JPH0215378Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention relates to a muting circuit, for example,
Used in double cassette tape recorders equipped with a mechanism for playback only and a mechanism for both recording and playback.

Conventional technology For example, a mechanism for playback only (hereinafter referred to as "A mechanism") and a mechanism for both recording and playback (hereinafter referred to as "A mechanism")
In a double cassette tape recorder equipped with a B mechanism, the playback signals from these A mechanisms,
The reproduction signal from the B mechanism, the recording signal to the B mechanism, etc. are switched and used in accordance with the mode switching.

This device has a configuration in which when switching the B mechanism to the playback state while the A mechanism is being played, the playback signal from the B mechanism is extracted instead of the playback signal from the A mechanism by switching a switch linked to the play button of the B mechanism. It is said that On the other hand, when switching from the external recording mode in which the external signal from the external terminal is recorded to the B mechanism to the dubbing recording mode in which the playback signal from the A mechanism is recorded to the B mechanism, the A mechanism is activated by switching the switch linked to the play button of the A mechanism. is in playback state, B
It is said that the mechanism is configured to enter dubbing recording mode.

The signal switching circuit is generally composed of a logic circuit using an IC, and in any of the above cases, the signal switching circuit is controlled by a play button or the like provided on the A mechanism and the B mechanism.

Problems that the invention aims to solve In the conventional double cassette tape recorder mentioned above, when the play button is operated, noise is generated, which causes discomfort to the listener, and when the play button is operated during recording, noise is generated. There were problems such as the data being recorded on the magnetic tape.

Means to Solve the Problem The present invention consists of a switching element that shorts the signal output terminal, a switch, a time constant circuit that turns on the switching element for a certain period of time when the switch is turned on, and a time constant circuit that turns on the switching element for a certain period of time when the switch is turned off. The above problem is solved by providing a time constant circuit that turns on the switch for a period of time, and provides a muting circuit that can reliably mute switching noise caused by turning on and off a switch with a simple circuit configuration. The purpose is to below,
One embodiment will be described with reference to the drawings.

Embodiment The figure shows a circuit diagram of an embodiment of the muting circuit according to the present invention. In the figure, _Q1 is a transistor for audio signal system muting, its emitter is grounded, its collector is connected to audio signal output terminal 1, and its base is connected to a resistor.
Connected to _R1 . The collector of the transistor Q ₂ is connected to the resistor R ₁ , its emitter is connected to the +B power supply, and its base is connected to the resistor R 1
It is connected to the +B power supply via R ₂ and to the resistor R ₃ . The emitter of transistor Q ₃ is grounded, and its collector is connected to a resistor
R ₃ and its base is grounded via resistor R ₄ .

S is a switch linked to a play button (not shown), whose movable contact piece is grounded, and whose contact point is connected to the signal switching circuit terminal 2;
capacitor C ₁ , resistor R ₂ and resistor R ₃ through resistor R ₅
It is further connected to the +B power supply via a diode D and resistors R ₆ and R ₇ . The connection point between resistor _R6 and resistor _R7 is a capacitor.
C ₂ , connected to the base of transistor Q ₃ via resistor R ₈ .

In the initial state when switch S is turned off, first, resistor R ₇ , capacitor C ₂ ,
Current flows through resistor R ₈ and the base-emitter of transistor Q ₃ to charge capacitor C ₂ , while transistor Q ₃ is base-biased and turned on, which causes transistors Q ₂ and Q _{1 to}
is turned on. When charging of capacitor C ₂ is completed, the base bias of transistor Q ₃ disappears, and transistors Q ₃ , Q ₂ , and Q ₁ are turned off.
On the other hand, no current flows through capacitor _C1 , so it is not charged.

Here, when you operate the play button, the switch S
is turned on. As a result, terminal 2 is set to ground potential, so the signal switching circuit is activated and signal switching is performed, while resistor R ₂ ,
A current flows through R ₅ , capacitor C ₁ , and switch S to charge capacitor C ₁ . Also, transistor _Q2 is base biased and turned on,
Transistor _Q1 is also turned on. transistor
When Q ₁ is turned on, terminal 1 is brought to ground potential, so that a so-called muting state is established and no switching noise is extracted to terminal 1.

On the other hand, the electric charge of the capacitor C ₂ that was being charged is transferred to the resistor R ₆ , diode D, switch S, resistor R ₄ ,
Discharged via R ₈ .

After transistors Q ₁ and Q ₂ are turned on, the time constant C ₁・
Transistor when time elapses due to R ₂ and R ₅
The base bias of Q ₂ is gone and the transistor
Q ₂ is turned off, transistor Q ₁ is also turned off, and the muting state is released.

Next, when you operate the play button again, the switch S
is turned off. As a result, terminal 2 is set to H level, so the signal switching circuit is deactivated, while
+B power supply to resistor R ₇ , capacitor C ₂ , resistor R ₈ ,
Current flows through the base-emitter of transistor _Q3 to charge capacitor _C2 , while transistor _Q3 is base biased and turned on, thereby turning on transistors _Q2 and _Q1 . By turning on the transistor _Q1 , a muting state is established as in the above case. By turning on the transistor Q ₃ , the charge in the capacitor C ₁ is discharged through the resistors R ₅ , R ₃ and the transistor Q ₃ .

After transistors Q ₁ and Q ₂ are turned on, the time constant C ₂・
Transistor when time elapses due to R ₇ and R ₈
The base bias of Q ₃ is gone and the transistor
Q ₃ is turned off, transistors Q ₂ and Q ₁ are also turned off, and the muting state is released.

Effects As described above, the muting circuit according to the present invention has a switching element that is turned on to short-circuit the signal output terminal, and is turned off to open the signal output terminal, and a switching element that is turned on and short-circuits the signal output terminal, and a switching element that is turned on and short-circuits the signal output terminal. A switch is connected to the power supply, the switch contact, and the switching element to open the contact.
There is a time constant circuit that is charged when the switch is turned on and turns on the switching element for a certain period of time, and discharged when the switch is turned off, and a time constant circuit that is connected to the power supply, the switch contacts, and the switching element, and is charged when the switch is turned off and turns on the switching element. The switch is turned on for a certain period of time, and it consists of a time constant circuit that is discharged when the switch is turned on, so it is possible to reliably mute the switching noise that occurs when the switch is turned on and off with a relatively simple circuit configuration. , does not cause discomfort to the listener, and
For example, when applied to a double cassette tape recorder, it has the advantage that switching noise is not recorded on the magnetic tape due to mode switching.

[Brief explanation of the drawing]

The figure is a circuit diagram of one embodiment of the circuit of the present invention. 1...Signal output terminal, S...Switch linked to play button, _Q1 to _Q3 ...Transistor, _R2 ,
R ₄ ~ _{R 8} ... Resistor, C ₁ , C ₂ ... Capacitor, D...
…diode.

Claims (1)

[Scope of utility model registration request] A switching element that shorts the signal output terminal when turned on and opens the signal output terminal when turned off; a switch that grounds the contact when turned on; and opens the contact when turned off; A contact point of the switch, a time constant circuit connected to the switching element, charged when the switch is turned on to turn on the switching element for a certain period of time, and discharged when the switch is turned off, the power source, and a time constant circuit connected to the switching element; , a time constant circuit connected to the switching element, charged when the switch is turned off to turn the switching element on for a certain period of time, and discharged when the switch is turned on.