JP2672664B2 - Recording / playback switching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a magnetic recording / reproducing apparatus such as a digital audio tape recorder (DAT) for transmitting a signal recorded on a magnetic tape through a head. The present invention relates to a recording / reproducing switching circuit which is used in a reproducing / amplifying circuit for amplifying a reproduced signal obtained as a result and is particularly suitable for integration.

(Prior Art) FIG. 10 shows a conventionally known magnetic recording / reproducing amplifier circuit. First, regarding the circuit configuration of the recording system, H in the figure is a rotary magnetic head, which is electrically connected via a rotary transformer. Arec is a recording amplifier, the input of which is connected to the recording input terminal RECIN and the output of which is connected to the head H, which operates only when recording by the switch S1.

Next, the circuit configuration of the reproduction system will be described. Head H
Is connected to the base of the input transistor Q1 via a coupling capacitor C1.
The power supply Vcc is divided by R1 and R2 and is given as a bias. The emitter of transistor Q1 is driven by constant current I1 and is grounded by capacitor C2.
It is also connected to the emitter of Q6, and the base of the transistor Q6 is connected to the power supply Vcc only when recording with the switch S2. The collector of the transistor Q1 is connected to the power supply Vcc via the resistor R3, and the base is connected to the power supply Vcc via the diodes Q3 and Q4 and is connected to the emitter of the transistor Q2 which is a grounded base circuit. The collector of the transistor Q2 is connected to the power supply Vcc via the load resistor R4, and is also connected to the base of the emitter follower transistor Q5. Transistor
The emitter of Q5 is pulled by a constant current I3,
It is output to the playback output terminal P Bout.

First, at the time of reproduction, since the switches S1 and S2 are on the P side, the recording amplifier Arec is in a non-operating state, and the transistor Q6
Is the same as not connected. The transistor Q1 operates at a constant current, but since the emitter is grounded by the capacitor C1, it operates as an emitter-grounded amplifier in terms of AC. The base of transistor Q2 is transistor Q3,
Although it is connected to the power supply Vcc by Q4, the operating resistance of the transistors Q3 and Q4 is as small as 26Ω when the constant current source I2 = 1mA, and the transistor Q2 operates as a grounded base amplifier. Therefore, the transistors Q1 and Q2 form a cascode amplifier. Since the transistor Q1 has to amplify a very small signal, it must have high gain and low noise amplification.
The constant current source I1 needs to be installed at a relatively large current value of about 500 μA to 5 mA. Therefore, without the resistor R3, the voltage drop of the resistor R4 will be too large and it will not operate at low power supply voltage, but by inserting the resistor R3,
The collector current of transistor Q1 is shunted to resistor R3
It reduces the voltage drop across R4.

From the above, the reproduced signal from the head H is
It is applied to the base of the transistor Q1 via C1, appears in the collector of the transistor Q2 amplified here, is further impedance-converted by the emitter follower of the transistor Q5, and is output to the reproduction output terminal PB out.

Next, at the time of recording, the switches S1 and S2 are on the R side, the recording amplifier Arec is in an operating state, and the transistor Q6 functions as a diode. Therefore, the emitter potential of the transistor Q1 is
Pulled up to Vcc-VBE (Q6). The reason for pulling up the emitter of the transistor Q1 is that the output potential of the recording amplifier Arec appears as high as 10 Vp-p with reference to the power source Vcc when the recording current is flowing to the head.
To be applied the base of the transistor Q 1 in through C1, unless you have on the emitter potential of the transistor Q1, because the transistor Q1 adversely affect the ON / OFF to the recording waveform.

Now, consider the case where the recording mode is switched to the reproduction mode. During recording, the emitter potential of the transistor Q1 rises (Vcc-VBE (Q6)), but the switch S
Since 1 and S2 are on the P side, the recording amplifier Arec is in a non-operating state, which is equivalent to the transistor Q6 being not connected to the capacitor C2. However, since the electric charge is accumulated in the capacitor C2 at the moment of reproduction, the transistor Q1
The emitter potential of remains at its original high. In this state, the reproduction amplifier cannot operate at all because the transistor Q1 is cut off. At this time, the constant current source I1 all flows into the capacitor C2 and discharges the electric charge of the capacitor C2, and the emitter potential of the transistor Q1 also drops accordingly, becoming a steady potential and the current of the constant current source I1 flows to the capacitor C2. It stops flowing, and the reproduction amplifier comes to perform normal amplification operation. That is, even if the switches S1 and S2 are switched from R to P, the reproducing operation is not started immediately, but after a certain delay time, the operation is started. Although this delay time varies depending on the constant setting, it is usually about 100 μsec to several msec.

On the other hand, regarding the capacitor C1, the voltage on the output side of the recording amplifier Arec of the capacitor C1 changes in response to the recording signal, but the impedance on the opposite side of the transistor Q1 is the input impedance of the base of the transistor Q1 is infinite. Therefore, the charge of the capacitor C1 does not change during reproduction and recording because it is determined by the values of the resistors R1 and R2 and is relatively high. This means that the potential difference across the capacitor C 1 does not change during reproduction or recording. Therefore,
It means that the base potential of the transistor Q1 becomes a normal potential from the moment the recording is started to be reproduced.

(Problems to be Solved by the Invention) In the above-mentioned conventional circuit, there is a slight delay time before a normal reproduction operation is started when switching from recording to reproduction, and there is no problem in simply switching from recording to reproduction. DAT (digital audio
A high-speed operation is required when switching between recording and reproduction in one track, such as after-recording operation of a tape recorder), and if there is a delay time of several hundred μsec / several msec,
It is impossible to perform after-recording operation.

This invention makes the delay time from recording to playback sufficiently short
It is an object of the present invention to provide a recording / reproducing switching circuit adaptable to an application requiring high-speed switching such as a post-recording operation of a DAT.

[Structure of the Invention] (Means for Solving the Problems) A recording / reproducing switching circuit of the present invention is a recording amplifier for supplying a recording current to a magnetic head in a recording state, and the magnetic head has a base via a first capacitor. Connected to the
The emitter is AC grounded via the second capacitor, the first transistor to which the constant current circuit is connected, the reproduction amplifier for amplifying the output reproduction signal of the magnetic head in the reproduction state, and the output terminal A first capacitor charging / discharging circuit which is connected to a second capacitor and is in an operating state only during a transition period from a reproducing state to a recording state to rapidly charge the second capacitor, and a first input terminal is connected to the first capacitor. A voltage detection circuit connected to the emitter of the transistor and a second input terminal connected to the first reference potential, and a controlled terminal connected to the output terminal of the voltage detection circuit, the output terminal of which is the second And a second capacitor charging / discharging circuit that is connected to the capacitor and is in an operating state only during a transition period from a recording state to a reproducing state to rapidly charge the second capacitor. That.

