JPH0370925B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite amplifier including a pair of amplifiers, and for example, to an amplifier suitable for a preamplifier of a reproduction signal system of a tape recorder.

A reproduction signal system of a tape recorder is equipped with a preamplifier, a line amplifier, and a power amplifier for amplifying the reproduction signal of the magnetic head. and,
A muting circuit is added to such a reproduction signal system in order to prevent abnormal sounds from occurring at the start of operation. Therefore, when a muting circuit is installed in the final stage power amplifier, the output of the line amplifier is used as a monitor output, etc., so it is meaningless to perform a muting operation only on the output of the power amplifier. Further, when the muting circuit is installed in both the line amplifier and the power amplifier, there is a drawback that the circuit configuration becomes complicated and the muting control becomes complicated. Further, when a muting circuit is installed in a preamplifier, since music selection signals and the like are generally taken out from the output of the preamplifier, there is a possibility that it will be impossible to take out such control signals.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a composite amplifier in which a plurality of amplifiers are installed together to obtain a plurality of outputs with different characteristics, and the configuration is simplified by partially sharing each amplifier.

That is, the composite amplifier of the present invention includes a signal source (magnetic head 8) that generates a signal to be amplified, a DC bias power supply 10 that generates a DC bias voltage,
First and second transistors 16 and 18 whose emitters are commonly connected are installed, and an input signal to be amplified from the signal source is applied to the base of the first transistor with the DC bias voltage as a reference potential, a first amplifier 2 that amplifies the input signal by applying the DC bias voltage from the DC bias power source to the base of the second transistor; and third and fourth transistors 48 and 50 whose emitters are commonly connected. An input signal to be amplified from the signal source is applied to the base of the third transistor in common with the first transistor, and a resistor 6 is connected to the base of the fourth transistor.
A first differential amplifier 40 to which the DC bias voltage is applied from the DC bias power supply via the DC bias power source 8 is installed, and an active load (transistors 56, 58) common to the first differential amplifier is connected to the collector. fifth and sixth transistors 52 and 54 provided on the side and having a common emitter;
a second differential amplifier, wherein the DC bias voltage is applied from the DC bias power supply to the base of the transistor, and the DC bias voltage is applied from the DC bias power supply to the base of the sixth transistor via the resistor. 42, and a seventh transistor 62 connected in series to the emitters of the third and fourth transistors of the first differential amplifier and having a constant voltage applied to its base;
and an eighth transistor 64 connected in series to the emitters of the fifth and sixth transistors of the second differential amplifier and having a control voltage applied to its base, a muting circuit 44 is provided, Amplifying the level-adjusted input signal by controlling the operating current by connecting the constant current source 60 to the first or second differential amplifier by making the seventh or eighth transistor conductive with a voltage. It is equipped with a second amplifier 4 for taking out the output.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the composite amplifier of the present invention. This composite amplifier is provided with first and second amplifiers 2 and 4, and an input terminal 6 formed in common with these amplifiers 2 and 4 is connected to a magnetic head 8 as a signal source that generates a signal to be amplified. is connected. Each of the amplifiers 2 and 4 is supplied with a common bias input from a DC bias power supply 10 installed for the magnetic head 8.

The amplifier 2 is composed of a differential amplifier 12 and a buffer amplifier 14, and amplifies the reproduced signal from the magnetic head 8, and its output is used as, for example, a music selection signal, etc.
Connected to circuit systems that do not require muting. The differential amplifier 12 is composed of first and second transistors 16 and 18, transistors 20 and 22, and a constant current source 24, and a DC bias is applied to the base of the transistor 16 from a DC bias power supply 10 via a magnetic head 8. At the same time, a reproduction signal is applied from the magnetic head 8, and a DC bias is applied to the base of one transistor 18 from a DC bias power supply 10 via a resistor 26. The output of this differential amplifier 12 is the transistor 1
8 and 22, and in order to take out this output to the outside, the buffer circuit 14 is composed of a transistor 28 and a resistor 30.
The collector of No. 8 is connected to the power supply terminal 32 to form an emitter follower circuit. An output terminal 34 is formed at the emitter of the transistor 28, and a feedback circuit is formed by interposing a resistor 36 between the output terminal 34 and the base of the transistor 18.

