JPS587473Y2 - Magnetic head circuit of magnetic recording device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a magnetic head circuit of a magnetic recording device such as a tape recorder, and more specifically, the secondary winding of an oscillator output transformer is ungrounded (floating) and an electronic The present invention relates to a magnetic head circuit in which a bias current switching circuit according to the present invention is connected between a secondary winding and ground, thereby eliminating harmful effects caused by leakage of a high frequency bias signal and click noise caused by turning on and off a switch.

Recent tape recorders are equipped with a recording bias switching circuit in order to optimally use a plurality of magnetic tapes with different performances.

A conventional magnetic head circuit having this type of recording bias switching circuit will be explained with reference to FIG.
An oscillation circuit 1 that generates an AC bias signal of 00 kHz includes a transistor circuit section 2 constituting an oscillator, a primary winding 4 of an output transformer 3 coupled to this, and an intermediate point between the primary winding 4. It consists of a capacitor 5 connected to ground, a secondary winding 6 of the output transformer 3, and a capacitor I connected in parallel to the secondary winding 6.

A DC bias power supply terminal 8 is connected to the intermediate point of the primary winding 4, and one end of the secondary winding 6 is grounded.

Although the oscillation circuit 1 is shown in block form in this drawing, it is composed of known oscillators such as a Hartley-type oscillator, a Colpitt-type oscillator, and a vibrator-type oscillator.

In order to protect the oscillation circuit 1 configured as described above from both erasing and recording, an erasing magnetic head 9 is connected between one end 6a of the secondary winding 6 and the ground. A recording magnetic head 13 is connected between one end 6a of the line 6 and ground via an AC bias current adjusting capacitor 10 or 11 and a changeover switch 12.

Note that a recording signal supply circuit 14 is also connected to the recording magnetic head 13.

In the circuit configured in this way, the switch 12 is connected to the contact 12a.
Magnetic tape for erasing and recording is inserted into the running magnetic tape.
When the rads 9 and 13 are brought into contact with each other, the recording is erased by the erasing magnetic head 9 to which an alternating current signal sent from the oscillation circuit 1 is applied.

Further, recording is performed by a recording magnetic head 13 to which an AC bias signal limited by the impedance of the capacitor 10 and a recording signal supplied from a recording signal supply circuit 14 are applied.

When using magnetic tapes with different performances in this apparatus, it is necessary to change the alternating current bias current value of the recording magnetic head 13.

In the device shown in FIG. 1, since the impedance value of capacitor 10 and the impedance value of capacitor 11 are different,
By switching the switch 12 from contact 12a to contact 12b, the bias current value is changed, and it is possible to apply a substantially optimal bias signal to magnetic tapes of different performance.

By the way, in order to operate the changeover switch 12 manually, it must be placed near the operation panel of the tape recorder, away from the oscillation circuit 1 and the magnetic head 13.

Therefore, the conductive wire connected to the changeover switch 12 becomes long, and other circuits such as an amplifier circuit and a meter arranged near the conductive wire are affected by leakage of the high frequency bias signal flowing through the conductive wire.

Of course, if a shielding device is provided, it is possible to eliminate the adverse effects caused by leakage, but it is not a good idea because it increases the cost.

In order to solve the above-mentioned drawbacks, as shown in FIG.
, the transistor control circuit including the changeover switch 1γ provided on the operation panel has a DC circuit configuration, and when the switch 17 is turned on to the contact 17a, a signal to turn on the transistor 15 is given from the DC bias power supply terminal 18, and the contact It is conceivable that when the switch 17 is turned on to the terminal 17b, a signal that turns on the transistor 16 is applied from the terminal 18.

With this configuration, even if the conducting wire connecting the transistors 15, 16 and the changeover switch 17 is close to another circuit, the adverse effects of the AC bias signal will not occur because it is a DC circuit.

However, the other end 6b of the secondary winding 6 is grounded, and the
Since the capacitor 10 or 11, the transistor 15 or 16, and the magnetic head 13 are sequentially connected between one end 6a of the next winding 6 and the ground, a direct current is generated each time the transistor 15 or 16 is turned on or off. There is a drawback that a change in current flows through the magnetic head 13, and this is recorded as click noise.

Further, there is a possibility that the magnetic head 13 may be magnetized by direct current due to the direct current component.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic head circuit for a magnetic recording apparatus that can eliminate the drawbacks that occur in the apparatus shown in FIG. 1 and the apparatus shown in FIG.

The present invention, which is distantly related to the above object, includes an oscillation circuit including an output transformer having an ungrounded secondary winding for supplying an AC bias signal, and an erasing magnet connected in parallel to the ungrounded secondary winding. a recording magnetic head, one end of which is connected to one end of the non-grounded secondary winding and a recording signal supply circuit, and the other end of which is connected to ground; and the other end of the non-grounded secondary winding. a series circuit of a recording bias current adjusting capacitor and an electronic switch connected between the recording bias current adjusting capacitor and ground, and applying a DC control signal to the electronic switch to make the electronic switch conductive in response to switching of the recording bias current. The present invention relates to a magnetic head circuit of a magnetic recording device including an electronic switch control circuit connected to a control electrode of the electronic switch.

According to the present invention, the secondary winding of the oscillation output transformer is floating (ungrounded), and a bias switching circuit consisting of a bias adjustment capacitor and an electronic switch is connected between the secondary winding and ground. Since the electronic switch is controlled by a DC signal, no matter where the circuit for controlling the electronic switch is installed, the AC bias signal will not leak through it.

