JPS5838845B2 - Method for preventing abnormal signal generation in small tape recorder - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a method for preventing abnormal signal generation in a small tape recorder, and more specifically, to a small tape winding shaft! - A method for preventing a magnetic head from generating an abnormal signal.

Many of the compact or ultra-compact tape recorders have a case that is made of a light metal such as aluminum.

The mechanism and electric circuit of the tape recorder are built into this outer casing, but because the space inside the casing is extremely narrow, each component is placed close to the other.

In addition, electrical circuits and electrical circuit components are installed on printed circuit boards and are built into them, but because printed circuit boards are also very small, the input and output of amplifier circuits in electrical circuits are also extremely close together, and electrical and magnetic Not desirable.

Therefore, in an electric circuit in such a state, the following drawbacks occur.

Since a relatively large current flows through the output transformer in an electric circuit, the magnetism generated by this is also large.
This adversely affects the magnetic head through the air and the metal case.

That is, part of the output signal is magnetically fed back to the magnetic head, causing the magnetic head to oscillate or generate an abnormal signal.

This drawback becomes more noticeable especially when the output level is high.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preventing abnormal signal generation in a small tape recorder, which eliminates such drawbacks.

The present invention will be explained below with reference to an illustrated example.

Note that this example describes a case where the present invention is applied to an ultra-small tape recorder that uses a well-known micro cassette tape, but the present invention can also be applied to a tape recorder that uses a compact cassette tape and other tape recorders. Of course.

FIG. 1 is a perspective view showing a well-known micro cassette tape 1 and a micro tape recorder 2 to which this cassette tape 1 is installed.

In FIG. 1, the tape recorder 2 has a rectangular outer casing made of metal such as aluminum.
The left side is the front, and the right side is the rear.

A mounting portion 2a for the cassette tape 1 is provided in the upper half near the front.

Inside the mounting portion 2a, a tape supply shaft 4 and a tape winding shaft 5 are disposed at predetermined positions, penetrating through the decorative board 3, as well as positioning shafts for correctly determining the mounting position of the cassette tape 1. The pin 6.7 and the capstan 8, which transports the tape at constant speed, extend out.

Furthermore, a lug detection member 9 for preventing mistaken erasure of the installed cassette is exposed on the outer side near the front inside the mounting section 2a.
In conjunction with the pressing operation of a recording operation button, which will be described later, the presence or absence of a lug for preventing accidental erasure of the installed cassette is detected.

Inside the cassette mounting section 2a near the rear of the recorder, there are an erasing head 10, a recording/playback magnetic head 11, a pinch roller 12, and a mounting cassette retaining member 13, which are respectively mounted on immovable substrates to be described later. positioned.

The erasing head 10 is composed of a permanent magnet, and when a recording operation button (to be described later) is pushed to a predetermined position, it moves in conjunction with this and comes into contact with the magnetic tape surface in the installed cassette, thereby eliminating the need for recording tracks. Erase the recorded signal.

The magnetic head 11 moves in the longitudinal direction of the casing in conjunction with the pressing operation of a playback operation button, which will be described later, and comes into contact with the magnetic tape surface of the installed cassette to perform recording or playback operations.

Further, the pinch roller 12 moves in conjunction with the pressing operation of a playback operation button, which will be described later, and presses against the capstan 8 via the expanded magnetic tape in the mounting cassette, and cooperates with the capstan to release the tape. serves to transport.

Micro cassette tape 1 mounted on the mounting section 2a
As is well known, the tape hub 1 for winding the tape can be rotated freely with some play in the cassette body 1a.
b, 1c are arranged, one tape hub 1b is fitted to the tape supply shaft 4, and the other tape hub 1c is fitted to the tape winding shaft 5, respectively, and the inward projections of each hub 1b, 1c are When the shafts 4 and 5 are engaged with the outward protrusions of the shafts 4 and 5, and one of the shafts 4 and 5 is tilted or driven,
Both hubs 1b and 1c also rotate in the same direction, so that the tape wound on one hub is wound on the other hub.

In addition, the micro cassette tape 1 has positioning holes 1d and 1 which fit into the positioning pins 6.7, respectively.
e, and a capstan insertion hole 1f are drilled,
Furthermore, lugs 1g and 1h for preventing erroneous erasure are provided on the left and right side wall surfaces, respectively.

After the micro cassette tape 1 formed in this way is mounted on the mounting section 2a, the mounting section is attached to the transparent window section 2b.
It is covered with an opening/closing lid 2c having an opening/closing lid 2c.

Further, an operation panel 2d is provided at the front of the recorder 2, and the panel surface includes a volume adjustment knob 14, a built-in microphone net section 15, an external microphone connection jack 16, and an earphone jack 17. In addition, operation buttons 18 are provided for performing tape fast forward, cue, tape rewind, and review operations.