(Operation) By the means described above, the electric potential of the second capacitor causes the emitter potential of the first transistor to become high at the moment when the recording operation is changed to the reproduction operation.
When the emitter potential is higher than the steady potential as compared with the reference potential of, the second capacitor charging / discharging circuit discharges the second capacitor, and the emitter potential of the first transistor is rapidly lowered. When the emitter potential drops to a substantially steady potential, the voltage detection circuit detects it, and the second capacitor charge / discharge circuit is turned off to stop the reduction of the emitter potential of the first transistor.

The same applies when a comparison circuit is inserted between the output terminal of the voltage detection circuit and the non-control terminal of the second capacitor charging / discharging circuit.
The operation is the same except that the comparison circuit is inserted in the middle.

(Embodiment) An embodiment of the present invention will be described below in detail with reference to the drawings.

In FIG. 1, the recording system will be described first. The input terminal of the recording amplifier Arec is connected to the recording input terminal RECIN, and the output terminal is connected to the rotary magnetic head H. Only when recording amplifier Ar
ec becomes operational.

Next, the reproduction system is as follows. Input transistor
A bias voltage is applied to the base of Q1 by resistors R1 and R2, and at the same time, a head H is connected via a capacitor C1. The base of the collector of the transistor Q1 is connected to the power supply Vcc through the diodes Q3 and Q4 and is connected to the emitter of the transistor Q2 which is a grounded base circuit, but at the same time is connected to the power supply Vcc through the resistor R8. There is. The collector of the transistor Q2 is connected to the power supply Vcc via the load resistor R9, and the emitter follower Q17
Of the transistor Q17, and the emitter of the transistor Q17 is connected to the reproduction output terminal P Bout, which serves as the reproduction output.

On the other hand, the emitter of transistor Q1 is transistor Q18.
The collector of is connected and operating current is given,
At the same time, it is AC-connected by the capacitor C2, and the transistor Q1 acts as a grounded emitter. The emitter of the transistor Q1 is also connected to the base of the transistor Q5 of the differential amplifier composed of the transistors Q5 and Q6. The base of the transistor Q6 is the resistor R15 and the transistor Q5.
15, connected to the voltage dividing point of the power supply Vcc by the resistors R13 and R14. The collector of transistor Q6 is transistor Q8
Connected to the base of diode Q7 and resistor R10
It is grounded by the series circuit. The collector of transistor Q8 is connected to power supply Vcc, and the emitter is resistor R12.
It is connected to the base of the transistor Q9 via and is grounded by the resistor R11. The collector of the transistor Q9 is connected to the emitter of the transistor Q1 and the emitter is grounded. The bases of the transistors Q10 and Q11 are coupled to each other, and are connected via a resistor R3 to an R / P terminal which is at L level during reproduction and H level during recording. The collector of the transistor Q10 is connected to the base of the transistor Q9, the collector of the transistor Q11 is connected to the input side of the current mirror composed of the diode Q12 and the transistor Q13 via the resistor R4, and the output side of this current mirror is The base and emitter are connected to the base of a transistor Q14, which is connected by a resistor R7,
The emitter of the transistor Q14 is connected to the emitter of the transistor Q1.

Where Arec is the recording amplifier, C1 is the first capacitor,
C2 is the second capacitor, Q1 is the first transistor, Q1-
The part consisting of Q4, Q17, R8, and R9 is the playback amplifier, Q11-
The part composed of Q14, R4, and R7 is the first capacitor charging circuit, the part composed of Q5, Q6, Q16, and R16 is the voltage detection circuit, and the part composed of Q7 to Q10 and R10 to R12 is the second. It corresponds to the capacitor charging circuit of.

Next, consider the operation. First, at the time of reproduction, since the switch S1 is on the P side, the recording amplifier Arec is inactive. At this time, since the R / P terminal is at the L level, the transistors Q10 and Q11 are turned off and the reproducing system is in the operating state. That is, the base of the input transistor Q1 is biased by the voltage obtained by dividing the power supply Vcc by the resistors R1 and R2, and the emitter is pulled by the constant current circuit by the transistor Q18.
Since it is grounded at, the emitter is grounded in terms of AC. The transistor Q2 is a grounded base circuit, and the transistor Q1 and the transistor Q1 form a cascode circuit. The resistor R8 divides the collector current of the transistor Q1 so that the entire collector current of the transistor Q1 does not flow to the transistor Q2. Transistor Q2
The signal appearing at the collector of is impedance-converted by the emitter follower of the transistor Q17, and is reproduced output terminal P Bo
It is output to ut. At this time, the base potential of the transistor Q6 is about several hundred mV (V
BE-several hundred mV) If set low, transistor Q6 will be cut off and all collector current of transistor Q16 will flow to transistor Q5. Therefore, diode Q7,
Transistors Q8 and Q9 are also off. This means that the second condenser charging circuit is inactive. Further, since the transistor Q11 is off, the transistors Q12 to Q14 are also off, and the first capacitor charging circuit is also in the non-operation state.

Since the switch S1 is set to the R side during recording, the recording amplifier Arec is in the operating state, and the recording input terminal RECIN
A current corresponding to the signal input to is output from the recording amplifier Arec, and this current flows to the head H to record the signal on the magnetic tape.

Further, since the R / P terminal is at the H level during recording, the transistors Ω10 and Q11 are turned on, and the transistor Q9 is turned on regardless of whether the transistor Q8 is turned on or off when the transistor Q10 is turned on. In other words, this means that the second capacitor charging circuit is inactive.

Further, when the transistor Q11 is turned on, I (Q12) = [Vcc-VF (Q12) -VCE (Q11 (SAT)) appears in the diode Q12.
/ (R4 + R5)] current flows, and this current is a diode
It is turned back by the current mirror of Q12 and transistor Q13 to turn on transistor Q14 so that the emitter potential of transistor Q1 is Vcc-VR6-VCE (Q13 (SAT))-VBE (Q14).
Up to.

In other words, the first capacitor charging circuit causes the capacitor C2 at the time of transition from the reproducing state to the recording state.
Is to be rapidly charged, and after the emitter potential of the transistor Q1 reaches a predetermined voltage and charging is completed, there is a function of maintaining the voltage, but the charging function is lost.

The emitter potential of the transistor Q1 is raised so that the base potential VB (Q5) of the transistor Q5 is the transistor Q6.
When it becomes higher than the base potential of the transistor Q5, the transistor Q5 is cut off, the collector current of the transistor Q16 all flows to the transistor Q6 and turns on the diode Q7 and the transistor Q8, but since the transistor Q10 is on, the transistor Q9 is turned on. However, the emitter potential of the transistor Q1 remains high.