Further, the amplifier 4 is configured to control the output signal level based on the control input, and in this embodiment, the first and second differential amplifiers 40, 42,
A muting circuit 44 that adjusts the operating current of each differential amplifier 40, 42 based on an external control input to control the output signal level, and each differential amplifier 40, 4
Output buffer circuit 46 that combines and takes out the outputs of the two outputs.
It is composed of. That is, the differential amplifier 40,
42 is composed of a third transistor 48, a fourth transistor 50, a fifth transistor 52, a sixth transistor 54, transistors 56 and 58 as active loads, and a constant current source 60, and the muting circuit 44 is a 7 and 8 transistors 62 and 64. The base of transistor 48 is commonly connected to the base of transistor 16, and the bases of transistors 50 and 54 are commonly connected to feedback terminal 66. A constant DC bias is applied to this feedback terminal 66 from the DC bias power supply 10 via a resistor 68. Further, a bias input terminal 70 is formed at the base of the transistor 62, and a bias voltage Vb as a reference voltage is applied to this bias input terminal 70. Further, a control input terminal 72 is formed at the base of the transistor 64, and a muting control voltage Vc is applied to this control input terminal 72. The output of each differential amplifier 40, 42 is the transistor 50, 54, 5.
The output buffer circuit 46 is composed of a transistor 74 and a resistor 76 in order to combine and extract the outputs from the collectors of the 8 collectors. An output terminal 78 is formed at the emitter of the transistor 74, and an equalizer element 80 is inserted between the output terminal 78 and the feedback terminal 66.

The operation will be explained based on the above configuration. A constant DC bias is applied to each amplifier 2, 4 and the magnetic head 8 from a common DC bias power supply 10, and the reproduction signal of the magnetic head 8 is amplified by the amplifier 2, and its amplified output is taken out from the output terminal 34. .

On the other hand, the reproduced signal from the magnetic head 8 is transmitted to the amplifier 4.
The operating currents of the differential amplifiers 40 and 42 are controlled by the muting circuit 44, and its output signal level is adjusted based on the muting control voltage Vc applied to the control input terminal 72. That is, at the start of operation, the bias voltage Vb applied to the base of the transistor 62
When the muting control voltage Vc is set higher, the differential amplifier 40 side is suppressed, and the reproduction signal output of the magnetic head 8 is suppressed during the period when the control voltage Vc is high. When the control voltage Vc becomes lower than the voltage Vb, the differential amplifier 40 becomes operational, its output is applied to the base of the transistor 74, and the amplified output is taken out from the output terminal 78. This amplified output passes through a line amplifier and a power amplifier (not shown) to drive a speaker and the like. In this way, by providing the amplifier 4 with muting control and the amplifier 2 without muting control in the preamplifier that amplifies the reproduced signal from the magnetic head 8, the preamplifier can perform muting control depending on its purpose. Signals that do not require muting control, such as music selection control output, can be extracted from the amplifier 2 as is. Furthermore, by configuring the amplifiers 2 and 4 in this way, desired frequency characteristics can be given to each amplifier 2 and 4 by an equalizer element, etc.
Any frequency characteristics can be set. In particular, regarding the setting of amplification gain, each amplifier 2, 4
It can be set freely for each.

FIG. 2 shows another embodiment of the invention, in which the same parts as in the embodiment shown in FIG. 1 are given the same reference numerals. Although the above embodiments have been described with a single magnetic head, this embodiment shows a case where magnetic heads are individually installed for left and right channels, such as in stereo reproduction. That is, buffer circuits 82 and 84 are installed for each magnetic head 8R and 8L installed for each channel, and a reproduction signal is supplied to the amplifier 2. In this case, the buffer circuit 82 is composed of a transistor 86, a constant current source 88, and a resistor 90, and similarly, the buffer circuit 84 is composed of a transistor 86', a constant current source 88', and a resistor 90.
Consists of 0'. In this case, the bias input and output signals are fed back to the base of the transistor 18 of the amplifier 2 via a buffer circuit 92, and the buffer circuit 92 is composed of a transistor 94 and a constant current source 96. , a feedback terminal 98 is formed at the base of the transistor 94, a bias is applied to the feedback terminal 98 via the resistor 26, and an output signal is sent to the output terminal 3.
4 through a feedback resistor 36.

