JPS6218973Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a shock noise prevention circuit for an audio device such as a tape recorder.

Recently, portable audio devices such as tape recorders with radios have become popular, but such audio devices have a problem with the noise called "shock noise" that occurs when the power is turned on. Various circuits have been developed to prevent such shock noise, but many have complex circuit configurations and are expensive, making them unsuitable for widespread use in audio equipment.

The present invention has been developed in view of these points, and will be described in detail below with reference to the illustrated embodiments. In the figure, 1 is a power switch, and 2 is a preamplifier circuit that is supplied with power and becomes operational when the power switch 1 is closed, and receives a low-level signal such as a magnetic tape playback signal. It is equipped with an input terminal 3. Reference numeral 4 denotes a negative feedback circuit provided to set the gain of the preamplifier circuit 2, and resistors 5, 6, and 7 set the feedback amount, feedback frequency, etc.
and a capacitor 8, etc., and a capacitor 9 is connected between the negative feedback path and ground. 10 is a variable resistor to which the signal amplified by the preamplifier circuit 2 is applied and adjusts the level of the signal; 11 is activated when power is supplied by closing the power switch 1; The main amplifier circuit 12 receives the signal whose level has been adjusted by the variable resistor 10, and the speaker 12 receives the signal amplified by the main amplifier circuit 11 and emits the signal. 13 and 14 are a resistor and an adjustment variable resistor provided to adjust the level of the output signal of the preamplifier circuit 2, and are connected to a signal transmission line 15 and between the signal transmission line 15 and the ground, respectively. There is. Reference numeral 16 denotes a muting diode inserted and connected within the signal transmission path 15, and is connected so that the output signal of the preamplifier circuit 2 is applied to the cathode side. 17 is a bias resistor connected to apply a bias voltage from the negative feedback circuit 4 to make the muting diode 16 conductive in a normal operating state; 18 and 19 are connected to the output side and the main circuit of the preamplifier circuit 2, respectively; This is a DC blocking capacitor provided on the input side of the amplifier circuit 11.

The present invention is constructed as described above, and its operation will be explained next. When the power switch 1 is closed, power is supplied to the preamplifier circuit 2 and the main amplifier circuit 11 through the power switch 1, and the amplifier circuits 2 and 11 enter a steady operating state after a predetermined period of time. When power is supplied to the preamplifier circuit 2, a DC voltage immediately appears at its output terminal, and the DC voltage is differentiated by a capacitor 18, a resistor 13, and an adjusting resistor 14 to become a pulse-like signal. Such a signal is input to the main amplifier circuit 11, amplified, and emitted as a shock sound from the speaker 12. However, in the circuit of the present invention, a muting diode 16 is inserted and connected in the signal transmission path 15. The pulse-like signal generated when the power is turned on is not input to the main amplification circuit 11, and no sound is emitted from the speaker 12. That is, when power is supplied to the preamplifier circuit 2, the above-mentioned signal is generated, but since the charging operation of the capacitor 9 forming the negative feedback circuit 4 is performed gradually, the charging potential of the capacitor 9 becomes a predetermined potential. Until then, the muting diode 16 is in a non-conducting state, and no noise is input to the main amplifier circuit 11 during that time.
In this way, the noise that occurs when the power is turned on, that is, the shock sound, is prevented from being emitted from the speaker 12, but after a predetermined period of time, the charged potential of the capacitor 9 rises above a predetermined value, so the anode of the muting diode 16 is biased. A bias voltage is applied through the muting resistor 17, and the muting diode 16 becomes conductive. Therefore, in the normal operating state, the magnetic tape playback signal etc. amplified by the preamplifier circuit 2 is not blocked by the muting diode 16, but is applied to the variable resistor 10, level-adjusted, and then sent to the main amplifier circuit. 11. The reproduced signal etc. input to the main amplification circuit 11 is sufficiently amplified and then applied to the speaker 12 and emitted as a sound, so that the user can listen to the reproduced signal etc. without any trouble.

As explained above, the shock noise prevention circuit of the present invention connects and inserts a diode in the signal transmission path, and uses the charging potential of the capacitor that constitutes the negative feedback circuit that sets the gain of the preamplifier circuit. The control prevents the noise signal generated from the preamplifier circuit from being input to the main amplifier circuit when the power is turned on, making the configuration extremely simple. is suitable.

[Brief explanation of drawings]

The illustrated circuit is one embodiment of the shock noise prevention circuit of the present invention. Explanation of main figure numbers, 1...Power switch, 2...
Preamplifier circuit, 4 ... Negative feedback circuit, 11... Main amplifier circuit, 15... Signal transmission line, 16... Muting diode, 17... Bias resistor.

Claims (1)

[Scope of utility model registration request] a preamplifier circuit to which a small level signal is input and has a negative feedback circuit; a main amplification circuit to which a signal amplified by the preamplifier circuit is input and further amplifies the signal; A capacitor constituting a feedback circuit and connected between the negative feedback path and ground; and a capacitor inserted and connected in a signal transmission path between the preamplifier circuit and the main amplification circuit, and the charging potential of the capacitor is set to a predetermined value. A shock noise prevention circuit for an acoustic device comprising a muting diode that is biased into a conductive state by the DC voltage from the negative feedback circuit when the voltage rises above a certain value.