Furthermore, since no electronic switch is connected in series with the magnetic head, changes in direct current caused by turning on and off the electronic switch will not flow to the magnetic head and be recorded as click noise.

Embodiments of the present invention will be described below with reference to the drawings.

However, in Figures 3 and 4, the numbers 1 to 11 and 13
The structures and functions of the components indicated by 18 to 18 are substantially the same as those of the components having the same reference numerals in FIGS. 1 and 2, and therefore their explanations will be omitted.

In FIG. 3, which shows the magnetic head circuit of a tape recorder according to the first embodiment of the present invention, the transformer secondary winding 6 of the oscillation circuit 1 is not grounded and is in a floating state. An erasing magnetic head 9 is connected in parallel to the secondary winding 6 in an ungrounded state.

Furthermore, the recording magnetic head 13 is connected to one end 6 of the non-grounded secondary winding without using a bias switching circuit such as a capacitor or a switch.
a and ground.

A bias adjustment capacitor 10 and an electronically switched transistor 1 are connected between the other end 6b of the secondary winding 6 and the ground.
5 and a series circuit of a bias adjustment capacitor 11 and a transistor 16 as an electronic switch are connected, respectively.

The bases, which are the control electrodes of the transistors 15 and 16, are connected to the changeover switch 1 provided on the operation panel of the tape recorder.
7, and a DC bias voltage of 10 B volts is applied to the ground terminal 18 by operating the changeover switch 17.

Although the recording signal supply circuit 14 is shown as a block,
More specifically, it is connected in parallel to the magnetic head 13 via a bias trap circuit.

In the circuit configured as described above, the output of the secondary winding 6 is applied floatingly and directly to the erasing magnetic head 9.

On the other hand, the recording magnetic head 13 has a capacitor 10.
Alternatively, a bias current adjusted at 11 is applied.

That is, when the switch 17 is turned on to the contact 17a, a DC voltage of 10 B is applied to the base of the transistor 15 from the terminal 18.
A bias current is applied between the emitters and is turned on, so that a bias current limited by the impedance of the capacitor 10 flows to the recording magnetic head.

Further, when the switch 17 is turned on to the contact 17-b, the transistor 16 is turned on, so that a bias current limited by the impedance of the capacitor 11 flows to the recording magnetic head 13.

In this embodiment, the transistors 15.16 are selectively turned on by the changeover switch 17, but if both transistors 15.16 were configured to be turned on at the same time, the two capacitors 10° 11
It is possible to flow a limited bias current by the composite impedance of .

As can be understood from the explanation so far, the transistor 15
, 16 can be provided close to the oscillation circuit 1, and these transistors 15, 16 are DC controlled by a changeover switch 17 provided on the operation panel. Even if the conductor wires connected to the transistors 15, 16 are located far away from the transistors 15, 16 and are close to other circuits, the bias signal will not leak from the bias switching circuit and affect other circuits.

The disconnected secondary winding 6 is not grounded, and a bias switching circuit consisting of a bias adjustment capacitor 10, 11 and transistors 15 and 16 is connected between the other end 6b of the secondary winding and the ground. , the direct current component flowing through the transistors 15 and 16 does not flow to the magnetic head 13, and recording of click noise due to changes in the direct current does not occur.

DC magnetization of the twisted magnetic head does not occur.

In FIG. 4 showing a magnetic head circuit according to a second embodiment of the present invention, the transistor 15 connected in series to the capacitor 10 in the embodiment of FIG. 3 is removed, and the capacitor 10 is directly grounded. has been done.

Therefore, when transistor 16 is off, capacitor 1
A bias current limited by 0 flows, while a bias current limited by both capacitors 10 and 11 flows when transistor 16 is on.

Even with this configuration, the same effects as in the first embodiment can be obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and can be further modified.

For example, the circuit configuration of the oscillation circuit 1 may be modified in various ways.

The bias current may be switched in two or more stages.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional magnetic head circuit, Fig. 2 is a circuit diagram showing a state where the changeover switch in Fig. 1 is replaced with a transistor, and Fig. 3 is a tape according to the first embodiment of the present invention. FIG. 4 is a circuit diagram showing a magnetic head circuit of a recorder. FIG. 4 is a circuit diagram showing a magnetic head circuit according to a second embodiment of the present invention. In addition, in the symbols used in the drawings, 1 is an oscillation circuit,
6 is a secondary winding, 9 is an erasing magnetic head, 10.11 is an AC bias current adjustment capacitor, 13 is a recording magnetic head, 14 is a recording signal supply circuit, 15 and 16 are switching transistors, and 17 is a changeover switch. It is.

Claims (1)

[Claims for Utility Model Registration] An oscillation circuit that operates an output transformer having an ungrounded secondary winding for supplying an AC bias signal, an erasing magnetic head connected in parallel to the ungrounded secondary winding, etc. a recording magnetic head, one end of which is connected to one end of the non-grounded secondary winding and a recording signal supply circuit, and the other end of which is connected to ground; and the other end of the non-grounded secondary winding and ground. a series circuit of a recording bias current adjusting capacitor and an electronic switch connected between the circuit, and a series circuit including a recording bias current adjusting capacitor and an electronic switch; A magnetic head circuit for a magnetic recording device, comprising an electronic switch control circuit connected to a control electrode of the electronic switch.