUT SIGNAL, SAID REGULATING MEANS INCLUDING CAPACITIVE DELAY MEANS FOR EXTENDING THE REGULATING ACTION THEREOF OVER A PREDETERMINED PERIOD OF TIME AFTER SAID CONTROL VOLTAGE HAS ASSUMED A PREDETERMINED VALUE, SAID DELAY MEANS INCLUDING RESISTOR AND CAPACITOR MEANS DETERMINING A CHARGING TIME CONSTANT BELOW 200 MSEC. AND A DISCHARGE TIME CONSTANT OF AT LEAST 150 SEC., AND AUXILIARY MEANS FOR TEMPORARILY CHANGING SAID DISCHARGE TIME CONSTANT TO AT LEAST 20 SEC. AND NOT EXCEEDING 50 SEC., SAID AUXLIARY MEANS INCLUDING SECOND RESISTOR MEANS AND AUXILIARY SWITCH MEANS FOR PLACING SAID SECOND RESISTOR MEANS IN CIRCUIT WITH SAID CAPACITOR MEANS WHENEVER DESIRED.