Furthermore, a large number of air holes 19 for speakers are provided on the upper surface near the rear of the recorder 2, and a speaker 24 (see Fig. 3) is located inside the recorder corresponding to the air holes.
is installed.

Further, as shown in FIG. 2, the operation buttons of the tape recorder 2 are arranged on the left side wall of the lower half where the mounting portion 2a is provided, as viewed from the front of the recorder 2.

FIG. 2 is a view of the tape recorder 2 viewed from the diagonally rear lower part on the left side, showing the arrangement positions of each operation button.

The operation buttons of this tape recorder 2 include a recording operation button 20,
A playback operation button 21 and a stop operation button 22 are arranged in order from the front of the recorder 2, as shown in FIG.

To put the recorder 2 into the playback state, simply push the playback operation button 21 to a predetermined position, and when to put the recorder 2 into the recording state, turn both the recorder operation button 20 and the playback operation button 21 toward the inside of the recorder 2. Push it in.

Furthermore, in order to cancel the playback state and the recording state, the stop operation button 22 may be pressed.

Note that the member indicated by the reference numeral 23 in FIG. 2 is a storage lid for the power battery.

The above is the external configuration of the ultra-small tape recorder 2 to which the present invention is applied.

Next, an example of an electric circuit incorporated in this tape recorder 2 will be explained with reference to FIG.

In FIG. 4, the output signal from the recording microphone 25 is input to a first amplifier 26 via a recording/playback switch S1, and the output of the amplifier 26 is connected to a variable resistor. It is adapted to be added to the second amplifier 28 by the amplifier 27 .

The output of this amplifier 28 is applied through a coupling capacitor 29 to the base of a transistor 30 which provides third stage amplification.

A bias resistor 3 is connected to the base of this transistor 30.
1 and the emitter are connected to an emitter resistor 32, respectively.

Further, the second amplifier 28 is supplied with an operating voltage from a positive voltage supply line 35 through a resistor 33 and a capacitor 34p decoupling circuit, and the first amplifier 26 is supplied with an operating voltage through a resistor 33 and a capacitor 34p decoupling circuit. An operating voltage is supplied from the positive voltage supply line 35 through the decoupling circuit of the capacitor 37 and the decoupling circuit described above.

Further, a primary coil 38 of a coupling transformer 38 is connected to the collector of the width increasing transistor 30 and the line 35.
a is connected.

The final stage amplification circuit in this electric circuit is composed of a push-pull amplification circuit.

Therefore, the third stage amplifier transistor 30 and the final stage amplifier circuit are electromagnetically coupled by the coupling transformer 38.

That is, the final stage amplifier circuit includes a pair of transistors 39 and 40 whose respective bases are connected to both ends of the secondary side coil 38b of the coupling transformer 38 and whose emitters are connected to each other. , a voltage dividing resistor 4 that applies an operating voltage to the midpoint of the secondary coil 38b of the transformer 38.
1.42 and an output lance 43.

The collectors of the transistors 39 and 40 are respectively connected to both ends of the primary coil 43a of the transformer 43, and the middle point is grounded.

Also, the emitters of the transistors 39 and 40 are connected to the line 35.

Therefore, the amplified output signal is induced in the secondary coil 43b of the output transformer 43 by the final stage amplifying circuit configured as described above.

An earphone jack 44 is connected to the output end of the secondary coil 43b of the output transformer 43.

As is well known, the earphone jack 44 includes a movable contact terminal 44b, a fixed contact terminal 44a, and a fixed terminal 44G.
In normal life, the movable contact piece terminal 44b and the fixed contact piece terminal 44a are in contact with each other, and the fixed contact piece terminal 44a is in contact with the movable contact piece terminal 44b.
a is connected to the output end of the secondary coil 43b.

Note that the fixed terminal 44C is grounded.

Further, the movable contact piece terminal 44b is connected to the movable contact piece terminal S3a of the recording/playback changeover switch S3.

A resistor 45 is connected between one fixed terminal S3b and ground of this switch S3, and the other fixed terminal S3
A speaker 24 is connected between C and ground.

Further, one end of the secondary coil 43b of the output transformer 43 is connected to a bias oscillation transformer 47 through a resistor 46, and the transformer 47 is connected to one end of a coil of a recording/reproducing magnetic head 48.

The bias oscillation transformer 47 is connected to the bias power supply 49.
When the tape recorder 2 records data, it works together with the magnetic head 48 to apply a bias voltage to the magnetic head 48.

Note that the other end of the secondary coil 43b of the output transformer 43 is grounded.

Further, the other end of the coil of the magnetic head 48 is connected to the other fixed terminal 81C of the changeover switch S1 and one fixed terminal S2b of the recording/playback changeover switch S2.

