JPS5913087B2 - magnetic recording and playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording/reproducing apparatus which is capable of obtaining an optimum recording bias current for various magnetic tapes having different characteristics.

25-Generally, the optimum recording bias current value for magnetic tape used in tape recorders etc. varies depending on various factors such as the material, shape, and coating thickness of the magnetic material coated on the tape, but it is necessary to obtain good recording and playback characteristics. An optimum recording bias current of 30 current is required regardless of the type of magnetic tape.

For this reason, in the past, recording was done using a low frequency signal (for example, 400H2 or 1KH2) while manually varying the recording bias current, and setting the optimal value, that is, the highest sensitivity bias that maximizes the playback level, or a slightly deeper bias than the above 35 bias. Recently, devices such as JP-A-48-33806 | JP-A No. 48-55713 have been invented, which are adjusted to the recording bias current value.

However, with these methods, when the recording bias current vs. playback level characteristics differ as shown in Figure 2, the value will be close to the maximum value for the magnetic tape with characteristic A, and close to the maximum value for the magnetic tape with characteristic B. There is a risk that the recording bias current value will be set to a considerably deep value exceeding the maximum value, and the setting value of the recording bias current will deviate by a wide margin.

In the magnetic recording and playback process, this recording bias is the basis of various characteristics, and in terms of dynamic range and frequency characteristics, if the setting value of the recording bias current mentioned above deviates by a wide range, favorable results will not be obtained. . The present invention takes such drawbacks into consideration and provides a magnetic recording/playback device that can automatically obtain a deep recording bias current that lowers the playback level beyond the maximum value to a certain prescribed level even for magnetic tapes with different characteristics. We aim to provide the following.

Hereinafter, an explanation will be given with reference to FIG. 1 showing an embodiment of the present invention and a timing chart shown in FIG. 3 showing its operating state.

First, a general description will be given of the operation in a normal recording/playback state, that is, recording/playback of signals such as musical tones or voices.

The signal from the recording input terminal 7 is amplified by the recording amplifier 5 via the connected relay contact RLla as shown by the solid line.
The signal is combined with the recording bias from the recording bias oscillator 10 and supplied to the recording head 2, where it is recorded on the magnetic tape 4. The magnetic tape 4 travels in the direction indicated by the arrow and is reproduced by the reproduction head 3, amplified by the reproduction amplifier 6, and led out to the reproduction output terminal 8 via the relay contact RLlb connected as shown by the solid line. Next, the operation when setting the optimum recording bias current value for a magnetic tape with certain characteristics will be explained.

First, when this recording and reproducing apparatus is put into a well-known recording and reproducing state (not shown in the figure), the recording SW indicated by S1 is closed and a power supply voltage of 10B is supplied to the oscillation voltage control cape device 11.

Next, when the normally open type starting SWS2 is instantaneously pressed, the transistors Ql25, Ql26 and the transistor Q! 339Q1
Two relay holding circuits consisting of 34 are 0N, that is, relay R.
Ll and RL2 become 0N, and each relay contact RLla-
C, RL2a, and b are connected to the side shown by the broken line.

