JPS59190704A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To extract signals before and after muting control by forming an output terminal 3 for an amplification output at the output side of an amplifier and providing a buffer circut which performs the muting control over the amplification output. CONSTITUTION:An input signal to be amplified is supplied from a signal source such as a magnetic head to an input terminal, and an amplifier 4 constitutes a preamplifier which is supplied with the signal directly from the signal source. The output terminal 6 to which an amplification output which is not brought under the muting control is led out is formed on the output side of this amplifier 4, and the buffer circuit 8 which performs the muting control over the amplification output is installed. Consequently, the amplification output V01 of the amplifier 4 is supplied from the output terminal 6 to a signal processing system which does not require the muting control and an amplification output V02 is supplied from the output terminal 12 of the buffer circuit 8 to a signal processing system which requires the muting control through the buffer circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and particularly to muting control thereof.

Muting control on the playback output of a tape recorder is often performed at the final power amplification stage that takes out the audio output, but when the line output is taken out from the amplifier at the previous stage, the line output is the one before the muting control. Therefore, if muting control is applied to the preamplification stage connected to the magnetic head, it will be inconvenient to take out signals that do not require muting control, such as music selection signals.

The object of the present invention is to provide an amplifier circuit that can take out a signal after muting control and a signal before muting control in a subsequent stage of an amplifier for signal amplification.

The present invention is characterized in that the output side of an amplifier that amplifies an input signal from a signal source is configured to output the amplified output to the outside, and a buffer circuit is installed to perform muting control on the amplified output. do.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of the amplifier circuit of the present invention. In the figure, an input terminal 2 is supplied with an input signal to be amplified from a signal source such as a magnetic head, and an amplifier 4 constitutes a preamplifier to which a signal is directly supplied from the signal source. An output terminal 6 for taking out an amplified output without muting control is formed on the output side of the amplifier 4, and a high frequency circuit 8 for performing muting control on the amplified output is installed. This high frequency circuit 8 is equipped with an amplifier with a gain of 1 and a muting control circuit that controls the amplification operation of the amplifier and performs muting control. A control input terminal IO for providing a control input is formed in the half sofa circuit 8, and an output after muting control is taken out from an output terminal 12.

According to such a configuration, the amplified output V o H of the amplifier 4 is used in a signal processing system that does not require muting control.
can be given from the output terminal 6, and an amplified output V o 2 can be given from the output terminal 12 of the signal processing system requiring muting control via the hash sofa circuit 8. Therefore, if such an amplifier circuit is installed in a reproduction circuit of a tape recorder, a music selection signal etc. can be taken out from the output terminal 6, and an audio signal requiring muting can be taken out from the output terminal I2. Furthermore, since muting control is performed using an amplifier with a gain of 1, the amount of transient, ie, generation of pop noise, can be suppressed to a level that does not pose a problem.

FIG. 2 shows a specific circuit of the amplifier circuit, and the same parts as in FIG. 1 are given the same reference numerals.

In the figure, an amplifier 4 is constituted by a differential amplifier, and a magnetic head 16 is connected between an input terminal 2 formed as a non-inverting input terminal (G) of this amplifier and a DC Hibs circuit 14. The amplified output is fed back from the output side via the feedback circuit 18 to the inverting input terminal (-) of 4, and a DC bias is supplied from the n;1 DC bias circuit 14. Feedback circuit 18 is resistor 20.22
．． 24 and a capacitor 26. Further, the DC bias output generated at the output terminal 28 of the DC bias circuit 14 is given to the magnetic heads and amplifiers of other channels.

Further, the high frequency circuit 8 is provided with an amplifier 30 with a gain of 1 and a muting control circuit 32 that controls the amplification operation of the amplifier 30 and performs muting control. That is,
The amplifier 30 is equipped with a pair of transistors 34 and 36 that have common emitters and constitute a differential amplifier.The emitters of the transistors 34 and 36 are connected to the collector of a transistor 38 that regulates the operating current. The base of the transistor 40 and the base/collector of the transistor 420 are commonly connected to the base of the transistor 40,
The emitter of each transistor 38.40.42 is connected to ground (
A reference potential terminal 44 (GND) is connected to the formed reference potential line.

Transistor 42. base collector and power terminal 46
A constant current source 48 is connected between the power supply line and the power supply line to which the power supply voltage Vcc is applied. 1-ransistor 42
and the transistor 38 or the transistor 40 constitute a current inversion circuit, and the constant current supplied from the constant current source 48 becomes the operating current of the transistor 34.36 through the current inversion circuit consisting of the transistor 42.38. An operating current is supplied to the amplifiers of other channels from an output terminal 50 formed at the collector of the transistor 40 constituting the current inversion circuit.

