JPS6030857Y2 - Level display device for magnetic recording and reproducing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an output level display device for a magnetic recording/reproducing device associated with a built-in test tone circuit for instantaneously checking the frequency characteristics of each loaded tape.

In particular, this project finely adjusts the recording bias current to obtain a flatter frequency response, even though tapes of the same type have slightly different high-frequency characteristics depending on the manufacturer. The present invention provides an output level display device that enables more accurate reading and monitoring of output levels.

Recently, several types of tapes such as high-density tapes are used in audio magnetic recording and reproducing devices, aiming at recording and reproducing with even higher fidelity.

These several types of tapes include CrO2, HL, Fe
- Since tapes such as Cr have different magnetic materials, coercive forces, etc., it is designed to switch the optimum bias current, recording/playback equalizer, etc. for each tape depending on the type of tape.

Therefore, the optimum bias current and recording/playback equalizer characteristics for each tape are usually adjusted to the optimum state at the time of manufacture.

By the way, in order to achieve higher fidelity playback, the overall frequency response including the recording/playback system must have a flat frequency response that extends from the low range to the high range, especially for high-end equipment up to around 12.5KHz. desired.

Furthermore, in order to obtain a good S/N ratio, it is desirable to operate the recording input level near the magnetic saturation point during recording.

However, as is well known, the tape sensitivity and frequency characteristics unique to magnetic tape are controlled by the bias current and recording input level, and qualitatively the bias current that produces the minimum distortion is generally located near the area where the maximum output is obtained. Are known.

Therefore, the recording bias is usually adjusted to a higher current to obtain an output level 1 dB lower than the bias current which obtains the highest output with the lKH2 signal.

Furthermore, when the frequency becomes different, especially at a higher frequency, the recording wavelength becomes shorter and the bias current at the maximum output point changes due to the self-demagnetizing effect, and the state of distortion also changes.

Therefore, in general, if the best condition is achieved at low frequencies, the bias current will be adjusted to a larger value at higher frequencies.
Has little effect on distortion.

For this reason, such a method is usually used to adjust the optimum bias current value when manufacturing this type of device.

However, even if the bias current and equalizer characteristics are set to optimal values in advance and switched according to the various types of tapes mentioned above, when adjusting the settings in advance during manufacturing, it is necessary to use the same type of tape from a different manufacturer than the standard tape used. For example, if a standard tape from company A is adjusted at the time of manufacture and tapes from other manufacturers B, C, and D are used, as shown in Figure 1, in the high frequency range, each manufacturer has a There is a variation of about 2 dB, and strictly speaking, recording and playback do not necessarily have a flat overall frequency characteristic.

Therefore, in a high-performance device, it is desirable that the optimum bias current be coarsely adjusted according to the type of tape using the method described above, and also finely adjusted by the user for each loaded tape.

This proposal was made in consideration of this point, and when looking at the relationship between bias current and output level using frequency as a parameter, as shown in Figure 2, the signal current is constant with respect to frequency in the low frequency range, that is, in the range where the recording wavelength is large. At a frequency at which constant current recording is performed, for example 400 Hz, the output does not change much with a bias change of several mA to the decimal place, and at high frequencies, that is, frequencies at which constant current recording is impossible mainly due to self-demagnetization. For example, at 8KHz, exactly
Focusing on the fact that it is possible to obtain a change of several d that is consistent with adjusting the variation in the output level by manufacturer shown in Figure 1, it is intended to enable precise adjustment of frequency characteristics, especially high frequency characteristics. It is.

Therefore, the present invention is equipped with a well-known single tone oscillator or test tone circuit of 400 Hz and 8 KHz, and a bias current fine adjustment knob is also provided in a position that is easy for general users to operate.

By the way, frequency characteristics are generally measured at 400Hz and 8KH2 in the input-to-output characteristics as shown in Figure 3.
In either case, the recording input level must be measured at a level that changes linearly, that is, at a recording input level that is not affected by self-demagnetizing effects in the high range.

Therefore, the JIS standards and the like stipulate that measurements should be made at a recording input level that is 10 to 20 dB lower than the OVU input level.

