JPS5923217Y2 - Built-in microphone power switching circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a power switching circuit for a built-in microphone in a magnetic recording/playback device. It is an object of the present invention to provide a power supply switching circuit for a built-in microphone that can prevent howling of the microphone.

An example of a conventional magnetic recording/playback device capable of monitoring a built-in microphone in a recording state will be described with reference to FIG.

FIG. 1 shows the main circuits of a tape recorder. In the playback state, the recording and playback selector switches 1 and 1 operate in conjunction with each other. 2. 3 reproduction side terminals 1a, 2a, 3a and common terminals 1b, 2b.

3b is short-circuited, (+81) is not supplied to the built-in microphone 4, so it does not operate, and the playback signal from the magnetic head 5 is transmitted to the recording/playback amplifier 6, resistor R1, volume control R1, and The speaker 8 is driven through the main amplifier 7.

Also, in the recording state, the recording/playback selector switch 1. 2.
3 recording side terminals IC, 2C, 3C and common terminal 1b.

Since 2b and 3b are short-circuited, power (+Bt) is supplied to the built-in microphone 4 through the resistors R2 and R3, so the built-in microphone 4 operates, and its output passes through the capacitor C1 and the resistor R4. The signal is input to the recording/playback amplifier 6, and is amplified by the recording/playback amplifier 6.

A part of the output of the recording/playback amplifier 6 is divided by a resistor R1 and a resistor R5 to a level that does not cause howling, and then passes through a volume VR1 and a main amplifier 7 to drive a speaker 8, while the remaining part is not shown. is input to the magnetic head 5 via a predetermined circuit, and recorded on a magnetic tape by the magnetic head 5.

However, normally, the recording/playback selector switch 1. 2. 3 is shorting switch (terminal 1a, lb, I
C, 2a, 2b.

2C, 3a, 3b, and 3C are all connected during switching), so when switching from the playback state to the recording state, the terminals 3a, 3 of the recording/playback selector switch 3
If the terminals 1a, lb, and IC of the recording/playback switch 1 are short-circuited before the terminals b and 3C are short-circuited, or when switching from the recording state to the playback state, the terminal 1C of the recording/playback switch 1 becomes the terminal 1a. If the terminal 3C of the recording/playback switch 3 is not short-circuited to the terminals 3a and 3b before it is not short-circuited to , lb, the built-in microphone 4 operates because the resistor R5 is not grounded. However, the human power signal to the main amplifier 7 does not reach an appropriate level, which causes a howling phenomenon between the built-in microphone 4 and the speaker 8.

Of course, on the other hand, there is a switching timing between the recording and playback switch 1 and 3, and when switching from playback to recording, the recording and playback switch 3 is set before the terminals 1a, lb, and IC of the recording and playback switch 1 are short-circuited. Terminals 3a, 3b
, 3C are short-circuited, and when switching from recording to playback, the terminal 3C of the recording/playback selector switch 3 is connected to the terminal 3a,
It is conceivable that the terminal 1C of the recording/playback switch 1 is not short-circuited to the terminals 1a and lb before it is not short-circuited to the terminal 3b. Changeover switches have the drawbacks of poor mass production, high cost, and the need for special switches.

The present invention is intended to eliminate the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to the drawings.

In FIG. 2, reference numeral 9 denotes a recording/playback selector switch, the playback side terminal 9a of the record/playback selector switch 9 is connected to the base of the transistor Q1 via a resistor R6, and the common terminal 9b is connected via a resistor R7. It is connected to the collector of transistor Q1, and the recording side terminal 9C is connected to the power supply (10B2
)It is connected to the.

Further, the recording/playback changeover switch 9 is interlocked with the recording/playback changeover switches 10 and 11.

The emitter of the transistor Q1 is grounded,
A connection point between the collector and the resistor R7 is connected to the built-in microphone 12 via a resistor R8.

The connection point between the built-in microphone 12 and the resistor R8 is connected to the recording/playback selector switch 1 via a capacitor C2 and a resistor R9.
It is connected to the recording side terminal 10C of 0.

The playback side terminal 10a of the recording/playback switch 10 is connected to the magnetic head 13, and the common terminal 10b is connected to the recording/playback amplifier 14 and the volume VR via the resistor R1o.
Connected to one end of 2.

The other end of the volume vR2 is grounded, and the movable piece is connected to the speaker 16 via the main amplifier 15.

The connection point between the resistor R1o and one end of the volume VR2 is connected to the recording side terminal 11C of the recording/playback switch 11 via the resistor R1□, and the playback side terminal 11a of the recording/playback switch 11 is connected to either is not connected and is in an open state, and the common terminal 11b is grounded.

Next, the operation will be explained.

In the playback state, the playback side terminal 9a of the recording/playback selector switch 9
and the common terminal 9b are short-circuited, so the transistor Q
1 is completely disconnected from the power supply (10B2) and does not operate at all, and in the recording state, the recording side terminal 9C of the recording/playback switch 9 and the common terminal 9b are short-circuited, so the base of the transistor Q1 is in an open state. It doesn't work at all.

Therefore, in the recording state and the playback state, the operation is exactly the same as that described for the circuit of FIG. 1.

However, when switching the recording/playback selector switch 9, the terminal 9
When a, 9b, and 9C are short-circuited, a current flows from the power supply element B2 to the base of the transistor Q1 via the resistor R6, and a current also flows to the collector via the resistor R7, turning the transistor Q1 on, and the power supply ( Since the built-in microphone 12 is divided by the resistor R7 and the transistor Q1, sufficient power is not supplied to the built-in microphone 12 and it does not operate.

Therefore, when switching from the playback state to the recording state, the terminal 11a of the recording/playback changeover switch 11.

If terminals 9a, 9b, and 9C of the recording/playback switch 9 are short-circuited before 11b and 11C are short-circuited, or when switching from the recording state to the playback state, the terminal 9C of the recording/playback switch 9 Before terminals 9a and 9b are short-circuited, terminal 1 of recording/playback selector switch 11
Even if R1C is not short-circuited to terminals 11a and 11b, the built-in microphone 12 does not operate although the resistor R1 is not grounded.
No howling phenomenon occurs between the built-in microphone 12 and the speaker 16.

The present invention can be implemented as described above, and has a simple configuration in which one transistor is added to the conventional circuit, and uses a conventional changeover switch to suppress /'% ringing of the built-in microphone during recording/playback switching operation. It can be prevented, and its industrial utility value is extremely large.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the main parts of a conventional tape recorder;
The figure is a circuit diagram showing an embodiment of the present invention. 9-11...Recording/playback selector switch, 9a-11a
...Playback side terminal, 9b to 11 b...Common terminal, 9
0 to 11 C...Recording side terminal, 12...Built-in microphone, R6-R8...Resistor, Ql...Transistor, (10B2)...Power supply.

Claims (1)

[Scope of utility model registration request] A shorting type first recording/playback selector switch inserted into the power supply circuit of the built-in microphone, a collector connected to a common terminal of the first recording/playback selector switch via a first resistor, and a second a transistor connected to the built-in microphone via a resistor, whose base is connected to the playback terminal of the first recording/playback selector switch via a third resistor, and whose emitter is grounded; and the output of the recording/playback amplifier. a shorting-type second recording and playback switch inserted at the end of the switch; the recording side terminal of the first recording and playback switch is connected to the power supply of the built-in microphone; teeth,
Leave the playback side terminal open, and ground the common terminal.
A power supply switching circuit for a built-in microphone, characterized in that a recording side terminal is connected to a main volume via a fourth resistor and connected to an output terminal of the recording/playback amplifier via a fifth resistor.