JPS599446Y2 - Muting control signal generation circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a muting control signal generation circuit, and in particular to a muting control signal generation circuit for preventing the so-called pop sound that occurs when the power switch is turned off in an amplifier having a decoupling capacitor in the power line. Regarding circuits.

In audio equipment, a pop sound may be generated when the power switch is turned off, but this is because a decoupling capacitor is installed in the power supply line of the amplifier, and the terminal voltage of the capacitor drops with a predetermined time constant. However, during this process, the amplifier becomes unstable and exhibits transient phenomena.

Various muting circuits have been devised to prevent the popping sound from occurring. These muting circuits detect when the power is turned off and generate a muting control signal, and this control signal activates the muting switch. However, the circuit structure is complicated and the number of circuit elements is large.

On the other hand, some audio equipment is equipped with a plurality of signal generation sources, such as a cassette tape playback section and a tube section, and the signal output from each of these signal sources is selectively switched and applied to one main amplifier. A structural method has been adopted in which the signal switching is performed by switching the power supply to each signal source.

When the above-mentioned muting circuit is added to this type of audio equipment, there is a drawback that the circuit structure becomes even more complicated.

The object of the present invention is to provide a muting control signal generation circuit having a simple circuit structure suitable for the above-mentioned type of audio equipment.

The present invention will be explained below with reference to the accompanying drawings.

The figure is a circuit diagram showing an embodiment of the present invention.

The amplifier 1 selectively receives each output signal OUT from a cassette tape playback section 2 and a tuner section 3 as signal generating means at an input IN and amplifies the output signal OUT.

The supply signal of the output signal to the amplifier 1 is switched by a combination of a changeover switch S1 and a power switch S2.

In detail, the changeover switch S1 consists of two interlocking switches Sla and Slb, the movable contacts of both of which are connected to the power supply VCC and the power supply line of the amplifier 1, respectively, and one of the fixed contacts of both of them. The Tap e contacts are commonly connected and also connected to the power supply line of the tape reproducing section 2.

The figure shows one switching state of the changeover switch S1, both of which are Tap.
In this state, the power supply Vcc is directly supplied to the power supply line of the amplifier 1 via the changeover switch S1, and the power supply Vcc is also supplied to the tape playback section 2 via the switch Sla. As a result, the tape reproducing section 2 is activated, and its output becomes the input of the amplifier 1.

On the other hand, the power switch S2 is connected to two interlocking series-connected switches S2a and S2b, and the series connection point thereof is connected to the power line of the tuner section 3.

The series connection circuit of these switches S2a and S2b is connected to Tun, which is the other fixed contact of the changeover switches Sla and Slb.
It is connected between the et contacts.

Therefore, the other switching state of the changeover switch S1, that is, Tu
When switching to the ner contact side, the power supply Vcc is applied to the amplifier 1 via the power switch S2, and is also applied to the tuner section 3 via the power switch 32a.

Therefore, the tuner section 3 is activated by closing the power switch S2, and the output of the tuner section 3 is applied to the input of the amplifier 1.

In addition, the selector switch S1 is set to T when the cassette half is installed.
T at the ape contact point and when ejecting the cassette half.
It is designed to automatically switch to each unet contact point.

Furthermore, a series resistance circuit of resistors R1 and R2 is connected between the power lines of the tape playback section 2 and tuner section 3, and this resistance value is equal to the resistance value between each power line of the tape section and tuner section and the ground line. It is set significantly larger than the resistance r.

Further, a resistance dividing circuit consisting of resistors R3 and R4 is connected to both ends of a coupling capacitor C provided in the power supply line of the amplifier 1, which generates a divided output of the terminal voltage.

A PNP} transistor Q1 whose emitter is connected to the series connection point of the resistors R3 and R4 is provided, and the base is connected to the resistor R. and R2 are connected to the series connection point.

Further, the collector serves as a base input of a muting transistor Q2 via a resistor R5, and the transistor Q2 is connected between the output of the amplifier 1 and ground, and conduction/non-conduction is controlled by the collector output of the transistor Q1.

In this structure, if we assume that the cassette half or tape is installed at a predetermined location in the tape playback unit 2, the switch S1 is switched to the Tap e contact side, so that the tape playback output is applied to the amplifier. ing.

In this state, the decoupling capacitor C of the amplifier 1 is charged to Vcc, and the emitter of the transistor Q1 is connected to the emitter bias voltage V by the resistors R3 and R4.
E is supplied and becomes .

The base of the transistor Q1 is supplied with a base bias voltage VB by resistors R1 and R2.

This r represents the resistance between the power supply line of the tape section 2 or the tuner section 3 and the ground, and as described above <R 1 + R 2>
If r is selected, power will not be supplied to the tuner section 3.

In the above equations VE and ■8, R1=R2 and R3≧
Set as R4 ■1≦+VCC, VB>+V
Since it becomes CC, PNP} Langisuda Q1 is in the off state.

Therefore, no signal is output to the collector output of the transistor Q1, the muting transistor Q2 is also turned off, and the tape reproduction output is led to the OUT of the amplifier 1.

On the other hand, when the cassette half is ejected from the tape reproducing section 2, the switch S1 is switched to the Tunr contact.

If the power switch S2 is closed at this time, the power supply Vcc is supplied to the tuner section 3, and a tuner output signal is derived from the output OUT of the amplifier 1 in the same manner as described above.

Also in this case, R++R2>r (r is the resistance of the tape playback section)
Therefore, power is not substantially supplied to the tape reproducing section 2.

Next, when you open the power switch S2 from this state,
The base of transistor Q1 is disconnected from the power supply and the charged capacitor C.

Therefore, the emitter voltage VE of the transistor becomes higher than the base voltage VB, and the transistor is turned on.

Therefore, the discharged charge of the capacitor C flows to the collector through the transistor Q1, turning on the transistor Q2 and enabling a muting operation.

This operation is performed even when the changeover switch S1 is switched, the movable contact of the changeover switch S1 is connected to two fixed contacts, ie, Tun.
It is clear that the muting operation is completely the same since there is a state in which neither the er contact nor the ape contact is contacted.

In this example, a bipolar transistor is used as a means for detecting a gap between the divided voltage of the terminal voltage of the capacitor C and the voltage of the series resistor circuit (R., R2) and operating when this exceeds a predetermined value. Although Q1 is used, it goes without saying that the muting switch Q2 may be controlled using, for example, a field effect transistor or a relay element.

Furthermore, although the case where the signal generating means includes a tape reproducing section and a tuner section has been described, it is obvious that the present invention can also be applied to cases where other circuits are used.

According to the present invention, it is possible to construct a muting control signal generating circuit only by using switches, resistors, and switching elements, so that the circuit can be simple and inexpensive.

Furthermore, the muting control signal generation circuit according to the present invention is configured so that the muting effect is performed by using the discharged charge of the decoupling capacitor when the power is turned off and when switching signals. The number of parts used in equipment etc. can be reduced.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the present invention. Explanation of symbols of main parts 1...Amplifier, 2...
...Tape playback section, 3...Tuner section, S
1... Selector switch, S2... Power switch, C... Coupling capacitor,
Q. ...Transistor, R1 to R5...
·resistance.

Claims (5)

[Scope of utility model registration request] (1) A muting control signal generation circuit for an audio device including first and second signal generation means and an amplifier having a decoupling capacitor in a power supply line and amplifying the output signal of the signal generation means, two interlocking power switches connected in series with each other, the series connection contacts of which are connected to the power supply line of the first signal generating means; and each power supply line of the amplifier and the second signal generating means, and also connects the power supply and the power supply line of the amplifier via a series connection circuit of the power switch in the second switching state. An interlocking selector switch,
A series resistance circuit connected between the power lines of the first and second signal generating means, a voltage difference between a voltage at a series connection point of the series resistance circuit and a divided voltage of the terminal voltage of the decoupling capacitor is a predetermined value. detecting means for detecting that the muting control signal has been reached and generating a muting control signal;
The application of the output signal to the amplifier is switched by selectively supplying power to the amplifier, and a muting effect is performed when the power switch is turned off and when the changeover switch is switched. A muting control signal generation circuit characterized by: (2) The detection means is composed of a transistor, the base of the transistor is connected to the series connection point of the series resistance circuit, a divided voltage of the terminal voltage is applied to the emitter of the transistor, and a voltage divided from the terminal voltage is applied from the collector of the transistor to the A muting control signal generating circuit according to claim 1, characterized in that the muting control signal generating circuit derives a muting control signal. (3) The resistance value of the series resistance circuit is larger than each resistance value between the power supply line of the first and second signal generating means and the reference potential, Claim 1 The muting control signal generation circuit according to item 1 or 2. (4) The divided voltage of the terminal voltage is the output of a dividing circuit in which first and second resistors are connected in series in this order at both ends of the coupling capacitor. The muting control signal generation circuit according to item 1, item 2, or item 3. (5) The series resistance circuit includes third and fourth resistors having equal resistance values, and the resistance value of the first resistor is selected to be greater than or equal to the resistance value of the second resistor. A muting control signal generation circuit according to claim 4 of the utility model registration claim.