Here, let us consider the transient operation when switching from recording to reproduction. In the following description, the delay time of the transistor is sufficiently short compared to the time constant of the capacitor and can be ignored. When recording is reproduced, the switch S1 is set to the P side and the recording amplifier Arec is turned off. At the same time, the R / P terminal is set to the L level, so that the transistors Q10 and Q11 are turned off and the diode Q12 and the transistors Q13 and Q14 are also turned off. At this moment, the emitter potential of the transistor Q1 is VE (Q1) = Vcc-VR6-VCE (Q13 because there is charge in the capacitor C2.
(SAT))-VBE (Q14) and high. As a result, the transistor Q5 is turned off, the collector current of the transistor Q16 all flows to the transistor Q6, and the diode Q7,
Since the transistor Q8 is turned on and the transistor Q10 is in the off state, the transistor Q9 is turned on. When the transistor Q9 is turned on, the collector current rapidly discharges the capacitor C2, and the emitter potential of the transistor Q1 rapidly drops. When the emitter potential of the transistor Q1 decreases and the base potential of the transistor Q5 and the base potential of the transistor Q6 become almost equal, the collector current of the transistor Q16 flows in both the transistors Q5 and Q6. When the emitter potential of the transistor Q1 drops, VB (Q5) <VB (Q6), the transistor Q6 turns off and the diode Q7 and the transistor Q8 also turn off to stop the rapid discharge. In other words, the second capacitor charging circuit rapidly charges the capacitor C2 when the recording state transits to the reproducing state.

At this time, the emitter potential of the transistor Q1 is only several hundred mV higher than the steady voltage, so that the current of the transistor Q18 alone can reach the steady state of the emitter potential of the transistor Q1 in a short time. .

According to this embodiment, it is possible to quickly shift from the recording state to the reproducing state. If an appropriate constant is selected, the switching time required for DAT after-recording, which is tens of microseconds or less, can be sufficiently achieved.

FIG. 2 shows a second embodiment of the present invention.
The same parts as those in FIG. 1 are designated by the same reference numerals, and different parts will be mainly described here.

The emitter of the input transistor Q1 is connected through a resistor R13 to the bases of the transistors Q5 and Q6 of opposite polarities to which the emitters are connected, and the base of the transistor Q5 is resistors R14 and R15 and a diode.
It is connected to the voltage dividing point of power supply Vcc by Q7 and resistor R10.
The collector of the transistor Q8 is connected to the cathode side of the diode Q9 of the diode Q9 and the current mirror of the transistor Q10, and the emitter side of the transistor Q10 is connected to the emitter of the transistor Q1 to which the capacitor C2 is connected. The base of transistor Q11, Q12 are connected to each other via a resistor R3 to the R / P terminals, the cathode collector via a resistor R4 diode Q9 transistor Q 12, the collector of the transistor Q11 is the transistor Q8 the base Respectively connected to.

Since the R / P terminal is at the L level in the steady state during reproduction, the transistor Q12 is off and the diode Q13,
Transistors Q14 and Q15 are off. This means that the first capacitor charging circuit is inactive.

If the base potential of the transistor Q5 is set higher than the base potential of the transistor Q1 by about 1V corresponding to VBE + several hundred mV, the transistors Q5 and Q6 are turned on, the emitter potential of the transistor Q8 is raised, and the transistor Q8 is turned off.
As a result, the diode Q9 and the transistor Q10 are also turned off, and the diode Q9 and the transistor Q10 forming the current mirror do not appear to be connected to the capacitor C2. This means that the second capacitor charging circuit is inactive.

During recording, the R / P terminal goes high and transistor Q1
1, Q12 is turned on, regardless of whether transistor Q6 is ON or OFF, transistor Q8 is turned off and diode Q9 and transistor Q10 are also turned off.
Karen Miller does not appear to be connected to capacitor C2. In other words, this means that the second capacitor charging circuit is inactive.

When the transistor Q12 is turned on, the diode Q13 has a current I (Q13) = [Vcc-VF (Q13) -VCE (Q12 (SA
T))] / (R4 + R5) flows, and this current is turned back by the current mirror of the diode Q13 and the transistor Q14 to turn on the transistor Q15 and raise the emitter potential of the transistor Q1.

In other words, the first capacitor charging circuit causes the capacitor C2 at the time of transition from the reproducing state to the recording state.
Is to be rapidly charged, and after the emitter potential of the transistor Q1 reaches a predetermined voltage and charging is completed, there is a function of maintaining the voltage, but the charging function is lost.

When the emitter potential of the transistor Q1 the pulled at elevated base potential of the transistor Q 1 is becomes higher than 2VBE voltage lower than the base potential of the transistors Q5, transistors Q5, Q6 emitter potential of the transistor Q8 is lowered to cut off The transistor Q8 tries to turn on, but the transistor Q8 does not turn on because the transistor Q11 is on, and the emitter potential of the transistor Q1 remains high.

When recording is changed to reproduction, the switch S1 is set to the P side, the recording amplifier Arec is turned off, and at the same time, the R / P terminal is set to the L level.
The transistors Q14 and Q15 are also turned off.

Transistor during the transition at the moment of switching to playback
The emitter potential of Q1 is higher due to the charge of capacitor C2. Therefore, transistor Q6 is off and transistor
Since Q11 is also off, transistor Q8 is on. When the transistor Q8 turns on, its collector current turns on the current mirror of the diode Q9 and the transistor Q10. The capacitor C2 is rapidly discharged by the current of the diode Q9 and the transistor Q10, and the voltage of the capacitor C2, that is, the emitter potential of the transistor Q1 is rapidly decreased. When this decrease causes the emitter potential of the transistor Q1 to become lower than the voltage lower than the base potential of the transistor Q5 by 2VBE, the transistors Q5 and Q6 are turned on at that point.
Depending on the collector current of transistor Q6, transistor Q8
The emitter potential of the transistor rises and the transistor Q8 turns off,
Stop rapid discharge of capacitor C2. In other words, the second capacitor charging circuit rapidly discharges the capacitor C2 when the recording state transits to the reproducing state. At this time, since the emitter potential of the transistor Q1 is only several hundred mV higher than the steady voltage, the current from the transistor Q18 alone does not take much time.
The emitter potential of the transistor Q1 can reach a steady state. In this way, it is possible to quickly shift from the recording state to the reproducing state.

FIG. 3 shows a third embodiment of the present invention.
The paths for amplifying the signals of the recording system and the reproducing system are the same as those in FIG. 1, and the different points will be mainly described here.

The input transistor Q1 has an emitter whose base is R11,
A current limiting resistor is connected to the emitter of transistor Q5 connected to the voltage dividing point of power supply Vcc in diodes Q12 and Q13 and resistor R12.
Connected via R10. The collector of the transistor Q5 is connected to the bases of the transistors Q6 of the transistors Q6 and Q7 connected in Darlington, and the collector of the transistor Q7 is connected to the emitter of the transistor Q1. The bases of transistors Q8 and Q9 are tied together,
It is connected to the R / P terminal via R3. Transistor Q8
The collector of the transistor is the base of the transistor Q6
The collector of Q9 is connected to the cathode side of the diode Q10 and the diode Q10 of the current mirror of the transistor Q11 via the resistor R4.

