JPS5916328B2 - Tape recorder bias adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bias adjustment device for a tape recorder.

In general, the recording bias value of a tape recorder is set to a value at which the 1Kll2 recording/playback signal reaches its peak, taking into consideration the distortion rate, high frequency saturation level, etc.
The reference tape is used to adjust the value to a value that is lower than B or 1 dB.

However, various kinds of magnetic tapes are commercially available, and in order to maximize the performance of each tape, it is necessary to set a bias value suitable for each tape. 0 For this reason, an increasing number of tape recorders are equipped with a bias adjustment device that adjusts the bias value according to each tape.

FIG. 1 shows a block diagram of a conventional adjustment device.

In the conventional device shown in FIG. 1, when the tape recorder is put into the recording state, the bias signal obtained from the bias signal generator 11 is passed through the bias current regulator 14 to the recording head 16.
When the test switch 12 is pressed, a bias adjustment signal of 1KlI2 is supplied from the adjustment signal generator 20 to the recording head 016 through the recording amplifier 15 and recorded on the magnetic tape 17. The recording signal is immediately played back by the playback head 18, passes through the playback amplifier 19 and the meter amplifier 21, and indicates its level to the level meter 22. Here, the bias current regulator 14 is operated to set the bias current so as to decrease by a predetermined value from the 1KH2 peak or .5 peak level to obtain the optimum bias. However, the bias characteristics of the 1KH2 signal are very broad, and even if the bias value is varied within a range of ±30% of the peak bias value, only a level change i0 of about 1 dB can be obtained.
For this reason, large errors occur due to level fluctuations, and it is also very difficult to stably and precisely set the peak bias value of the 1KH2 signal from the level meter reading. Therefore, such a conventional bias setting j5 method is not preferred in practice. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an optimum bias setting device for easily setting the optimum bias value for each tape.

In the present invention, the peak bias value of a certain predetermined frequency signal of 1K1Iz or more is detected, and the optimal bias value is calculated from that value.

That is, as shown in FIG. 2, the bias characteristics of a magnetic tape vary in peak bias value and inclination before and after the peak depending on the recording frequency. In Figure 2, the horizontal axis shows the bias current when the 1-imaginary peak bias is set to 100 (fl), and the vertical axis shows the reproduction output when the peak level of 10z is set to 0 dB, and curves 1, 2, and 3 are respectively 1? , 4 tastes, 8
It shows my bias characteristics. As can be seen from Fig. 2, the bias characteristic of 11 (1 Iz) shown by curve 1 is very broad and it is difficult to detect the peak bias. Because it appears clearly, it is easy to detect the peak bias value with high accuracy.
The Ryu's bias characteristics also have a clear peak, but because the difference in recording level between tapes is large, it is necessary to make the gain of the meter indicator variable, which makes the circuit complex and impractical. Next, when comparing the peak bias value of 1L and the peak bias value of 4K11z, there is a constant relationship regardless of the tape for tapes of the same type, for example, for normal tapes there is a 1! (The 11z peak bias value is approximately 25% higher than the 4L peak bias value.In the present invention, the 11z peak bias value and 1K
Utilizing the property that the ratio to the peak bias value of a predetermined frequency set to 1Iz or more is constant regardless of the tape, the peak bias value is first detected with a frequency signal higher than 11 (11z), which makes it easy to detect the peak bias value. By setting and then increasing the obtained bias value at a constant rate, a 1K & peak bias value or a bias value that decreases by a predetermined value from the peak level is obtained.Hereinafter, specific embodiments of the present invention will be described. Explain.

