JPS5948444B2 - How to adjust the high frequency bias of a tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting high frequency recording bias of a tape recorder.

Conventionally, the recording bias amount of a tape recorder is adjusted for each machine on the production line, and is 1K as shown by curve a in Figure 1.
This is a fixed bias amount set at a point of 0 to -0.5 dB with respect to the peak value of the bias versus reproduction output level characteristic curve of the H2 signal.

Recently, a wide variety of magnetic tapes for tape recorders are commercially available, so this fixed bias amount is set at several levels depending on the type of tape, and the user can switch it depending on the tape being used. Some tape recorders are designed to do this. However, since there are considerable variations in the characteristics of magnetic tapes even if they are of the same type, the fixed amount of bias depending on the type of tape often does not provide the optimal recording bias. be. Therefore, it is desirable that the user be able to set the optimum bias amount for each tape to be recorded prior to recording.

The present invention aims to satisfy this requirement and provide an easy method for setting the optimum bias point.An example of this is given below in the case of a so-called two-head tape recorder that cannot be monitored during recording. Let's explain this with reference to the figure as an example.

In Figure 2, 1 is a recording/playback switch, 2 and 3 are switches that can be switched when recording an audio signal and when adjusting a bias, 4 is a switch that can be switched when playing back an audio signal and adjusting a bias, and 5 is used for both recording and playback. It is a magnetic head.

When recording an input audio signal, switch 1 is switched to the contact R side, and switches 2 and 3 are switched to the contact S side.

Then, the audio signal through the terminal 10 is supplied to the head 4 through the recording amplifier 11 and the equalizer amplifier 12, and the high frequency bias signal from the bias oscillator 13 is supplied to the head 5, and the audio signal is recorded on the magnetic tape 6. The signal is recorded.

At this time, the amount of high frequency bias from the bias oscillator 13 is a set constant amount. That is, a constant voltage determined by the variable resistor 14VR of the voltage setting circuit 14 is supplied to the variable power supply circuit 15, a constant voltage from this is supplied to the bias oscillator 13, and the amount of the high frequency bias signal is variable. It is assumed to be a constant value determined by the resistance setting. When reproducing the recorded signal, the switch 1 is switched to the contact P side, and the switch 4 is switched to the contact S side. At this time, the reproduction signal from the head 5 is led out to the output terminal 18 through the reproduction equalizer amplifier 16 and the line amplifier 17.

Next, to adjust the amount of high frequency bias, first switch switch 1 to contact R side, switches 2 and 3 to contact A side, and record a constant frequency signal for bias adjustment as follows. do.

That is, 20 is an oscillator, which is a relatively high frequency signal with a large change in the bias reproduction output characteristic curve, for example, 10? An oscillation signal is obtained, which is sent to the level adjuster 2.
1, its level is brought to an appropriate level, and a DC voltage is superimposed on it. The output of this level adjuster 21 is then supplied to a gate circuit 22, which controls the output SA of the free-running multivibrator 23.
(FIG. 3A), the output signal of the level adjuster 21 is gated by being turned on during the period T when it is "1", and the signal S from which an oscillation signal of 100z is intermittently extracted.
B (B in the same figure) is obtained, and this is the recording equalizer amplifier 1.
2 to the head 5.

On the other hand, the bias signal from the bias oscillator 13 is superimposed on this, and 10? The signal is recorded on tape 6. The amount of the high frequency bias signal from the bias oscillator 13 at this time is as follows.

That is, the output signal SA of the free-running multivibrator 23 is supplied to the sawtooth wave forming circuit 24, and from this, a sawtooth wave voltage Sc (FIG. 3C) which increases during the period when the signal SA is "1" is obtained. It will be done. This sawtooth wave voltage Sc is made to be the same as the change in voltage obtained from this circuit 14 when the movable element of the variable resistor 14VR of the voltage setting circuit 14 is slid from one end to the other end. This sawtooth wave voltage Sc is supplied to the bias oscillator 13 through the variable power supply circuit 15. Therefore, the output signal of this bias oscillator 13,
Therefore, the high frequency bias signal is such that its amount varies depending on the sawtooth voltage. Thus, 101
(The signal 11z is recorded with the bias amount gradually changed during period T.

Next, switch 1 was switched to the contact P side, switch 4 was switched to the contact A side, and the 1
0? play the signal.

That is, the output signal of the reproduction equalizer amplifier 16 is
The amplifier 25 converts the signal into a predetermined level signal, which is supplied to the rectifier circuit 27 through the buffer amplifier 26, where it is converted into a rectified and detected signal SD(
FIG. 3D) is obtained.

This signal SD is 1 for each period T as shown by curve b in FIG.
0? The bias vs. reproduction output characteristic curve of the signal is obtained. -6dB of the peak value of this characteristic curve b
The point corresponds to the -0.5 dB point of the characteristic curve a of 10z, and the -0.5 dB point of the reproduction output of the characteristic curve b corresponds to the -0.5 dB point of the characteristic curve a of 10z.
The position of 6 dB is the position where the optimum bias setting should be made.
Therefore, by making the voltage setting circuit 14 obtain the voltage at the slope part of the sawtooth wave voltage Sc corresponding to the position -6 dB of the peak value of the reproduced output, which is the optimum bias point, the optimum setting bias amount can be obtained. can be adjusted.

Therefore, in this invention, the following steps are taken.