Where Arec is the recording amplifier, C1 is the first capacitor,
C2 is the second capacitor, Q1 is the first transistor, Q1-
The part consisting of Q4, Q14, Q15, R6, R7 is a reproduction amplifier,
The portion composed of Q9 to Q11, R4 and R5 corresponds to the first capacitor charging circuit, Q5 corresponds to the voltage detection circuit, and the portion composed of Q6 to Q8, R8 and R9 corresponds to the second capacitor charging circuit.

In the reproduction time constant state, the R / P terminal is at L level and the transistor Q9 is off, so the diode Q10,
Transistor Q11 is off. The anode potential of the diode Q12 is several hundred mV higher than the base potential of the transistor Q1.
If it is set high, the transistor Q5 is turned off, the transistors Q6 and Q7 are also turned off accordingly, and the previous transistor Q11 is turned off, so that the capacitor C2 is not charged or discharged.

Since the R / P terminal is at the H level during recording, the transistors Q8 and Q9 are turned off. By turning on the transistor Q 8, the base of the transistor Q6 regardless of the ON / OFF state of the transistor Q5 is because it is grounded and the shunt, the transistor Q6 transistor Q7 is also turned off and off. In other words, this means that the second capacitor charging circuit is inactive. Further, when the transistor Q9 is turned on, a current flows through the transistor Q10, the transistor Q11 is turned on, and the emitter potential of the transistor Q1 is raised. In other words, the first capacitor charging circuit rapidly charges the capacitor C2 when transitioning from the reproducing state to the recording state, and after the emitter potential of the transistor Q1 reaches a predetermined voltage and charging is completed. Has the function of maintaining the voltage but loses the charging function. As a result, the transistor Q5 is turned on, but the transistor Q7 is not turned on because the transistor Q8 is turned on. Therefore, the emitter potential of the transistor Q1 remains high.

When recording is changed to reproduction, the switch S1 is set to the P side, the recording amplifier Arec is turned off, and at the same time the R / P terminal is set to the L level, so the transistors Q8 and Q9 are turned off and the diode Q1 is turned on.
0, the transistor Q11 is also turned off. At the moment of transition at the moment of switching from recording to reproduction, the emitter potential of the transistor Q1 remains high because of the charge of the capacitor C2. Therefore, since the transistor Q5 is on and the transistor Q8 is off, the transistors Q6 and Q7 are on. The collector current of the turned-on transistor Q7 rapidly discharges the capacitor C2, and the voltage of the capacitor C2, that is, the potential of the base of the transistor Q1 rapidly drops. When the base potential becomes equal to or lower than the potential on the anode side of the diode Q12, the transistor Q5 is turned off, the transistors Q6 and Q7 are also turned off, and the rapid discharge of the capacitor C2 is stopped. In other words, the second capacitor charging circuit rapidly charges the capacitor C2 when transitioning from the recording state to the reproducing state. Since the emitter potential of the transistor Q1 at this time is only several hundred mV higher than the steady voltage, it is possible to reach the steady state with only the current of the transistor Q16 in a short time. In this way, the recording state can be quickly changed to the reproducing state.

FIG. 4 shows a fourth embodiment of the present invention.
First, the recording system will be described. The input terminal of the recording amplifier Arec is connected to the recording input terminal RECIN, the output terminal is connected to the magnetic head H, and the recording amplifier Arec is in the operating state only in the recording state by the switch S1.

The reproduction system has a resistor R1 at the base of the input transistor Q1,
The vice voltage is added by R2, but at the same time the capacitor
The head H is connected via C1. Transistor Q1
The collector of the base has a power supply Vc via diodes Q3 and Q4.
Transistor Q2 connected to c and grounded
Is connected to the emitter of the
Connected to Vcc. The collector of the transistor Q2 is connected to the load resistor R4, the emitter-follower transistor Q8 is connected to the base, and the emitter of the transistor Q8 is connected to the reproduction output terminal P Bout, which serves as a reproduction output. The emitter of transistor Q1 is current source I1
Are connected to each other to provide an operating current, but at the same time, they are AC-grounded by the capacitor C2, and the transistor Q1 functions as a grounded emitter. The emitter of the transistor Q1 is also connected to the base of the transistor Q5 of the differential amplifier composed of the transistors Q5 and Q6. The base of the transistor Q6 is the power supply Vcc due to the resistor R6, the diode Q7 and the resistor R7.
Is connected to the partial pressure point of. The collector of the transistor Q6 is connected to the power supply Vcc by the load resistor R5 and is also connected to the non-inverting input + of the differential amplifier A1. Differential amplifier A
The inverting input of 1- is connected to the reference voltage V1 and the output is connected to the base of the transistor Q10 via the resistor R8. The base of the transistor Q10 is a transistor Q9 whose base is connected to the power supply Vcc through a resistor R9 and a switch S3.
Connected to the collector. The collector of the transistor Q10 whose emitter is grounded is connected to the emitter of the transistor Q1. The emitter of the transistor Q1 is connected to the emitter of the transistor Q11, and the collector of the transistor Q11 is directly connected to the base of the transistor Q11 via the switch S2 and the power supply Vcc.

Where Arec is the recording amplifier, C1 is the first capacitor,
C2 is the second capacitor, Q1 is the first transistor, Q1-
The part consisting of Q4, Q8, R3 and R4 is the reproduction amplifier, Q11 is the first capacitor charging circuit, and the part consisting of Q5, Q6, R5 and I3 is the voltage detecting circuit, Q9, Q10 and R9. The corresponding portion corresponds to the second capacitor charging circuit.

The operation during playback will be described. At this time, switch S1
Is on the P side, and the recording amplifier Arec is in a non-operating state. Since the switches S2 and S3 are on the P side, the reproducing system is in operation. The base of the input transistor Q1 is a resistor R1,
It is biased by the voltage divided by R2, and the emitter is stretched by the constant current source I1. At the same time, however, it is grounded by the capacitor C2, so it is an emitter grounded circuit in terms of AC. Transistor Q2 is grounded base,
A cascode circuit is formed with the transistor Q1. The resistor R3 divides the collector current of the transistor Q1 so that the collector current of the transistor Q1 does not entirely flow to the transistor Q2. The signal appearing at the collector of the transistor Q2 is impedance-converted by the emitter / follower of the transistor Q8 and output to the reproduction output terminal PBout.
At this time, if the anode potential of the transistor Q7 is set lower than the base potential of the transistor Q1 and higher by about several hundred mV, the transistor Q5 is cut off and the constant current I3 all flows to the transistor Q6 and the voltage of the resistor R5. Due to the drop, the voltage of the non-inverting input + of the differential amplifier A1 becomes lower than the reference voltage V1. As a result, the output of the differential amplifier A1 becomes L level, and the transistor Q10 maintains the OFF state regardless of ON / OFF of the transistor Q9. This is the second
It means that the capacitor charging circuit of is in the non-operating state. Further, the transistor Q11 is off because the switch S2 is on the P side, and the first capacitor charging circuit is also in the non-operating state.

