JPH0449161B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a magnetic recording/reproducing signal device for switching recording/reproducing states.

Configuration of a conventional example and its problems FIG. 1 shows a circuit diagram of a conventional magnetic recording/reproducing device. 1 is a recording bias transmission circuit, 2 is a magnetic head for both recording and playback, 3 is a recording microphone, 6 is an amplifier, 7 is an automatic gain control circuit, 8 is a recording signal amplifier, and _S1 is for switching between the recording state and the playback state. The switch _S2 is a switch for switching signals.

Next, to explain the operation, when switch _S1 is connected to side A and sufficient time has elapsed after the power is turned on (about 1 second or more), it will operate in the recording state, and microphone recording signal amplifier 4 and amplifier 6 will be activated. , the automatic gain control circuit 7, the recording signal amplifier 8, and the recording bias signal oscillation circuit 1 are in the operating state, and the reproduction signal amplifier 5 is in the cutoff state. Therefore, the signal from the microphone 3 is amplified by the micro recording signal amplifier 4 and sent to the signal switching switches S2 _a to c, the capacitor 111, and the resistor 11.
5 to amplifier 6. This amplifier 6
The amplified signal is taken out to terminal B as a monitor signal, and is also applied to recording signal amplifier 8 where it is amplified and taken out to terminal J as a recording signal.
This signal is connected to a resistor 12 for frequency correction of the recording signal.
1. A bias signal from the recording bias oscillation circuit 1 is applied to the recording/reproducing head 2 via the capacitor 122, and the signal from the head is recorded on the magnetic tape.

Next, when switch S ₁ is connected to side B and sufficient time has passed after the power is turned on, the playback state is entered, the playback signal amplifier 5 and amplifier 6 are activated, and the microphone recording signal amplifier 4 and automatic gain control are activated. Circuit 7, recording signal amplifier 8, recording bias oscillation circuit 1
into the cut-off state. Then, the signal recorded on the magnetic tape is detected by the head 2, is amplified by being applied to the reproduced signal amplifier 5, and is applied to the amplifier 6 via switches _S2 a to c, a capacitor 111, and a resistor 115.
After being amplified by this amplifier 6, it is taken out to terminal B as a reproduced signal.

In this way, when enough time has passed after the power is turned on, the recording state or the playback state is entered, but immediately after the power is turned on, whether switch _S1 is connected to the a side or the b side, the feedback of the playback signal amplifier 5 is capacitor 1
01, the DC potential of the outputs of the playback signal amplifier 5 and the microphone recording signal amplifier 4 rises rapidly.
It is further amplified by amplifier 6 and becomes the B output.
There was a drawback that a shot sound called "poko" was output, and another drawback was that the shot sound at point B was amplified by the amplifier 8 and recorded.

Furthermore, the shock sound output from the amplifier 8 is applied to the automatic gain control circuit 7, which operates to reduce the input signal to the amplifier 6. This automatic gain control circuit 7 operates to reduce the gain instantaneously (20 to 70 msec) when a large signal is input, and to reduce the input signal of the amplifier 6 for a while (3 to 5 seconds) even when the signal becomes small. do. Therefore, the gain control circuit 7 operates with the shock sound generated when the power is turned on in the recording state, and the gain control circuit 7 does not operate for a while after the power is turned on, even though the recording signal is small. There was a problem in that the gain control circuit 7 was activated, resulting in a low-level recording state.

Purpose of the Invention The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide a magnetic recording/reproducing device which can reduce shock noise when the power is turned on and can prevent malfunction of an automatic gain control circuit caused by the shock noise.

