JPS5824255Y2 - Tape recorder oscillation circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to an oscillation circuit of a tape recorder for supplying erasing current to the erasing head and supplying bias current to the recording and playback heads. The purpose of this invention is to provide an excellent oscillation circuit in which the erase current, bias current, etc. change very little even when the head block is replaced.

Generally, the oscillation circuit of a tape recorder is often constructed as shown in FIG.

That is, in FIG. 1, 1 and 2 are transformers for oscillation,
resistor, 3 is an oscillation transformer, 4 is a resonance capacitor, 5
6 indicates an erasing head, 6 a resistor, and 7 a recording head.

Incidentally, in this type of oscillation circuit, the oscillation frequency fo is determined by the following equation, and if the inductance of the erasing head 5 changes, the oscillation frequency fo will also change at the same time.

However, in equation 1), Ll is the secondary inductance of the transformer 3, L2 is the inductance of the erasing head 5, and C
1 is the capacitance of the capacitor 4.

Figure 2 shows the connection relationship between the oscillation circuit and the recording amplifier, and 8 in the figure represents transistors 1 and 2 shown in Figure 1.
, an oscillation circuit consisting of a transformer 3, a capacitor 4, and an erasing head 5, 9 a recording amplifier for amplifying the recording signal, and 10 a trap circuit for preventing the output of the oscillation circuit 8 from having an adverse effect on the recording amplifier 9. .

Therefore, the trap circuit 10 is set so that its impedance is maximum at the oscillation frequency fo of the oscillation circuit 8, as shown in FIG.

However, as mentioned above, when the inductance of the erasing head 5 changes, the oscillation frequency fo of the oscillation circuit 8 changes as well, so the impedance of the trap circuit 10 also changes significantly, and as is clear from FIG. The bias current applied to the head 7 also changes significantly.

In this way, according to the oscillation circuit of a conventional tape recorder, when the inductance of the erasing head changes, the oscillation frequency itself changes significantly, and the oscillation output and the bias current applied to the recording head change accordingly. This makes replacing the erasing head electrically extremely difficult.

That is, since there is generally more or less variation in the inductance of the erasing head, replacing the erasing head will almost always result in a change in its impedance.

Therefore, as a result of this, the oscillation frequency changes, and when the recording bias current changes, the recording level itself on the magnetic tape also changes significantly, resulting in a significant deterioration of the sound quality itself.

For the erase head, the erase current itself changes due to a change in the oscillation output voltage 5, and the erase rate deteriorates.
This is extremely inconvenient, as the magnetic tape itself may become damaged due to the rise in temperature of the erase head, making it extremely difficult to replace the erase head itself.

This proposal eliminates the above-mentioned conventional drawbacks,
The present invention uses an oscillator whose oscillation frequency does not change even when the erase head is replaced, and provides an excellent oscillation circuit in which the erase current bias current and the like do not change.

The oscillation circuit of the present invention will be described below with reference to drawings of an embodiment.

FIG. 5 is a schematic electrical connection diagram of one embodiment of the oscillation circuit of the present invention, in which 11 is an oscillator that oscillates at a predetermined frequency related to the inductance of the erasing head 17;
18 is an amplifier for amplifying the output of the oscillator 11 and supplying specified erasing current and bias current to the erasing head 17 and recording head 19, respectively; 13 is the erasing head 17 and a coil 14 and a capacitor connected in parallel thereto; 15, a parallel resonant circuit consisting of a resistor 16; 20, a trap circuit 21 for preventing the output from the oscillator 11 from adversely affecting the recording amplifier 21; a trap circuit 21 for amplifying the recording signal;
This is a recording amplifier that applies voltage to the recording head 19 via the recording head 19.

In the above embodiment, since the parallel resonant circuit 13 is connected as a load of the amplifier 12, the output voltage of the amplifier 12 changes approximately in proportion to the impedance of the parallel resonant circuit 13.

