JPS6017045Y2 - Tape recorder muting circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a muting circuit for a tape recorder.

A high-grade tape recorder, generally called a tape deck, is used by being connected to an amplifier having a large output, so it is necessary to suppress the generation of noise as much as possible.

Recently, tape recorders with a function to create a no-signal portion without recording unnecessary signals have become popular.

In order to perform such an operation, this type of tape recorder is equipped with a circuit called a muting circuit which attenuates the level of the signal.

The present invention aims to provide an optimal muting circuit, and will be described in detail with reference to illustrated embodiments.

The illustrated circuit is a recording circuit in which the present invention is implemented. In the figure, 1 is an input terminal to which a signal obtained from a microphone or the like is applied, and 2 is a pre-amplifier that amplifies the signal applied to the terminal 1. An amplifier circuit, 3 and 4 are first and second resistors inserted and connected in series in the signal transmission path 5, 6 is a recording amplifier circuit, 7 is a bias oscillation circuit, and 8 is a recording head.

9 is a first muting transistor whose collector is connected to the common connection point of the first resistor 3 and the second resistor 4 and whose emitter is grounded; 10 is the second muting transistor;
This is a second muting transistor whose collector is connected to the output side of the resistor 4 and whose emitter is grounded.

Reference numeral 11 has a resistor 12, the collector of which controls the operation of the first and second muting transistors 9, 10.
13 and Zener diodes 14 and 15 to the bases of the transistors 9 and 10, and supplies a bias current to the bases of the first mutating transistor 9 and the second muting transistor 10 via a bias resistor 16. The first control transistor is connected to the power supply line 17 and has its emitter grounded, and its base is connected to the power supply line 17 via a resistor 18.

19 is a second control transistor whose collector is connected to the base of the first control transistor 11 and whose emitter is grounded; 20 is a second control transistor whose collector is connected to the base of the second control transistor 19 through a resistor 2; It is a third control transistor connected to the power supply line 17 via 22 and whose emitter is grounded.

A fourth control transistor 23 controls the operation of the third control transistor 20, and its collector is connected to the base of the third control transistor 20 via a Zener diode 24 and to the power supply line 17 via a resistor 25.
and the emitter is grounded.

The base of the fourth control transistor 23 is connected to a muting operation control circuit 27 via a resistor 26 and to the power supply line 17 via a time constant circuit 30 connected to a capacitor 28 and a resistor 29.

31 is a switch that is closed when creating a non-signal portion on the magnetic tape, and is connected to the first control transistor 11.
connected between the base and ground.

In such a configuration, the Zener voltage of the Zener diode 24 is set to a value at which the third control transistor 20 is inverted from the on state to the off state when the voltage of the power supply line 17 drops a little, that is, the voltage of the third control transistor 20 is lower than the voltage value of the power supply line 17. It is set to be approximately equal to the value obtained by subtracting the rising voltage value of 20.

Further, the time constant of the time constant circuit 30 is set to be larger than the time required for the amplifier circuit and the like to stabilize after power is turned on.

The present invention is constructed as described above, and its operation will be explained next.

The illustrated state is a recording operation state, and when power is supplied by the timer device in this state, a predetermined voltage is applied to the power supply line 17.

As a result, the charging current of the capacitor 28 constituting the time constant circuit 30 flows as the base current of the fourth control transistor 23, and the fourth control transistor 23 remains on for a predetermined time, that is, until the capacitor 28 is completely charged.

Therefore, during that time, the third control transistor 20 is in the off state, the second control transistor 19 is in the on state, and the first
Control transistor 11 is turned off.

Therefore, the first muting transistor 9 and the second
A high voltage is applied to the base of the muting transistor 10, and the muting transistors 9 and 10 are in an on state during that time.

Therefore, noise generated until the amplifier circuit, electric motor, etc. reach a steady state is bypassed through the collector-emitter of the first and second muting transistors 9 and 10, and the noise is transferred to the recording head 8. It is never recorded on magnetic tape.

Then, after a predetermined period of time has elapsed, the fourth control transistor 23 that was in the on state is reversed and returned to the off state, and accordingly, the third control transistor 20 is turned on, the second control transistor 19 is turned off, and the first control transistor 23 is turned on. Transistor 11 is turned on.

As a result, the first mutating transistor 9 and the second muting transistor 10 are inverted to the OFF state, so that the recording signal amplified by the preamplifier circuit 2 is applied to the recording amplifier circuit 6 without being bypassed and is recorded. The head 8 records the information onto the magnetic tape.

