JPH0127359Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an audio control circuit in a television receiver or the like.

Some television receivers have a built-in sound field expansion circuit in order to obtain a sound field expansion effect.

FIG. 1 shows a conventional audio control circuit incorporating a sound field expansion circuit. In the figure, 1 is a DC voltage application terminal for volume control, and a DC voltage is applied to this terminal 1. 2 is a current limiting resistor, 4 and 5 are voltage dividing resistors, 3 is a buffer transistor, 4,
5 is a voltage dividing resistor, 6 is a diode, and 7 is a switch linked to a switch (not shown) for turning on/off the sound field expansion circuit 9.

The sound field expansion circuit 9 receives left and right audio signals R, L.
It consists of a synthesis circuit 10 for synthesizing the signals, a delay circuit 11, a phase shift circuit 12, and adders 13 and 14. 15 is an audio amplification circuit in the volume control circuit 16; this audio amplification circuit 15 controls the bias of the transistor 3 by changing the control voltage V applied to the DC voltage application terminal 1; connected resistor 17
The audio output of the audio amplifying circuit 15 is controlled by the voltage output across the audio amplifier circuit 15.

18 and 19 are left and right power amplification circuits, and each of these power amplification circuits 18 and 19 is connected to a changeover switch 2.
The internal speakers 22 and 23 are switched and connected to external speakers 24 and 25 via the speakers 0 and 21, respectively.

In the above configuration, if the DC voltage V applied to the DC voltage application terminal 1 decreases, the transistor 3
When the bias of the audio amplifier circuit 15 decreases, the audio output of the audio amplifier circuit 15 increases, and in the opposite case, the audio output decreases.

On the other hand, the left and right audio signals R and L applied to the sound field expansion circuit 9 are synthesized by a synthesis circuit 10, this synthesized signal is delayed for a predetermined time by a delay circuit 11, and this delayed signal is applied to the left audio signal R. are applied to the audio signal L on the left side in the same phase and in opposite phase to the left audio signal L by the phase shift circuit 12, and these signals are applied to the adder 13,
Add at 14. In this way, by adding the delayed signal to the original signal, the sound field expansion effect is exhibited.

In the sound field expansion circuit 9, when the delayed signal is added to the original signal, since the delayed signal is in phase with the original audio signal R on the left side, the amplitude of the synthesized signal is greater than that of the original signal. Therefore, if the control voltage V applied to the DC voltage application terminal 1 is lowered, the bias of the transistor 3 is lowered, and the audio output of the audio amplification circuit 15 is increased to increase the volume, the ratings of the speakers 22 and 23 used are Exceeding this may distort the sound or damage the speakers 22, 23.

To prevent this, conventionally, when the sound field expansion circuit 9 is turned on, the switch 7, which is linked to the switch that turns on and off the sound field expansion circuit 9, is also turned on. When switch 7 is turned on, a voltage obtained by dividing the +B voltage by resistors 4 and 5 is applied to the base of transistor 3 via diode 6 and switch 7, so that the bias of transistor 3 is below a certain value, that is, The volume level is maintained so that it does not fall below a certain value. As a result, the volume of the speakers 22 and 23 used is suppressed below the rated value, causing the sound to be distorted and the speakers 22 and 23 to be used.
There is no risk of damaging the 23.

However, depending on the receiver, as shown in the figure,
Internal speaker 2 built into this receiver
In addition to 2 and 23, another external speaker 2
Some devices are equipped with connection terminals 20 and 21 for connecting the terminals 4 and 25.

Even if you connect the external speakers 24, 25, which can produce a volume sufficiently higher than the ratings of the internal speakers 22, 23, to the connection terminals of such a receiver, and try to achieve a large sound field expansion effect, the above-mentioned problem will not occur. When the sound field expansion circuit 9 is on, the switch 7 is turned on as described above, and the divided voltage of the resistors 4 and 5 is applied to the base of the transistor 3 via the diode 6 and the switch 7. Therefore, the bias of the transistor 3 is suppressed to a certain value or less, and the external speakers 24 and 25 have a disadvantage that they cannot produce a large sound field expansion effect.

This invention was made in order to eliminate the drawbacks of the conventional ones mentioned above, and by providing a switch that operates in response to a changeover switch for switching the audio output from the internal speaker to the external speaker, it is possible to connect the external speaker. It is an object of the present invention to provide an audio control circuit that can obtain maximum output even if a sound field expansion circuit is activated at times.

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

In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. 8 outputs audio from internal speaker 2
This switch is interlocked with a changeover switch for switching from external speakers 2 and 23 to external speakers 24 and 25, and this switch 8 is interlocked so that it is turned off when the changeover switch is on the external speaker side.

Therefore, even when the sound field expansion circuit 9 is working, that is, the switch 7 is on,
Since the switch 8 is off when an external speaker is connected, the base of the transistor 3 is disconnected from the +B voltage. This releases the clip on the base voltage of the transistor 3, making it possible to control the volume over the entire range of the control voltage from the DC voltage application terminal 1, making it possible to obtain the maximum output from the external speaker. .

Further, when the internal speaker is connected, the switch 8 is turned on and the volume is limited as in the case of FIG. 1, so that the sound will not be distorted or the speaker will be damaged.

In the above embodiment, a case was shown in which a contact switch 8 linked to the audio output changeover switch was provided, but in order to suppress the increase in the number of switch circuits, a high impedance element was connected to the changeover switch itself. This allows you to use electronic switches to achieve your goals.

As mentioned above, this invention not only prevents audio distortion and damage to the speakers by limiting the volume when connecting internal speakers, but also prevents the maximum output even if the sound field expansion circuit is operating when external speakers are connected. There is an advantage that you can get

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional audio control circuit, and FIG. 2 is a circuit diagram showing an embodiment of the audio control circuit according to this invention. 1... DC voltage application terminal, 2, 4, 5... Resistor, 3... Transistor, 7... First switch, 8... Second switch, 9... Sound field expansion circuit, 20, 21 ...Selector switch, 16...Volume control circuit, 22, 23...Internal speaker, 24,
25...External speaker. In addition, the same symbols in the figure are
Indicates the same or equivalent part.

Claims (1)

[Scope of utility model registration request] a first switch that operates in response to on/off of the sound field expansion circuit; a volume control circuit that limits the volume to below a certain level via the first switch; and the first switch and the volume control circuit. and a second switch provided between the switch and the switch, which operates in correspondence with a switch for switching the audio output of the sound field expansion circuit from the internal speaker to the external speaker. An audio control circuit characterized in that the second switch is configured to cut off the connection between the first switch and the volume control circuit when the switch is connected to an external speaker.