During recording, the switch S1 is switched to the R side, and the recording amplifier Arec is in an operating state. At this time, the current corresponding to the signal input to the recording input terminal RECIN is
The current is output from rec, and this current flows to the head H to record a signal on the magnetic tape. In the reproducing system, since the switch S2 is on the R side, the transistor Q11 operates as a diode, and the emitter potential of the transistor Q1 is Vcc-VBE (Q
Up to 11). In other words, the first capacitor charging circuit rapidly charges the capacitor C2 when transitioning from the reproducing state to the recording state, and after the emitter potential of the transistor Q1 reaches a predetermined voltage and charging is completed. Has the function of maintaining the voltage but loses the charging function. As a result, when the base potential of the transistor Q5 becomes higher than the base potential of the transistor Q6, all the current of the constant current source I3 flows to the transistor Q5 and Ic (Q5) =
Since it becomes 0, the voltage drop of the resistor R5 also becomes 0. Then, the voltage of the non-inverting input + of the differential amplifier A1 becomes higher than the reference voltage V1 of the inverting input −, so the output of the differential amplifier A1 becomes H level, and the transistor Q10 tries to turn on, but the switch S3 also Since it is on the R side, the transistor Q9 turns on and the transistor Q10 does not turn on, and this state is maintained thereafter. In other words, this means that the second capacitor charging circuit is inactive.

The transitional operation when switching from recording to reproduction is as follows. When the recording mode is switched to the reproducing mode, the switch S1 is set to the P side, and the recording amplifier Arec is deactivated. At the same time, since the switch S2 is also on the P side, the transistor Q11 is turned off. At this moment, the emitter potential of the transistor Q1 has the electric charge of the capacitor C2, so VE (Q1)
= Vcc-VBE (Q11), which is in a high state. Therefore, the base potentials of the transistors Q5 and Q6 are VB (Q5)> VB (Q6)
Therefore, the transistor Q6 is turned off and the voltage drop across the resistor R5 is zero. At this time, since the voltage of the non-inverting input + of the differential amplifier A1 is higher than the reference voltage V1 applied to the inverting input −, the output of the differential amplifier A1 becomes the H level and tries to turn on the transistor Q10. Since it is on the side, the transistor Q9 is off,
The transistor Q 16 is turned off as it is, the capacitor C 2 is rapidly discharged by its collector current, and the voltage of the capacitor C 2,
That is, the emitter voltage of the transistor Q1 rapidly drops. When the emitter potential of transistor Q1 drops and the base potentials of transistors Q5 and Q6 become almost equal, a constant current source
The current of I3 flows through the transistors Q5 and Q6. Furthermore, the emitter potential of the transistor Q1 drops and VB (Q5) <VB
(Q6) The transistor Q5 is turned off, the current of the constant current source I3 flows into the transistor Q6, and the voltage drop of the resistor R5 causes the voltage of the non-inverting input + of the differential amplifier A1 to become lower than the reference voltage V1. As a result, the output of the differential amplifier A1 becomes L level, and the transistor Q10 is turned off to stop the rapid discharge. In other words, the second capacitor charging circuit rapidly charges the capacitor C2 when the recording state transits to the reproducing state. At this time, the transistor Q1
Since the emitter potential of is only several hundred mV higher than the stationary voltage, the emitter potential of the transistor Q1 can reach the stationary potential in a short time only with the current of the constant current source I1. As described above, also in this embodiment, it is possible to quickly shift from the recording state to the reproducing state.

FIG. 5 shows a fifth embodiment of the present invention. Here, the recording amplifier and the magnetic head are omitted. The circuit connected to the power supply Vcc on the upper side is the part that actually amplifies the signal. This circuit uses a transistor Q7 as an emitter follower instead of the diode Q7 in FIG. Since only the points shown in are different, the description thereof will be omitted. Here, a circuit connected to the lower power source Vcc for switching between the recording and reproducing states will be described.

The differential amplifier of the transistors Q14 and Q15 connected to the lower power supply Vcc is a comparison circuit for comparing the collector potential of the transistor Q22 and the collector potential of the transistor Q16. The output of the transistor Q14 drives the Turlington circuit of the transistors Q25 and Q26 via the current mirrors of the transistors Q16 and Q17. Also, the transistor Q24, which is turned on / off by the control signal input to the R / P terminal, turns on / off the transistors Q25 and Q26, and the transistor Q23 passes through the current mirror composed of the diode Q27 and the transistor Q28. ON / OFF control.

During playback, the base potential of transistor Q7 is a transistor
If it is set several hundred mV higher than the base potential of Q1, transistor Q5 will be cut off and transistor Q11 will be cut off.
All the current I3 flowing through the collector of the transistor Q6 flows to the transistor Q6 and the voltage drop across the resistor R becomes large, and the base potentials of the transistors Q14 and Q15 of the differential amplifier are VB (Q14) <VB (Q15).
And transistor Q14 turns off. As a result, the transistors Q16 and Q17 are turned off, and the transistors Q25 and Q26 are also turned off. Since the R / P terminal is at the L level, the transistor Q23 is off, and the diode Q27 and the transistors Q28 and Q29 are also off.

Since the R / P terminal is at the H level during recording, the transistors Q23 and Q24 are turned on. This allows transistor Q2 to be used with or without the collector current of transistor Q17.
5, Q26 is off. Further, since the transistor Q23 is on, the diode Q27, the transistors Q28, Q29
When the transistor Q26 is turned off, the emitter potential of the transistor Q1 is changed to Vcc-VCE (Q28 (SA
T))-VBE (Q29).

When switching from recording to reproduction, the R / P terminal goes from the H level to the L level, so that the transistor Q23 is turned off, which also turns off the transistor Q27, the transistors Q28, and Q29. At the moment of switching, the emitter potential of transistor Q1 remains high due to the charge of capacitor C2, so VB (Q5)
> VB (Q6) and no current flows in transistor Q6, so VB (Q14)> VB (Q15) and transistor Q1
4 turns on and transistors Q16 and Q17 also turn on. At this time, since the R / P terminal is at the L level, the transistor Q23 is off. This allows the transistor Q25,
Q26 turns on, the capacitor C2 discharges rapidly, and the emitter potential of the transistor Q1 drops rapidly. When the emitter potential of the transistor Q1 decreases and the emitter potential of the transistor Q5 becomes lower than the base of the transistor Q6, current flows in the transistor Q6, VB (Q14) <VB (Q15), the transistor Q14 turns off, and the transistor Q16, Q1
7 is also turned off. Therefore, the transistors Q25 and Q26 are turned off. At this time, the emitter potential of the transistor Q1 is only several hundred mV higher than the steady state voltage, so the emitter potential of the transistor Q1 can reach the steady state potential only in a short time with the constant current I1 flowing in the transistor Q9. You can Thus, also in this embodiment, it is possible to quickly shift from the recording state to the reproducing state.

