JPS6122373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a display in a magnetic recording/reproducing apparatus in which an optimum recording bias current can be obtained for various magnetic tapes having different characteristics.

[Conventional technology]

In general, 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. An optimal recording bias current is required regardless of the type of tape.

For this reason, in the past, recording was done using a low-frequency signal (for example, 400Hz or 1KHz) while manually varying the recording bias current to reach the optimum value, that is, recording at the highest sensitivity with the maximum playback level, or recording at a slightly deeper level than the above recording. Recently, devices such as JP-A-48-33806 and JP-A-48-55713 have been invented, which are based on the bias current value. However, with these methods, when the recording bias current vs. playback level characteristics differ as shown in Figure 2, the value approaches the maximum value for the magnetic tape with characteristic A, and 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 value, and the recording bias current setting value will deviate significantly. This recording bias is the basis of various characteristics in the magnetic recording and playback process, and in terms of dynamic range and frequency characteristics, if the setting value of the recording bias current mentioned above deviates significantly, favorable results may not be obtained. At the same time, inventions such as Japanese Patent Laid-Open No. 48-37105 have been made regarding display, but these inventions include a method for displaying whether or not the recording bias automatic adjustment device is operating during the period when the recording bias current is automatically adjusted. Since there is no indication, there is a drawback that the user feels very uneasy when using the product.

[Object of the present invention]

The present invention takes such drawbacks into consideration and provides automatic recording bias adjustment that automatically obtains a deep recording bias current that causes the playback level to exceed the maximum value and drop to a certain specified level even for magnetic tapes with different characteristics. It is an object of the present invention to provide a magnetic recording and reproducing device that is equipped with a display device that displays that the device is in operation while the device is in operation, thereby dispelling the user's sense of anxiety.

〔Example〕

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 sent to the recording amplifier 5 via the relay contact RL1a connected as shown by the solid line.
The signal is amplified by the recording bias oscillator 10, is combined with the recording bias from the recording bias oscillator 10, is supplied to the recording head 2, and 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 RL1b 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 device is put into a well-known recording and reproducing state (not shown in the figure), the recording switch indicated by SI is closed and the power supply voltage +B is supplied to the oscillation voltage control device 11.

Next, when the normally open type starting SW/S2 is instantaneously pressed, two relay holding circuits consisting of transistors Q125, Q126 and transistors Q133, Q134 are turned on, that is, relays RL1 and RL2 are turned on, and the contacts RL1a to RL2a of each relay are turned on. , b are connected to the side indicated by the broken line. D122 and D134 are reverse current prevention diodes that prevent malfunctions due to mutual interference between the two relay holding circuits. At this point, the recording signal on the magnetic tape is switched to the reference signal (for example, 400Hz or 1KHz) from the low frequency oscillator 9, and as mentioned above, the reference signal recorded on the magnetic tape 4 is played back by the playback head 3 and then fed to the playback amplifier 6. The signal is amplified and applied to the base of the transistor Q141 of the rectifier and smoothing circuit 14 via the relay contact RL1b. On the other hand, if we pay attention to the control voltage generator 12, the starting SW/
Simultaneously with the pressure contact of S2, relay contacts RL1c and RL2a are switched as shown by the broken lines, and the capacitor C, which had memorized the characteristics of the magnetic tape used last time as a voltage, is switched as shown by the broken line.
121 is connected to a negative voltage power supply -B through a resistor R122, and is charged to a voltage even more negative than the above-mentioned storage voltage. This charged voltage is applied to FET Q121,
The voltage is impedance-converted by an impedance conversion circuit constituted by the transistor Q122, and is derived from the collector of the transistor Q122, and a portion of the voltage is applied to the base of the transistor Q123. Now, the voltage applied to the base of transistor Q123 is the Zener voltage Vz121+VBE123 of Zener diode D121 (transistor Q123
When the voltage between the base and emitter reaches the voltage required to flow the collector current of transistor Q123,
ON, transistor Q124 is also ON, and the relay holding circuit of transistors Q125 and Q126 is
OFF, and relay RL2 becomes OFF. This corresponds to the x point shown in FIG. Relay RL2
When turned off, the contacts of RL2a and RL2b are connected as shown by the solid line, and the capacitor C121 is connected to the positive voltage power supply +B through the resistor 121. Therefore, the capacitor C121, which had been charged to a negative voltage, is forcibly discharged and approaches zero voltage. Here the starting and stopping device 13
When a stop command signal is not issued, when the voltage of capacitor C121 approaches zero, transistor Q129 turns off and at the same time transistor Q1
28 is OFF and transistor Q127 is ON, forming a relay holding circuit.
5. Q126 is turned on again, that is, relay RL2 is turned on, and capacitor C121 is charged to a negative voltage to obtain a repetitive waveform. Changes in the charging voltage of capacitor C121 are shown by Z and Z' in FIG. If the capacitor maximum charging voltage approximated by (Vz121 + VBE123) is Ec, |Ec| If the resistance R121≠R122 is approximately a triangular wave, the above waveform will be approximately a sawtooth wave. Also resistor R121,
By changing the resistance value of R122 or the capacitance of capacitor C121, the repetition period, that is, the frequency can be changed.

Furthermore, 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, focusing on the recording bias oscillator 10 and the oscillation voltage control device 11, the voltage of the capacitor C121 derived from the collector of the transistor Q122 acts as a voltage-impedance conversion element.
Applied to the gate of FETQ113, this FET,
Impedance between drain and source of Q113
The recording bias current is varied by changing RDS113. 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-controlled oscillator, and supply an oscillation voltage that is stable against disturbances, that is, a recording bias current to the recording head 2. supply. This rectifies the oscillation voltage with diodes D101 and D102,
The transistor Q111 is divided by the resistor R111 and the impedance RDS113 between the drain and source of the FET Q113 and applied to the base of the transistor Q112, and the ratio of the reference voltage Vz111 created by the Zener diode D111 and the voltage applied to the base of the transistor Q112 is determined by the voltage applied to the base of the transistor Q112. This can be obtained by controlling the collector-emitter voltage VCE111 of the recording bias oscillator 10 and varying the power supply voltage of the recording bias oscillator 10 to control the oscillation voltage of the recording bias oscillator 10. Here, the following relationship holds true between the drain-source impedance PDS113 of the FET Q113 and the gate applied voltage.

VGS: Gate applied voltage Vp: Pinch-off voltage gmo: Mutual conductance when VGS=OV Therefore, when the capacitor C121 is going from negative voltage to zero voltage, the above RDS113 decreases and is divided by resistors R111 and RD113. The voltage applied to the base of transistor Q112 decreases, the collector current of transistor Q112 decreases, and the collector-emitter voltage VCE111 of transistor Q111 decreases.
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 C121 is charged to a negative voltage in relay RL2ON, the recording bias current decreases, and conversely, capacitor C121 is forcibly discharged and is becoming zero voltage (relay RL2 is
(OFF), the recording bias current operates to increase.

Here, the signal level detection device 15 consisting of the rectification and smoothing circuit 14, the peak direct memory circuit 17, and the first comparison circuit 18 will be described in detail.
The reference reproduction output signal from is applied to the rectifier and smoothing circuit 14 via relay contact RL1b. That is,
This rectification and smoothing circuit 14 takes the input signal through a transistor Q141 whose collector is grounded, rectifies it by taking out diodes D141 and D142, and rectifies the input signal by connecting the capacitors C141 and C142 and the transistor Q1.
42 and take it out. This transistor Q
The signal obtained from the emitter terminal of transistor Q142 is applied to the base point P of transistor Q183, which is one input terminal of first comparator circuit 18, via diode D172. On the other hand, the transistor Q142
The emitter of is grounded through the attenuator VR1, and the signal obtained from its sliding terminal is connected to the diode D17.
1 to the base point O of the transistor Q182, which is the other input terminal of the first comparator circuit 18, and the capacitor C171. This diode D1
71 and the capacitor C171 constitute the memory circuit 17. In this way, transistor Q142
The peak value output signal taken out from the emitter of is applied as it is to the point P, while the peak value output signal whose level is suitably lower than the output level obtained from the emitter end of the transistor Q142 is taken out from the sliding terminal of the attenuator VR1. It is applied to the memory circuit 17 and also to the O point. That is, point O in Figure 3,
As shown in the output waveform at point P, as the recording bias is varied from point X from shallow to deep, each output signal rises while maintaining the initially set level difference, but when the peak bias is When it exceeds the peak value, the level of the P point output decreases due to the significant demagnetization effect caused by the recording bias magnetic field, but the O point output stores the peak value in the memory circuit 17 and moves in parallel while maintaining that value. A point is reached where the points intersect, ie, both levels coincide. This intersection point corresponds to the completion of the operation, 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 Q182 and Q183 of the first comparison circuit 18 also match, and the transistor Q181 whose base emitter is connected between both ends becomes OFF.