However, as is well known, the VU meter normally provided in high-end machines of this type has a scale display as shown in FIG. 4, and the deflection of the pointer with respect to the input voltage is specified as shown in FIG.

As a result, when this VU meter is used to measure frequency characteristics as described above, the pointer hardly swings, and it cannot be used as an output level meter for such measurements.

Therefore, the purpose of this proposal is to make the above-mentioned fine adjustment of the bias current possible under the condition of measuring accurate frequency characteristics, by making the six slight output level changes that are always available in this type of high-end machine. The point is to adapt it so that it can be directly read with a VU meter.

In addition, the feature of this project is that the meter amplifier that supplies the meter input voltage to the VU meter has two different amplification degrees, and in particular, the QVU meter needle swings significantly with a change of several dB.
A test tone circuit is provided with a gain control switch that selectively switches between a first amplification degree that outputs an output at the nearby input voltage of the meter and a second amplification degree that outputs an output at the original specified voltage of the VtJ meter. The meter amplifier is configured to automatically switch to the first amplification degree when the frequency characteristics are measured as described above using the meter amplifier.

The present invention will be explained below with reference to the drawings of the embodiments.

For convenience, the same or equivalent parts in each figure are given the same reference numerals.

FIG. 6 shows a configuration diagram of the main parts of this embodiment, where 1 is an input terminal for a recording signal, 2 is an amplifier for this signal, and 3 is a recording amplifier.
1 indicates a recording equalizer.

Further, 4 is a recording head, 5 is a magnetic tape, 6 is a high frequency bias oscillator, and 61 is used to finely adjust the bias current.

7 is a reproduction head, 8 is a reproduction amplifier, 81 is a reproduction equalizer, and 9 is a VU meter.

These are the same as those normally provided in known magnetic recording and reproducing devices, so detailed explanations will be omitted.

Reference numeral 11 designates a test tone circuit, in which 111 is a single-tone oscillator with a low frequency, for example, 400 Hz in this case, and 112 is a single-tone oscillator with a high frequency, for example, 8 kHz.

Further, 12 is a selection switch which selectively takes out the output signal from the test tone circuit 11 and the recording signal output from the amplifier 2 and inputs it to the well-known recording amplifier 3.

Therefore, the switch 113 of the test tone circuit 11 is a switch that selectively switches between the 400 Hz signal output and the 8 KHz signal.

From this test tone circuit 11, a 400Hz oscillator 1
Both the 8KH2 oscillator 11 and the 8KH2 oscillator 112 output voltages at the same level.

This output level is -10 lower than the QVU level in advance.
The output level is adjusted by a variable resistor (not shown) to reduce the output level by ~-20 dB.

What should be noted here is that the output level of the test tone circuit 11 corresponds to the so-called recording level of the path leading to the playback system via the recording amplifier 3 and tape 5, which govern the input-to-output characteristics of this device. It is.

Therefore, if the frequency characteristics are to be accurately checked and adjusted, the output level of the test tone circuit 11 is selected to correspond to the linear part of the input-to-output characteristics.

On the other hand, the meter amplifier 10 provides a meter input voltage to the VU meter 9, and has two different amplification degrees, a first and a second degree, and which of these two amplification degrees to operate is determined by the gain control switch 13. Can be switched.

Such a meter amplifier 10 can be realized using a well-known circuit connection as shown in FIG. 7, for example.

In this circuit, resistors R1 and R2 are connected to switch 1 as shown in Figure 6.
3 are closed to connect them in parallel, and by inserting these resistors R1 and R2 between the base and collector of transistor Q2, the overall gain of transistors Q1 and Q2 is increased.

Further, when the switch 13 is opened as shown in FIG. 7, only the resistor R is inserted between the base and collector of the transistor Q2, and the gain decreases.

Therefore, the meter input voltage applied to the VU meter 9 is governed by the switch 13.

Here, the amplification degree of the meter amplifier 10 when the switch 13 is closed is referred to as a first amplification degree for convenience, and the amplification degree when the switch 13 is opened and lowered is referred to as a second amplification degree.

When the meter amplifier 10 is operating at the second amplification degree,
It is designed so that an input voltage is applied to the VU meter 9 to display a specified VU level.

