JPH0743807Y2 - Tape player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a tape player such as an auto reverse tape player.

[Conventional technology]

Conventionally, in a tape player such as an auto-reverse tape player, as shown in FIG. 3, two pickup coils of a reproducing magnetic head corresponding to the reproducing direction are used as signal sources.
2a and 2b are installed, and differential amplifiers 6a and 6b are installed for each pickup coil 2a and 2b. Each differential amplifier 6a,
6b includes a current mirror circuit 8 as a common active load.
And a constant current source 12 for supplying an operating current is installed. When any one of the pickup coils 2a and 2b is selected, each differential amplifier corresponding to the selection.
A differential switch circuit 14 that switches the operating current by the constant current source 12 is installed in 6a and 6b. This differential switch circuit
A switching input is applied to the switch 14 through a switch 28 and a time constant circuit 30 which are switched according to the selection of the pickup coils 2a and 2b, and either one of the differential amplifiers 6a and 6b is corresponding to the switching input. The voltages V _a and V _b required for the selective operation are applied through the voltage setting circuit 26.

When the switch 28 is switched to the contact a side, the capacitor 302 of the time constant circuit 30 passes through the resistor 301 and the power supply voltage V _cc.
Is added, the battery is slowly charged with a time constant determined by the resistor 301 and the capacitor 302. Base voltage V _a of the transistor 14a, as shown by A ₂ to A of FIG. 4, the base-emitter voltage V _F of the forward voltage drop 2V _F to the transistor 265 by the diode 262 and 263 of the voltage setting circuit 26 The added voltage becomes 3V _F. At this time, the transistor
14a becomes conductive instead of the transistor 14b, and the constant current of the constant current source 12 flows to the transistor 14a side. Therefore, when the switch 28 is switched to the contact a side, the differential amplifier 6a is in the operating state, the input signal _Via applied to the input terminal 4a is amplified, and is input from the output terminal 42 through the output stage amplifier 16. the output signal V _o based on the signal V _ia taken out.

Further, when the switch 28 is switched to the contact b side, the capacitor 302 is discharged through the resistor 301. For this reason,
The base voltage V _a of the transistor 14a is A _{1 in} FIG.
As shown in, it is reduced to the voltage V _F obtained by subtracting the base-emitter voltage V _F of the transistor 264 from 2V _F determined by diode 262 and 263 of the voltage setting circuit 26. This voltage V
_{Since F} is lower than the base voltage V _b of the transistor 14b,
Transistor 14b will conduct instead of transistor 14a. Therefore, when the switch 28 is closed on the contact b side, the differential amplifier 6b is an operating state, the input signal V _ib applied to the input terminal 4b is amplified, the input signal V _ib through the output stage amplifier 16 An output signal V _o based on is taken out from the output terminal 42.

[Problems to be solved by the device]

By the way, as described above, the time constant circuit 30 is used to switch the voltages V _a and V _b from the voltage setting circuit 26 to the differential switch circuit 14.
As shown in FIG. 4A, the addition of the signal can suppress a sudden voltage change and prevent the generation of a transient sound due to the voltage change.

However, when switching the operation of the transistors 14a and 14b, when the base voltage V _a (= 2V _F ) of the transistor 14a crosses the base voltage V _b of the transistor 14b as shown in A of FIG. Exists at the same time, there is a transient section in which the differential amplifiers 6a and 6b simultaneously become active. Further, since there is an offset in the differential amplifiers 6a and 6b, an unnecessary operation state is delayed and occurs beyond such an interval in which the operation switching becomes ambiguous. Therefore, as shown in B of FIG. way, referred to as pop sound transient sound signal is generated, which is taken out as an output signal V _o from the output terminal 42 through the output stage amplifier 16. this is,
It is something that the listener feels as an abnormal sound.

Conventionally, in order to prevent the occurrence of such an abnormal sound, a mute circuit 41 is installed on the output side of the output stage amplifier 16, and the switching operation of passing or blocking the output signal V _o is interlocked with the switching of the switch 28. Although measures have been taken to cut off the transient sound signal at the time of switching the input, the timing for controlling the mute circuit 41 was realized by an external circuit, which had the drawbacks of complicating the configuration and increasing the number of parts. It was

Therefore, an object of the present invention is to provide a tape player that realizes a muting operation from an electrical change inside the circuit due to input switching, and prevents generation of transient sound due to input switching.

[Means for Solving the Problems]

As shown in FIG. 1, the tape player of the present invention has a first magnetic head (pickup coil 2a) for extracting a reproduction signal from a magnetic tape on the basis of a constant DC bias voltage and the DC bias voltage. And a second magnetic head (pickup coil 2b) for extracting a reproduction signal from the magnetic tape, and a first and second transistors (61, 62) having a common emitter. A current mirror circuit (8) is connected as an active load to the base of the first transistor, and a reproduction input from the first magnetic head is applied to the base of the first transistor,
The difference between the first amplifier (differential amplifier 6a) for extracting the reproduction input and the third and fourth transistors (63, 64) having a common emitter is applied to the base of the transistor of the above-mentioned DC bias voltage. A differential pair, the current mirror circuit is connected to the differential pair as an active load common to the first amplifier, and the reproduction input from the second magnetic head is added to the base of the third transistor. , The fourth
A second amplifier (differential amplifier 6b) for taking out the reproduction input by applying the DC bias voltage to the base of the transistor and a fifth amplifier on the emitter side of the first and second transistors of the first amplifier. (14a) of the second amplifier, and the sixth transistor (14b) is connected in series to the emitter side of the third and fourth transistors of the second amplifier, and the emitters of the fifth and sixth transistors are made common. , A reference voltage (Vb) is applied to the base of the sixth transistor, and an operation switching voltage is applied to the base of the fifth transistor, and the fifth transistor or the sixth transistor is selectively selected depending on the magnitude relationship between the two. A differential switch circuit (14) for turning on and a reference voltage generating circuit (voltage setting circuit 26) for generating the reference voltage for turning on the sixth transistor. The differential switching circuit and the fifth and sixth are connected between the emitter and the ground point of the transistors of said fifth transistor and said sixth
Current source (constant current source 12) for supplying an operating current to the first amplifier or the second amplifier according to the conduction of the transistor
And an operation changeover switch (switch 28) connected between the voltage source (power supply Vcc) and the ground point to generate a voltage in accordance with the changeover, and the voltage generated by the changeover of the operation changeover switch. An operation changeover voltage generating circuit (time constant circuit 30) for generating an operation changeover voltage having a large increase / decrease change, and applying this operation changeover voltage to the base of the fifth transistor of the differential switch circuit; Two
Output amplifier (16)
And a seventh transistor (403) which is connected between the output section of the output stage amplifier and the grounding point and conducts by a mute signal applied to the base to suppress extraction of the output of the output stage amplifier. , An eighth transistor (264) that conducts to draw a current and flow the current to the ground side through the operation changeover switch when the reference voltage is applied to the base and the operation changeover switch is changed over to the ground point side. ), A ninth transistor (265) that conducts and draws current from the voltage source when the reference voltage is applied to the base in common with the eighth transistor and the operation changeover switch is switched to the voltage source side. ),
A current mirror circuit (transistor) that supplies the current to the eighth transistor and extracts the current
341, 342), and a current mirror circuit or a tenth transistor (344) for selectively supplying the current from the ninth transistor to generate the mute signal, which is constant from the switching of the operation changeover switch. And a mute signal generation circuit (34) for suppressing extraction of the output by turning on the seventh transistor for a certain period of time.

[Action]

Each input signal is amplified by the first and second amplifiers installed for each input signal. An operating current is supplied to each amplifier to secure the operation, and the operating current is selected by the differential switch circuit based on the switching input. In this case, the required voltage is set by the reference voltage generating circuit for switching the operation of the differential switch circuit.

Then, the mute signal generation circuit detects the operation switching based on the potential change caused by the switching of the operation switching switch and generates the mute signal. This mute signal is added as a control input to the mute circuit installed on the signal output side. The mute circuit is controlled to the mute state in the optimum operation switching section, and unnecessary transient sound is generated due to the input switching. To be prevented.

〔Example〕

 FIG. 1 shows an embodiment of the tape player of the present invention.

As the first and second magnetic heads, for example, two pickup coils 2a and 2b are installed in a single reproducing magnetic head, and one terminal side is commonly connected to each pickup coil 2a and 2b so that a bias voltage V _BS has been added. The reproduction signal of each pickup coil 2a, 2b is input terminal 4a,
Input signals V _ia and V _ib are individually applied to 4b. Differential amplifiers 6a and 6b are installed as first and second amplifiers corresponding to these input signals V _ia and V _ib . Since the embodiment is an auto-reverse tape player, two pickup coils 2a and 2b are installed according to the reproducing direction, and a pair of differential amplifiers 6a and 6b is installed corresponding to this, but 3 If the above input signals are present,
An input stage amplifier is also installed corresponding to them.

