JPS5948446B2 - 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 the amount of high frequency bias current in a tape recorder.

Conventionally, the amount of high-frequency bias current in a tape recorder is adjusted for each machine on the production line. have been adjusted to be at the same level.

Moreover, this is usually adjusted with one type of tape, and it is rare that similar characteristics can be obtained with a wide variety of commercially available tapes. Furthermore, tape recorders incorporating so-called Dolby noise reduction devices have the disadvantage that deviations in frequency response characteristics are rather amplified. Therefore, it is important to ensure that the overall frequency characteristics with respect to the amount of bias current are flat. To achieve this, the user of the tape recorder must set the high frequency bias for each tape to be recorded before recording. It is desirable to be able to adjust the amount of current. However, in the case of a two-head tape recorder that does not allow tape monitoring, in order to adjust the frequency characteristics using high-frequency bias control, the recording and playback operations must be repeated several times, making the adjustment process difficult. In addition to being difficult to use, it was also extremely difficult to find the optimal point, making it virtually impossible for the user to make adjustments.

In view of the above-mentioned points, the present invention provides a high-frequency bias adjustment that allows a user to easily adjust the amount of high-frequency bias current for various magnetic tapes even in a two-head tape recorder. It is intended to provide a method. An example of the method of this invention will be described below with reference to the drawings, taking the case of a two-head tape recorder as an example.
Let me explain.

In FIG. 1, 1 is a recording/playback selector switch, 2 and 3 are switches to be switched between when recording an audio signal and when adjusting a high frequency bias, and 4 is a switch to be switched between when playing back an audio signal and when adjusting a high frequency bias.ゝ 5 is a magnetic head for both recording and playback.

To record an audio signal and play it back, press switch 2.
-4 to the contact S side. During recording, the switch 1 is switched to the contact R side, and the audio signal through the input terminal 10 is supplied to the head 5 through the recording amplifier 11 and recording equalizer amplifier 12, and the bias signal from the high frequency bias oscillator 13 is supplied to the head 5. The audio signal is superimposed on this and supplied to the head 5, and the audio signal is recorded onto the tape 6.

The amount of bias current from the high frequency bias oscillator 13 at this time is a predetermined amount adjusted as described later.

That is, 14 is a voltage setting circuit, which includes a variable resistor VRA.
is provided, a voltage Ev corresponding to the position of the movable element is obtained from this, this voltage Ev is supplied to the variable power supply circuit 15, and a constant voltage corresponding to this voltage Ev is obtained from this, This is supplied to the bias oscillator 13.

The bias oscillator 13 is connected to this variable power supply circuit 15.
The amount of bias current is controlled by the voltage from the voltage setting circuit 14, and in this case, it is set to a constant amount according to the voltage Ev from the voltage setting circuit 14. During reproduction, the switch 1 is switched to the contact P side, and the audio signal extracted by the head 5 is led out to the output terminal 18 through the reproduction equalizer amplifier 16 and the line amplifier IT.

Next, when adjusting the amount of high frequency bias current, switches 2 to 4 are switched to the contact A side. Then, the bias amount is adjusted by one recording and reproduction of the adjustment signal in the following manner. That is, 20 and 21 are oscillators, which respectively obtain a signal with a relatively higher frequency than the oscillator 20, for example, a signal S1 of 10 GHz, and a signal with a relatively lower frequency than the oscillator 21, for example, a signal S2 of 333 Hz. , these signals S1 and S2 are supplied to level adjusters 22 and 23, respectively, and controlled to appropriate levels, and a DC component is superimposed, and the output signal of this level adjuster 22 is supplied to gate circuits 24 and 25. be done.

Further, 26 is a free-running multipipulator, from which a rectangular wave signal SA (FIG. 2A) of a constant period is obtained.