FIG. 6 shows a sixth embodiment of the present invention.
The paths for amplifying the signals of the recording amplifier and the reproduction system are the same as those in FIG. 4, and the only difference is the means for detecting the emitter potential of the transistor Q1. The emitter of the transistor Q1 is connected to the base of the transistor Q whose emitter is connected to the reference potential V1, and the collector of the transistor Q5 is a load resistor.
It is connected to the power supply Vcc via R6 and
It is connected to the base of the follower transistor Q6. The emitter of the transistor Q6 is connected to the inverting input − of the differential amplifier A1 whose non-inverting input + is connected to the reference potential V2,
The circuit is the same as that of FIG. 4 except that it is connected to the lower power supply Vcc.

In the reproducing operation, the switch S1 is on the P side, so that the recording amplifier Arec is in the non-operating state. Since the switches S2 and S3 are also on the P side, the reproducing system is in operation. If the reference potential V1 is set lower than the base potential of the transistor Q1 by about 1V (2 × VBE−several hundred mV), the transistor Q5 cuts off and no current flows, so the voltage drop of the resistor R6 is 0. Inverting input of differential amplifier A1 −
Is higher than the reference potential V2. Then, the output level of the differential amplifier A1 becomes L level, and the transistor
The transistor Q9 is off regardless of the ON / OFF state of Q8.

Since the switch S2 is on the R side during recording, the transistor Q10 acts as a diode to raise the emitter potential of the transistor Q1, but VE (Q1) -V1 is 0.7V (VB
E), transistor Q5 turns on and the resistance R
The voltage drop of 5 becomes large. Inverting input of differential amplifier A1 −
Since the voltage of is lower than the non-inverting input + voltage (V2),
The output of the differential amplifier A1 goes high and tries to turn on the transistor Q9, but since the switch S3 is on the R side, the transistor Q8 is on and the transistor Q9 is off.

When switching from recording to reproduction, the switch S1 is on the P side and the recording amplifier Arec is in the non-operating state, and at the same time, the switch S2 is also on the P side, so that the transistor Q10 is turned off.
At this moment, the emitter potential of the transistor Q1 is the capacitor
The state is high due to the charge of C2, the transistor Q5 is turned on, and the voltage drop across the resistor R5 is also large. At this time,
The voltage of the inverting input − of the differential amplifier A1 is lower than the voltage (V2) of the non-dark input +. The output of the differential amplifier A1 is H
At the level transistor Q9 tries to turn on and switch S3
Since it is also on the P side, the transistor Q8 is turned off, the transistor Q9 is turned on as it is, the capacitor C2 is rapidly discharged by its collector current, and the emitter of the transistor Q1 is rapidly lowered. The emitter of the transistor Q1 is VE (Q
1) When -V1 becomes smaller than 0.7V, the transistor Q5 turns off and the voltage drop across the resistor R5 becomes zero. The voltage of the inverting input-becomes higher than the reference voltage V2, the output of the differential amplifier A1 becomes L level, and the transistor Q10 is turned off to stop the rapid discharge. At this time, the emitter potential of the transistor Q1 is only several hundred mV higher than the steady-state voltage, and then the emitter potential of the transistor Q1 can reach the steady-state potential with the constant current I1 alone in less time. . As described above, also in this embodiment, it is possible to quickly shift from the recording state to the reproducing state.

FIG. 7 shows a seventh embodiment of the present invention.
The paths for amplifying the signals of the recording amplifier and the reproduction system are the same as those in FIG. 4, except for the emitter potential detecting means of the transistor Q1. The emitter of the transistor Q1 is connected to the emitter of the transistor Q5 whose emitter is connected to the emitter of the transistor Q6 of opposite polarity, the collector of the transistor Q6 is grounded via the load resistor R8, and the inverting input of the differential amplifier A1. −, Differential amplifier
The non-inverting input + of A1 is connected to the reference potential V1. The output of the differential amplifier A1 is connected to the base of the transistor Q12, and the emitter of the transistor Q12 is connected to the emitter of the transistor Q1.

During reproduction, the switches S2 and S3 are also on the P side, and the reproduction system is operating. If the anode potential of the diode Q7 is set several hundred mV higher than the base potential of the transistor Q1, the transistors Q5 and Q6 will be cut off and no current will flow, there will be no voltage drop across the resistor R8 and the differential amplifier A1 The voltage of the inverting input-is lower than the reference voltage V1. Therefore, the output of the differential amplifier A1 becomes H level and the transistor
Since the base potential of Q12 is raised, the transistor Q12 is turned off, which is equivalent to the fact that the transistor Q12 is not connected to the capacitor C2.

When recording, switch S2 is on the R side, so a constant current source
The constant current I1 of I1 flows into the capacitor C2. At this time, the relation with the constant current I2 of the constant current source I2 needs to be set to I1> I2. This raises the emitter potential of the transistor Q1, but VE (Q1) -VB (Q6) is 1.4V (2 x VBE).
Higher than, transistors Q5 and Q6 turn on and resistance
Increase the voltage drop across R8. Then, the voltage of the inverting input − of the differential amplifier A1 becomes higher than the voltage (V1) of the non-inverting input +, but since the switch S3 is on the R side, the differential amplifier A1 is not affected by the input state. It is in operation. The output of the differential amplifier A1 has a high impedance (it may be at H level), and the transistor Q2 maintains the OFF state.

When switching from recording to playback, switch S1 is set to P
Since the recording amplifier Arec is in the non-operating state and the switch S2 is also in the P side at the same time, the constant current of the constant current source I1 does not flow into the capacitor C2. This moment the transistor Q1
The emitter potential of is still high due to the charge of the capacitor C2, the transistors Q5 and Q6 are turned on, and the voltage drop of the resistor R8 is also large. Therefore, the voltage of the inverting input − of the differential amplifier A1 is higher than the voltage (V1) of the non-inverting input +, and the switch S3 is on the P side and the differential amplifier A1 is in the operating state. The output is at the L level, the transistor Q12 acts as an emitter follower, and the emitter potential of the transistor Q1 rapidly drops. This emitter potential decreases and VE (Q1) -VB (Q6) is 1.4V (2 x VB
When it becomes smaller than E), transistors Q5 and Q6 turn off,
The voltage drop across the resistor R28 becomes zero. Then the differential amplifier A1
The voltage at the inverting input of − becomes lower than the voltage at the non-inverting input + (V1), the output of the differential amplifier A1 goes up, and
Q12 is cut off. At this time, since the emitter potential of the transistor Q1 is only several hundred mV higher than the steady voltage, the constant current source I2 alone can reach the steady voltage of the emitter potential of the transistor Q1 in a short time. it can. In this way, this embodiment can quickly shift from recording to playback.

