JPS59886B2 - magnetic recording and playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording/playback device that can always automatically adjust a recording bias current to an optimal value for magnetic tapes with different characteristics, and its purpose is to reduce the adjustment time required for automatic adjustment. It's about shortening it.

Generally, the magnetic tape used in a tape recorder has a recording bias current of -
The recording sensitivity characteristics are different, and therefore the optimal bias value is also different. For this reason, in conventional tape recorders, two or three preset bias points can be switched using a switch.
Variable resistors were used to continuously vary the bias, but they all had drawbacks such as being cumbersome to operate and not necessarily matching the optimum bias point for all magnetic tapes.

Recently, in order to eliminate these drawbacks, devices with automated adjustment have been proposed (Japanese Patent Publication No. 45-102145, Japanese Patent Application Laid-Open No. 48-55713). However, these devices have disadvantages in that the time required for adjustment is long and that adjustments cannot be made with sufficiently high precision, so that sufficient performance cannot always be obtained for practical use. FIG. 1 shows changes in bias current and accompanying changes in reproduction output level in a conventional device. Three solid curves A, B, and C in Figure 1
are curves showing changes in playback level for different types of tapes, where the optimal bias points for tapes A, B, and C are P, Q, and R, respectively. As is clear from Fig. 1, in the conventional device, the time required for automatic adjustment varies depending on the tape, such as TA, TB, and Tc.
In the case of Tape C etc., the adjustment time was undesirably long. The first step in reducing adjustment time with conventional equipment is
It is sufficient to increase the rate of increase of the bias current as shown by the broken line in the figure.

As a result, the curves A, B, and C in FIG. be shortened. However, in a general recording/playback device of this type, the recording head and the playback head are separated by a distance l, and if the tape speed is Vp, then the tape running time between the recording head and the playback head is Td---l/ Because of Vp, a change in playback level always has a delay of Td than a corresponding change in recording bias. Therefore, an adjustment error Δi62Td (Δib/Δ) of the recording bias current occurs. Therefore, it is necessary to keep the rate of increase Δih/Δ of the recording bias current ib sufficiently small, and there is a limit to increasing the rate of increase. The present invention eliminates the above-mentioned conventional drawbacks and provides a device that can automatically set the recording bias to the optimum value in a short time, with high precision.

In the present invention, by switching the change in recording bias into two stages, for example, the speed of change is increased in areas other than the vicinity of the adjustment point related to adjustment errors, and the rate of change is made sufficiently slow in the vicinity of the adjustment point, thereby reducing adjustment time and adjusting error. It measures the reduction of An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

In Fig. 2, S, S2 are switches driven by relay 1, which are connected as shown by the solid line in normal recording and playback conditions, and the signal input from input terminal 2 is recorded and played back to output terminal 3. Output.

At this time, switch S3 is connected as shown by the solid line, and supplies a constant recording bias to the recording head. When performing automatic recording bias adjustment, first connect switch S3 as shown by the broken line. As a result, the triangular wave generator 5 is connected to the recording bias variable circuit 7 through the analog memory 6. Next, by momentarily pressing the adjustment start switch S4, the flip-flop 4 is reversed, the triangular wave generator 5 is reset, and triangular wave generation is immediately started. As a result, the recording bias current increases as shown in FIG. 3C. On the other hand, due to the reversal of flip-flop 4, relay 1 is turned on at the same time.
becomes ON, and the switches S, , S2 are connected as shown by the broken lines. As a result, the 400 Hz sine wave signal generated by the reference signal generator (400 Hz) 9 is mixed with the recording bias generated by the bias oscillator 8 at point P, and the high frequency bias is recorded from the recording head 11 onto the magnetic tape 12. Ru. The recorded signal further passes through a reproduction head 13 and a reproduction equalizer 14, is converted to a DC level by a rectifier 15 and a smoothing circuit 16, and is sent to a differentiation circuit 17. Here, the change in the reference signal reproduction voltage has a single peak characteristic as described above, and therefore, immediately after the recording bias variable starts, the differentiating circuit 1
The output of No. 7 takes a relatively large positive value. This differential value changes as shown in FIG. 3e after the variable starts. Differential output is amplifier 1
8, a negative DC voltage is further superimposed, and the input of the Schmitt trigger 19 shifts in the negative direction as shown in FIG. 3f, compared to FIG. 3e. Therefore, the output of the Schmitt trigger 19 is
It changes as shown in Figure g, and becomes 0N immediately after the variable starts. This output is further input to the input terminal Q of the time constant switching circuit 20. Here, the time constant switching circuit 20 is configured as shown in FIG.
It is possible to switch between T,=R-C and T2=(R1+R2)C. The input terminal Q is connected to the coil side of the relay 24, and the relay 24 is set to 0N by the above input.
Therefore, the resistor R, is short-circuited, and the time constant is T2=(R, +R
2) Changes from C to T1=R2C. Here, the triangular wave generator 5 is configured so that its rising speed changes in proportion to the time constant of the time constant switching circuit 20, and as the time constant changes, the rising speed increases to a large value. Changes to
In this way, near the peak bias, that is, the DO in FIG.
Point W is reached in a short time by a triangular wave with a high rising speed. When the signal change reaches point W, the Schmitt trigger 19
The output becomes 0FF, opening the relay 24 in Fig. 4,
The time constant T,=R2C changes to T2-(R,+R2)C, and the rising speed of the triangular wave changes to a small value as shown in Figure 3c, so the increasing speed of the bias current becomes sufficiently slow and the adjustment is made. The aforementioned bias current error ΔI at the point can be suppressed to a sufficiently small value despite the shortening of the adjustment time.
The reference signal that has reached the peak level in this way has a differential value of zero, and the Schmitt trigger 22 is set to ON through the inverter 21. In addition, the Schmitt trigger 22
The output of flip-flop 4 inverts flip-flop 4 and puts analog memory 6 into a memory holding state, while releasing relay 1 and connecting switches Sl and S2 as shown by solid lines. As a result, the recording bias is maintained at an optimum value, and normal recording and playback can be performed at the adjusted bias point. In addition, the second
As shown in FIG. 5, the analog memory 6 in the figure includes a reed relay 25, a field effect transistor 26, a capacitor CO
, resistors R3 and R4, and stores the electric charge stored in the capacitor CO by blocking leakage using a reed relay and a field effect transistor 26.

Therefore, the memory is retained even after the power is turned off. In addition, in the above embodiment, the j-ray 24 was used for switching the time constant shown in FIG.
An element that performs a similar switching operation, such as a transistor, may be substituted.

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

1. The optimal recording bias can always be automatically set for any magnetic tape.

2. It is industrially useful because it can be realized with a simple device.

3. It is also effective against changes in the optimum bias point caused by aging or replacement of the recording head. 4. Adjustment can be made in a short time, allowing the user to use the tape recorder more easily.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing changes in recording bias current and playback level of a conventional magnetic recording/playback device, Fig. 2 is a block diagram of a magnetic recording/playback device according to an embodiment of the present invention, and Fig. 3 a-g.
4 is an electric circuit diagram of the time constant switching circuit of the apparatus of the present invention, and FIG. 5 is an electric circuit diagram of the analog memory of the apparatus of the present invention. 1...Relay, 2...Input terminal, 3.
... Output terminal, 4 ... Flip-flop, 5 ... Triangular wave generator, 6 ... Analog memory, 7 ... Recording bias variable circuit, 8・
... Bias oscillator, 9 ... Reference signal generator, 10 ... Amplifier circuit, 11 ... Recording head, 12 ... Magnetic tape, 13...
...Reproduction head, 14...Reproduction equalizer, 1
5... Rectifier, 16... Smoothing circuit, 1
7...Differential circuit, 18...Amplifier, 1
9... Schmitt trigger, 20... Time constant switching circuit, 21... Inverter, 22...
...Shimitu trigger.

Claims (1)

[Claims] 1 means for recording a reference signal while varying the amount of recording bias; means for reproducing the recorded reference signal and detecting an optimum recording bias value based on changes in the playback level; A magnetic recording and reproducing apparatus comprising means for holding a value, the magnetic recording and reproducing apparatus comprising means for switching the variable speed of the recording bias amount at a predetermined value of the reproduction level.