A differential pair composed of first and second transistors 61 and 62 is installed in the differential amplifier 6a, and a differential pair composed of third and fourth transistors 63 and 64 is installed in the differential amplifier 6b. amplifier
6a and 6b have transistors 81 and 82 as a common active load.
And a constant current source for supplying an operating current by a constant current.
12 are installed.

In order to selectively switch the operations of the differential amplifiers 6a and 6b, a differential switch circuit 14 is installed as an operation switching circuit that causes a constant current of the constant current source 12 to flow to either one of the differential amplifiers 6a and 6b. There is. The differential switch circuit 14 includes each differential amplifier 6a,
It is composed of a differential pair of fifth and sixth transistors 14a and 14b installed between 6b and the constant current source 12, and the conduction states of the transistors 14a and 14b are selectively controlled. Therefore, when the transistor 14a becomes conductive, the differential amplifier 6a
When the operating current flows through the transistor 14b and the transistor 14b becomes conductive, the operating current flows through the differential amplifier 6b, and one of the differential amplifiers 6a and 6b is controlled to be in the operating state.

The amplified outputs of the differential amplifiers 6a and 6b are added to the common output stage amplifier 16 and amplified. This output stage amplifier
Reference numeral 16 is composed of transistors 161, 162 and constant current sources 163, 164. The output signal V _o taken out from the output point on the emitter side of the transistor 162 is supplied to the differential amplifiers 6a, 6b.
It is fed back to the feedback terminal 18 through the equalizer element 20.
A bias voltage V _BS is applied to the feedback terminal 18 through the resistor 22 and the capacitor 24.

In order to realize input switching by selecting the operation of the differential amplifiers 6a and 6b, the transistor 14 of the differential switch circuit 14 is
Voltages V _a and V _b are set from a voltage setting circuit 26 provided as a reference voltage setting circuit to each of the bases a and 14b. That is, in the voltage setting circuit 26, a constant current is caused to flow from the constant current source 261 to the diodes 262 and 263 connected in series to generate a forward drop voltage 2V _F , and this voltage 2V _F is applied between the base and emitter of the transistor 264. while shifting the level of the voltage V _F through, thereby level shifting the voltage 3V _F through between the base and emitter of the transistor 265. Therefore, through this voltage setting circuit 26, the transistor 14
The base of a could take a voltage between V _F and 3V _F.

A voltage of 2V _F is applied to the base input side of the transistor 14b. When the switching input applied by the switching of the switch 28 as the operation switching switch is composed of the resistor 301 and the capacitor 302 which form the operation switching voltage generating circuit for converting the sudden potential change by the switch 28 into the gradual operation switching voltage. It is applied to the switching input terminal 32 through the constant circuit 30.

Therefore, when the switch 28 is closed to the contact a side, the capacitor 302 is charged through the resistor 301, and the charging voltage gradually increases due to the time constant composed of the resistance value of the resistor 301 and the capacitance of the capacitor 302. The base voltage V _a of the transistor 14a is gradually set from V _F to 3V _F according to the charging of the capacitor 302, as indicated by A ₂ in A of FIG. Therefore, a transistor whose base voltage V _b is 2V _F
The transistor 14a becomes conductive instead of 14b, and the differential amplifier 6a
Becomes an operating state, the input signal _Via from the pickup coil 2a is selected and amplified, and is added to the output stage amplifier 16.

Further, when the switch 28 is closed to the contact b side, the capacitor 302 is discharged by being grounded through the resistor 301, and the base voltage V _a of the transistor 14a is caused by the time constant composed of the resistance value of the resistor 301 and the capacitance of the capacitor 302. Is
As indicated by A ₁ in A of FIG. 2, the voltage gradually decreases from 3V _F to V _F. As a result, the transistor 14b having the base voltage _Vb of 2V _F becomes conductive instead of the transistor 14a, the differential amplifier 6b becomes in the operating state, the input signal V _ib from the pickup coil 2b is selected and amplified, and the output stage Added to amplifier 16.

