JPS6267705A - Tape recorder with built-in microphone - Google Patents

Abstract

PURPOSE:To eliminate the countermeasure against howling by using a mechanical switch only to turn on/off a power line of a built-in microphone and grounding the power line at turn-off directly or via a resistor R. CONSTITUTION:The power line of the built-in microphone 1 is turned on/off by a switch SW1-2 via a bias resistor R1 and grounded via a resistor R4 when the built-in microphone 1 is turned off. A minute current flowing from a low frequency muting circuit is prevented by the grounding via the resistor R4, the current activates the built-in microphone 1 to prevent generation of howling. It is desirable that the resistance of the resistor R4 is reduced at a minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tape recorder with a built-in microphone.

Conventional technology FIG. 2 shows a conventional tape recorder with a built-in microphone.

In Figure 2, built-in microphone 1 has a dubbing switch S.
The p + B power supply is applied as a bias through W1, and the output of the built-in microphone 1 is connected to the capacitor C1 and the resistor R.
2 to the recording/reproduction changeover switch SW2. When the recording/reproducing switch 1sW2 is in the recording R position, the output of the built-in microphone 1 is applied to the recording/reproducing amplifier 2 via the capacitor 05. TR1 is a switching transistor whose base is grounded via a capacitor C4, and a resistor R4 is inserted between the base and collector.
The emitter of the switching transistor TR1 is connected to the built-in microphone 1 via a resistor R3. The collector of the switching transistor TR1 is connected to the first terminal B of the dubbing switch SW1 via a resistor R5 and to a low frequency muting circuit via a diode D1.

In such a conventional tape recorder with a built-in microphone, the dubbing switch SW1 is connected to the second and third terminals.
In order to prevent built-in microphone 1 from operating during dubbing, built-in microphone 1 is set to 0FFL by switching the switching transistor TR1 installed in the power supply line of built-in microphone 1, and at the same time, when built-in microphone 1 is operated, no-ring occurs. To prevent this, muting was applied to the low frequency signal via diode D1.

Problems to be Solved by the Invention However, in the conventional device, due to the difference in time constant between the rise and fall of the low frequency muting circuit and the rise and fall of the built-in microphone 1, Uring may occur. Further, at 077 o'clock in the built-in microphone 1, a minute current flows from the low frequency muting circuit, which may cause the built-in microphone to operate and cause howling.

For this reason, it is necessary to adjust the switching timing 9 to prevent howling, and to provide a diode D1 in the line to the low frequency muting circuit in order to prevent a minute current from flowing into the built-in microphone 1. Sorry for the high cost.

SUMMARY OF THE INVENTION The present invention has been made to solve these conventional problems, and aims to provide a tape recorder with a built-in microphone that enables ON/OFF control of the built-in microphone with a simple circuit configuration. do.

Means for Solving the Problems The tape recorder with a built-in microphone of the present invention can turn the built-in microphone's power line ON-OFF (...
Another feature is that at 077, the power supply line is grounded directly or via a resistor R.

Function: The tape recorder with a built-in microphone of the present invention turns on the power line of the built-in microphone using a mechanical switch.

Since it is grounded directly or through the resistor R at 077, the built-in microphone will not operate due to the minute current from the low frequency muting circuit and generate howling, and the built-in microphone will not turn on.
, the OFF control can be performed with a simple circuit) and there is no need to take any special measures against ringing.

Embodiment A tape recorder with a built-in microphone according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the invention. In Fig. 1, the power line of the built-in microphone 1 is turned on and off by the switch 5W1-2 via the bias resistor R1, and the switch 5W1-1 connects the built-in microphone 1 to ground via the resistor R4 at 077. ing. The grounding provided by the resistor R4 prevents a small current from flowing in from the low frequency muting circuit, and this current causes the built-in microphone 1 to operate, thereby preventing the occurrence of no-ring. However, it is desirable that the value of the resistor R4 be as small as possible.

Effects of the Invention As described above, the tape recorder with a built-in microphone of the present invention allows the built-in microphone to be turned off only by a mechanical switch.
This can be done with a simple circuit that turns off N and OFF, and can prevent the secondary problem of howling), and is extremely cost-effective and practical.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a tape recorder with a built-in microphone according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional tape recorder. 1... Built-in microphone, R1, R,... Resistor, 5W1-1.5W1-2... Dubbing switch.

Claims (1)

[Claims] The power line of the built-in microphone is interrupted by a dubbing switch, and the power line is interlocked with the dubbing switch so that the microphone does not operate due to a minute current flowing from other circuits connected to the power line that is disconnected when the dubbing switch is disconnected. A tape recorder with a built-in microphone in which the above power line is grounded with a switch or grounded via a resistor.