JPS6130326Y2 - - 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 when the power is turned on, such devices generate a noise called shock noise that is generated from the amplifier circuit, especially the preamplifier circuit to which low-level signals are input. It becomes a problem. 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. 4 is a negative feedback circuit provided to set the gain of the preamplifier circuit 2, and resistors 5, 6, 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 is the output terminal of the preamplifier circuit 2 and the main amplifier circuit 11
This is a muting diode inserted and connected in the signal transmission path 14 between the input terminal of the preamplifier circuit 2 and the output terminal of the preamplifier circuit 2 to be applied to the cathode side. 15 is a first bias resistor connected between the anode of the muting diode 13 and the power supply; 16 is a base connected to the power supply side terminal of the capacitor 9 constituting the negative feedback circuit 4 via a resistor 17; It is a control transistor whose emitter is grounded and whose collector is connected to the cathode side of the muting diode 13 via a second bias resistor 18. 19 and 20 are the output side of the preamplifier circuit 2 and the main amplifier circuit 11, respectively.
This is a DC blocking capacitor installed on the input side of the

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 waveform-shaped into a panel-shaped signal by the capacitor 19 and the like. Such a signal is input to the main amplifier circuit 11, amplified, and emitted as a shock sound by the speaker 12. In the circuit of the present invention, a muting diode 13 is inserted and connected in the signal transmission path 14. Therefore, when the power is turned on, the pulse-like signal generated from the preamplifier circuit 2 is not input to the main amplifier circuit 11 and is sent to the speaker 12.
No more sound is emitted. That is, when power is supplied to the preamplifier circuit 2, the above-mentioned pulse-like signal is generated, but since the charging operation of the capacitor 9 constituting the negative feedback circuit 4 is performed through the resistor 7, etc., its charging potential gradually increases. As a result, the control transistor 16 remains non-conductive until its charging potential exceeds a predetermined value. Therefore, during that time, the muting diode 13 is in a non-biased state and is in a non-conducting state, and the above-mentioned pulse-like signal is blocked from being input to the main amplifier circuit 11 by the muting diode 13, so that no shock noise is produced. No sound is emitted from the speaker 12. 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 capacitor 9
Since the charging potential of the control transistor 16 rises to a predetermined value or more, the control transistor 16 which has been in a non-conducting state is reversed to a conducting state. When the control transistor 16 is reversed to a conductive state, a bias circuit for the muting diode 13 is formed by the first bias resistor 15, the second bias resistor 18, and the control transistor 16, and the muting diode 13 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 13, but is applied to the variable resistor 10, level-adjusted, and then sent to the main amplification circuit. It is input to the 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.

In this embodiment, the muting diode 1
Although the control transistor 16 for controlling the bias circuit No. 3 is connected between the signal transmission line 14 and the ground, it can also be connected between the power supply and the signal transmission line 14.

As explained above, the shock noise prevention circuit of the present invention involves inserting and connecting a diode in the signal transmission path, and using the bias circuit of the diode to charge the capacitor that constitutes the negative feedback circuit that sets the gain of the preamplifier circuit. By controlling a control transistor controlled by electric potential, the noise signal generated from the preamplifier circuit is prevented from being input to the main amplifier circuit when the power is turned on, making the configuration extremely simple and popular. The present invention is suitable as a shock noise prevention circuit for acoustic equipment.

[Brief explanation of the drawing]

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, 13... Muting diode,
14...Signal transmission path, 15...First bias resistor, 16...Control transistor, 18...Second
Bias resistance.

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 that constitutes a feedback circuit and is connected between the negative feedback path and ground, a muting diode that is inserted and connected in the signal transmission path between the preamplifier circuit and the main amplification circuit, and A shock noise prevention circuit for an audio device, comprising a control transistor that is inverted to a conductive state when the charged potential of the capacitor rises above a predetermined value to form a bias circuit for the muting diode.