Amplifier with howling-preventing circuit

Claim 2

The combination of an amplifying circuit, a first smoothing power circuit adapted to be connected to an AC power source for supplying DC power to said amplifying circuit so as to operate the latter and having a relatively large discharging time constant when disconnected from said AC power source, change-over switch means having first and second states, actuating means for said change-over switch means energizable to drive said change-over switch means to said first state and permitting the return of said change-over switch means to said second state upon deenergizing of said actuating means, a second smoothing power circuit also adapted to be connected to the AC power source for supplying DC power to energize said actuating means and having a relatively small discharging time constant when disconnected from said AC power source, and holding circuit means for holding said change-over switch means in said first state thereof for a predetermined time after said first and second smoothing power circuits are disconnected from said AC power source.

Claim 3

The combination according to claim 1; in which said holding circuit means is connected with said first smoothing power circuit through said change-over switch means in said first state of the latter so that said relatively large discharging time constant of the first smoothing power circuit establishes said predetermined time that said change-over switch means is held in said first state thereof after said first and second smoothing power circuits are disconnected from the AC power source.

Claim 4

The combination according to claim 2; in which said holding circuit means includes a transistor having first and second states and being connected with said first smoothing power circuit in said first state of the change-over switch means, means for maintaining the energizing of said actuating means by the DC power from said first smoothing power circuit in response to said transistor being in said second state of the latter, and means normally maintaining said transistor in said first state of the latter and switching said transistor to said second state of the transistor in response to the disconnection of said first and second smoothing power circuits from said AC power source.

Claim 5

The combination according to claim 3; further comprising a power transformer having primary winding means for connection to said AC power source and secondary winding means connected with said first and second smoothing power circuits; and in which said means normally maintaining said transistor in said first state of the latter includes a detecting circuit connected with said secondary winding means to be charged when said primary winding means is connected with said AC power source and to maintain said first state of the transistor in response to the charging of said detecting circuit, and said detecting circuit has a smaller discharging time constant than said first and second smoothing power circuits.

Claim 6

The combination according to claim 1; further comprising voltage-controlled control means having operative and inoperative conditions in which said actuating means is energizable by the DC power from said second smoothing power circuit and deenergized, respectively; and in which said holding circuit means is connected with said first smoothing power circuit through said change-over switch means in said first state of the latter for developing a control voltage from said DC power supplied by said first smoothing power circuit after said first and second smoothing power circuits are disconnected from the AC power source, and said control voltage is applied to said control means for maintaining the latter in its operative condition for said predetermined time.

Claim 7

The combination according to claim 5; further comprising means for normally applying a control voltage from said second smoothing power circuit to said control means for maintaining the latter in its operative condition when said first and second smoothing power circuits are connected with said AC power source.

Claim 8

The combination according to claim 6; in which said holding circuit means includes a transistor having first and second states and being connected with said first smoothing power circuit in said first state of the change-over switch means and with said control means for applying said control voltage to the latter when said transistor is in said second state of the latter, and detecting means maintaining said transistor in said first state of the latter when said first and second smoothing power circuits are connected to said AC power source and switching said transistor to said second state in response to the disconnection of said smoothing power circuits from said AC power source.

Claim 9

A recording and reproducing apparatus comprising an amplifying circuit, a first smoothing power circuit adapted to be connected to an AC power source for supplying DC power to said amplifying circuit so as to operate the latter and having a relatively large discharging time constant when disconnected from said AC power source, a second smoothing power circuit also adapted to be connected to said AC power source for producing DC power and having a relatively small discharging time constant when disconnected from said AC power source, auxiliary circuit elements operable by said DC power from the second smoothing power circuit, first and second change-over switch means each having recording and reproducing positions for establishing the requisite connections of said amplifying circuit and auxiliary circuit elements for recording and reproducing operations, respectively, of the apparatus, first and second actuating means for said first and second change-over switch means, respectively, each of said actuating means being energizable by said DC power from said second smoothing power circuit to drive the respective change-over switch means to said recording position and permitting the return of said respective change-over switch means to said reproducing position upon deenergizing of the corresponding actuating means, first and second voltage-controlled control means connected with said first and second actuating means, respectively, and each having operative and inoperative conditions in which the respective actuating means is energizable by the DC power from said second smoothing power circuit and deenergized, respectively, means for applying a control voltage to said first and second control means from said second smoothing power circuit by way of said first change-over switch means when the latter is in said recording position so as to maintain said first and second control means in said operative positions thereof, holding circuit means connected with said first smoothing power circuit through said second change-over switch means in said recording position of the latter for developing an auxiliary control voltage from said DC power supplied by said first smoothing power circuit after said first and second smoothing power circuits have been disconnected from said AC power source, and means for applying said auxiliary control voltage from said holding circuit means to said second control means for maintaining the latter in said operative condition thereof, and thereby continuing said second change-over switch means in said recording position, at least until the DC power from said first smoothing power circuit has declined sufficiently to make said amplifying circuit inoperative upon the disconnection of said first and second smoothing power circuits from said AC power source.