A mute signal generation circuit 34 is provided to detect the operation switching from the potential change caused by the switching of the switch 28 and generate the mute signal V _c . That is, on the collector side of the eighth transistor 264 of the voltage setting circuit 26, one diode-connected transistor 341 of the current mirror circuit is installed, and the collector of the other transistor 342 is common to the collector of the ninth transistor 265. Connected to each collector and ground terminal
Resistor 343 is connected between 36 and 36. A transistor 344, to which the current flowing out from each of the transistors 265 and 342 is added to the base, is installed between the collector of the transistor 344 and the power supply terminal 38 and a resistor 34 as a load.
5 is connected. Therefore, as the operation of the differential switch circuit 14 is switched, in a section where the switch 28 is closed on the contact a side, a current I _a flows through the transistor 265 from the resistor 301 side as shown in C of FIG. Further, in the section in which the switch 28 is closed on the contact b side, the current I _b flows from the transistors 341 and 264 to the resistor 301 as shown by D in FIG. When the transistor 341 current I _b flows, flows to the base of transistor 344 through a current I _b 'is the transistor 342 which corresponds to the current I _b by a current mirror effect. Therefore, as shown in E of FIG. 2, the base voltage of the transistor 344 changes corresponding to the current I _a or the current I _b ′, and based on this voltage change, as shown in F of FIG. High and low 2 where the operation switching section T _m becomes high (H) level
Mute signal V _c which is represented by a voltage change in the level is caused. In FIG. _2F , V _SAT represents the saturation voltage when the transistor 344 is conducting.

On the output side of the output stage amplifier 16, a mute circuit 40 that selectively controls the output signal V _o to be in the cutoff state in the mute section is installed. In this mute circuit 40, a seventh transistor 403 is installed on the output side of the output stage amplifier 16 via a capacitor 401 and a resistor 402. Since the base of the transistor 403 is applied with the mute signal V _c shown in F of FIG. 2, the transistor 403 conducts in the H level section and controls the output signal V _o to the cutoff state. When the transistor 403 is not conductive, the output is the output signal V _o from the terminal 42 is taken out, for example, via an output amplifier 44, it is reproduced as an audio signal through the speaker 46.

According to such a configuration, by switching the contact a of the switch 28 to the contact b or from the contact b to the contact a, as shown in A of FIG.
The base voltage V _{a of} 14a is switched to V _F (V _a <V _b ) and 3V _F (V _a > V _b ) centering on the base voltage V _b of the transistor 14b side, and the voltage change is a time constant circuit. 30
The voltage setting circuit
The current I _a (C in FIG. 2) flowing through the transistor 265 of 26,
Due to the current _Ib (D in FIG. 2) flowing through the transistor 264 through the transistor 341, a voltage change corresponding to the operation switching occurs as a change in the base voltage of the transistor 344 as shown in E of FIG. In response to this voltage change, the mute signal V _c shown by F in FIG. 2 is generated in the mute signal generation circuit 34, and the transistor 403 of the mute circuit 40 becomes conductive in the H level section of the mute signal V _c .
The conduction section is equal to the operation switching section T _m that requires mute.

Therefore, as shown in FIG. 2B, in the operation switching section T _m , the transient sound signal generated due to simultaneous conduction of the differential amplifiers 6a and 6b in a short section is generated by the transistor 40.
It is cut off by continuity of 3. Therefore, the output terminal 42
A differential amplifier 6a, 6b of the selection operation, the input signal V _ia selected, only the output signal V _o based on V _ib is reproduced from the speaker 46 through the output amplifier 44.

In such a tape player, the mute circuit
40 is a differential amplifier 6a, 6b, an output stage amplifier 16, a voltage setting circuit
26, a mute signal V that represents an optimum mute section based on electrical changes of the voltage setting circuit 26 inside the amplifier circuit together with a portion configured by an IC such as the mute signal generation circuit 34.
_Since it is possible to control the mute circuit 40 by obtaining _c and it is not necessary to set the mute timing with an external circuit as in the past, external parts can be reduced, the circuit configuration can be simplified, and a highly reliable muting operation can be achieved. Is obtained.