In this case, the period TA of the signal SA is set to be "month", for example, 350 msec. The period TB, which is "O", is, for example, 50 msec. Then, the rise of this rectangular wave signal SA triggers the monostable multipipulator 2T as a delay circuit, and from this, for example, 6
msec7? It becomes "1" from the time when ' is delayed, and it becomes "1" during the period Tc from that point to the end position of the period TB.
A signal SB (FIG. 2B) is obtained. Then, the signal SA causes the gate circuit 24 to become "1" for a period T.
A is turned on, and 10KII from the level adjuster 22
The signal z is gated to obtain the signal Sc (C in the figure), and the gate circuit 25 uses the signal SB to
1'' during the period Tc, the level adjuster 23
The next 333Hz signal is gated, and from this the signal S
D (D in the same figure) is obtained. These signals Sc and SD are supplied to a mixer 2T, from which the mixed signal SE (
E) in the same figure is obtained, and this is supplied to the head 5 via the switch 2, the equalizer amplifier 12, and the contact R of the switch 1. On the other hand, a high frequency bias signal from the bias oscillator 13 is superimposed on this and supplied to the head 5. signal S
E is recorded.

The amount of bias current from the bias oscillator 13 at this time is as follows.

That is, the signal SA from the free-running multipipulator 26 is Ξ
The Ξ square wave voltage SF (FIG. 2 F) which linearly falls during the period TB and linearly rises during the period TA is obtained by being supplied to the square wave forming circuit 28, and thereby the variable power supply circuit 15 The output voltage of the bias oscillator 13 is changed so that the current amount of the output high-frequency bias signal SG (G in the figure) of the bias oscillator 13 gradually decreases during the period TB and gradually increases during the period TA.

Note that the change in the rising portion of this Ξ-angle wave voltage SF is equal to the change in voltage obtained when the movable element of the variable resistor VRA of the voltage setting circuit 14 is moved from one end of the resistance to the other end. It is like that.

In this way, the 10 KHz signal is recorded with the bias amount gradually increasing, and the 333 Hz signal is recorded with the bias amount gradually decreasing. In this case, the signal SE is recorded via a capacitor, and therefore, clicks are recorded at the beginning and end of the no-signal portion of the signal SE.

The signal recorded in this way is played back by the head 5,
The playback signal is supplied to the AGC amplifier 29 through the playback equalizer amplifier 16 and the contact A side of the switch 4, where the signals whose sensitivities differ depending on the type of tape are corrected and become at the same level. It will be done like this.

The output signal of this AGC amplifier 29 is then supplied to a detector 31 via a low-pass filter 30, from which the recorded click SH (H in Figure 2) is obtained.
The rising edge of this pulse triggers the monostable multino q-bulator 32, from which a square wave signal SI (same figure) is obtained, and the trailing edge of this triggers the monostable multivibrator 33, which generates the sampling pulse. SJ (J in the same figure) is obtained. On the other hand, the output signal of the AGC amplifier 29 is passed through a high-pass filter 34 to a rectification circuit 35.
is supplied to the 10Z signal reproduction output SK (
K) in the same figure is obtained, and this is the sampling hold circuit 3.
6, the overbiased slope portion of the output SK is sampled by the sampling pulse SJ from the monostable multivibrator 33, and the sampled voltage is held.

In this case, the monostable multivibrator 32 acts as a variable delay circuit, and its time constant circuit is provided with a variable resistor VRB, which changes the pulse width of the signal SI and therefore the generation position of the sampling pulse SJ with respect to the output SK. It will be done. This variable resistor RB is interlocked with the variable resistor VRA of the voltage setting circuit 14 that changes the amount of high-frequency bias current, and also generates a triangular wave voltage SF corresponding to the amount of high-frequency bias such that the reproduced output SK is at the sampled level. The voltage setting circuit 14 is operated so that a voltage equal to the predetermined voltage of the slope portion is obtained. The output signal of the AGC amplifier 29 is also supplied to a rectifier circuit 38 via a low-pass filter 37, from which a reproduced output SL of a 333 Hz signal (L in FIG. 2) is obtained, which is supplied to a peak hold circuit 39. and its peak level is held. ．． Then, the hold voltage EA from the sampling hold circuit 36 and the hold voltage EB from the peak hold circuit 39 are supplied to a differential amplifier 40 as a comparator, and their levels are compared. EA is the voltage 'EB
Greater than, less than, equal to, and whether are displayed.

Although not shown, the indicator 41 may include, for example, 2
These two light emitting diodes are connected in opposite directions between the collectors of the two transistors constituting the differential amplifier 40, so that the voltage EA is greater than the voltage EB or When you're small,
Only one of the two light emitting diodes is made to emit light, and the hold time constants of both hold circuits 36 and 39 are slightly different, so that when both voltages are equal, the two light emitting diodes emit light alternately. You can use something like this.