The changeover switch S1 has a movable contact terminal S1a connected to the input end of the first amplifier 26, and one fixed terminal S1b connected to the output end of the microphone 25.

Further, the changeover switch S2 has a movable contact terminal S.
2 a is grounded, and the other fixed terminal S 2 c
is connected to the oscillation transformer 47.

In addition, the changeover switch S1. S2 and the changeover switch S3 are interlocked, and in the playback state of the tape recorder, as shown in the figure, the movable contact terminal Sl a s
S2a t S3a are respectively the other fixed terminal S1c
, S2c, and S3c, and in the recording state, one of the fixed terminals S1b, S2b, and S3c, respectively, is switched to
3b.

The electrical circuit configured in this manner is formed on a printed circuit board 50 and incorporated into the housing of the tape recorder 2 as shown in FIG.

Furthermore, it goes without saying that the speaker 24, microphone 25, and magnetic head 48 in the electric circuit are arranged at predetermined positions within the housing.

In this way, the electric circuit is installed in a narrow space, and when this electric circuit is activated, the magnetism of the output lance 43 passes through the air and the metal case to the magnetic head 48, as shown in FIG. This adversely affects the magnetic head 48 and causes the magnetic head 48 to generate an abnormal signal.

In the present invention, in order to prevent the problem that the magnetic head generates an abnormal signal or oscillates, as shown in FIG. A part of the signal is extracted through the lead wire 51, and the lead wire is connected to the input/output terminal 48a of the magnetic head 48,
This can be eliminated by arranging it close to 48b.

As is well known, the phases of the output currents Ia and Ib appearing at both terminals of the output transformer 43 are completely inverted, that is, they differ by 1800 degrees.

Therefore, its magnetism also has an opposite phase depending on the current.

The present invention skillfully utilizes this fact that the phases are reversed, extracts a magnetic field having a phase opposite to the magnetic field of the output signal of the magnetic head 48 from the output transformer 43, and transfers it to the terminal of the magnetic head 48. By guiding the magnet to the vicinity, the magnetism generated in the output lance 43 cancels out the entry into the magnetic head 48, thereby preventing the magnetic head from generating an abnormal signal.

That is, as shown in FIG. 4, the output signal current Ia flows through one end of the output transformer 43 connected to the collector of the transistor 39, and the output signal current Ia flows through the other end of the output transformer 43 connected to the collector of the transistor 40. , output signal current Ib flows.

The phases of these two types of currents Ia and Ib are completely reversed, and therefore the magnetic fields generated by these currents are also completely reversed.

Therefore, for example, the magnetic field caused by the current Ia is applied to the magnetic head 4.
In this case, one end of the lead wire 51 is connected to the transformer 4 through which the current Ib flows.
3, and the other end of the lead wire 51 is connected to the input/output terminals 48a, 48 of the magnetic head 48, as shown in FIG.
Place it close to b.

The lead wire 51 is formed by printing a conductive wire or a conductive foil on the printed circuit board 50 on which an electric circuit is formed, as shown in FIG.

In this way, the current Ib at the other end of the output lance 43 is led out by the lead wire 51, and is directed to the magnetic head 48.
A magnetic field is generated near the input/output terminals 48a and 48b.

This magnetic field has a phase reversed by 180 degrees from the magnetic field caused by the output signal current Ia that acts on the magnetic head 48, so that the two cancel each other out.

Therefore, the magnetism that adversely affects the magnetic head 48 is removed, and the magnetic head 48 is prevented from generating abnormal signals or oscillating.

It goes without saying that whether the lead wire 51 is drawn out from one end or the other end of the output lance 43 is determined depending on the phase of the magnetism that enters the magnetic head 48 in the air and through the metal case.

As described above, according to the present invention, it is possible to provide an abnormal signal generation prevention method that can easily prevent abnormal signals from occurring in a small tape recorder by simply adding one lead wire.

[Brief explanation of drawings]

1 and 2 are perspective views of an ultra-compact cassette tape recorder to which the present invention is applied, and FIG. 3 is a sectional view of essential parts of the tape recorder, showing a state in which the magnetic field of the output transformer has an adverse effect on the magnetic head. 4 is an electric circuit diagram of a tape recorder to which the present invention is applied, and FIG. 5 is a plan view of the main part of a printed circuit board showing the arrangement of lead wires. 43... Output lance, 48... Magnetic head, 48a, 48b... Input/output terminal,
51... Lead wire.

Claims (1)

[Claims] 1. A part of the current having the opposite phase to the magnetic output from the output lance of the push-pull amplifier, which enters the magnetic head through the metal case and the air, is extracted from the push-pull amplifier using a lead wire, and this lead wire A method for preventing abnormal signal generation in a small tape recorder, characterized in that the tip of the magnetic head is disposed near an input/output terminal of the magnetic head.