JPS5830645B2 - magnetic recording and reproducing device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an AC bias magnetic recording and reproducing device such as a tape recorder, and is capable of automatically adjusting and setting an optimal AC bias current value according to the type and characteristics of the magnetic tape used. The present invention provides a magnetic recording and reproducing device.

First, a recording head drive circuit of a conventional magnetic recording/reproducing apparatus of this type will be explained with reference to FIG.

As shown in Fig. 1, the amount of AC bias current in the conventional example is variable at three points using a preset method, and each preset bias current amount is adjusted to capacitors C1 and C2 for each magnetic tape having typical characteristics. ，
After being finely adjusted by C3, it is fixed.

As described above, since this kind of conventional apparatus is of a preset type, the user has to select the optimum bias position of the magnetic tape from the preset selector before using the tape recorder.

For this reason, when using the tape recorder, the user felt troublesome.

In addition, as mentioned above, in the preset method, the bias current value is set for each tape with typical characteristics, but in reality, many tapes have an optimal point between the preset points, and therefore each tape has its own typical characteristics. It was not possible to bring out the full performance of the tape.

Figure 2 shows the bias characteristics at I KHz, and the AC bias recording and reproducing bias characteristics of all magnetic tapes are similar curves, always having the maximum reproduction output point,
There is always a third harmonic lowest distortion point.

Generally, the above two points, that is, the maximum reproduction output point and the lowest third harmonic distortion point do not coincide, and the maximum reproduction output point is slightly shifted toward the lower bias current side.

Therefore, it is common practice to find an optimal bias that is a compromise between reproduction output and distortion rate.

The present invention provides a magnetic recording/reproducing apparatus that can automatically set the optimum AC bias regardless of the type of magnetic tape.One embodiment of the present invention will be described below with reference to FIG. 3.

In FIG. 3, 1 is a start switch, 2 is a flip-flop, 3 is a function generator, 4 is a bias oscillator that generates an AC bias, and 5 is an electronic volume. Levels change over time.

6 is an audio signal input terminal, 7 is a reference signal generator, 8
is an input amplifier, 9 is a bias trap, 10 is a recording head, 11 is a magnetic tape, 12 is a playback head, 13 is a playback equalizer amplifier, 14 is a playback line amplifier, and 15 is a changeover switch, which is usually used as a recording/playback changeover switch. used.

16 is a reproduction output terminal, and 17 is a band pass filter for extracting the fundamental wave component of the reference signal (frequency fo), and the center frequency of this band pass filter 17 is fo.

18 is an automatic gain controller (AGC); 19 is a bandpass filter for extracting the third harmonic component of the reference signal; the center frequency is 3fo;

20 is a low frequency amplifier, 21.22 is a rectifier, 23.24
is a smoothing circuit, 25 is a differential comparator, 26 is a differentiation circuit, 27
is a Schmitt trigger (ST'), and 28 is a flip-flop (FF).

In FIG. 3, first, by closing switch 1, flip-flop 2 is inverted, and AC bias adjustment is started.

That is, by inverting the flip-flop 2, the function generator 3
starts and produces a monotonically increasing (or decreasing) voltage.

Due to the temporal change in this voltage, the resistance value of the electronic volume 5 increases or decreases, and the AC bias current changes as shown by the curve IB in FIG. 4.

The reference signal generated from the reference signal generator γ is sent to the contact Sta,
It is superimposed on the AC bias output from the electronic volume 5 through the input amplifier 8 and the bias trap 9, and is applied to the recording head 1.
0 is recorded on the magnetic tape 11.

The recorded signal is converted into an electric signal by the playback head 12, and further reaches the bandpass filter 17 and AGC 18 via the playback equalizer amplifier 13, playback line amplifier 14, and contact S2a.

Only the fundamental wave component of the reference signal is extracted by the bandpass filter 17, and this fundamental wave component is passed through the rectifier 21. It is converted to a DC level by the smoothing circuit 23, and the differential comparator 25
is applied to the non-inverting input terminal of

On the other hand, the signal controlled to a defined level by the AGC 18 is applied to the bandpass filter 19, and the third signal in the reference signal is
Only the harmonic components are taken out, amplified by a low frequency amplifier 20, converted to a DC level by a rectifier 22 and a smoothing circuit 24, and inputted to an inverting input terminal of a differential comparator 25.

The differential comparator 25 compares the fundamental wave component level with the third
A voltage difference from the next harmonic level is taken out, and this difference voltage is applied to the differentiating circuit 26.

The fundamental wave component and the third harmonic component for a constant level signal are shown in curve 1 in Figure 4. (3) Therefore, the differential voltage changes as shown by the curve AV in FIG.

Therefore, the output voltage of the differentiating circuit 26 is the curve Vd in FIG.
The sign changes at the bias current value point 'm'.

As a result, the Schmidt IJ gas 27 generates a negative pulse.

The flip-flop 28 is inverted by a negative pulse, and is inverted by a negative pulse from the Schmitt trigger 27, stopping the function generator 3 and fixing the alternating current bias, which changes over time, at an optimum value.

The output voltage of the function generator 3 at this time is stored for a long time by the electronic volume 5.

The electronic volume 5 may be a potentiometer driven by a motor, or may be a combination of a high input resistance element (for example, FET) 30, a low leak capacity 31, and a relay 32 as shown in FIG.

In addition, the band pass filters 17 and 19 each have an S/N of
If a sufficient value can be obtained, a low-pass filter or a bypass filter with steep cutoff characteristics can be used instead.

The function generator may be formed by an integrating circuit as shown in FIG. 6, or simply may be constructed by only resistors and capacitors as shown in FIG. 7.

The present invention has the above configuration, and according to the present invention, the following effects can be obtained.

(1) Regardless of the type of magnetic tape, the optimal AC bias can always be automatically set.

(2) For this reason, tape recorder users must identify the type of magnetic tape and select the tape selector (bias position).
There is no need to set .

(3) Even if the characteristics change due to wear of the magnetic head, etc., it can always be used with the best AC bias.

(4) Even if the type of magnetic tape is unknown, it can be used with the best recording bias.

(5) It can be manufactured at low cost with a simple circuit configuration.

[Brief explanation of drawings]

Figure 1 is an electrical circuit diagram of the main parts of a conventional magnetic recording and reproducing device.
Fig. 2 is a diagram showing the relationship between AC bias current, reproduction output, and third harmonic distortion, Fig. 3 is a block diagram of the main parts of a magnetic recording and reproducing apparatus in an embodiment of the present invention, and Fig. 4 is a diagram showing the relationship between AC bias current, reproduction output, and third harmonic distortion. An explanatory diagram of the operation of the device of the present invention, FIG. 5 is an electric circuit diagram of an example of an electronic volume used in the device of the present invention, and FIGS. 6 and 7 are electric circuit diagrams of function generators used in the device of the present invention, respectively. It is. 1...Start switch, 2...Flip-flop, 3...Function generator, 4...
Bias oscillator, 5...Electronic volume, 6.
...Audio signal input terminal, 7...Reference signal generator, 8...Input amplifier, 9...
...bias trap, 10...recording head,
11... Magnetic tape, 12... Playback head, 13... Playback equalizer amplifier, 14
...Reproduction line amplifier, 15...Selector switch, 16...Reproduction output terminal, 1γ...
... Band pass filter, 18... Ripple gain adjuster, 19... Band pass filter, 20.
...Low frequency amplifier, 21.22 ... Rectifier, 23.24 ... Smoothing circuit, 25 ...
・Differential comparator, 26... Differential circuit, 27...
...Schmitt trigger, 28...flip-flop.

Claims (1)

[Claims] 1. a bias oscillator that generates an alternating current bias, means for changing the amplitude of the alternating current bias from the bias oscillator over time, means for superimposing a reference signal on the alternating current bias that changes over time, A recording head for recording a superimposed signal on a magnetic tape, a reproducing head for reproducing the signal recorded on the magnetic tape, and a first filter means for extracting a basic component of a reference signal from the reproduced signal from the reproducing head. and second filter means for extracting the third harmonic component from the reproduction reference signal;
a rectifier for rectifying the respective outputs of the first and second filter means, a comparison means for comparing the outputs of the respective rectifiers, a differentiating means for differentiating the output of the comparing means, and an output of the differentiating means that is zero. 1. A magnetic recording and reproducing apparatus characterized by comprising means for stopping and fixing the temporal change of the alternating current bias at the point where the alternating current bias becomes .