JPS606892Y2 - Tape recorder muting circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tape recorder, and particularly to a muting circuit that suppresses noise generation.

A high-grade tape recorder called a tape deck is used by being connected to an amplifier with a high output.

Unlike popular tape recorders, such a tape recorder is in operation even when the tape recorder is stopped because power is supplied to the electric motor that drives the amplifier circuit and capstan.

Therefore, the noise output from such an amplifier circuit will be amplified by a high-output amplifier, causing discomfort to the user.

To improve this point, sterilization tape recorders are equipped with a muting circuit.

The circuit shown in Figure 1 is a conventional example, and in the figure, 1 is an input terminal to which a signal reproduced from a magnetic tape is applied, 2 is an amplifier circuit, and 3 is connected to the input terminal of an amplifier with a large output. This is the output terminal.

4 is a muting transistor whose collector and emitter are connected between the signal transmission path 5 and the ground; 6 is a muting transistor whose collector is connected to the base of the muting transistor 4 via a resistor 7 and a Zener diode 8; The muting transistor 4 is a control transistor whose emitter is grounded, and has the function of controlling the on/off operation of the muting transistor 4.

The base of the control transistor 6 is connected via a resistor 9 to an output terminal 11 of a power supply circuit 10 that supplies power to the amplifier circuit 2.

A capacitor 13 is connected between the base of the control transistor 0 and the ground, and together with the resistor 9 constitutes a time constant circuit 14.

Note that 12 is a resistor for discharging. Reference numeral 15 denotes a muting switch which is closed in a stopped state and opened by a regeneration operation, and is connected between the base of the control transistor 6 and ground.

Further, the collector of the control transistor 6 and the output terminal 11 of the power supply circuit 10 are connected via a resistor 16.

Reference numeral 17 denotes a main switch, which has the function of supplying power to the power supply circuit 10 and also supplying power to the electric motor that drives the capstan.

Next, the operation of the conventional example configured as above will be explained.

In the stopped state, the muting switch 15 is in the closed state, and when the main switch 17 is closed, a predetermined voltage appears at the output terminal 11 of the power supply circuit 10, the amplifier circuit 2 becomes operational, and the motor starts rotating. Drive the capstan.

In such a stopped state, the base of the control transistor 6 is grounded by the muting switch 15, so the control transistor 6 is in an off state.

As a result, a high voltage is applied to the base of the muting transistor 4 from the output terminal 11 of the power supply circuit 10, and the transistor 4 is turned on.

Therefore, the signal on the signal transmission line 5 is bypassed between the collector and emitter of the muting transistor 4, and no signal such as noise appears at the output terminal 3.

When a playback operation is performed from such a stopped state, the drive mechanism of the tape recorder enters the playback state and the muting switch 15 is opened.

As a result, the control transistor 6 which was in the off state is turned on after being delayed for a predetermined time by the time constant circuit 14 made up of the resistor 9 and the capacitor 13.

When the control transistor 6 is reversed to the on state, the muting transistor 4 which was in the on state is reversed to the off state.

Therefore, the signal reproduced by the magnetic head is transmitted to the amplifier circuit 2.
The signal is amplified to a predetermined level and then output to the output terminal 3.

Although the conventional muting operation shown in FIG. 1 is performed as described above, it has the following problems.

That is, when the main switch 17 is closed or power is supplied by the timer device after a playback operation has been performed and the tape recorder is in the playback state, the control transistor 6 is turned on after a predetermined time since the muting switch 15 is in the open state. Therefore, the muting transistor 4 is turned off.

There will be no problem if the amplifier circuit 2 is in a steady operating state when the muting transistor 4 is reversed to the off state, that is, the muting operation is canceled, but if it is not in a steady operating state, There is a problem in that noise generated from the amplifier circuit 2 is output from the output terminal 3 and emitted from the speaker.

A method for solving this problem is to use a time constant circuit 14 that delays the inversion operation of the control transistor 6 to the on state.
It is conceivable to increase the time constant, but if this time constant is increased, a muting operation is required in the normal case, that is, when performing a regeneration operation when power is being supplied and the amplifier circuit 2 is in a steady operating state. This will cause the user to feel uncomfortable.

The present invention aims to provide a muting circuit that is improved in this respect, and will be described with reference to the embodiment shown in FIG.

Components that are the same as those in the conventional example shown in FIG. 1 are given the same reference numerals.

As is clear from the drawings, the present invention includes a first time constant circuit 14.
A second time constant circuit 30 consisting of a resistor 18 and a capacitor 19 is inserted and connected between the output terminal 11 of the power supply circuit 10 and the output terminal 11 of the power supply circuit 10.

Next, the operation of such a circuit will be explained.

In the stopped state when the main switch 17 is closed, power is supplied from the power supply circuit 10 to the amplifier circuit 2, and the amplifier circuit 2 is in a steady state and the second time constant circuit 20
A capacitor 19 constituting the circuit is charged through a resistor 18.

Further, since the muting switch 15 is closed, the control transistor 6 is in an off state, and therefore the muting transistor 4 is in an on state to perform a muting operation.

When a playback operation is performed in such a state, the drive mechanism of the tape recorder enters the playback state and the muting switch 15 is opened.

As a result, after a predetermined time period set by the time constant circuit 14 with a rate of 1, the control transistor 6 is inverted to the on state, and the muting transistor 4 is inverted to the off state.

Next, a case will be described in which power is supplied by closing the main switch 17 or by a timer device after a regeneration operation state is established by a regeneration operation.

In the playback state where power is not supplied, the muting switch 15 is in an open state, and the first time constant circuit 14
and a capacitor 13 constituting the second time constant circuit 20
．． 19 is in a non-charging state.

When power is supplied in such a state, the power supply circuit 1
Since power is supplied to the amplifier circuit 2 from 0 and the control transistor 6 is in the off state, the muting transistor 4 is in the on state to perform a muting operation.

and a second time constant circuit 20 and a first time constant circuit 14
After a predetermined time delay, the control transistor 6 is turned on.

As a result, the muting transistor 4 is reversed from the on state to the off state, and the muting operation is canceled.

This muting operation cancellation is delayed by the time constant of the second time constant circuit 20 compared to when switching from a stop state where power is supplied to a regeneration state, so that the amplifier circuit 2 is in a steady state during that time. Therefore, the noise generated by the amplifier circuit 2 is not outputted from the output terminal 3.

As explained above, in the present invention, when a playback operation is performed from a stopped state where power is being supplied, the muting operation is canceled by a delay using the first time constant circuit, and a timer device or the like is used to release the muting operation in the playback state. Since the muting operation is canceled at the time of supply by a delay using the first and second time constant circuits, it is possible not only to prevent noise from being output to the output terminal, but also to eliminate the muting operation cancellation time. Since it is not longer than that, it does not cause discomfort to the user.

[Brief explanation of the drawing]

The circuit shown in Figure 1 is a conventional muting circuit,
The figure shows one embodiment of the present invention. Explanation of main drawing numbers, 2... Amplifier circuit, 4...
...Muting transistor 5...
Signal transmission line, 6... Control transistor, 10
......Power supply circuit, 14.20...Time constant circuit, 15...Muting switch,
17... Main switch.

Claims (1)

[Scope of utility model registration request] A muting device in which a power supply circuit that supplies power to an amplifier circuit, etc., and a collector-emitter connection between a signal transmission path and ground, and a bias current is supplied to the base from the power supply circuit during muting operation. a control transistor whose collector-emitter is connected between the base circuit of the transistor and ground to control the on/off operation of the muting transistor; a first time constant circuit that inverts the control transistor after a predetermined time to turn off the muting transistor by opening a muting switch in response to operation of a playback operation button; A muting circuit for a tape recorder, comprising a second time constant circuit connected between the circuit and the power supply circuit.