The output of each transistor 34, 36 is taken out from its collector, and transistors 52, 54, which are configured as diodes and have a common base and collector, are connected between the collector and the power supply line with their emitters facing the power supply line. There is. 1- The bases of transistors 56.58 are commonly connected to the base and collector of transistors 52.54,
The emitters of each transistor 56, 58 are commonly connected to a power supply line. The transistor 52 and the transistor 56, and the transistor 54 and the transistor 58 together constitute a current inversion circuit. A transistor 6 is connected between the collector of the transistor 58, 56 and the reference potential line.
0.62 are connected, and the base and collector of l. transistor 56.62
An output terminal 12 is formed at the collector of the amplifier 30, and the base of the transistor 36 is connected to this output point, so that the amplifier 30 constitutes a full feedback amplifier. Further, the base of the transistor 36 is connected to the DC bias circuit 14 via a resistor 63.

A transistor 64 of the muting control circuit 32 is connected between the collector and emitter of the transistor 42 of the amplifier 30 with the emitter facing the reference potential point, and the control input terminal 10 is connected to the base of the transistor 64 via a resistor 66. It is formed. In this embodiment, the control input terminal 10
A switch 68 for switching muting is connected between the power line and the power supply line.

The operation will be explained based on the above configuration. switch 6
8 is open, the reproduction signal is given from the magnetic head 16 to the amplifier 4, and its amplified output Vol is sent to the output terminal 6.
is extracted as a signal without muting control from
It can be taken out from the output terminal 12 via 0. In this case, since the switch 68 is open, the amplified output 'J o 2 generated at the output terminal 12 becomes a signal at the same level as the output Vol at the output terminal 6 due to the gain l of the amplifier 30.

Next, when the switch 68 is closed, the power supply voltage Vcc is applied to the control input terminal 10, and the transistor 4 becomes conductive. As a result, the base-collector and emitter of the transistor 42 are short-circuited by the conduction of the transistor 64, the operating current of the transistors 34 and 36 is cut off, and the amplification operation thereof is canceled. That is, the output of the output terminal 12 is in a no-signal state. In this case, even if the operation of the amplifier 30 stops, the DC potential remains constant because the output terminal 12 is connected to the bias circuit 14 via the resistor 63, and the gain of the amplifier 30 is 1, so , it is possible to suppress the generation of transient pop noises associated with switching.

Further, in the muting control, the output impedance during muting can be freely set by the resistance value of the resistor 63. Furthermore, for an amplification system with multiple inputs, the muting control circuit 32, constant current source 48, and transistor 42 are commonly configured, and the control input terminal 10
By forming these in common, muting control can be performed simultaneously using direct current.

Further, FIG. 3 shows another embodiment of the present invention, and the amplifier circuit of this embodiment includes a pair of amplifiers 4A and 4B, and corresponding to the amplifiers 4A and 4B, a buffer circuit 8A, 8B is installed. Each amplifier 4A, 4B
Input signals are individually given to the input terminals 2A and 2B from the signal source, and the muting signal output is sent to the buffer circuit 8.
A, 8B output terminals 12A, 12B respectively.

When combining and extracting amplified outputs that do not require muting control, the output impedance of each amplifier 4A and 4B is set low, and a resistor 70.7 is connected to each output terminal.
2, an output terminal 74 is formed in common, and signals that do not require muting, such as music selection signals, can be synthesized and taken out from this output terminal 74.

Although the embodiment has been described by taking the preamplifier section of a tape recorder as an example, the present invention can be used to amplify signals provided from various signal sources.

As explained above, according to the present invention, a buffer circuit is installed on the output side of an amplifier, and muting control is performed by this buffer circuit, so that a signal that does not require muting is transferred from the amplifier from the buffer circuit. The muting signal output can be selectively taken out, and transients associated with muting control can be suppressed to a sufficiently low level that they do not pose a problem.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an amplifier circuit of the invention, and FIGS. 2 and 3 are circuit diagrams showing other embodiments of the invention. 4...Amplifier, 8...Buffer circuit.

Claims (1)

[Claims] An amplifier circuit characterized in that a buffer circuit is installed on the output side of an amplifier that amplifies an input signal from a signal source so that the amplified output is taken out to the outside, and that performs minting control on the amplified output. .