JPS6240807A - Muting circuit - Google Patents

Abstract

PURPOSE:To suppress a noise from a loundspeaker by executing an on/off inverting operation of a muting transistor by selecting a circuit whose control time is different. CONSTITUTION:A control circuit is divided into (a) and (b) through a diode D4 and D5 by a base resistance R1 of a muting transistor Q1. In this state, when a power source has been cut, an emitter potential of a Q4 for switching control falls earlier than a base potential, a charge voltage of a capacity C3 is biased in the forward direction, and a Q2 for control becomes on and the Q1 becomes on. Accordingly, a noise can be suppressed. Subsequently, Q7 for discharging a Q6 for muting of a large output amplifier 4 is provided through R7, and when the power source has been cut, discharge is executed exactly. As a result, a noise which is generated extending over a comparatively long time from an amplifier when the power source has been turned on and has been cut can be made to correspond to a control inversion time of the circuit (a), an also an impulsive noise of a comparatively short time at the time of switching and operation can be made to correspond to a control inversion time of the circuit (b).

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a muting circuit that suppresses the generation of noise when operating switches in tape recorders and radio receivers.

Conventional technology □ ``A cassette tape recorder with a radio receiver that has a large output suppresses the noise generated from the speaker when the power is turned on, when the tape recorder section operates, or when the operation of the radio tape is switched, so as not to cause discomfort to the user. Equipped with a muting circuit to prevent this from happening.

FIG. 2 shows a conventional muting circuit. In Fig. 2, 1 is an input terminal to which tape playback signals and receiver signals are selected and added using a function switch, 2 is an amplifier circuit, 3 is a volume control, 4 is an amplifier with a large output, 26 is a speaker, 6 is a power supply circuit, and '7 is a main switch. Ql is a muting transistor whose collector and emitter are connected between the transmission line and ground, and Q2 is a muting transistor whose collector is connected to the base of the muting transistor Q1 via a resistor R1. Also, the emitter '7 is a control transistor connected to the power supply circuit 6, and acts to control on/off of the muting transistor Q1. Q3 is emitter grounded and collector
The emitter is provided with a charging capacitor C1, and the collector is a bypass transistor for the charging capacitor C1, which is connected to the base of the control transistor Q2. R2Id is a resistor connected between the emitter and the base of the control transistor Q2, and forms a time constant circuit together with the charging capacitor C1. R5 is a base resistance of the bypass transistor Q5, which is connected to the mute switch 8 via the reverse current blocking diode D1, and the other terminal of the switch is connected to the power supply circuit 6. A capacitor C2 connected to the power supply circuit is connected to a base resistor R5 of a single-path transistor Q5 via a diode D2. 9
is a plunger signal terminal output by the tape play switcher, which is also connected to the base resistor R3 via a diode D5. R4 is a resistor for discharging the capacitor C2. 7 is a main switch, and power supply circuit 6
It also has the function of supplying power to the amplifier 4 and the motor of the tape deck.

Next, the operation will be explained. When the main switch is closed, a predetermined voltage appears in the power supply circuit 6, the amplifier 2.4 becomes operational, and the tape deck circuit is also energized. At this time, the moment the amplifier 2 reaches steady operation, noise is generated. On the other hand, the bypass transistor Q6 is turned on while the current is flowing due to the charging current of the capacitor C2 in the emitter of the control transistor Q2 connected to the power supply circuit 6 and the base circuit of the bypass transistor Q3. . The charging current flows through the time constant circuit of the grounded base and emitter of the transistor Q2 and the charging capacitor C1, so that the control transistor Q2 is activated for a predetermined period of time.
turns on and then the mute 6 vane ink transistor Q1 also turns on, and by selecting the time of this time constant circuit to be longer than the time for the amplifier to stabilize, the noise caused by the amplifier 2 can be suppressed. Next, when the time constant of capacitor C1 and resistor R2 is exceeded, charging current no longer flows to capacitor C1, so control transistor Q2 is turned off, muting transistor Q1 is also turned off, and the signal appearing at input terminal 1 is turned off. is output to amplifier 4. Next, when the main switch 7 is closed and in operation, the muting switch 8 linked to the function switch is closed at the moment of switching, and the plunger circuit linked to the play switch of the tape deck is operated. When the power supply voltage is applied, the diodes D3. Dl is the base resistance R3
The bypass transistor Q5 is turned on through the circuit, and the muting transistor Q1 is turned on in the same way as above, and both the function switching noise and the noise caused by the control of the tape deck are suppressed for a predetermined period of time determined by C1 and R2. It turns out.