Claim 10

A recording and reproducing apparatus comprising an amplifying circuit, a first smoothing power circuit adapted to be connected to an AC power source for supplying DC power to said amplifying circuit so as to operate the latter and having a relatively large discharging time constant when disconnected from said AC power source, a second smoothing power circuit also adapted to be connected to said AC power source for producing DC power and having a relatively small discharging time constant when disconnected from said AC power source, auxiliary circuit elements operable by said DC power from the second smoothing power circuit, first and second change-over switch means each having recording and reproducing positions for establishing the requisite connections of said amplifying circuit and auxiliary circuit elements for recording and reproducing operations, respectively, of the apparatus, first and second actuating means for said first and second change-over switch means, respectively, each of said actuating means being energizable by said DC power from said second smoothing power circuit to drive the respective change-over switch means to said recording position and permitting the return of said respective change-over switch means to said reproducing position upon deenergizing of the corresponding actuating means, first and second voltage-controlled control means connected with said first and second actuating means, respectively, and each having operative and inoperative conditions in which the respective actuating means is energizable by the DC power from said second smoothing power circuit and deenergized, respectively, means for applying a control voltage to said first and second control means from said second smoothing power circuit by way of said first change-over switch means when the latter is in said recording position so as to maintain said first and second control means in said operative positions thereof, holding circuit means connected with said first smoothing power circuit through said second change-over switch means in said recording position of the latter for developing an auxiliary control voltage from said DC power supplied by said first smoothing power circuit after said first and second smoothing power circuits have been disconnected from said AC power source, and means for applying said auxiliary control voltage from said holding circuit means to said second control means for maintaining the latter in said operative condition thereof, and thereby continuing said second change-over switch means in said recording position, at least until the DC power from said first smoothing power circuit has declined sufficiently to make said amplifying circuit inoperative upon the disconnection of said first and second smoothing power circuits from said AC power source.

Claim 11

A recording and reproducing apparatus according to claim 8; in which said first and second control means are constituted by first and second transistors, respectively, which are conductive and non-conductive in said operative and inoperative conditions, respectively, each of said first and second transistors being connected in series with said respective actuating means and having a base electrode to which a control voltage is applicable for rendering the respective transistor conductive.

Claim 12

A recording and reproducing apparatus according to claim 9; in which said holding circuit means includes a third transistor having conductive and non-conductive states and establishing said auxiliary control voltage only in said non-conductive state, and detecting means maintaining said third transistor in said conductive state when said first and second smoothing power circuits are connected to said AC power source and switching said third transistor to said non-conductive state in response to the disconnection of said smoothing power circuits from said AC power source.

Claim 13

A recording and reproducing apparatus according to claim 10; in which said detecting means has a discharging time constant substantially smaller than the discharging time constants of said first and second smoothing power circuits.

Claim 14

A recording and reproducing apparatus according to claim 8; further comprising first and second input terminals for receiving record-initiation and record-releasing pulse signals, respectively, means connecting said first input terminal with said second control means so that the latter is initially changed to said operative condition thereof in response to the reception of a record-initiation pulse signal, means for initially causing said first control means to assume said operative condition in response to the switching of said second change-over switch means to said recording position of the latter, and means connecting said second input terminal and said first control means to change the latter from its operative condition to its inoperative condition in response to the reception of a record-releasing pulse signal.

Claim 15

A recording and reproducing apparatus according to claim 8; further comprising means for applying a control voltage to said first control means from said first smoothing power circuit by way of said second change-over switch means when the latter is in said recording position so as to also maintain said first control means in said operative condition thereof, and thereby also continue said first change-over switch means in said recording position, at least until said DC power from said first smoothing power circuit has declined sufficiently to make said amplifying circuit inoperative upon the disconnection of said first and second smoothing power circuits from said AC power source.