Dl22 and Dl34 are reverse current prevention diodes that prevent malfunctions due to mutual interference between the two relay holding circuits. At this point, the magnetic tape recording signal is transmitted to the low frequency oscillator 9.
Reference signal from (e.g. 400Hz or 1KHz)
As mentioned above, the reference signal recorded on the magnetic tape 4 is reproduced by the reproduction head 3, amplified by the reproduction amplifier 6, and applied to the base of the transistor Ql4l of the rectifier and smoothing circuit 14 via the relay contact RLlb. On the other hand, focusing on the control voltage generator 12, at the same time as the starting SWS2 is pressed, the relay contacts RLlc and RL2a are switched as shown by the broken lines, and the capacitors C and 2l, which had recorded the characteristics of the magnetic tape used last time as voltages, are switched as shown by the broken lines. is connected to the negative voltage power supply -B through the resistor Rl22, and is charged to a voltage even more negative than the above-mentioned storage voltage. This photoelectric voltage is FETQ
The voltage is impedance-converted by an impedance conversion circuit consisting of transistor Q122 and transistor Q122, and a part of the voltage is applied to the base of transistor Q123. Now, the voltage applied to the base of the transistor Ql23 is the Zener voltage V2l2l+VBEl2 of the Zener diode Dl2l.
3 (the voltage between the base and emitter required to flow the collector current of transistor Ql23), transistor Ql23 becomes 0N, transistor Ql24 also becomes 0N,
The relay holding circuit of transistors Ql25 and Ql25 is 0
It becomes FF and relay RL2 also becomes 0FF. This is the third
This corresponds to the point X shown in the figure. With the relay RL2 turned 0FF, the contacts of RL2a and RL2b are connected as shown by the solid line, and the capacitor Cl2l is connected to the positive voltage power supply +B through the resistor Rl2l. Therefore, the capacitor Cl2, which had been photoelectrically charged to a negative voltage, is forcibly discharged and approaches zero voltage.If the start and stop device 13 does not issue a stop command signal, the voltage of the capacitor Cl2l becomes zero. When approaching , transistor Ql29 becomes 0FF, and at the same time, transistor Ql28 becomes 0FF1, transistor Ql27 becomes 0N, and transistor Ql25, which constitutes a relay holding circuit,
Ql26 becomes 0N again, that is, relay RL2 becomes 0N, and capacitor Cl2 is photoelectronized to a negative voltage, resulting in a repetitive waveform. Changes in the charging voltage of the capacitor Cl2l are shown by Z and Z' in FIG. Said (2121+BEl23
) is the capacitor maximum charging voltage approximated by Ep, I
If Eci is B and +B, the change in the charging voltage of the capacitor Cl2l will be approximately linear, and the resistor Rl2l = Rl22
If so, the repetitive waveform is approximately a triangular wave, and the resistance Rl2l
If \Rl22, the above waveform becomes a substantially sawtooth wave. Also, the resistance values of resistors Rl2l and Rl22 or capacitor Cl2
By changing the capacitance of l, the repetition period or frequency can be changed. Further, if this repetition period f is set as f>T with respect to the time T from recording by the recording head 2 to being reproduced by the reproducing head 3, the measurement error due to T can be reduced.

Next, the voltage of the capacitor Cl2l derived from the collector of the transistor Ql22 focusing on the recording bias oscillator 10 and the oscillation voltage control device 11 is applied to the gate of the FET Qll3 as a voltage-to-impedance conversion element. Impedance R between the drain and source of this FETQll3.

The recording bias current is varied by changing 8ll3.

To explain this operating state in detail, the recording bias oscillator 10 and the oscillation voltage control device 11 are paired together to form a kind of voltage suppression type oscillator, and the oscillation voltage, that is, the recording bias current, which is stable against external disturbances is supplied to the recording head 2. It is intended to be supplied to This is done by rectifying the oscillation voltage with diodes DlOl and DlO2, dividing it by resistor Rlll and impedance RDSll3 between the drain and source of FET Qll3, and applying it to the base of transistor Qll2, and then applying it to the base of transistor Qll2.
The reference voltage Vzllll created by and the transistor Ql
The collector-emitter voltage V of the transistor Qll is determined by the ratio of the voltage applied to the base of the transistor Qll. This can be obtained by controlling the oscillation voltage of the recording bias oscillator 10 by controlling E,ll and varying the power supply voltage of the recording bias oscillator 10. Here's the FET Qll
3 drain-source impedance RDSll3
and the gate applied voltage have the following relationship. VGS;
Gate applied voltage Vp; Pinch-off voltage GmO; Mutual conductance when VGS = 0v, and hence capacitor Cl2l changes from negative voltage to zero voltage\
In some cases, the above R.

8ll3 decreases and resistance Rllll and RDS! The voltage applied to the base of the transistor Qll2 divided by 13 decreases, the collector current of the transistor Qll2 decreases, and the collector-emitter voltage V of the transistor Qll.

Ell also decreases, the power supply voltage supplied to the recording bias oscillator 10 increases, and the recording bias current increases. That is, when the voltage of capacitor Cl2l is charged to a negative voltage (relay RL2ON), the recording bias current decreases, and conversely, when capacitor Cl2l is forcibly discharged to zero voltage (relay RL2 is 0FF), the recording bias current decreases. The recording bias current operates to increase. Now, the signal level detection device 15 consisting of the rectification and smoothing circuit 14, the peak value storage circuit 17, and the first comparison circuit 18 will be described in detail.The reference reproduction output signal from the reproduction amplifier 6 is transmitted to the relay contact RLl.
b to the rectifier and smoothing circuit 14. That is,
This rectification and smoothing circuit 14 takes out the input signal via a transistor Ql4l whose collector is grounded, and connects it to a diode Dl4l.
4l, Dl42, rectified by capacitor Cl4l, C
142 and transistors Q and 42 to smooth the signal and take it out. The signal obtained from the emitter terminal of this transistor Ql42 is passed through the diode Dl72 to the first comparator circuit 18.
The base P of transistor Ql83, which is one input terminal of
applied to a point. On the other hand, the emitter of the transistor Ql42 is grounded via an attenuator VRl, and the signal obtained from its sliding terminal is transmitted via a diode Dl7l to the transistor Ql8, which is the other input terminal of the first comparator circuit 18.
It is applied to the base O point of 2 and the capacitor Cl7l. This diode Dl7l and capacitors C and 7l constitute a memory circuit 17. In this way, the transistor Q,
The peak value output signal taken out from the emitter of transistor Ql42 is applied as it is to the point \P, while the peak value output signal whose level is appropriately lower than the output level obtained from the emitter terminal of the transistor Ql42 is applied from the sliding terminal of the attenuator VRl. is taken out and applied to the memory circuit 17 and at the O point. That is, as shown in the output waveforms at points O and P in Figure 3, as the recording bias is varied from point X from shallower to deeper, each output signal changes to the initially set level difference. However, when the peak bias is exceeded, the demagnetizing effect of the recording bias magnetic field becomes noticeable and the level of the P point output decreases, but the O point output stores the peak value in the storage circuit 17 and returns to that value. is moved in parallel while maintaining , and a point is reached where point O and point P intersect, that is, the two levels match.
This intersection coincides with the operation completion point, that is, the best recording bias amount for the magnetic tape 4. At this intersection point, that is, the point where both levels match, both collector terminal voltages of the transistors Ql82 and Ql83 of the first comparator circuit 18 also match, and the transistor Q, whose base emitter is connected between both ends, also matches.
8l becomes 0FF. Moreover, on the other hand, the above reproduction level and resistance R
A second comparison circuit 19 compares the reference voltage V2O at the Q point obtained by dividing +B from 2Ol and R2O2,
If the reproduction level is higher than the reference voltage V2O, the transistors Q and 9l become 0FF.

This corresponds to point Y shown in FIG. Furthermore, within the start-up and stop device 13, three gates are connected to the base of the transistor Ql3l.

The first gate is connected to the relay holding circuit in the control voltage generator 12 via diodes D,,l, and the second gate is connected to the first comparator circuit 18 via the diode Dl32.
The third gate is connected to the second comparator circuit 19 via a diode Dl33, and a NOR circuit is formed from this transistor Ql3 and the three gates connected to its base. That is, only when all these three gate inputs are gone is the transistor Ql3l
becomes 0FF, the transistor Ql32 connected to this transistor Q,,l turns on, and the transistor Ql34 connected to this transistor Ql32 becomes 0FF.
As a result, the holding circuit of the relay RLl becomes 0FF, cutting off the power supply to the relay RLl, and the relay contacts RLla-c are connected to the solid line side. Therefore, when the relay contact RLlc is opened, the capacitor Cl2l holds the voltage just before the relay contact RLlc was opened, and the recording bias current becomes a constant current proportional to the voltage of the capacitor Cl2l, and all operations of this device are completed and normal operation resumes. It enters recording and playback mode. The second comparator circuit 19 is provided to prevent the apparatus from malfunctioning due to effects such as dropouts and level fluctuations of old magnetic tapes with low recording bias currents.

Relay contact RL2b is an erasing circuit for erasing the memory of the characteristics of the previously used magnetic tape while the recording bias current is decreasing. In addition, the light emitting diode LED connected to the emitter of the transistor Ql34 in the start and stop device 13 lights up when the transistor Ql34 is 0N, that is, the device is in operation, to indicate whether or not the device is in operation. It is something.

In addition, the values of resistors Rl2l and Rl22 can be changed to the tape speed switching SW.
By switching in conjunction with the above, the optimum value can be set for each tape speed as well.

As mentioned above, the device of the present invention has a NOR circuit having three gates in the start/stop device 13, and the recording bias current required for the recording tape is determined only when all three gate inputs become 0FF. , will be remembered. That is, the first gate detects that the recording bias current is increasing, the second gate detects that the recording and playback level of the reference signal has decreased from the maximum value to a specified level, and the second gate detects that the recording bias current is changing in the increasing direction. Since the stop device will not operate unless the three conditions of detecting that the recording and playback level of the reference signal is above the specified level from the gate 3 at the same time are obtained, the optimum recording bias current for each can be obtained. Malfunctions caused by magnetic tape dropouts, level fluctuations, etc. can be completely prevented. In addition, the recording bias current is continuously varied using a triangular wave or sawtooth wave in which the voltage changes linearly, and the delay time until the signal recorded on the magnetic tape by the magnetic head is played back by the playback head can be adjusted. Since the period of the triangular wave or sawtooth wave is set to be larger by a light amount, an accurate recording bias current can be obtained.

Furthermore, by changing the period of the triangular wave or sawtooth wave in conjunction with tape speed switching, the recording bias current can be determined within the minimum necessary time according to each tape speed. Also, as shown in Figure 2, there are various recording bias current vs. output characteristics of magnetic tapes, such as those with sharp characteristics and those with broad characteristics. By varying the attenuator VRl, the desired overbias point can be set freely and accurately using the signal level detection circuit 15 according to the invention.

In this way, with the device of the present invention, the recording bias current, which is the basis of the recording and playback characteristics, can always be set to the optimum value based on a constant standard for any magnetic tape of any characteristics, and the characteristics of various magnetic tapes can be maximized. It is something that can be done.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a recording bias current versus reproduction level characteristic, and FIG. 3 is a timing chart for explaining the operation of the circuit diagram shown in FIG. 1. 1, V... Tape reel, 5... Recording amplifier, 6... Playback amplifier, 7... Recording input terminal, 8... Playback output terminal, 9...
...Low frequency oscillator, 15... Signal level detection device.

Claims (1)

[Claims] 1. A means for recording a reference signal while varying a recording bias current, a means for reproducing the recorded signal, and a means for automatically varying the recording bias current according to the level of the reproduced signal. A magnetic recording/reproducing device comprising: a triangular wave or sawtooth wave generator; a recording bias oscillator whose recording bias current changes in proportion to the voltage of the waveform; a detection device for detecting that the playback level has decreased to a predetermined level from a maximum value; a device for automatically stopping the generator when an output signal is emitted from the detection device; and a device for automatically stopping the generator when the generator is stopped. A magnetic recording and reproducing device comprising: a voltage holding device that holds a waveform voltage. 2. The device according to claim 1, wherein the frequency of the triangular wave or the sawtooth wave can be switched in conjunction with a tape speed switching device. 3. A stop device for a triangular wave or sawtooth wave generator is used when the recording bias current is increasing and the playback level exceeds the maximum value and falls to the first specified level, and when the playback level is at the second specified level. Claim 1, characterized in that it operates only when a condition greater than a predetermined level is satisfied.
The magnetic recording and playback device described in Section 1. 4. The magnetic recording and reproducing apparatus according to claim 1, characterized in that a voltage variable impedance element is inserted in the oscillation voltage control feedback loop as means for varying the recording bias current. 5 In the device described in claim 3, the device that detects that the playback level has exceeded the maximum value and decreased to the first specified level rectifies and smoothes the playback signal, and outputs the smoothed signal as it is. The voltage is applied to one input terminal of the differential amplifier, passed through an attenuator that attenuates only the drop that is desired to be detected, and then applied to the other input terminal of the differential amplifier through a peak value storage circuit consisting of a diode and a capacitor. 1. A magnetic recording and reproducing device comprising a signal level detecting device that compares and detects that the differential amplifier output level difference is substantially zero. 6. A magnetic recording and reproducing device according to claim 5, comprising a memory erasing circuit that erases the peak value memory while the recording bias current is on a decreasing trend.