JPH07101481B2 - Amplifier circuit - Google Patents

Description

The present invention relates to an amplifier circuit used in a tape player or the like for switching the reproduction equalizer characteristic depending on the type of tape.

(B) Conventional technology Since so-called normal tape and metal tape differ in high-frequency compensation during recording, it is necessary to switch the high-frequency range of the equalizer characteristic according to the tape during reproduction. For example, NA
According to the B (National Association of Broadcasters) characteristics, the low frequency time constant of both tapes is 3180 μsec,
In the high range, the normal tape is set to 120 μsec and the metal tape is set to 70 μsec.

FIG. 1 is a circuit diagram schematically showing a conventional amplifier circuit.

In the figure, 1 is an amplifier circuit, 2 is a tape head,
The resistors R1, R2, R3 and the capacitor C1 form a feedback loop. R4 is a reference resistor and C2 and C3 are DC blocking capacitors.

The switching of the reproduction equalizer characteristic is performed by changing the time constant of the feedback loop by operating the mechanical changeover switch SW provided in the feedback loop.

However, for example, in a stereo device, since the two amplifying circuits described above are used, the changeover switch SW is set to 2
The disadvantage is that the device is expensive because it requires a circuit.

On the other hand, the changeover switch SW is attached to an operation panel of a stereo device or the like, but in order to suppress noise induction and oscillation, it is necessary to shorten the wiring length of the switch SW. Therefore, it also has a drawback that there are many restrictions on the installation position of the amplifier circuit.

Also, a stereo device requires four wires to this switch, which is not suitable for downsizing and cost reduction.

(C) Purpose The present invention provides an amplifier circuit that can switch the reproduction equalizer characteristic at low cost, has few restrictions on the installation position, is suitable for downsizing of the device, and does not generate a pop sound when the characteristic is switched. Its main purpose is.

(D) Configuration An amplifier circuit according to the present invention is an audio amplifier circuit that switches the frequency compensation characteristics of a reproduction equalizer, and includes an amplifier having an input positive terminal, an input negative terminal and an output terminal, and a base connected to the output terminal. A first and a second transistor each having a first and a second transistor, and a first and a second resistor connected in series between the input negative terminal and the output side of the second transistor, and a first capacitor arranged in parallel with the first resistor. One feedback circuit, a second feedback circuit including a third resistor connected between the output sides of the first and second transistors and the first feedback circuit, and outputs connected to the bases of the first and second transistors, respectively. A flip-flop circuit having a terminal and an inverting output terminal, the flip-flop circuit interlocking with a changeover switch, and the bases of the first and second transistors. Of the first resistor, the first and second transistors are turned on and off to select the first and second feedback circuits to switch the frequency compensation characteristic, and the fourth resistor connected in series between the input negative terminal and the ground. And a second capacitor are connected to make the first and second feedback circuits a DC full-feedback configuration so that the potentials on the output sides of the first and second transistors are constant before and after the characteristic switching.

(E) Embodiment FIG. 2 is a circuit diagram schematically showing an embodiment of the present invention which constitutes a part of a reproduction equalizer.

In the figure, the tape head 2 is connected to the positive terminal of the amplifier 1 via a DC blocking capacitor C3. On the other hand, amplifier 1
Is supplied to the bases of the transistors Tr1 to Tr3 via the current limiting resistors R11 to R13 connected in parallel. The resistors R11 to R13 are set to a value sufficiently smaller than the input resistance seen from the bases of the transistors Tr1 to Tr3. The collectors of the transistors Tr1 to Tr3 are grounded, and their emitters are connected to the power supply line via load resistors R14 to R16.
In addition to being connected to Vcc, it is also connected to the bases of transistors Tr4 to Tr6.

The collectors of the transistors Tr4 to Tr6 are the power line Vcc
Connected to. The emitter of the transistor Tr4 is grounded via the resistor R17, and the emitter is connected to the output terminal To.
Connected to. The emitter of transistor Tr5 is resistor R18
It is grounded via and is connected to the feedback resistor R3. The emitter of the transistor Tr6 is connected to the other end of the resistor R3, the feedback resistor R2 and the resistor R1 connected in parallel,
It is connected to the negative terminal of the amplifier 1 via the compensation capacitor C1. The negative terminal is grounded via the reference resistor R4 and the DC blocking capacitor C2. Therefore, this feedback loop has a DC full-feedback configuration.

On the other hand, 3 is a flip-flop that is controlled in conjunction with a mechanical changeover switch provided on an operation panel (not shown), and its output and inverted output are transistors Tr5 and T5.
Given to the base of r6 respectively.