Therefore, if the parallel resonance conditions are selected so that the impedance of the parallel resonant circuit 13 changes proportionally according to the change in the inductance of the erase head 17, the erase current supplied to the erase head 17 can be substantially reduced regardless of the change in the inductance of the erase head 7. It can be kept constant.

That is, referring to FIG. 5, let the oscillation frequency of the oscillator 11 be fo.

At this time, assuming that the resonant frequency of the parallel resonant circuit 13 is also fo, the resonant characteristics of the parallel resonant circuit 13 will be as shown in FIG. 6A.

When the inductance of the erasing head 17 constituting the parallel resonant circuit 13 becomes smaller and the resonant frequency of the parallel resonant circuit 13 becomes higher, the resonance characteristics are respectively shown in FIGS.
It changes like this.

Therefore, when the resonance characteristic is A, the impedance of the parallel resonant circuit 13 with respect to the oscillation frequency fo is a, and when the resonance characteristic is B and C, the impedance of the parallel resonant circuit 13 with respect to the oscillation frequency fo is, respectively,
becomes.

Then, the value is changed every time the relationship a>b>c holds true.

This means that as the inductance of the erasing head 17 becomes smaller, the impedance of the parallel resonant circuit 13 with respect to the oscillation frequency fo also becomes smaller, meaning that both change proportionally to each other.

Therefore, even if the erasing head 17 is replaced and its inductance changes, the impedance of the parallel resonant circuit 13 changes proportionally, and accordingly, the amplifier 12 applies an oscillation output proportional to the impedance of the parallel resonant circuit 13. Therefore, the erasing current flowing through the erasing head 17 as a whole becomes approximately constant, making replacement of the erasing head 17 extremely easy.

Note that the inductance of the erasing head 17 and the oscillation frequency fo
As is clear from FIG. 6, the inductance of the parallel resonant circuit 13 in the oscillator 1
This is a case where the oscillation frequency fo of the parallel resonant circuit 13 is always lower than the resonant frequency of the parallel resonant circuit 13, and this is an essential requirement.

The relationship between the inductance of the erasing head 17 and the impedance of the parallel resonant circuit 13 with respect to the oscillation frequency fo can be easily adjusted by adjusting the value of the resistor 16.

On the other hand, for the recording head 19, the oscillator 11 itself oscillates at a constant frequency regardless of the inductance of the erasing head 1T, so even if both the erasing head 17 and the recording head 19 are replaced, the bias flowing to the recording head 19 remains The current hardly changes and the drawbacks of the conventional method can be completely eliminated.

As is clear from the above embodiments, according to the oscillation circuit of the present invention, even if the inductance of the erase head changes when replacing the head block, the erase current flowing through the erase head can be kept approximately constant, and the head block replacement itself This makes it extremely easy to use, which is extremely advantageous in practice.

[Brief explanation of the drawing]

Figure 1 is an electrical connection diagram of a conventional oscillation circuit, Figure 2 is a block diagram showing the relationship between the conventional oscillation circuit and a recording amplifier, and Figures 3 and 4 are diagrams for explaining the conventional oscillation circuit. FIG. 5 is a schematic electrical connection diagram of the oscillation circuit of the present invention, and FIG. 6 is an explanatory diagram of the oscillation circuit. 11...Oscillator, 12.18...Amplifier, 13...
・Parallel resonant circuit, 14... Coil, 15... Capacitor, 16... Resistor, 17... Erase head, 19.
...Recording head, 20...Trap circuit, 21...
recording amplifier.

Claims (1)

[Scope of utility model registration request] It is composed of an oscillator that oscillates at a predetermined oscillation frequency and a parallel resonant circuit including an inductance of an erase head that receives the oscillation output of the oscillator as input, and is set so that the resonant frequency of the resonant circuit is always higher than the oscillation frequency of the oscillator. An oscillation circuit for a tape recorder, characterized in that: