Automatic level controller

Claim 2

An automatic level controller comprising: an audio terminal; an audio output terminal; a power source; an audio amplifying circuit connected between said audio input and output terminals for amplifying an audio signal applied to said audio input terminal and applying an amplified audio output signal to said audio output terminal; an audio level control circuit connected to the input terminal and adapted to be turned on and off by an audio level control signal applied thereto for controlling the audio level of the audio input signal applied to said audio amplifying circuit by bypassing to the ground a portion of said audio input signal; a switching circuit connected to said power source and operatively supplied with the output signal of said audio amplifying circuit and adapted to be turned on and off depending on whether or not the level of the audio output signal of said audio amplifying circuit exceeds a predetermined level, said switching circuit delivering one of two constant outputs having different potential levels from each other depending on the on state and off state; and a time constant circuit for setting the attack period and release period of control by said audio level control circuit in response to the application of the constant potential output from said switching circuit, wherein one of said constant potential outputs of said switching circuit applied through said time constant circuit to said audio level control circuit is so selected to cause said audio level control circuit to be turned on when the level of said audio output signal of said audio amplifying circuit exceeds said predetermined level.

Claim 3

An automatic level controller as claimed in claim 1, wherein said switching circuit comprises: a switching element operatively turned on and off respectively when the level of said audio output signal of said audio amplifying circuit does not exceed and exceeds said predetermined level, said switching element being connected in series with said power source for producing said constant potential outputs thereacross depending on the on state and the off state; and means for applying to said time constant circuit said constant potential outputs appearing across said switching element.

Claim 4

An automatic level controller as claimed in claim 2, wherein said constant potential output applying means comprises a diode having an anode and a cathode, said time constant circuit being connected across said switching element through said diode, and said diode being turned off and on in response to the turn-on and turn-off of said switching element, respectively, so that current from said power source can be supplied as said audio level control signal to said audio level control circuit when said diode is turned on.

Claim 5

An automatic level controller as claimed in claim 2, wherein said switching circuit comprises: a switching transistor acting as said switching element; a first resistor; and a second resistor, the input electrode of said switching transistor being connected through said first resistor and an output circuit of the audio amplifying circuit to said power source, while the output electrodes of said switching transistor are connected across said power source through said second resistor.

Claim 6

An automatic level controller as claimed in claim 2, wherein said diode is connected in the forward direction between said switching circuit and said time constant circuit, and is biased by said first and second resistors in such a manner that it is turned off and on when said switching transistor is turned on and off, respectively.

Claim 7

An automatic level controller as claimed in claim 4, wherein a second diode is connected in the forward direction in series with said current limiting first resistor between the input electrode of said switching transistor and the output circuit of said audio amplifying circuit.

Claim 8

An automatic level controller as claimed in claim 4, wherein a third resistor is connected across the base and emitter of said switching transistor.

Claim 9

An automatic level controller comprising: an audio input terminal; an audio output terminal; a power source; an audio amplifying circuit connected between said audio input and output terminals for amplifying an audio signal supplied to said audio input terminal and providing an amplified audio signal to said audio output terminal; an audio level control transistor having one input electrode and two output electrodes and connected at said output electrodes between the ground and the input terminal for controlling the audio level of the audio input signal applied to said audio amplifying circuit by bypassing to the ground a portion of said audio input signal; a protective resistor; a current limiting resistor; a time constant circuit; a switching transistor having one input electrode and two output electrodes and connected at said input electrode through said current limiting resistor and an output circuit of said audio amplifying circuit to said power source, and at one of said output electrodes to said power source through said protective resistor and grounded at the other one of said output electrodes, said switching transistor being switched over from one state to the other when the level of the audio output signal of said audio amplifying circuit exceeds a predetermined level; and a switching diode having two electrodes and connected at one electrode thereof to said power source through said protective resistor and at the other electrode thereof to said input electrode of said audio level control transistor through said time constant circuit, said switching diode being switched over from one state to the other in response to the switching of said switching transistor as a result of the detection of the audio output level thereby supplying current from said power source as an audio level control signal to said input electrode of said audio level control transistor.

Claim 10

An automatic level controller comprising: an audio input terminal; an audio output terminal; a power source; an audio amplifying circuit connected between said audio input and output terminals for amplifying an audio signal supplied to said audio input terminal and providing an amplified audio signal to said audio output terminal; an audio level control transistor having one input electrode and two output electrodes and connected at said output electrodes between the ground and the input terminal for controlling the audio level of the audio input signal applied to said audio amplifying circuit by bypassing to the ground a portion of said audio input signal; a protective resistor; a current limiting resistor; a time constant circuit; a switching transistor having one input electrode and two output electrodes and connected at said input electrode through said current limiting resistor and an output circuit of said audio amplifying circuit to said power source, and at one of said output electrodes to said power source through said protective resistor and grounded at the other one of said output electrodes, said switching transistor being switched over from one state to the other when the level of the audio output signal of said audio amplifying circuit exceeds a predetermined level; and a switching diode having two electrodes and connected at one electrode thereof to said power source through said protective resistor and at the other electrode thereof to said input electrode of said audio level control transistor through said time constant circuit, said switching diode being switched over from one state to the other in response to the switching of said switching transistor as a result of the detection of the audio output level thereby supplying current from said power source as an audio level control signal to said input electrode of said audio level control transistor.