On the other hand, the reference voltage at point Q obtained by dividing +B from the above playback level and resistors R201 and R202.
V20 is compared with the reference voltage V20 by the second comparison circuit 19, and if the reproduction level is higher than the reference voltage V20, the transistor Q191 is turned off. This is the third
This corresponds to point Y shown in the figure.

Furthermore, within the start-up and stop device 13, three gates are connected to the base of the transistor Q131. The first gate has a diode D131
The second gate is connected to the relay holding circuit in the control voltage generator 12 through the diode D13.
2 to the first comparator circuit 18, and the third
The gate of the transistor Q131 is connected to the second comparator circuit 19 via a diode D133, and a NOR circuit is formed from this transistor Q131 and the three gates connected to its base. That is, only when all three gate inputs disappear does the transistor Q131 turn off, and the transistor Q132 connected to this transistor Q131
turns on, transistor Q134 connected to this transistor Q132 turns off, and as a result, the holding circuit of relay RL1 turns off, cutting off the power supply to that relay RL1, and the relay contacts RL1a to RL1c are connected to the solid line side. be done. Therefore, by releasing relay contact RL1c, capacitor C121
holds the voltage just before the relay contact RL1c is released, and the recording bias current is maintained by the capacitor C121.
A constant current is generated that is proportional to the voltage of , and all operations of the device are completed and the device enters the normal recording and playback state.

The second comparator circuit 19 is provided to prevent the apparatus from malfunctioning due to effects such as magnetic tape dropout and level fluctuations when the recording bias current is low. Also, relay contact RL
2b is an erasing circuit for erasing the memory of the characteristics of the previously used magnetic tape while the recording bias current is decreasing.

Also, the transistor Q in the starting and stopping device 13
The light emitting diode LED connected to the emitter of transistor Q134 is turned on when the transistor Q134 is ON, that is, when the device is in operation, to indicate whether or not the device is in operation.

In addition, the values of resistors R121 and R122 can be adjusted to switch the tape speed.
By switching in conjunction with the above, the optimum value can be set for each tape speed as well.

[Effects of the present invention]

As mentioned above, the device of the present invention has a NOR circuit with 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 are turned OFF. and memorized. 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, it is necessary to obtain the optimal recording bias current for each. 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 or sawtooth wave whose 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 is controlled. Since the period of the triangular wave or sawtooth wave is set sufficiently large, an accurate recording bias current can be obtained. Furthermore, by changing the cycle 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 VR1, the desired overbias can be set freely and accurately using the signal level detection circuit 15 according to the present invention.

As described above, 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 magnetic tapes of any characteristics, and the device described above can be operated while the automatic adjustment device is in operation. Since the device is provided with a display means that lights up to indicate that the device is in operation and automatically turns off when the operation is completed, it can be easily determined whether or not the device of the present invention is in the process of setting, giving the user a sense of security. In addition, it is possible to maximize the characteristics of various magnetic tapes.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure shows recording bias current vs. playback level characteristics, and FIG. 3 is a timing chart for explaining the operation of the circuit diagram shown in FIG. 1. 1, 1'... Tape reel, 5... Recording amplifier, 6... Playback amplifier, 7... Recording input terminal, 8
...Reproduction 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. In a magnetic recording/playback device equipped with an automatic recording bias adjustment device comprising a means for stopping and holding the recording bias current at a constant value, and a display means for operating and displaying when the recording bias current is in variable operation, the display means always By operating the open type start switch, the automatic recording bias adjustment device is held in the operating state, and at the same time it is activated, the automatic recording bias adjustment device lights up to indicate that it is in operation, and the automatic recording bias adjustment device has completed its operation. A magnetic recording/playback device characterized in that the light is automatically turned off at certain times.