FIG. 8 shows an eighth embodiment of the present invention.
Incidentally, here, a recording amplifier similar to the embodiment shown in FIG.
The magnetic head is omitted. The part that actually amplifies the signal is the same as the circuit up to now, and only the part related to switching is different. Transistors Q6 and Q7 and transistors Q14 and Q15 are transistors of opposite polarities whose emitters are connected to each other and form a complementary differential amplifier, which is used for voltage comparison and detection.

At the time of reproduction, if the base potential of the transistor Q6 is set higher than the base potential of the transistor Q1 by about 1 V (VBE + several hundred mV), the transistors Q6 and Q7 are cut off and the voltage drop of the resistor R5 becomes 0, The emitter potential of the transistor Q8 becomes Vcc-VBE (Q8). On the other hand, transistor Q
The base potential of 15 is Vcc (vR15 + VBE + VF (Q16) + VF)
(Q17)).

Here, if the voltage drop of the resistor R15 is several hundred mV or more,
The transistors Q14 and Q15 are turned off. Transistor Q15
Is off, transistor Q29 remains off. Since the R / P terminal is at the L level, the transistor Q25 is off, the current of the transistor Q19 flows into the transistor Q26, and this current also flows into the transistor Q27, turning off the transistor Q20 and turning off the transistor Q21.
Will also be off.

Since the R / P terminal is at the H level during recording, the transistors Q24 and Q25 are turned on. Since the transistor Q24 is on, the transistor Q29 is off regardless of the presence / absence of current in the transistor Q15. Further, since the transistor Q25 is turned on, the diode Q26 and the transistor Q27 are turned off, the current of the transistor Q20 flows, the transistor Q21 is turned on, and the transistor Q29 is turned off. Have been raised to.

When recording is switched to reproduction, the R / P terminal goes from the H level to the L level, so that the transistor Q25 is turned off. As a result, the transistors Q26 and Q27 are turned on, and the transistor Q2
0 and Q21 are turned off. By the way, at the moment of switching, since the emitter potential of the transistor Q1 remains high due to the charge of the capacitor C2, the transistors Q6 and Q7 are off. As a result, the transistors Q14 and Q15 are turned on, and the transistor Q24 is turned off, so that the transistor Q29 is turned on, the capacitor C2 is rapidly discharged, and the emitter potential of the transistor Q1 is rapidly lowered. When the base potential of the transistor Q1 drops, the transistors Q6 and Q7 turn on, the voltage drop of the resistor R5 lowers the emitter potential of the transistor Q8, turns off the transistors Q14 and Q15, and turns off the transistor Q29 to stop the rapid discharge. At this time, the transistor
Since the emitter potential of Q1 is only several hundred mV higher than the steady voltage, the constant potential of the transistor Q10 can reach the steady potential of the transistor Q1 in a short time. In this way, it is possible to quickly switch from recording to reproduction.

FIG. 9 shows a ninth embodiment of the present invention.
Incidentally, the recording amplifier and the magnetic head are omitted as in FIG. The part that actually amplifies the signal is the same as the circuit up to now, and only the circuit related to switching is different here. That is, the emitter of the transistor Q1 is also connected to the emitter of the transistor Q5 via the current limiting resistor R6 of the transistor Q5, and the collector of the transistor Q6 is connected to the bases of the transistors Q14 and Q15 forming the differential amplifier. And this differential amplifier Q1
4, The output of Q15 is designed to discharge capacitor C2.

During playback, the base potential of transistor Q5 is a transistor
If it is set higher than the base potential of Q1 by about several hundred mV, the transistor Q5 turns on and the voltage drop of the resistor R5 results in VB (Q15)> VB (Q14).
Current flows through transistor Q15 and transistor Q14
Turns off. Therefore, the diode Q16, the transistor Q17, the diode Q25, and the transistor Q26 also remain off. Since the R / P terminal is at L level,
The transistor Q22 is turned on, the diode Q23 and the transistor Q24 are turned off, and the transistors Q18 and Q19 are also turned off.

Since the R / P terminal is at H level during recording, the transistor Q20 turns on, the current source lines of the transistors Q8 to Q12, Q21 are grounded to GND, these transistors are turned off, and the playback amplifier Inactive state. Since the transistor Q22 is also turned off, the diode Q23, the transistor Q24, the diode Q18, and the transistor Q19 are turned on, and the emitter potential of the transistor Q1 is raised.

When recording is switched to reproduction, the R / P terminal goes from the H level to the L level, so that the current source transistors of Q8 to Q12 and Q21 are activated. In addition, since the transistor Q22 also turns on, the diode Q23, the transistor Q24, the diode Q18, and the transistor Q19 will be turned off in the future.
There is no function to raise the emitter potential of Q1. By the way, the emitter potential of the transistor Q1 at the moment of switching is high due to the charge of the capacitor C2, and the transistor Q5 is off. Therefore, VB (Q15) <V
B (Q14), which causes transistor Q14 to turn on and turn on diode Q16, transistor Q17, and diode Q2.
5. The transistor Q26 is also turned on to rapidly discharge the electric charge of the capacitor C2, and the emitter potential of the transistor Q1 rapidly drops. When the base potential of the transistor Q1 drops, the transistor Q5 turns on, and the voltage drop across the resistor R5 causes VB (Q15).
> VB (Q14), the transistor Q14 is turned off and the transistor Q26 is turned off to stop the rapid charging. At this time, since the emitter potential of the transistor Q1 is only several hundred mV higher than the steady voltage, only the constant current of the transistor Q8 can reach the steady potential of the transistor Q1 in a short time. In this way, it is possible to quickly switch from recording to reproduction.