[Effect of device]

As described above, according to the present invention, the mute signal is formed according to the voltage change caused by the operation switching of the plurality of amplifiers installed corresponding to the plurality of input signals, and the mute signal is output by the mute signal. Since the extraction is suppressed, the mute section can be optimized, the mute timing does not need to be formed externally, and the circuit configuration can be simplified. In addition, the transient sound accompanying the operation switching is generated. Can be reliably removed, and only the output signal based on the input signal selected by the operation switching of the amplifier can be taken out, so that it is possible to provide the tape player in which the transient sound due to the input switching does not occur.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the tape player of the present invention, FIG. 2 is a diagram showing a mute operation in the tape player shown in FIG. 1, and FIG. 3 is a circuit diagram showing a conventional tape player. FIG. 4 is a diagram showing generation of a transient sound due to input switching in the tape player shown in FIG. 2a ... pickup coil (first magnetic head) 2b ... pickup coil (second magnetic head) 6a ... differential amplifier (first amplifier) 6b ... differential amplifier (second amplifier) 8 ... Current mirror circuit 12 Constant current source 14 Differential switch circuit 14a Fifth transistor 14b Sixth transistor 16 Output stage amplifier 26 Voltage setting circuit (reference voltage generation circuit) 28 ...... Switch (operation changeover switch) 30 ...... Time constant circuit (operation changeover voltage generation circuit) 34 ...... Mute signal generation circuit 61 ...... First transistor 62 ...... Second transistor 63 ...... Third transistor 64 ...... 4th transistor 264 ...... 8th transistor 265 ...... 9th transistor 341, 342 ...... Transistor (current mirror circuit) 344 ...... 10th transistor 403 ...... 7th transistor

Claims (1)

[Scope of utility model registration request] 1. A first magnetic head for extracting a reproduction signal from a magnetic tape based on a constant DC bias voltage, and a second magnetic head for extracting a reproduction signal from the magnetic tape based on the DC bias voltage. , A differential pair including first and second transistors having a common emitter, a current mirror circuit is connected to the differential pair as an active load, and the first magnetic head is provided at the base of the first transistor. From the third and fourth transistors having a common emitter and a first amplifier for extracting the reproduction input by applying the DC bias voltage to the base of the second transistor. A pair, the current mirror circuit is connected to the differential pair as an active load common to the first amplifier, and the base of the third transistor is connected to the front side of the current mirror circuit. A second amplifier for extracting the reproduction input by applying the reproduction input from the second magnetic head and applying the DC bias voltage to the base of the fourth transistor, and the first and first amplifiers of the first amplifier. A fifth transistor is provided on the emitter side of the second transistor, and a third transistor of the second amplifier is provided.
And a sixth transistor connected in series to the emitter side of the fourth transistor, the fifth and sixth transistors have a common emitter, and the base of the sixth transistor has a reference voltage and the fifth transistor has the fifth transistor. An operation switching voltage is applied to the base of the differential switch circuit to selectively bring the fifth transistor or the sixth transistor into a conductive state according to the magnitude relationship between the two, and the reference for rendering the sixth transistor conductive. A reference voltage generating circuit for generating a voltage, and a reference voltage generating circuit connected between the emitters of the fifth and sixth transistors of the differential switch circuit and a grounding point to electrically connect the fifth transistor or the sixth transistor. And a current source for supplying an operating current to the first amplifier or the second amplifier, and a voltage source and a ground point. An operation changeover switch for generating a voltage in response to the changeover, and an operation changeover voltage having a gentle increase / decrease in response to the voltage generated by the changeover of the operation changeover switch. Of an operation switching voltage generating circuit applied to the base of the fifth transistor, an output stage amplifier for amplifying and taking out the output of the first or second amplifier, and an output section of the output stage amplifier and the ground point. A seventh circuit connected between the second stage and the second stage, which conducts by a mute signal applied to the base and suppresses the output of the output stage amplifier
When the operation selector switch is switched to the ground point side by applying the reference voltage to the transistor and the base, an eighth current is conducted to draw the current to the ground side through the operation selector switch. A transistor, when the reference voltage is applied to the base in common with the eighth transistor to switch the operation changeover switch to the voltage source side,
A ninth transistor which is conductive and draws a current from the voltage source, a current mirror circuit which supplies the current to the eighth transistor and takes out the current, and the current is selected from the current mirror circuit or the ninth transistor And a tenth transistor that is supplied with the mute signal to generate the mute signal, and the seventh transistor is turned on for a certain period of time after the operation changeover switch is switched to suppress the extraction of the output. A tape player comprising: a circuit.