This embodiment is an optimum bias adjustment device for a three-head tape recorder, and a block diagram of the main part is shown in FIG. In Fig. 3, the bias adjustment test switch 12 provided on the panel surface of the tape deck is turned on when the deck is in the recording state.
When a and 12b are pushed to the test side, the bias signal obtained from the bias signal generator 11 is attenuated by a predetermined ratio determined for each tape system by the attenuator 13, and then sent to the recording head 16 through the manual bias current regulator 14. Supplied. For example, 4K1 from the adjustment signal generator 20 at the same time.
The Iz adjustment signal is supplied to a recording head 16 through a recording amplifier 15 and recorded on a magnetic tape 17. The recorded 4K11z signal is immediately played back by the playback head 18, and the playback level is indicated by the level meter 22 through the playback amplifier 19 and meter amplifier 21. Here, the bias current regulator 14 is operated so that the indicated value of the level meter 22 reaches a peak, and when the peak is obtained, the test switch 12 is returned to the normal side, thereby short-circuiting the attenuator 13 and achieving a predetermined value. The bias becomes deeper by the same percentage, and an optimum bias current corresponding to a 1K11z peak bias can be supplied to the recording head 16. In this embodiment, a non-lock type push switch is used as the test switch 12, and while pressing the test switch 12, the adjustment knob of the bias current regulator 14 is rotated.
The optimum bias state is reached by releasing the test switch 12 after setting the peak, and the optimum bias suitable for each tape can be obtained easily and in a short time.

FIG. 4 shows a specific circuit of the bias current adjustment portion in the present invention. This circuit has a configuration including the bias signal generator 11, test switch 12, attenuator 13, and bias current regulator 14 shown in FIG. In FIG. 4, the bias oscillation circuit 31 changes its oscillation voltage in proportion to the current voltage, and the transistor 33 constitutes a constant current circuit, and adjusts the bias adjustment variable resistor 34 inserted into the collector. By this, transistor 32
The base voltage of the bias oscillation circuit, that is, the power supply voltage of the bias oscillation circuit can be adjusted. Now, when the power supply Cc is applied to the circuit shown in Fig. 4 and the test switch 37 is set to the test side, the resistance 35
Since a resistor 36 is inserted in series with , the base voltage of the transistor 33 increases by a certain voltage compared to the normal state, and the collector current of the transistor 33 decreases by a certain amount. When the variable resistor 34 for bias adjustment is adjusted here, the base potential of the transistor 32 changes, and the power supply voltage of the bias oscillator 31 is adjusted. Therefore, the bias current changes and can be adjusted to the peak bias for the 40z bias adjustment signal. 31a is a recording bias output terminal, and 31b is led to an erase head.

When the test switch 37 is set to the normal side after the peak bias is obtained as described above, the resistor 36 is short-circuited, the power supply voltage of the bias oscillator 31 is increased by a certain percentage, and a predetermined optimum bias current value is obtained. It is something. As described above, it is an object of the present invention to provide a tape recorder that makes it possible to easily and accurately set the optimum bias value suitable for each magnetic tape used, and that can bring out the maximum performance of the tape. was completed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main part of a conventional bias adjustment device, FIG. 2 is a bias characteristic diagram of a magnetic tape, FIG. 3 is a block diagram of the main part of a bias adjustment device showing an embodiment of the present invention, and FIG. 4 3 is a specific circuit diagram of the bias adjustment section of FIG. 3. FIG. 11...Bias signal generator, 12, 37...
...Test switch, 13...Attenuator, 1
4...Bias current regulator, 15...
Recording amplifier, 16... Recording head, 17...
...magnetic tape, 18...playback head, 19
...Reproduction amplifier, 20 ...Adjustment signal generator, 21 ...Meter amplifier, 22 ...
Rubel meter, 31...Bias oscillation circuit, 3
2, 33...Transistor, 34...
Variable resistor, 35, 36... Resistance.

Claims (1)

[Claims] 1. A recording test switch that reduces the recording bias current by a predetermined percentage, a bias current regulator that can increase or decrease the bias current, a bias adjustment signal generator that generates a predetermined frequency signal of 1 KHz or more, and the variable bias It consists of a recording head that records current and a predetermined frequency signal on a tape, a playback head that plays back the same, and display means that displays the playback output level from the playback head. Bias adjustment characterized in that when a peak bias is obtained for the bias adjustment signal by adjusting a current regulator, the recording test switch is released and a bias current increased by a predetermined percentage is supplied to the recording head. Device.