That is, the output signal SD of the rectifier circuit 27 is supplied to the attenuator 28, and a signal whose level is attenuated by 6 dB is obtained. , a level EA attenuated by DB from the peak level of the signal SD is held. On the other hand, the output signal of the AGC amplifier 25 is supplied to a detection circuit 31 via a low-pass filter 30.

The recording signal SB has a DC component, and since this is recorded via a capacitor, the detection circuit 31
A pulse SE (FIG. 3E) generated at a break in the signal of 0 Vb is obtained. Then, the monostable multivibrator 32 is triggered by the rising pulse of this pulse SE, that is, the pulse at the leading edge of the period T. In this case, the monostable multivibrator 32 functions as a variable delay circuit and has a variable resistor 32VR in its time constant circuit, so that the pulse width of its output pulse SF (FIG. 3F) can be varied.

This variable resistor 32VR is connected to the bias oscillator 13.
The variable resistor 1 of the voltage setting circuit 14 sets the bias amount of
Has the same change characteristics as 4VR, and variable resistance 14VR
When the movable element of the variable resistor 32VR is slid from one end to the other end, the pulse width of the output pulse SF can be changed from OT to OT. Then, the output pulse S of this monostable multipipulator 32
The monostable multipipulator 33 is triggered by the trailing edge of F, from which a sampling pulse SG (G in the same figure) is obtained, and this sampling pulse SG causes the output signal S of the rectifier circuit 2T to
D is sampled and its sampled value EB is held. This sample hold circuit 34
A hold voltage EB from the peak hold circuit 29 is supplied to one input terminal of a differential amplifier 36 as a comparator through a buffer amplifier 35, and a hold voltage EA from the peak hold circuit 29 is supplied to the other input terminal of the differential amplifier 36. The two voltages are compared, and whether the voltage EB is greater than, less than, or equal to the voltage EA is indicated by the indicator 3T.

Then, while watching this indicator 37, slide the movable element of the variable resistor 32VR of the monostable multipipulator 32 from the other end toward the one end, and the pulse width of the output signal SF is indicated by the arrow in FIG. , the sampling position with respect to the signal SD is changed, and the hold voltage E
Make A and EB equal. Although not shown, this indicator may include, for example, the differential amplifier 36.
two light emitting diodes facing oppositely to each other are connected between the collectors of the first and second transistors constituting the
Furthermore, by changing the time constant of hold voltage EA (!: EB), one light emitting diode will emit light when there is a difference between the two voltages, and the two diodes will blink alternately when both voltages are equal. It is possible to use a circuit like this.

In this way, the variable resistor 32VR is adjusted so that the voltage EA and
When the sampling hold voltages EB become equal, the variable resistor 14VR of the voltage setting circuit 14 changes to the variable resistor 3.2V.
Since the voltage setting circuit 14 is linked to R and R, the voltage setting circuit 14 can obtain a voltage corresponding to the optimal bias position of the reproduction output characteristic curve of the slope part of the sawtooth wave voltage Sc.

Therefore, the above-mentioned recording and reproduction of the 10 KHz signal and adjustment of the variable resistor 32VR are performed before recording the input audio signal.
If this is done for each tape to be recorded, the amount of high frequency bias will always be the optimum amount suitable for that tape.

As described above, according to the method according to the present invention, the user can easily set the optimum bias amount for each tape.

Moreover, since a relatively high frequency signal, for example a 10K11z signal, was used as the bias adjustment signal,
The change in the bias-reproduction output characteristic curve of this signal near the optimum bias point has a steep slope, and when obtaining the optimum bias point from the change in the vicinity of the optimum bias point of the bias-reproduction output characteristic curve of a conventional 1KHz signal, Compared to this, there is an advantage that the optimum point can be easily set.

Furthermore, according to the method of the present invention, even with a so-called two-head tape recorder in which playback cannot be monitored during recording, the user can adjust the bias by one recording and playback. .

In the illustrated example, the variable resistor 14V of the voltage setting circuit 14
R and the variable resistor 32VR of the time constant circuit of the monostable multipipulator 32 are separately provided with the same characteristics.
In this case, the variable resistors 14VR and 32VR can also be used as one variable resistor.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a bias-reproduction output characteristic curve, Fig. 2 is a system diagram for explaining an example of the method of this invention, and Fig. 3 is a diagram showing a bias-reproduction output characteristic curve.
The figure is a waveform diagram for explaining the same. 5 is a recording/playback magnetic head, 20 is an oscillator, 23 is a free-running multivibrator, 24 is a sawtooth wave forming circuit, 13
is a bias oscillation circuit, 14 is a voltage setting circuit, 14VR is its variable resistor, 15 is a variable power supply circuit, 2T is a rectifier circuit,
29 is a peak hold circuit, 32 is a monostable multivibrator for determining the position of the sampling pulse, 32
VR is a variable resistor of the time constant circuit, 33 is a sampling pulse forming circuit, 34 is a sampling hold circuit, 3
6 is a differential amplifier as a comparator, and 37 is an indicator.

Claims (1)

[Claims] 1 A relatively high frequency signal is recorded with a high frequency bias voltage change characteristic that changes like a sawtooth wave, and this recorded signal is reproduced. A variable resistor associated with the resistor is provided, and a sampling pulse is generated from the reproduction output at a position a time selected by adjustment of the variable resistor from the reference position; The reproduced output is sampled and held, this sample-and-hold voltage and the peak-hold voltage of the reproduced output are level-compared, and the variable resistor is adjusted so that both voltages have a predetermined relationship. A high frequency bias adjustment method for a tape recorder, in which a high frequency bias amount of an input signal to be recorded is set.