JPS6216442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting circuit, and in particular, it is an object of the present invention to provide a muting circuit that can be expected to operate reliably with a simple configuration by performing digital operation.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a case where the muting circuit according to the present invention is applied to a tape recorder.
1 is a pre-stage amplifier, 2 is a main amplifier, 3 is a drive motor for the tape recorder, 4 is a battery as a power source, 5 is a mechanical mechanism of the tape recorder driven by the drive motor 3, and 6 is a tape recorder drive motor. A trigger switch 7 closes when an operation button (not shown) starts operating, and a motor switch 7 that operates in conjunction with the trigger switch 6 when an operation button other than the stop operation button is operated and maintains the closed state unless released. , 8 is an R-S flip-flop circuit having a set input terminal S, a reset input terminal R, and an inverted output terminal; 9 is a positive input terminal to which a reference voltage is applied; a negative input terminal to which an input signal is applied; R
-S Set input terminal S of flip-flop circuit 8
A first comparison circuit 10 is connected to a negative input terminal to which a reference voltage is applied, a positive input terminal to which an input signal is applied, and an output terminal connected to the reset input terminal R of the R-S flip-flop circuit 8. A second comparison circuit, 11, 12, and 13 are first, second, and third bias resistors for supplying bias to the first and second comparison circuits 9 and 10, 13 is an inverter, and 14 is the inverter 13. and a switching transistor whose base is connected to the inverting output terminal of the flip-flop circuit 8 via a resistor 15; 16 is a short-circuiting transistor whose base is connected to the inverting output terminal via a resistor 17; and 18 is a switching transistor 16. 19 is a detection switch for detecting the end of operation of a circuit changeover switch switched by the mechanical mechanism of the tape recorder; 20 is a detection switch when the trigger switch 6 is closed; It is a control transistor that exhibits a conductive state when the first comparator circuit 9 is in a conductive state and applies a trigger signal to the first comparator circuit 9.

Here, the operation of the tape recorder will be briefly explained. When an operation button for starting an operation, such as a record button or a playback button, is operated, the trigger switch 6 and the motor switch 7 are closed, and the drive motor 3 starts rotating. Since the trigger switch 6 is of an automatic return type, it will be automatically opened once it is closed, but the motor switch 7 will remain closed unless it is forcibly released, so the drive motor 3 will not rotate. sustain. Thus, the drive motor 3 drives the mechanical mechanism 5 through its initial rotation, and brings the tape recorder into a state corresponding to the operated operation button. Further, the mechanical mechanism 5 includes an electric circuit of a tape recorder,
For example, a recording/playback switch (not shown) for switching the recording equalizer circuit, playback equalizer circuit, etc.
Since the mechanical mechanism 5 has a switching function, when the mechanical mechanism 5 is in a state corresponding to the operated operation button, the electric circuit is also in the corresponding state. At that time, the detection switch 19 that detects the end of the switching operation is switched in accordance with the previous recording/re-switching switch, and is located at the position shown by the solid line when the playback button is pressed, and located at the position shown by the dotted line when the record button is pressed. However, by using a switching type switch, instantaneous
The terminal 19a can be grounded.

On the other hand, when an operation button that does not require a subsequent operation, such as a stop button, is pressed, the motor switch 7 is opened and the trigger switch 6 is closed for a short time. Therefore, the drive motor 3 stops after driving the mechanical mechanism 5 to a stopped state.

Next, the operation of the muting circuit will be explained.
The muting circuit in a tape recorder is
It is necessary to prevent the switching noise that occurs when the operation button is operated and the noise that occurs during the transient period until the switched electric circuit stabilizes.

If the tape recorder is now in a stopped state, the trigger switch 6 and motor switch 7 are in a closed state, and the drive motor 3 is stopped. Therefore, the control transistor 20 is in an off state,
No set input is applied from the first comparator circuit 9 to the set input terminal S of the R-S flip-flop circuit 8, and the inverted output terminal is "H". Therefore, the discharge transistor 16 is on and the switching transistor 14 is off. The capacitor 18 is in a completely discharged state. At that time, the detection switch 19 is assumed to be in the position indicated by the solid line in the figure.

In this state, when the regeneration button is pressed at time A, the trigger switch 6 and motor switch 7 are closed, the drive motor 3 rotates, and the mechanical mechanism 5 enters the regeneration state. On the other hand, when the trigger switch 6 is closed and then automatically reset, a positive pulse shown in FIG. 2A is applied to the base of the control transistor 20, and the collector voltage of the control transistor 20 increases as shown in FIG. , becomes "L" for a short time. By properly setting the bias using the first to third resistors 11 to 13, when the collector voltage of the control transistor 20 becomes "L" for a short time, the output signal of the first comparison circuit 9 becomes "H" for a short time. , the "H" signal is applied to the set input terminal S of the R-S flip-flop circuit 8, and the inverted output terminal becomes "L" as shown in FIG. 2C.
Therefore, the switching transistor 14 is turned on, the input terminal of the main amplifier 2 is grounded and muting is started, and at the same time the shorting transistor 16 is turned off and charging of the capacitor 18 is started.
The capacitor 18 is charged by the battery 4 through the resistor 21, and the voltage across it gradually increases as shown in FIG. 2D. The voltage across the capacitor 18 is applied to the positive input terminal of the second comparator circuit 10, but when the voltage across the capacitor 18 exceeds the reference voltage applied to the negative input terminal, the voltage across the capacitor 18 is applied to the positive input terminal of the second comparison circuit 10.
An "H" signal is generated at the output terminal of the RS flip-flop circuit 8 and is applied to the reset input terminal R of the R-S flip-flop circuit 8 as a reset signal. Therefore, the inverting output terminal of the R-S flip-flop circuit 8 is "H".
Therefore, the base voltage of the switching transistor 14 becomes "L", the switching transistor 14 is turned off, and muting is canceled.
At the same time, the shorting transistor 16 is turned on, the capacitor 18 is discharged, and the second comparison circuit 10
The signal applied to the positive input terminal of becomes “L”,
The input signal to the reset input terminal R of the R-S flip-flop circuit 8 also becomes "L".

Therefore, muting is performed for a certain period of time _T1 after the playback button is operated, and noise accompanying switching can be prevented from occurring.

Next, a case will be described in which a tape recorder in a playback state is changed to a recording state. If the stop button is pressed to stop the reproduction state at time B, the motor switch 7 is opened and the trigger switch 6 is closed for a short time. Drive motor 3
rotates due to inertia for a predetermined period of time, causing the mechanical mechanism 5 to shift from the regeneration state to the stop state.

On the other hand, when the trigger switch 6 is closed for a short time, the control transistor 20 is turned on, and muting is performed by the same circuit operation as when the playback button is operated. Therefore, the noise generated when the stop button is operated is also effectively eliminated by the mutating.

Subsequently, when the recording button is pressed at time C, the trigger switch 6 and motor switch 7 are closed, the drive motor 3 rotates, and the mechanical mechanism 5 shifts to the recording state. At this time, the various recording/reproducing changeover switches are driven by the mechanical mechanism 5 and are switched from the playback state to the recording state, and at the same time the detection switch 19 is also switched from the playback position indicated by the solid line to the recording position indicated by the broken line. Muting is started immediately by closing the trigger switch 6. However, since the switching of the recording/reproducing switch is accompanied by the movement of the mechanical mechanism 5, a time delay occurs, and it takes time for the circuit switched by the previous recording/reproducing switch to become stable.

Therefore, when operating an operation button that does not involve switching the recording/playback switch, muting is performed for a sufficient period of time for the mechanical mechanism 5 to switch, so that the signal generation time is as short as possible, and the operation button does not involve switching the recording/playback switch. When operating the operation button, a time-variable muting circuit is required to obtain a sufficient muting time, taking into account the time required for the switched circuit to stabilize.

When changing from the playback state to the stop state and then to the recording state, the trigger switch 6 is closed for a short time by pressing the record button at time C, and the control transistor 2 is closed.
0 is turned on for a short time, an "H" signal is applied from the output terminal of the first comparator circuit 9 to the set input terminal S of the R-S flip-flop circuit 8, and the inverted output terminal becomes "L", so that the switching transistor 14 is turned on, and mutating is performed immediately. At the same time, the shorting transistor 16 is turned off and charging of the capacitor 18 is started. At time D, when the movable contact piece of the shooting type detection switch 19 moves from the short-circuited state between the terminals 19a and 19b to the short-circuited state between the terminals 19b and 19c, the terminal 19a is grounded in the middle of the movement. Ru. Therefore, at time D, when the charge accumulated in the capacitor 18 is discharged to the ground via the detection switch 19, the voltage across the capacitor 18 becomes zero, and then the switching state to the ground is released. Charging of the capacitor 18 is started again. When the voltage across the capacitor 18 reaches a predetermined value, an "H" signal is generated at the output terminal of the second comparison circuit 10, which is applied to the reset input terminal R of the R-S flip-flop circuit 8, and the inverted output terminal is The signal becomes "H", the switching transistor 14 is turned off, the shorting transistor 16 is turned on, and muting is canceled.

As is clear from FIG. 2D, when the switching of the recording/reproduction switch is involved, the muting time is the time T2 from the closing of the trigger switch 6 to the switching of the detection switch 19, and the time R- ₂ from the switching of the detection switch 19 to the switching of the detection switch 19. The sum T ₁ + time T ₁ until the S flip-flop circuit 8 enters the reset state
It becomes T ₂ . Therefore, a sufficient amount of muting time is achieved, including time for the switched circuit to stabilize.

Particularly, in a tape recorder in which a mechanical mechanism is driven by a drive motor of this kind and a recording/playback switch is switched by the mechanical mechanism, the time from pressing the operation button to the end of switching is variable, and the muting circuit according to the present invention By making the time from the end of switching to the end of muting constant, the above-mentioned variations can be sufficiently absorbed.

As described above, since the muting circuit according to the present invention uses a flip-flop circuit, it is possible to start and end muting and perform the muting operation digitally. When switching is not required, the muting release time is set to be approximately the same as the end of the switching operation of the operation switching mechanism, and when switching of the changeover switch is required, such as during recording, muting is continued until the recording circuit is stabilized even after the switching operation of the operation switching mechanism is completed. This allows you to perform mutating to the minimum extent necessary. In the embodiment, the inverting output terminal of the flip-flop circuit is connected to the switching transistor 1 via an inverter.
4, but the non-inverting output terminal Q
When using a flip-flop circuit with
The non-inverting output terminal Q may be directly connected to the base of the switching transistor 14.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing waveforms of each part thereof. Explanation of main figure numbers, 8...R-S flip-flop circuit, 9, 10... Comparison circuit, 14... Switching transistor, 18... Capacitor, 19
...Detection switch.

Claims (1)

[Claims] 1. In a tape recorder whose operation switching mechanism is driven by a motor, a trigger switch is temporarily closed in response to the operation of an operation button, and a trigger pulse generated when the trigger switch is closed is used to set and generate a muting signal. a flip-flop circuit that grounds a signal path in response to the mutating signal and bypasses a signal passing through the signal path; a short-circuiting device controlled by the muting signal; It consists of a controlled capacitor and a circuit switching detection switch that instantaneously discharges the capacitor in conjunction with a switching switch that is selectively switched by the operation switching mechanism. sets the flip-flop circuit, generates a muting signal, operates the switching element, starts muting, and starts charging the capacitor, and when the capacitor is charged to a predetermined amount, resets the flip-flop circuit and cancels the muting, When the changeover switch is changed by the operation changeover mechanism, the circuit changeover detection switch temporarily discharges the capacitor that is being charged, restarts charging from the beginning, and delays the capacitor from being charged to a predetermined amount to set the time for canceling mutating. A mutating circuit characterized by an extension.