In this case, the bias amount-reproduction output characteristic curve of a low frequency signal, ie, 333 Hz in this example, is almost flat, and even if the bias amount changes slightly, the magnitude of the reproduction output hardly changes.

In contrast, higher frequencies, i.e. 10KIIz in this example
According to the signal bias amount vs. reproduction output characteristic curve, if the bias amount changes slightly, the reproduction output level changes greatly. From this, if the bias amount is selected so that the reproduced output level of the 10D signal is equal to the peak level of the reproduced output of the 333 Hz signal, the overall frequency response to the bias amount will be approximately the same from 333 Hz to 100 Hz. It becomes flat. Therefore, while watching the indicator 41 mentioned above, the variable resistor RB that controls the sampling position is adjusted so that the sampling hole Y pressure EA becomes equal to the peak hold voltage EB.

In this way, the output voltage Ev of the voltage setting circuit 14 is such that the amount of bias current from the bias oscillator 13 is 101
The reproduction level of the CIIz signal becomes a value equal to the peak level of the reproduction output of the 333 Hz signal, and the amount of bias current becomes optimal.

Therefore, the above-mentioned recording and playback of the adjustment signal and adjustment of the variable resistor VRB are performed before recording the input audio signal.
If this is done for each tape to be recorded, the high frequency bias current amount will always be optimal for that tape, and the frequency characteristics of the playback signal will be almost flat from low frequency signals to high frequency signals. Becomes a characteristic. As described above, according to the method according to the present invention, the user can easily adjust the optimum bias amount for each tape used.

Moreover, even with a two-head type tape recorder, there is an advantage in that adjustment can be made in one recording/playback operation. In the illustrated example, the variable resistor VR of the voltage setting circuit 14
A and the variable resistor VRB of the time constant circuit of the monostable multipipulator 32 are separately provided with similar characteristics, and are made to work together.
A and VRB can also be used as one variable resistor. Also, in the example shown in the figure, the high frequency signal is where the bias amount gradually increases, and the low frequency signal is where the bias amount is gradually increased. I recorded each of the parts that gradually decreased,
Conversely, a high frequency signal may be recorded in a gradually decreasing portion, and a low frequency signal may be recorded in a gradually increasing portion.

Further, the length of the period TA (5 TB) may be selected to a length that allows a sufficient peak value of the bias-reproduction output characteristic curve to be obtained.

[Brief explanation of the drawing]

FIG. 1 is a system diagram for explaining an example of the method of this invention,
FIG. 2 is a waveform diagram for explaining this. 11 is a recording amplifier, 12 is a recording equalizer amplifier, 13
is a high frequency bias oscillator, 14 is a voltage setting circuit, VRA
is a variable resistor for setting the voltage, 16 is a regenerative equalizer amplifier, 11 is a line amplifier, 20 and 21 are oscillators, 24 and 25 are gate circuits, 26 is a free-running multivibrator, 28 is a Ξ angle wave forming circuit, 31 is a click detector, 32 is a monostable multivibrator, VRB is a variable resistor for varying the output pulse width, 32 is a monostable multivibrator as a sampling pulse forming circuit, 34 is a high-pass filter, and 37 is a low-pass 35 and 38 are rectifier circuits, 36 is a sampling hold circuit, 39 is a peak hold circuit, 40 is a comparator, and 41 is an indicator.

Claims (1)

[Claims] 1 The amount of high frequency bias current is gradually increased and decreased according to the triangular wave, and a relatively high frequency signal is generated.
a relatively low frequency signal, and one with the above increasing part,
Record the other at the decreasing portion, play it back, detect the reference position for the triangular wave from this playback output, and adjust the variable resistor from the reference position to the relatively high position at which the time determined by adjusting the variable resistor has elapsed. The variable resistor is adjusted so that the reproduced output level of the frequency signal is equal to the peak level of the reproduced output of the relatively low frequency signal, and the variable resistor determines an amount of high frequency bias with respect to the input audio signal. A method for adjusting the high frequency bias of a tape recorder in relation to a variable resistor.