Next, the operation for creating a no-signal portion on the magnetic tape will be explained.

In this case, the switch 31 may be closed in the above-described recording operation state.

That is, when the switch 31 is closed, the base of the first control transistor 11 is grounded, so that the transistor 11
is reversed to the off state.

As a result, a high voltage is applied to the bases of the first mutating transistor 9 and the second muting transistor 10, and the transistors 9 and 10 are turned on.

Therefore, the signal flowing through the signal transmission path 5 is bypassed between the collectors and emitters of the transistors 9 and 10, so that no signal is applied to the recording head 8, and a no-signal portion is formed on the magnetic tape.

Next, normal muting operation will be explained.

When fast forwarding or rewinding during recording operation, the noise generated by the switching of various parts will be heard in the preamplifier circuit 2.
However, prior to the switching, a control signal is output for a predetermined time from the muting operation control circuit 27 to turn on the fourth control transistor 23.

As a result, the third control transistor 20 is turned off, the second control transistor 19 is turned on, and the first control transistor 1 is turned off.
1 is turned off and the first and second muting transistors 9 and 10 are turned on, so that the above-mentioned noise is not recorded on the magnetic tape.

The muting operation of the muting circuit is performed in this manner, but next, a case will be described in which the power supply is cut off by a timer device or the like while the muting circuit is in the recording operation state.

When the power supply is cut off, the voltage of the power supply line 17 will gradually drop due to the influence of the smoothing capacitor, etc., but the Zener voltage value of the Zener diode 24 connected to the base circuit of the third control transistor 20 will be Since it is set to be approximately equal to the value obtained by subtracting the rising voltage value of the third control transistor 20 from the voltage value of the power line 17, when the voltage of the power line 17 falls, the Zener diode 24 is immediately reversed to the off state. .

As a result, the third control transistor 20 is inverted to the off state, causing the second control transistor 19 to be turned on and the first control transistor 11 to be turned off.

Therefore, the first and second muting transistors 9
, 10 are turned on, and the noise generated when the power supply is cut off is not recorded on the magnetic tape.

In this embodiment, the muting operation is performed using two transistors, but it is also possible to use three or more transistors.

A control transistor 11 is also connected to control the base bias of the muting transistor.
The control circuit that controls the operation of the circuit when the power is turned on and when the power is turned off is composed of three transistors 19, 20, 23, a Zener diode 24, a time constant circuit 30, etc., but it can also be constructed using reverse conductivity type transistors, etc. You can also do that.

Furthermore, although the muting transistors 9 and 10 are connected to the signal transmission path 5 on the input side of the recording amplifier circuit 9, they can also be connected to the output side.

As explained above, the muting circuit of the present invention not only has two transistors that perform the muting operation, but also connects them in the same signal transmission path, so the level of the signal passing through the signal transmission path is ignored. It has the feature that it can be made as small as possible.

Therefore, according to the present invention, it is possible not only to reliably prevent noise signals generated when the power is turned on and off to be recorded on the magnetic tape, but also to reliably prevent the recording of noise signals on the magnetic tape when forming a non-signal portion on the magnetic tape. The practical value of the present invention is very great since it is possible to form a no-signal area.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the muting circuit of the present invention. Explanation of main drawing numbers 2... Preamplifier circuit, 3...
...First resistance, 4...Second resistance, 5...
...Signal transmission path, 6... Recording amplifier circuit, 9.
...First mutating transistor 10
...Second mutating transistor, 1
1...First control transistor, 17...
...Power supply line, 19...Second control transistor, 20...Third control transistor, 23.
...Fourth control transistor, 27...
Muting operation control circuit, 30...time constant circuit.

Claims (1)

[Scope of utility model registration request] first and second resistors inserted and connected in series in a signal transmission path, and a first muting transistor whose collector is connected to a common connection point of the first and second resistors and whose emitter is grounded. and a second muting transistor whose collector is connected to the output side of the second resistor and whose emitter is grounded, and to supply a bias current to the bases of the first and second muting transistors. a bias resistor connected thereto, and a bias current connected to the bases of the first muting transistor and the second muting transistor when the transistors are in an on state; a control transistor which is connected between the base of the control transistor and ground and which is closed when a no-signal portion is formed and which turns off the control transistor while in the closed state; and a control circuit that turns off the control transistor for a predetermined time and during a voltage drop due to power cutoff, and controls the on/off operation of the control transistor by the opening/closing operation of the switch and the operation of the control circuit. A muting circuit for a tape recorder, characterized in that the on/off operations of the first muting transistor and the second muting transistor are controlled.