Problems to be Solved by the Six Vane Invention Although the conventional muting operation is performed as described above, it has the following problems. The muting operation is not performed when the power is turned off, and the muting operation time is fixed at a relatively long operation time to suppress it when the power is turned on.It is relatively long when switching functions such as tape radios. This increases the muting operation time and causes discomfort to the user. The present invention solves the above problems and does not use mechanical switches etc.
A muting circuit is provided using an electronic element configuration.

Means for Solving the Problems The muting circuit of the present invention has a first control circuit with a long control time and a second control circuit with a short control time to control the on/off inversion operation of the muting transistor by turning on and off the power.
The control circuit is selected to perform the operation.

Function: The muting circuit of the present invention suppresses noise generated from the amplifier for a relatively long period of time when the first control circulation vane path is switched on and off, and suppresses noise generated when switching functions or operating a tape deck. By providing a second control circuit that copes with noise suppression in a short period of time, it is possible to prevent discomfort caused by switching noise during use.

Embodiment FIG. 1 shows an embodiment of the present invention, and the same components shown in FIG. 2 are given the same reference numerals.

The feature of this example is that the base resistor R1 of the muting transistor Q1 connects the first
and second control circuits a and b. In the first control circuit 9, a power cutoff control transistor Q4 is connected to the collector of the bypass transistor Q3 through a diode D7 between the base, emitter, and ivy, and a series circuit of a resistor R5 and a capacitor C3 is connected to the base. The emitter of the control transistor Q2 is grounded through a capacitor C5 and connected to the power supply circuit through a reverse current blocking diode D6. Next, the operation of such a circuit will be explained. The operation when the power is turned on is the same as the conventional example, and the difference is when the power is turned off. However, when the power supply is cut off, the emitter potential of the cut-off control transistor Q4 connected to the power supply circuit falls earlier than the base potential due to the diode D7, so the charging voltage of the capacitor C3 is forward biased and turned on. , the base current of the control transistor Q2 flows to the ground side through the internal resistance of the power supply circuit, and the control transistor Q2 is turned on and the muting transistor Q1 is also turned on. Therefore, noise when the power is turned off can also be suppressed. Next, the transistor Q7 that discharges the muting capacitor C6 of the large output amplifier 4 is connected to the resistor R7.
By providing the battery through the power source, the discharge occurs without fail when the power is turned off, so it is reliable even when the power is repeatedly turned on and off. Therefore, it goes without saying that the 6-order second muting operation, in which the muting operation time can be set as the first time only when the power is cut off, is the same as in the conventional example. However, it can be fixed as the second time.

As described in the detailed description of the invention on page 9, the present invention can make the noise generated from the amplifier over a relatively long time when the power is turned on and off correspond to the control reversal time of the first muting control circuit. . It can also be used as a muting circuit for powering on and off large output amplifiers, and can completely suppress noise emitted from speakers. In addition, since the control reversal time of the second muting control circuit can be used to deal with pulse-like noise that occurs during a relatively short period of time when switching functions or operating a tape deck, it is possible for users of radio cassette recorders to On the other hand, noise does not cause discomfort.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a muting circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional muting circuit. 2...Amplification circuit, 4...Large output amplifier circuit, 6...Power supply circuit, 7...Main switch, a... First muting control circuit, b...Second muting control circuit.

Claims (1)

[Claims] In order to control the on/off operation of the muting transistor by turning on and off the power, a collector of a pnp type semiconductor is connected between the base circuit of the muting transistor and the ground, and a collector of an npn type semiconductor is connected to the base of the pnp type semiconductor. The emitter is grounded and the above p
A first control circuit having a first time constant is connected between the collector and emitter of the npn type semiconductor, the base of the np type semiconductor is connected to another power supply circuit, and the first control circuit controls the on/off operation of the muting transistor. A collector of a pnp type semiconductor is connected between the base circuit of the muting transistor and the ground in order to control the muting transistor with a time constant of 2.
The base of the np type semiconductor is equipped with a second control circuit grounded between the collector and emitter of the npn type semiconductor, and the first and second control circuits are predetermined when the power is turned on/off and the muting switch is operated. A muting circuit characterized in that the muting transistor is inverted after a period of time to turn off the muting transistor.