Structure of the Invention In order to achieve the above object, the present invention compares a changing voltage of a switching terminal whose voltage changes continuously immediately after power is turned on with first, second, and third comparison voltages set in advance. By connecting the switching terminal and the second comparison voltage when the power is turned on, the comparison circuit changes the voltage at the switching terminal to a second comparison voltage that is a voltage between the first comparison voltage and the third comparison voltage. A switch circuit is provided to set the voltage, and the recording state or the playback state is determined by comparing the second comparison voltage with the above-mentioned changing voltage, and this changing voltage is compared with the first and third comparison voltages. The output signal is used to shut off the amplifier, reduce the shock noise immediately after the power is turned on, and prevent the automatic gain control circuit from malfunctioning due to the shock noise when the power is turned on. It is something.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 shows a magnetic recording and reproducing apparatus according to an embodiment of the present invention. This figure 2 mainly adds the part W surrounded by the dotted line to the conventional example in figure 1, and a resistor 14 is connected between the power supply V _cc and the ground.
1,142,143,144 are connected in series to O,
Three comparison voltages P and Q are created, and differential amplifier transistors 145 and 14 are used as three comparison circuits.
6, 148, 149, and 151, 152 are provided. Also, the resistor 161 and capacitor 165 turn on the transistor 163 immediately after power is turned on,
The transistor 164 is used to bring the voltage at the terminal M and the voltage P to almost the same potential, and the resistor, capacitor, and transistor constitute a switch circuit.

Next, the operation will be explained. Recording/playback switch S ₁
is connected to the a side, and when sufficient time has elapsed (about 1 second or more) after the power is turned on, the recording bias oscillator circuit 1 becomes operational and the M voltage becomes higher than the P voltage, forming a comparison circuit. The transistor 148
In the OFF state, the transistor 149 is in the ON state, outputting an OFF signal to the terminal R to cut off the reproduction signal amplifier 5, and outputting an ON signal to the terminal T to turn on the microphone recording signal amplifier 4 and the recording signal amplifier 8. It works in the working state and in the recording state. On the other hand, when the recording/playback selector switch _S1 is connected to the b side and sufficient time has elapsed after the power is turned on, the recording bias oscillation circuit 1 is cut off because no power supply voltage is supplied, and the M
Since the voltage is lower than the P voltage, the transistor 149 constituting the comparison circuit is in the OFF state, the transistor 148 is in the ON state, and the terminal T is OFF.
A signal is output to turn off the microphone recording signal amplifier 4 and the recording amplifier 8, and an ON signal is output to the terminal R to turn the reproduction signal amplifier 5 into an operating state, thereby operating in a reproduction state. Even if _S1 is connected to either the a side or the b side, the amplifier 6 is in the recording and playback operation state as long as sufficient time has passed after the power is turned on.

When the power is turned on with the recording/playback selector switch _S1 set to the a side, if the M voltage is lower than the O voltage, the transistors 151 and 146 constituting the comparator circuit are turned off.
The S output becomes an OFF signal. When the M voltage is higher than the O voltage, transistors 146 and 152 are on.
Transistors 145 and 151 are turned OFF, and an ON signal for transistor 146 is output to terminal S. On the other hand, the recording/playback selector switch S ₁ is the power supply on the b side.
When the M voltage is higher than the Q voltage when ON, transistors 151 and 146 forming the comparison circuit are OFF.
Then, the S output becomes an OFF signal. When the M voltage is lower than the O voltage, the transistor 151 forming the comparison circuit is ON, the transistor 152 is OFF, and the transistor 145 forming the other comparison circuit.
is ON and the transistor 146 is OFF, so the terminal S outputs the ON output signal of the transistor 151. That is, an ON signal is output to the S terminal when the M voltage is above O and below Q, and an OFF signal is output when the voltage is between O and Q. Output R,
FIG. 8 shows the output states of the ON signals of S and T. Amplifier 6 only when the S terminal signal explained above is added to amplifier 6 and an ON signal is output to S terminal.
is set to an operating state, and when the S terminal is an OFF signal, the amplifier 6 is set to a cutoff state.

On the other hand, regardless of whether the recording/playback switch _S1 is set to the a side or the b side, when the power is turned on, the capacitor 16
5, resistors 161, 162, transistor 163,
A switch circuit consisting of 164 operates instantaneously,
Only while the capacitor 165 is being charged through the resistor 161, the transistor 163, and the resistor 162, the transistor 163 is turned on and supplies a sufficiently large base current to the transistor 164.
Since the transistor 164 obtains a sufficiently large base current, it becomes saturated, and the emitter-collector becomes a low impedance state, which is almost the same state as if the emitter-collector were connected. At this time, due to the transistor 164, the voltage at point M becomes approximately equal to the voltage at P. Furthermore, when the recording/playback switch _S1 is on the a side, the voltage _Vcc is applied to the resistor 154, so the capacitor 155 is charged via the resistor 154, and the M point is gradually charged starting from the P voltage as shown in FIG. Voltage increases. When the recording/playback switch _S1 is on the b side, the capacitor 155
is discharged through the resistors 154 and 156, so M
As shown in FIG. 7, the voltage at the point starts from the P voltage and gradually drops.

Therefore, even if a shock sound is output due to a sudden change in the DC potential of the microphone recording signal amplifier 4 or the reproduction signal amplifier 5 when the power is turned on, during the time when the M voltage changes from the P voltage to the O voltage, or , P
The time during which the voltage changes to Q voltage is determined by the amplifier 6
is cut off and the shock sound is not output to the B terminal, so that the shock sound when the power is turned on is not amplified by the amplifier 6 and output as a loud shock sound.

Next, the specific electric circuit of the amplifier 6 in FIG.
As shown in the figure, the signal from switch S ₂ is on capacitor 1
11, amplified by the transistors 208 and 209 of the differential amplifier via the resistor 115, and the transistor 20
8 to the transistor 211, from the transistor 211 to the transistor 217 via the transistor 214, and from the transistor 21
A signal is output from the collector of 7 to point B.

At this time, the signal at terminal S is added to the current mirror circuit of transistor 220 and diode 221, and since the collector of transistor 220 is connected to the bases of transistors 218 and 210, when the ON signal flows to terminal S, transistor 2
20, 218, 210 become operational, and transistors 208, 209, 211, 214, 217
becomes operational. On the other hand, transistors 217, 218, and 210 that do not output a signal to terminal S are in a cutoff state, and transistors 208, 209, and 21
1, 214, and 217 are also in the cutoff state. In this cutoff state, there is no signal output at output B. Even in this cut-off state, the resistor 114,
Since it is connected to point is approximately at the X point, so even if the amplifier 6 is switched between the operating state and the cutoff state by the S signal, the direct current change in the B output is small and there is almost no problem. Furthermore, since the M voltage changes slowly as mentioned above, the signal at the S terminal also does not have rapid rising or falling DC changes, so even if there is a DC change in the output of the amplifier 6, there is almost no "click" sound output. .

Power supply for playback signal amplifier 5 and microphone recording amplifier 4
Even if the value of the DC change when ON is large or small, if it is amplified by the amplifier 6, it will produce a loud shock noise, but the amplifier 6 is cut off to reduce the shock noise. Also, the recording amplifier 8 is connected to terminal T.
The T signal is ON-OFF, but at this time, the T signal does not have a sharp rise or fall DC change, and the gain of the recording amplifier 8 is low at 6 to 10 dB, so the J output has a "petit". There is no shock noise and the DC changes are small, so there is almost no problem.

Next, another embodiment is shown in FIG. In FIG. 4, the amplifier 6 in FIG. 2 is divided into two amplifiers 6a and 6b, and the front stage amplifier 6a is always operated, and the rear stage amplifier 6b is operated by applying an S signal. Shock noise can also be reduced in FIGS. 2 and 3, but if the gain of the amplifier 6 is large (for example, 40 dB), it is necessary to set the resistor 114 to a larger value than the resistor 112. The base current of the transistor 209 changes, the voltage drop across the resistor 114 changes, and this changing DC voltage changes slowly as the capacitor 113 is charged and discharged. , when the changing voltage is amplified by amplifier 6, B
There may also be a shock sound (small) in the output.
The configuration shown in Fig. 4 is an attempt to further reduce this, in which the gain of the front-stage amplifier 6a is increased (for example, 34 dB) and the gain of the latter stage is decreased (for example, 6 dB).
are doing. A specific example of the amplifiers 6a and 6b is shown in the fifth section.
As shown in the figure. The front stage amplifier 6a is a transistor 20
8, 209, 211, 214, and 217 are always in operation. On the other hand, the downstream amplifier 6b switches the transistors 241, 239, 235 between the operating state and the cutoff state by the signal at the S terminal so that the transistors 231, 232, 238 are put into the operating state or cut off. Since the gain of the amplifier 6b in the latter stage is small, the resistor 236
The value of resistor 23 can be configured to be small, and by turning on and off transistors 231 and 232,
There is almost no voltage change in amplifier 6b.
Since the gain is small, DC changes are not greatly amplified, so almost no DC changes are output to the B terminal, making it possible to further reduce the shock noise.

Next, in Figures 2, 3, 4, and 5, we were able to reduce the shock noise as described above.
The recording amplifier 8 is switched ON and OFF by the signal at the terminal T, and the shock sound at this time is small as mentioned above because the gain of the amplifier 8 is small (for example, 6 dB), but even among the small DC changes of the amplifier 8, it is a slightly large DC noise. At the time of change, it may be added to the automatic gain control circuit 7, and in this case, the automatic gain control circuit 7 may malfunction, lowering the input level of the amplifier 6, and not returning for a while (3 to 5 seconds). , can sometimes be a problem. For this purpose, as shown in the second, third, fourth, and fifth sections, a signal from the S terminal is applied to the automatic gain control circuit 7 (as shown by the dotted line in the figure). Turn off the gain control circuit. That is, the automatic gain control circuit 7 operates only during the period Y in FIG. During the same period as the amplifier 6 or 6b is cut off, the automatic gain control circuit 7 is cut off to prevent the automatic gain control from operating due to direct current fluctuations when switching the recording amplifier 8, thereby eliminating malfunctions.

The operation of the automatic gain control circuit 7 shown in FIGS. 3 and 5 is such that when a large signal is applied from the amplifier 8 to the automatic gain control circuit 7, the base DC voltage of the transistors 251 and 252 constituting the variable impedance element is changed by the circuit 253. When the transistors 251 and 251 conduct and the impedance becomes low, and the signal from the amplifier 8 becomes small, the circuit 253 is cut off and the circuit 253 is connected between the bases of the transistors 251 and 252 and the circuit 253. The transistors 251 and 25 are kept open for a while while the charging voltage of the capacitor 254 is discharged.
When transistors 251 and 252 are in a conductive state, they operate to lower the input level of the amplifier 6 or 6a for a while, and then transistors 251 and 252 are cut off.

Therefore, when the S terminal signal is OFF, the capacitor 254 is short-circuited, and when the S terminal signal is ON, the capacitor 254 is not short-circuited.
Even if switched by a signal, the automatic gain control circuit 7 is cut off when the M voltage is between the O voltage and the Q voltage, so that malfunctions of the automatic gain control circuit 7 can be reduced.

Also, the recording amplifier 8 is switched by the output signal of the T terminal, but the signal of the S terminal is also added, and when the signal of the S terminal is an ON signal, the signal of the T terminal is switched.
The recording amplifier 8 is operated only when ON signals are simultaneously output. In other words, if it is activated only during the time Y in FIG. 8 (it operates at the same time as the automatic gain control circuit 7 operates), the amplifier 8 does not amplify the small DC change in the amplifier 6 or 6b, so the output is further reduced. The J shot sound can be reduced.

The signal changeover switches _S2 in Figs. 2 and 4 are a to c.
Although it was explained only in Terminal A when switching from b to c,
It can be recorded and played back using other signals such as record playback signals and radio reception signals.

Also, since the comparison circuits in Figures 2 and 4 use two transistors, when the changing voltage M almost matches the preset O, P, and Q voltages,
Although the ON-OFF operation is switched, it goes without saying that the same operation can be performed even if a comparison circuit that operates with a varying voltage and a comparison voltage different from the voltages of the nuclei O, P, and Q is used. Also, in the switch circuit, M
A switch circuit that connects the voltage to any voltage between the O voltage and the Q voltage may be used.

Effects of the Invention As explained above, the present invention compares a variable voltage that continuously changes only for a certain period of time after power is turned on depending on the position of the recording/playback switch with preset first, second, and third comparison voltages. A comparison circuit that connects the voltage between the first and third comparison voltages when the power is turned on and a switch circuit that instantaneously connects the voltage between the first and third comparison voltages when the power is turned on are provided. It is possible to cut off the amplifier using the output signal compared with the output signal, thereby reducing the shock noise that occurs when the power is turned on in the recording or playback mode.It also prevents the automatic gain control circuit from malfunctioning due to the shock that occurs when the power is turned on in the recording mode. It is possible to prevent this from happening.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional magnetic recording and reproducing device, FIG. 2 is a block diagram of a magnetic recording and reproducing device according to an embodiment of the present invention, FIG. 3 is a detailed circuit diagram of the main parts of the device, and FIG. 4 is a block diagram of a conventional magnetic recording and reproducing device. 5 is a block diagram of a magnetic recording/reproducing device according to another embodiment of the present invention, FIG. 5 is a detailed circuit diagram of the main parts of the device, and FIGS. 6, 7, and 8 are explanatory diagrams of the operation of the device. be. 1... Bias oscillation circuit, 2... Head for recording and playback, 3... Microphone, 4... Microphone recording signal amplifier, 5... Playback signal amplifier, 6, 6
a, 6b...amplifier, 7...automatic gain control circuit,
8...Recording amplifier, _S1 ...Recording/playback selector switch, _S2 ...Signal selector switch.

Claims (1)

[Claims] 1. A first amplifier for playback signals, a second amplifier for recording signals.
Amplifier, 3rd amplifier that amplifies both the playback signal and recording signal, 4th amplifier for the recording signal, automatic gain control circuit, constant after power on depending on the position of the recording/playback switch for switching between recording and playback ON-OFF by comparing the changing voltage of the switching terminal that increases or decreases continuously over time with the first, second, and third comparison voltages obtained from the preset first, second, and third voltage terminals. A switch circuit is provided for instantaneously connecting the voltage of the switching terminal to the second comparison voltage when the power is turned on. When the switching terminal voltage becomes higher than the first comparison voltage or lower than the third comparison voltage, the third amplifier is turned on, and the switching terminal is turned off. 1. A magnetic recording and reproducing device characterized in that a recording state or a reproducing state is determined based on the magnitude relationship of a voltage with respect to a second comparison voltage. 2 The third amplifier has a front-stage amplifier and a rear-stage amplifier, and the amplifier always operates after the power is turned on. Immediately after the power is turned on, the switching terminal is momentarily connected to the second comparison voltage by a switch circuit, and the second comparison voltage is connected to the second comparison voltage. The magnetic recording/reproducing apparatus according to claim 1, characterized in that the magnetic recording/reproducing apparatus is configured to block signals. 3 Only the automatic gain control circuit or both the fourth amplifier and the automatic gain control circuit are cut off in the regeneration state, and immediately after the power is turned on, the switching terminal is instantaneously connected to the second comparison voltage by the switch circuit. and only the automatic gain control circuit or the fourth
2. The magnetic recording and reproducing apparatus according to claim 1, wherein both the amplifier and the automatic gain control circuit are cut off.