The amplifier 4 is connected to each magnetic head 8R,
Amplifiers 4R and 4L are installed for each magnetic head 8L to individually amplify the output of each magnetic head 8R and 8L, and the output is taken out from output terminals 78R and 78L.
With this configuration, even in a tape recorder that reproduces stereo signals, signal amplification with and without muting can be performed simultaneously.

Further, as shown in FIG. 2, a plurality of magnetic heads 8
R, 8L are installed, and if the signal without muting control is a composite signal of the reproduced signals from each magnetic head 8R, 8L, the signal composition is performed by buffer circuits 82, 84 consisting of emitter follower circuits.
Since the synthesized signal is sent to the amplifier 2, even if the number of channels increases, the amplifier 2
is fine as a single one. In other words, the amplification system in signal processing that does not involve muting control consists of a buffer circuit for the number of channels and an amplifier 2 common to each channel.
Since there is no need to install an amplifier 2 for each channel, the system is simplified.

As explained above, according to the present invention, first and second amplifiers are installed to which signals to be amplified are applied from a common signal source, and a DC bias voltage is applied to each amplifier from a common DC bias power source. Moreover, since the second amplifier takes out an output whose level is adjusted by an external control voltage, it is possible to output an output with level adjustment and an output without level adjustment separately, and the frequency characteristics of each output Amplification gain can be set arbitrarily, and
It is possible to simplify the configuration by applying bias using a common DC bias power supply to each amplifier, and it is possible to provide a composite amplifier that can take out a plurality of outputs with different characteristics from one input.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the composite amplifier of the invention, and FIG. 2 is a circuit diagram showing another embodiment of the composite amplifier of the invention. 2...first amplifier, 4, 4R, 4L...second
amplifier, 8... magnetic head (signal source), 10...
...DC bias power supply, 16...first transistor, 18...second transistor, 40...first
differential amplifier, 42... second differential amplifier, 44
...mutating circuit, 48...third transistor, 50...fourth transistor, 52...
Fifth transistor, 54...Sixth transistor, 56, 58...Transistor (active load),
60... Constant current source, 62... Seventh transistor, 64... Eighth transistor, 68... Resistor.

Claims (1)

[Claims] 1. A signal source that generates a signal to be amplified, a DC bias power supply that generates a DC bias voltage, and first and second transistors whose emitters are commonly connected, An input signal to be amplified from the signal source is applied to the base of the second transistor using the DC bias voltage as a reference potential, and the DC bias voltage is applied from the DC bias power supply to the base of the second transistor to amplify the input signal. an input signal to be amplified from the signal source, the base of the third transistor being connected to the base of the third transistor and the input signal to be amplified from the signal source in common with the first transistor; is added and the fourth
A first differential amplifier to which the DC bias voltage is applied from the DC bias power supply via a resistor is installed at the base of the transistor, and an active load common to the first differential amplifier is placed on the collector side. 5th and 6th with common preparation and emitters
The DC bias voltage is applied from the DC bias power supply to the base of the fifth transistor, and the DC bias voltage is applied from the DC bias power supply to the base of the sixth transistor via the resistor. second
a seventh transistor connected in series to the emitters of the third and fourth transistors of the first differential amplifier and having a constant voltage applied to its base; an eighth transistor connected in series to the emitters of the fifth and sixth transistors of the differential amplifier and having a control voltage applied to its base; a second amplifier that controls the operating current by connecting a constant current source to the first or second differential amplifier by making the seventh or eighth transistor conductive and extracting an amplified output of the level-adjusted input signal; A composite amplifier characterized by comprising: and.