JPH0212740Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to improvements in equalizer amplifiers.

Conventionally, an equalizer amplifier for reproducing LP records and SP records generally has a configuration as shown in FIG.

In other words, it is a negative feedback type in which the non-inverting input of differential amplifier 1 is used as the signal input terminal, the inverting input is grounded via resistor _R1 , and the amplified output is fed back to the inverting input via feedback resistor _R2 . In the amplifier circuit, the output of amplifier 1 is connected to the first one for playing LP records.
The impedance circuit 2 and the second impedance circuit 3 for reproducing SP records are connected, and one of the two circuits is switched by a switch 4 and connected to the inverting input of the amplifier 1.
This configuration provides LP record playback characteristics (RIAA characteristics are generally used; hereinafter referred to as RIAA characteristics) and SP record playback characteristics (hereinafter referred to as SP characteristics).

However, since such an equalizer amplifier has a configuration in which the first and second impedance circuits in the negative feedback loop are switched, a large click noise is generated depending on the switching timing of the switch 4.

The present invention improves on these conventional drawbacks, and will be explained below with reference to the drawings. In the figure, parts equivalent to those in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted.

In FIG. 2, a _third impedance circuit 6 consisting of a resistor R ₇ and a capacitor C ₄ connected in series in parallel with the resistor R 1 is connected, and the other end of the third impedance circuit 6 is connected to a switch with one circuit and two contacts. The fixed contact 5c is connected to one movable contact 5a of the switch 5, and the fixed contact 5c is connected to the SP characteristic, and the other movable contact 5b is connected to the SP characteristic.
The configuration corresponds to each of the RIAA characteristics.

This will be explained in more detail below.

(1) Switch switch 5 to movable contact 5b side.
When set to RIAA position, the gain A _R of the equalizer amplifier is A _R = Z ₁ + R ₁ / R ₁ = T _O (1 + jf / f ₂ ) (1 + jf / f ₄ ) / (1 + jf / f ₁
)(1+jf/f ₄ )...(1) where Z ₁ : Combined impedance of the first impedance circuit and resistor R ₂ T _O : DC gain ₁ to ₄ : Cutoff frequency.

Solving equation (1) for Z ₁ gives Z ₁ = R ₁ {T _O (1+jf/f ₂ )(1+jf/f ₄ )
−(1+jf/f ₁ )(1+jf/f ₂ )/(1+jf/f ₁ )(1
+jf/f ₃ )}...(2). Then, by setting the cutoff frequencies ₁ to ₄ in advance and determining R ₂ , R ₃ , C ₁ , and C ₂ using a well-known method so that Z ₁ satisfies equation (1), the solid line in Figure 3 is obtained. The RIAA characteristics shown in a can be realized.

(2) Switch switch 5 to movable contact 5a side and SP
When the gain _{A S of} the equalizer amplifier is set to _{the 3rd} impedance circuit and _the resistance
It becomes the composite impedance of R ₁ .

Here, it is assumed that Z ₂ having the following impedance characteristics is used to realize the SP characteristics.

Z ₂ = R ₁ (1+jf/fy)/(1+jf/fx) (y>x
)...(4) However, y and x are cutoff frequencies set to realize SP characteristics.

Substituting Z ₁ and Z ₂ from equations (2) and (4) into equation (3), A _S = {(1+jf/f ₁ )(1+jf/f ₃ )(jf/fy−jf/
fx) +T _O (1+jf/f ₂ ) (1+jf/f ₄ ) (1+jf/fx)
} /(1+jf/f ₁ )(1+jf/f ₃ )(1+jf/fy) =T _O (1+jf/f ₂ )/(1+jf/f ₁ )・G()...
(5) Here, G() is a function that represents the frequency characteristic of the error from the SP characteristic (frequency characteristic), and in direct current it is 1
becomes.

If the impedance Z 2 is determined so that Z ₂ = R ₁ (1+jf/f ₅ )/(1+jf/f ₃ ) in equation ( ₅₎ , G() will be minimized (approaching 1), Third
As shown by the dotted line b in the figure, SP characteristics can be approximately realized.

In this case, the SP characteristics differ from the ideal in the frequency range higher than the cutoff frequency ₅ , but in actual SP records, it is better to cut out the high frequencies from the viewpoint of noise, so setting ₅ to 8 to 20 KHz is practically acceptable. do not have.

In this example, Z ₂ = R ₁ (1+j2πC ₄ R ₇ )/1+j2πC ₄ (R ₁ +R ₇ ), so C ₄ = ₅ − ₃ /2πR _{1 3 5} R ₇ = ₃ / ₅ − ₃ R ₁ You can decide as follows.

FIG. 4 shows another embodiment of the present invention, in which the resistor R ₁ in FIG. 2 is divided by resistors R ₅ and R ₆ , and this dividing point is connected to the first movable contact 7a of the switch 7. Connect directly to the second movable contact 7b via the capacitor _C5 , and ground the fixed contact 7d to connect the first, second, and third movable contacts 7a, 7b, and 7c.
The configuration is compatible with the RIAA position (compatible with moving coil type pickups), SP position, and RIAA position (compatible with moving magnet type pickups).

In this embodiment, in the RIAA position compatible with a moving coil type pickup, the amount of feedback is reduced by shorting the resistor _R5 , and the overall gain is increased. Regarding the SP characteristic, the embodiment shown in Fig. 2 Each constant can be determined using a method similar to .

As described above, in the present invention, the non-inverting input of the differential amplifier is used as the signal input terminal, the inverting input is grounded via the resistor, and the amplified output is connected to the feedback resistor and the first terminal for playing LP records. In a negative feedback equalizer amplifier that feeds back to the inverting input via an impedance circuit, a third impedance circuit is connected in parallel with the resistor via a switch to obtain characteristics for playing SP records. Since the impedance on the ground side is changed, click noise that occurs when switching the switch can be prevented, and the third impedance circuit can also be configured with one capacitor or one capacitor and one resistor. Has excellent advantages.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a conventional equalizer amplifier, Fig. 2 is a diagram showing the configuration of the equalizer amplifier of the present invention, Fig. 3 is a frequency characteristic diagram, and Fig. 4 is a diagram showing the same but another embodiment. FIG. 1 is a differential amplifier, 2 and 6 are impedance circuits, and 5 is a switch.

Claims (1)

[Claims for Utility Model Registration] 1. The non-inverting input of the differential amplifier 1 is used as a signal input terminal, the inverting input of the differential amplifier 1 is grounded via a resistor R1, and the differential amplifier 1 The output is connected to a feedback resistor R2 and a first impedance circuit 2 having LP record playback characteristics.
In the negative feedback equalizer amplifier connected to the inverting input of the differential amplifier 1 through a parallel circuit with the resistor R1, a third impedance circuit 6 having SP record reproduction characteristics is connected in parallel with the resistor R1.
An equalizer amplifier characterized in that: is connected via a switch 5. 2. The above resistor R1 is divided into resistors R5 and R6, and a third impedance circuit 6 having SP record playback characteristics is connected via a switch 7 in parallel with one of the resistors R5 and R6. An equalizer amplifier according to claim 1 of the utility model registration claim characterized by: