JPS5895411A - Small-sized acoustic device - Google Patents

Abstract

PURPOSE:To prevent the shock sound and the hum sound due to power on even if an external speaker is connected at the power on time, by providing a transistor circuit, which is turned off for a certain time after power on, between the earth contact piece of a jack for connection of the external speaker and the earth. CONSTITUTION:A muting transistor TR7 is connected between the earth contact piece of a jack 5 for connection of an external speaker and the earth; and when a power supply switch 11 is made to start the operation of an amplifier 4, the jack 5 is disconnected from the earth for a while after power on and the output closed circuit of the amplifier 7 is not constituted because a delay circuit consisting of a resistance 12 and a capacitor 9 delays the turn-on operation of the muting TR7, and thus, the shock sound and the hum sound generated at the power on time are not outputted to the external speaker.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to small-sized audio equipment such as small-sized radio receivers and small-sized Arr recorders, and an object of the present invention is to provide an excellent small-sized audio equipment with a simple configuration.

In general, small radio receivers and tape recorders use small speakers and do not produce much low frequency range, so the shock noise that occurs when the power is turned on and the hum that occurs when using AC power are hardly noticeable. . Therefore, most of these small-sized audio devices are not provided with a muting circuit for preventing the above-mentioned shock noise and hum noise.

The present invention aims to reduce the shock noise and hum noise, which can be very harsh when using external speakers such as earphones or headphones in such small audio equipment. The objective is to provide an excellent compact audio device that can effectively prevent such problems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The compact audio device of the present invention will be described below with reference to drawings of one embodiment. In the figure, 1 is an input terminal to which a low frequency signal obtained from a radio receiving circuit, tape recorder body, etc. is applied, 2 is a preamplifier that amplifies the signal applied to input terminal 1, and 3 is a variable resistor for adjusting the volume. 4 is a main amplifier that further amplifies the signal input through the variable resistor 3, and 5 is a JL connected to the output terminal of the main amplifier 4.
A jack for connecting an external speaker, a home-work speaker connected to the output end of the main amplifier 4 via the contacts 5a and 5b of the 6C1 jack 5, and 7 is between the ground contact 6C of the Janok 5 and the ground. 8 and 9 are resistors and capacitors connected between the base and emink of the transistor 7, 10 is a power supply terminal, 11 is a power switch, 12 is a power switch 11
Resistors 13 and 14 connected between the base of the transistor 7 and the base of the transistor 7 are a resistor and a capacitor, respectively.

When using the built-in speaker 6 without connecting an external speaker to the jack 6 on the Doi Minoru/stream side, a shock or hum sound may occur when the power is turned on, as in the conventional case, but the built-in speaker 6 itself is relatively small. There's not a lot of bass, so there's almost no harshness to the ears.

Now, if we connect external speakers such as earphones and headphones to jack 5, these external speakers can effectively reproduce up to a relatively low range, so i-, g
The shock sound and hum sound may become louder and may be unpleasant to the ears. However, according to the above embodiment, since the muting transistor 7 is connected between the ground contact 5C of the jack 5 and the ground, these shock noises and hums can be effectively prevented. .

In other words, Jack 5, earphones, and belly button! - Even if the power switch 11 is turned on with an external speaker such as a horn connected, the power supply voltage applied to the power terminal 10 is immediately applied to the amplifiers 2 and 4, and a shock sound or noise is heard at the output terminal of the amplifier '4. - A hum sound appears, but in this case, the muting transistor 7 is off, and no yaw or hum sound is emitted from the external speaker. When the capacitor 9 is charged and the transistor 7 is turned on, the output of the amplifier 4 is applied to the external speaker, and the desired sound can be heard from the universal external speaker.

In this way, according to the above embodiment, the muting transistor 7 is connected between the ground contact of the jack 5 to which an external speaker is connected and the ground, thereby eliminating the shock noise and hum noise that occur when the power is turned on. Since the configuration is such that the output of the amplifier 4 is applied after a certain period of time by blocking the signal from being applied directly to the external speaker, noise and hum may occur when the external speaker is connected, causing a buzzing noise. This is extremely advantageous in practice.

As is clear from the above embodiments, according to the present invention, it is possible to effectively prevent shock and hum sounds when the power is turned on with a very simple configuration, and as a whole, a small and excellent audio device can be produced at low cost. It has the advantage of being able to provide

[Brief explanation of drawings]

The figure is a schematic electrical connection diagram of an embodiment of a small audio device of the present invention. 1... Input terminal, 2... Preamplifier,
3...Variable resistor, 4...Main amplifier, 5...Jack for external speaker connection, 6...
... Built-in speaker, 7 ... Muting transistor, 8, 12.13 ... Resistor,
9, 14... mark: capacitor, 1o: mountain: power terminal, 11... power switch. 'Name of agent: Patent attorney Toshio Nakao and one other person, I.

Claims (1)

[Claims] Connect a muting transistor between the ground contact of the external speaker connection jack and the ground, and connect a capacitor between the base and emitter of this transistor.
A small audio device in which the base of the above transistor is connected to a power switch via a resistor.