JPH0349122B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an equalizer circuit used in a signal reproduction circuit of a tape recorder, a record player, etc., and particularly relates to an equalizer circuit that uses two equalizer elements in an open loop circuit and a closed loop circuit. By combining open-loop characteristics and closed-loop characteristics, and making it possible to select an amount of negative feedback that is almost constant with respect to frequency, dynamic distortion (transient intermodulation distortion) caused by negative feedback is prevented. Regarding the equalizer circuit.

<Prior art> Conventionally, as an equalizer circuit used for signal reproduction in record players, etc., as shown in Figure 1, a negative feedback circuit having an equalizer element 1 that obtains an RIAA curve according to the RIAA standard is connected in two stages. An NF type equalizer circuit connected to amplifiers 2 and 3 is known. (For example, see the chapter ``2.5 Equalizer Design'' in ``Audio Amplifier'' by Tsuyoshi Taira, published by Nikkan Kogyo Shimbun, October 1963.) However, in this type of negative feedback equalizer circuit, the second As shown in the figure, the bare gain characteristics of the amplifiers 2 and 3 (characteristics of only the amplifiers without the equalizer element 1 connected) are A-line-like characteristics that are uniformly attenuated as the frequency gets higher; By connecting equalizer element 1 to the line and applying negative feedback, it attenuates from around the midrange, like the B line.
I try to create a frequency response close to the RIAA curve.

<Problem to be solved by the invention> Therefore, in such an equalizer circuit,
The difference between the output levels of line A and line B in FIG. 2 is the amount of negative feedback, and this amount of negative feedback increases from the middle range to the high range. Therefore, by applying a large amount of negative feedback from the midrange to the high range, the phase difference that occurs between the signals in amplifiers 2 and 3 and the negative feedback signal generates signal sum and difference components, resulting in cross-modulation. This caused the problem of increasing transient cross-modulation distortion.

On the other hand, as another equalizer circuit, a CR type equalizer circuit is known in which a CR type equalizer element 5 is connected to the output side of an amplifier 4, as shown in FIG.

However, since this equalizer circuit does not apply negative feedback, it does not cause the above-mentioned transient cross-modulation distortion, but it has the drawback that it cannot extract a large output signal.

Focusing on the above points, this invention reduces distortion during signal amplification by applying negative feedback, and also allows the amount of negative feedback to be arbitrarily selected, thereby providing uniform negative feedback in the effective frequency band. An object of the present invention is to provide an equalizer circuit that can prevent the occurrence of transient cross-modulation distortion caused by applying excessive negative feedback.

<Means for Solving the Problem> In order to achieve this object, the equalizer circuit of the present invention includes a first equalizer circuit on the output side of a constant current drive type amplifier.
A buffer amplifier is connected through the equalizer element, and a negative feedback circuit in which a second equalizer element is connected in series is connected between the output side of the buffer amplifier and the negative input side of the amplifier. The two equalizer elements are configured to have almost the same time constant.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 4 shows a block diagram of an equalizer circuit compliant with the RIAA standard for record players.

6 is a constant current drive type amplifier, and a CR type first equalizer element 7 is connected to the output side of this amplifier 6. This first equalizer element 7 is a known
This is a CR equalizer element, which consists of two CR circuits connected in series, each consisting of a capacitor and a resistor connected in parallel. (For example, "Audio Amplifier" by Tsuyoshi Taira,
(See chapter 2.5 Equalizer Design, published by Nikkan Kogyo Shimbun, October 1963) CR elements like this are divided into low, mid, and high ranges based on the combination of a capacitor and a resistor, that is, C and R. By connecting C and R in series or in parallel, three time constants can be set in the low, middle, and high ranges.

Further, a buffer amplifier 8 is connected to the output side of the first equalizer element 7 for converting output impedance.

Further, a negative feedback circuit 10 having an NF type second equalizer element 9 connected in series is connected to the output side of the buffer amplifier 8 and the negative input side of the amplifier 6. This second
The equalizer element 7 is composed of two CR circuits connected in series, each consisting of a capacitor and a resistor connected in parallel.
C and R are selected so that the time constant of the first equalizer element 7 and the time constant of the second equalizer element 9 are almost the same.

In the equalizer circuit having the above configuration, the input signal input to the amplifier 6 provides an output voltage corresponding to the load impedance of the first equalizer element 7 because the amplifier 6 is a constant current drive type amplifier.
Then, this output is passed through the first equalizer element 7 and subjected to the high-frequency attenuation effect with three time constants of this element 7, and is divided into three frequency positions as shown by line C in FIG. The slope changes with
An output signal with frequency characteristics having a curve close to the slope of the RIAA curve can be obtained. Furthermore, the buffer amplifier 8 converts the high impedance output to low impedance.

On the other hand, a part of the output of the buffer amplifier 8 is fed back to the negative input side of the amplifier 6 by the negative feedback circuit 10, and an NF type second
The equalizer element 9 applies negative feedback by the amount of negative feedback shown in FIG.

That is, the second equalizer element 9 of the negative feedback circuit 10
is composed of a resistor and a capacitor so that its time constant is almost the same as the time constant (three time constants approximating the RIAA curve) of the first equalizer element 7 connected to the output side of the amplifier 6. There is.

Therefore, the second equalizer element 9 operates to have an attenuation characteristic similar to the RIAA curve in the effective frequency band of the first equalizer element 7, and as shown by line D shown in FIG. An output having frequency characteristics is output from the equalizer circuit.

In this way, the amount of negative feedback applied by the second equalizer element 9 can be made almost constant in the effective frequency band, as shown in FIG. 5, and sufficient negative feedback can be applied to obtain the desired output. Even if this is applied, transient negative feedback will not be applied in a certain frequency range as in the conventional case, and it is possible to prevent the occurrence of transient cross-modulation distortion.

In the above embodiment, an equalizer circuit that complies with the RIAA standard for record players has been described, but the equalizer circuit with characteristics that comply with the NAB standard for playback frequency compensation of tape recorders and other standards such as DIN and JIS can also be described. It is also possible to configure it based on the basic idea of.

<Effects of the Invention> As explained above, according to the equalizer child circuit of the present invention, the buffer amplifier is connected to the output side of the constant current drive type amplifier via the first equalizer element, and the output side of the buffer amplifier and the amplifier are connected to each other via the first equalizer element. A negative feedback circuit with a second equalizer element connected in series is connected between the negative input side and the time constant of the first equalizer element and the time constant of the second equalizer element are made almost the same. , it is possible to operate with sufficient negative feedback, and it is also possible to obtain an even amount of negative feedback over almost the entire effective frequency band. It is possible to prevent the generation of transient cross modulation distortion without creating a negative feedback amount.

[Brief explanation of drawings]

1 and 3 are block diagrams of conventional equalizer circuits, FIG. 2 is a graph showing the frequency characteristics of the output of the circuit of FIG. 1, and FIG. 4 is a block diagram of an equalizer circuit showing an embodiment of the present invention. 5 are graphs showing the frequency characteristics of the output of the circuit. 6...Amplifier, 7...First equalizer element, 8
... Buffer amplifier, 9 ... Second equalizer element, 10 ... Negative feedback circuit.

Claims (1)

[Claims] 1 A buffer amplifier is connected to the output side of a constant current drive type amplifier via a first equalizer element, and a second equalizer element is connected in series between the output side of the buffer amplifier and the negative input side of the amplifier. An equalizer circuit, characterized in that a feedback circuit is connected, and the time constant of the first equalizer element and the time constant of the second equalizer element are made substantially the same.