JPS5928506Y2 - Tape recorder recording bias adjustment circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a recording bias adjustment circuit in a two-head tape recorder having an erasing head and a recording/playback head.

In tape recorders, especially cassette tape recorders, various tapes with different magnetic properties (e.g. CrO
2. Due to the use of FeCr, γ-Fe2O3), it is necessary to provide a bias current that flattens the recording and playback frequency characteristics depending on the tape, so many tapes are equipped with a bias current switching mechanism. In the case where the bias current is set in two or three stages and switching is performed, it is difficult to accurately match the bias current in accordance with the characteristics of magnetic tapes having various magnetic characteristics.

For this reason, some three-head tape recorders having independent recording and playback heads are equipped with a continuously variable bias adjustment circuit.

In the case of the above three heads, is it possible to easily check the bias current adjustment results by playing back at the same time as recording?For a two head tape recorder that also functions as recording and playback, recording and playback operations cannot be performed at the same time. It was extremely tedious as it had to be done repeatedly.

For example, bias current adjustment of the two-head tape recorder shown in FIG. 1 will be explained.

In Figure 1, 1 is a recording/playback head, 2 is an equalizer amplifier, 3 is a line amplifier, 4 is a meter amplifier,
5 and 6 are calibration oscillators for low frequency signals (for example, 400 Hz sine wave) and high frequency signals (for example, 10 KHz sine wave); 7
is a recording amplifier, 8 is a bias oscillator, 9 is a bias current selection switch (1: CrO2, 2: Fe
Cr, 3: γ-Fe2O3) 10 is a variable resistor for bias current adjustment, 11 is a calibration signal changeover switch, and 12 is an output indicator.

In order to adjust the bias current in the above configuration, the selector switch 9 is connected to a position suitable for the tape, and the low frequency signal is recorded.

Then, the low frequency signal is played back and the instruction of the indicator 12 is recorded, and then the high frequency signal is recorded and played back and the instruction of the indicator 12 is recorded.
Adjust the variable resistor 10 for bias current adjustment by eye so as to correct the difference between the instruction and the instruction when playing the low frequency signal, and then record and play back the low frequency signal and the high frequency signal again. Check whether the adjustment amount was appropriate according to the instructions in step 12.

In other words, the following operations must be repeated: low frequency signal recording, playback, instruction recording, high frequency signal recording, playback, instruction confirmation, adjusting variable resistor 10, low frequency signal recording, and so on. The operation is extremely cumbersome, and accurate adjustment requires a high level of skill, making it impractical.

This idea solves the drawbacks of the conventional example,
This is a bias adjustment circuit that allows bias adjustment to be made while observing the instructions from the indicator 12, and the drawings from FIG. 2 onwards will be described in detail.

FIG. 2 shows a calibration signal generator 21 used in the bias adjustment circuit of this invention, which generates a high frequency signal (for example, 10 KHz).
It consists of a sine wave) oscillator 6, a low frequency signal (for example, 400 Hz sine wave) oscillator 5, a square wave oscillator 13, and a switching circuit 14, the low frequency signal and the high frequency signal are switched by the square wave signal, and both signals appear alternately. A calibration signal is output.

As will be described later, the duty cycles of the rectangular wave signals are set to be different so that the indicator 12 can distinguish high-frequency signals and low-frequency signals by the time at which they are output (for example, a low-frequency signal is output for one second, a high-frequency signal is output for one second, and a high-frequency signal is output for one second). (for 3 seconds).

FIG. 3 shows an embodiment circuit of this invention, in which the switch SW
1. SW2 and SW6 are interlocked, and switches SW3 and SW
4. SW7 is linked.

The variable resistor 10 is for bias adjustment, and the variable resistor 10 is interlocked with a variable resistor 22 connected to the input terminal of the indicator amplifier 4.

Then, the variable resistor 22 and the variable resistor are adjusted so that the rate of change in the indicator 12 due to the change in the variable resistor 22 and the rate of change in the reproduced output due to the change in bias current due to the change in the variable resistor 10 are the same. Select 10 resistance values and resistance change characteristics.

Thus, switches SW1, SW2, SW6 are connected to terminal 1, sW3 . SW4. When SW7 is connected to the terminal RECj, a calibration signal in which a low frequency signal and a high frequency signal appear alternately is applied to the head 1 and recorded on the tape.

Then connect switches SW3, SW4, and SW7 to terminal 1-PL.
When the tape is played back by connecting to AYI, the playback levels of the low-frequency signal and the high-frequency signal appear alternately on the indicator 12.

If the bias current is at an appropriate value and the reproduction frequency characteristics are flat, the reproduction levels of the low-frequency signal and the high-frequency signal are the same, so the indicator 12 will show the same value, and the indication will be constant. There is.

However, if the bias current is not appropriate, the reproduction frequency characteristics will not be even, and the output levels will be different when reproducing the low frequency signal and the high frequency signal, and the indications of the indicator 12 will be different.

Therefore, in that case, record the indicated value when reproducing the low frequency signal (1 second), and operate the variable resistor 22 when reproducing the high frequency signal (for the next 3 seconds) to change the indicated value of the high frequency signal to the low frequency signal. Adjust to the indicated value of the signal.

At that time, the resistance value of the variable resistor 10 changes, and the bias current is set at a point where the output of the high frequency signal during reproduction becomes the same as the output of the low frequency signal.

That is, according to this invention, the calibration signal is recorded and played back, and the reproduction frequency is adjusted by operating the variable resistor 22 so that the reproduction level of the next high-frequency signal matches the reproduction level of the first low-frequency signal. The bias current can be set at a point where the current is even.

Also, by varying the variable resistor 10, the bias current changes and the playback level of the low-frequency signal also changes somewhat, but this is extremely small compared to the change in the playback output due to a change in the bias current of the high-frequency signal, so the above-mentioned operation is performed. It is possible to obtain a bias current that provides almost flat frequency characteristics by using only a bias current.

As explained above, this invention uses a calibration signal in which a low-frequency signal and a high-frequency signal appear alternately, and also connects a variable resistor 22 in conjunction with a variable resistor 10 for bias adjustment to the input stage of the indicator 12. With the provided configuration, it is possible to adjust the playback level of high-frequency signals by observing the indicator 12 and adjusting the variable resistor 22 to match the playback level of low-frequency signals, regardless of the magnetic characteristics of the tape. The bias current can be set so as to obtain a reproduction frequency characteristic, and the optimum bias current setting operation can be performed extremely quickly and accurately, which has extremely excellent practical effects.

[Brief explanation of the drawing]

Figure 1 is a conventional recording bias adjustment circuit diagram, Figure 2 is a circuit diagram of a calibration signal generator used in the recording bias adjustment circuit of this invention, and Figure 3 is a recording bias adjustment circuit diagram of an actual case of this invention. . 21 is a calibration signal generator for bias adjustment; 12 is an indicator;
10 is a variable resistor for bias adjustment, and 22 is a variable resistor.

Claims (1)

[Scope of utility model registration request] In a two-head tape recorder having an erasing head and a recording/playback head, a bias adjustment calibration signal generator 21 that alternately outputs signals of two different frequencies, low and high frequencies, and an indicator 12 circuit input stage are biased. Indicator input adjustment variable resistor 22 interlocked with adjustment variable resistor 10
A recording bias adjustment circuit for a tape recorder, characterized in that it is provided with.