[Effects of the Invention] As described above, according to the recording / reproducing switching circuit of the present invention, the time from the recording to the reproducing state can be rapidly changed to the reduction to the steady state.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention (corresponding to claims 1 and 3).
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q17, R8, R9 ...... Reproducing amplifier Q11 to Q14, R4 to R7 ...... First Capacitor charging circuit Q5, Q6, Q16, R16 ... Voltage detecting circuit Q7 to Q10, R10, R12 ... Second capacitor charging circuit FIG. 2 shows a second embodiment of the present invention (claims 1 and 4). Correspondence)
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q16, Q17, R8, R9 ...... Reproducing amplifier Q12 to Q15, R4 to R7 ...... First capacitor charging circuit Q5, Q6 ... Voltage detection circuit Q7 to Q11, R10, R12 ... Second capacitor charging circuit FIG. 3 shows a third embodiment of the present invention (corresponding to claims 1 and 6).
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q14, Q15, R6, R7 ...... Reproducing amplifier Q9 to Q11, R4, R5 ...... First capacitor charging circuit Q5 ... Voltage detection circuit Q6 to Q8, R8, R9 ... Second capacitor charging circuit FIG. 4 is a fourth embodiment of the present invention (corresponding to claims 2 and 3).
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q8, R3, R4 ...... Reproducing amplifier Q11 ...... First capacitor charging circuit Q5, Q6, R5, I3 ... Voltage detection circuit Q9, Q10, R9 ... Second capacitor charging circuit FIG. 5 shows a fifth embodiment of the present invention (corresponding to claims 2 and 3).
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q8, R3, R4 ...... Reproducing amplifier Q23, Q27 to Q29, R22, R26 ...... First capacitor charging circuit Q5, Q6, Q11, R5, R10 ... voltage detection circuit Q14 to Q17, Q21, R17, R19 to R21 ... comparison circuit Q24 to Q26, R24, R25 ... second capacitor charging circuit FIG. 6 shows a sixth embodiment of the present invention (corresponding to claims 2 and 4).
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q7, R3, R4 ...... Reproducing amplifier Q10 ...... First capacitor charging circuit Q5, Q6, R6, I3 ... Voltage detection circuit A1 ... Comparison circuit Q8, Q9, R8 ... Second capacitor charging circuit FIG. 7 shows a seventh embodiment of the present invention (corresponding to claims 2 and 5).
FIG. Arec ...... Recording amplifier C1 ...... First capacitor C2 ...... Second capacitor Q1 ...... First transistor Q1 to Q4, Q10, Q11, R3, R4 ...... Reproducing amplifier I1 ...... First capacitor charging circuit Q5, Q6, R8 ...... Voltage detection circuit A1 ...... Comparison circuit Q12 ...... Second capacitor charging circuit Fig. 8 shows an eighth embodiment of the present invention (corresponding to claims 2 and 5).
FIG. Arec …… Recording amplifier C1 …… First capacitor C2 …… Second capacitor Q1 …… First transistor Q1 to Q4, Q5, Q9, R3, R4 …… Reproducing amplifier Q20, Q21, Q27, R17, R18 ...... First capacitor charging circuit Q6 to Q8, R12, R5 ...... Voltage detection circuit Q14, Q15 ...... Comparison circuit Q24, Q28, Q29, R24 ...... Second capacitor charging circuit Fig. 9 shows the present invention. The circuit diagram which shows 9th Example (corresponding to Claim 2 and 6). Arec …… Recording amplifier C1 …… First capacitor C2 …… Second capacitor Q1 …… First transistor Q1 to Q4, Q6, Q7, R3, R4 …… Reproducing amplifier Q18, Q19, Q22 to Q24, R20 , R21 …… 1st capacitor charging circuit Q5, R5 …… Voltage detection circuit Q14, Q15, Q21, R19 …… Comparison circuit Q16, Q17, Q25, Q26, R15, R22 …… 2nd capacitor charging circuit 10th The figure is a conventional circuit diagram.

Claims (7)

(57) [Claims] 1. A recording amplifier for supplying a recording current to a magnetic head in a recording state, a base is connected to the magnetic head via a first capacitor, and an emitter is AC-grounded via a second capacitor. A reproducing amplifier including a first transistor connected to a constant current source for amplifying an output reproduced signal of the magnetic head in a reproducing state, and an output terminal connected to the second capacitor to change the reproducing state to the recording state. A first capacitor charging circuit which is in an operating state only during the transition period of 1 to rapidly charge the second capacitor, a first input terminal is connected to the emitter of the transistor, and a second input terminal is a first reference. A voltage detection circuit connected to the electric potential, a controlled terminal is connected to the output terminal of the voltage detection circuit, and its own output terminal is connected to the second capacitor. A recording / reproducing switching circuit comprising a second capacitor charging / discharging circuit which is in an operating state only during a transition period from the state to the reproducing state and rapidly charges the second capacitor. 2. A recording amplifier which supplies a recording current to a magnetic head in a recording state, and a base which is connected to the magnetic head through a first capacitor, and an emitter which is AC-grounded through a second capacitor. And a reproduction amplifier which includes a first transistor connected to a constant current source and which amplifies an output reproduction signal of the magnetic head in a reproduction state, and an output which is connected to the first capacitor and is in an operating state only during recording. A capacitor charging / discharging circuit, a voltage detection circuit having one input connected to the emitter of the transistor and the other input connected to a first reference potential, and one input connected to the output of the voltage detection circuit, The other input is connected to the second reference potential, the controlled input terminal is connected to the output terminal of the comparison circuit, and its own output terminal is connected to the second capacitor. And, recording reproducing switching circuit consisting of a recording state and a second capacitor discharge circuit to rapidly charge said second capacitor becomes only the operation state during the transition period to the playback state. 3. The voltage detection circuit is composed of a differential amplifier circuit having a first input connected to the emitter of a first transistor and a second input connected to a first reference potential. The recording / reproducing switching circuit according to claim 1 or 2. 4. A voltage detecting circuit comprising a second transformer having a base connected to an emitter of a first transistor, an emitter connected to a first reference potential, and an output from a collector. The recording / reproducing switching circuit according to claim 1 or 2. 5. A voltage detection circuit comprising a third transistor having a base connected to the emitter of the first transistor and a base connected to a first reference potential, an emitter connected to the emitter of the third transistor, and a collector. 3. The recording / reproducing switching circuit according to claim 1, wherein the recording / reproducing switching circuit comprises a fourth transistor having a polarity opposite to that of the third transistor for extracting an output from the third transistor. 6. The voltage detection circuit comprises a fifth transistor having an emitter connected to the emitter of the first transistor, a base connected to a first reference potential, and an output from the collector. The recording / reproducing switching circuit according to claim 1 or 2. 7. A recording amplifier for supplying a recording current to a magnetic head in a recording state, a base is connected to the magnetic head via a first capacitor, and an emitter is grounded AC via a second capacitor. A reproducing amplifier, which includes a first transistor connected to a constant current source, amplifies an output reproduced signal of the magnetic head in a reproducing state, and a reproducing amplifier connected to an emitter of the first transistor to detect a recording state and a reproducing state. Connected to the second capacitor and a voltage detection circuit for operating a transition from a reproducing state to a recording state in response to a recording / reproducing switching signal from the outside to activate the second capacitor to rapidly charge the second capacitor. No. 1 capacitor charging / discharging circuit and the second capacitor are connected to record according to the output of the voltage detecting circuit and the recording / reproducing switching signal. A recording / reproducing switching circuit comprising a second capacitor charging / discharging circuit which is in an operating state only during a transition period from the state to the reproducing state and rapidly charges the second capacitor.