Next, the operation of the above-described embodiment will be described.

For example, in the case of reproducing a normal tape, the output terminal Q of the flip-flop 3 becomes H level and the terminal becomes L level in conjunction with a changeover switch (not shown). As a result, the transistor Tr5 is set to ON and Tr6 is set to OFF.

Therefore, since the feedback loop is composed of the resistors R3 and R2, the capacitor C1 and the resistor R1 connected in parallel, the time constant of this loop in the high range is (R2 + R3) · C1.

On the other hand, in the case of reproducing a metal tape, the output of the flip-flop 3 is inverted by switching the changeover switch, and the transistor Tr5 is set to OFF and Tr6 is set to ON. As a result, the feedback loop is composed of the resistor R2, the capacitor C1 and the resistor R1 connected in parallel, and the high frequency constant of the feedback loop is R2 · C1.

As described above, as a result of selecting an appropriate feedback loop depending on the type of tape, the high frequency time constant of the reproduction equalizer characteristic corresponding to each tape is switched.

In addition, since the feedback loop of the embodiment has a DC total feedback configuration, when comparing the transistors Tr5 and Tr6 in the ON state,
The emitters of the transistors are equipotential.
Therefore, no so-called pop sound is generated when the flip-flop 3 is inverted and the feedback loop is switched.

In addition, although the amplifier circuit having two feedback loops has been described in the embodiment, the present invention is not limited to this, and it is possible to add a switching circuit, a flip-flop, or the like depending on the number of feedback loops. Can be applied to an amplifier circuit having a number of feedback loops.

(F) Effect Since the present invention controls a switching circuit by a flip-flop interlocked with a mechanical changeover switch and selects an appropriate feedback loop to switch the reproduction equalizer characteristic, the present invention is applicable to a stereo device or the like. By providing two amplifier circuits according to the present invention, the flip-flop of each amplifier circuit can be connected so as to interlock with one circuit changeover switch. Therefore, unlike the case where the conventional amplifier circuit is used in the stereo device, it is not necessary to use the changeover switch for the two circuits, and in such a case, the reproduction equalizer characteristic can be changed at low cost. Further, since the wiring to the mechanical switch is small, the device can be downsized.

Further, in the amplifier circuit according to the present invention, since the flip-flop is interposed between the feedback loop and the changeover switch, even if the wiring between the flip-flop and the changeover switch becomes long, the influence of noise induction or the like caused by this may be prevented. There is no reception. Therefore, since the installation position of the amplifier circuit is not limited by the installation position of the changeover switch, the degree of freedom of the installation position of the amplifier circuit and further the reliability of the circuit can be improved.

Further, according to the present invention, since the components forming the feedback loop are only resistors and capacitors and no mechanical switch is included, there is another effect that integration into an integrated circuit is easy, and pop noise is generated when the characteristics are switched. There is an advantage that does not occur.

[Brief description of drawings]

FIG. 1 is a circuit diagram schematically showing a conventional amplifier circuit, and FIG. 2 is a circuit diagram schematically showing an embodiment of the present invention. 1 ... Amplifier, 2 ... Tape head, Tr1-Tr6 ... Transistor, R1-R3 ... Feedback resistor, R4 ... Reference resistor, R11
~ R13 …… Resistor for current limiting, R14 ～ R18 …… Load resistance, C1
... Compensation capacitors, C2, C3 ... DC blocking capacitors,
3 ... Flip-flop.

Claims (1)

[Claims] 1. An audio amplifier circuit for switching the frequency compensation characteristic of a reproduction equalizer, which comprises an amplifier having an input positive terminal, an input negative terminal and an output terminal for connecting a tape head, and a base connected to the output terminal. A first feedback comprising first and second transistors having the first and second transistors, first and second resistors connected in series between the input negative terminal and the output side of the second transistor, and a first capacitor arranged in parallel with the first resistor. A second circuit comprising a circuit, a third resistor connected between the output sides of the first and second transistors, and the first feedback circuit.
A feedback circuit; and a flip-flop circuit having an output terminal and an inverting output terminal connected to the bases of the first and second transistors, respectively. The output signal is sent to the base of the second transistor, the first and second transistors are turned on and off, the first and second feedback circuits are selected to switch the frequency compensation characteristics, and the input negative terminal and the ground are connected in series. By connecting the connected fourth resistor and the DC blocking second capacitor, the first and second feedback circuits are configured as a DC full feedback structure, and the characteristics of the first and second transistors are changed before and after the characteristic switching by the inverting operation of the flip-flop circuit. An amplifier circuit characterized in that the output side is set to an equal potential.