Further, when operating at the first amplification degree, the VU meter 9 is designed so that the pointer of the VU meter 9 swings approximately near QVU with respect to the input voltage.

Therefore, the VU meter at this time does not display the VU level, but simply operates as a level meter.

As already mentioned, this first amplification degree is such that the output of the test tone circuit 11 is -10 to -20 dB below the QVU level.
It is set to compensate for the loss.

A switch 14 is connected to the input of the meter amplifier 10 configured in this way, and this switch 14 functions as a recording level meter when its movable contact is connected to the line 15 side, and also connects to the line 16 side. This is a changeover switch to use the VU meter 9 as a playback level meter when it is on.

Further, the above-mentioned gain control switch 13 is replaced by the selection switch 12.
and are linked in the relationship shown in Figure 6.

Therefore, as shown in Figure 6, select switch 1 is used to check the frequency characteristics and finely adjust the bias current.
When set to 2, the gain control switch 13 connects the resistors B1 and R2 in parallel and operates the meter amplifier 10 at the first amplification degree.

As a result, when the bias current is finely adjusted by the variable resistor 61, the VU meter 9 acts as a mere level meter, and its pointer swings within a range of several times around QVU, as described above.

At this time, if the movable contact piece of the changeover switch 14 is connected to the line 15 in the opposite direction as shown, the VU meter 9 will check the output level of the test tone circuit 11.

On the other hand, when the selection switch 12 is switched to the output side of the amplifier 2, the gain control switch 13 is opened and the meter amplifier 1
0 is operated at the second amplification degree.

As a result, the output of the meter amplifier 10 matches the input voltage applied to the VU meter 9 with the specified VU level display, and the meter 9 operates as an original VU meter.

Therefore, when the movable contact piece of the changeover switch 14 is connected to the line 16 as shown in FIG. 6, the VU meter 9 displays the VU level as a reproduction output level meter.

In addition, when connected to the line 15 side, the VU level is displayed as a recording level meter of the recording signal.

As described above, the present invention has realized a level display meter that can accurately read and adjust changes in frequency characteristics of several dB in the high frequency range that vary depending on the tape manufacturer.

Furthermore, it is possible to use a VU meter, which is normally provided in this type of device, as a level meter for reading such minute deflection of the pointer without affecting its original purpose.

[Brief explanation of the drawings] Figure 1 is a frequency characteristic diagram of tapes by manufacturer, Figure 2 is a characteristic diagram showing the relationship between recording bias current and output, Figure 3 is a characteristic diagram of input vs. output, and Figure 4 is a characteristic diagram showing the relationship between recording bias current and output. Figure 5 is a diagram showing the display board of the VU meter, Figure 5 is a diagram showing the relationship between the input voltage of the meter and the VU level, Figure 6 is a circuit diagram of an embodiment of the present invention, and Figure 7 is a circuit diagram of the main part of an embodiment of this invention. This shows that. 3... Recording amplifier, 9...-VU meter, 10... Meter amplifier, 11... Test tone circuit, 12... Selection switch , 13
...Gain control switch.

Claims (1)

[Scope of utility model registration request] A test tone circuit that generates multiple single tones ranging in pitch from low to high at an output level that is pre-matched to the recording input level within a range where the input-to-output characteristics change approximately proportionally over the entire frequency band from low to high frequencies. A first amplification degree is provided, which sends out an output corresponding to the input voltage of the meter where the pointer of the vU meter swings around the QVU scale when this single tone output signal is simultaneously recorded and played back, and the pointer of the VU meter swings around the QVU scale. A meter amplifier having a second amplification degree that sends out an output corresponding to the specified input voltage of the meter that swings depending on the level, and a gain control switch that selectively switches between the first amplification degree and the second amplification degree of this meter amplifier. and a selection switch for selectively taking out the output of the recording signal or the output of the test tone circuit, and a recording amplifier connected to the selection switch and giving the taken output to the magnetic tape as a recording signal,
A magnetic recording/reproducing device characterized in that the selection switch interlocks the gain control switch so that the meter amplifier has a second amplification degree when the output of the test tone circuit is input to the recording amplifier. level indicator.