JPS606899Y2 - equalizer circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an equalizer circuit, and particularly to a recording equalizer circuit for a tape recorder.

In order to make the most of the characteristics of the head and tape, optimal recording compensation, optimal bias, and optimal playback compensation are required.

In particular, a recording equalizer circuit is used to optimally adjust the amount of recording compensation according to the frequency characteristics of each head and the characteristics of each tape. It is common to avoid current feedback circuits using passive elements such as R.

In such an equalizer circuit, if C, R, etc. are varied in order to perform optimal compensation, both the resonant frequency fo and the selectivity Q will change at the same time. It is impossible to compensate for only the high frequency range (fo).

Therefore, in order to flatten the overall frequency characteristic, it is necessary to rely on methods of adjusting reproduction equalizers, biases, etc., which should not be adjusted in the first place.

However, this method has the disadvantage that it adversely affects sound quality, distortion rate, etc., and as a result, the original characteristics of the head and tape cannot be fully utilized.

Furthermore, since the coil L is used, the volume occupied by the circuit increases, and in order to match the characteristics of various commercially available tapes, multiple coils, volumes, and resistors are provided using switches, and the configuration requires switching between them. There is also the disadvantage that a plurality of large coils must be used, and the circuit footprint described above increases significantly.

The purpose of the present invention is to provide a recording equalizer circuit that can compensate for the midrange and high range independently, has a simple circuit configuration, and occupies a small volume.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, which is a recording equalizer circuit using a so-called active filter circuit consisting of an operational amplifier OP1 and a resistive element and a capacitive element.

The input signal IN is applied to one input terminal of the operational amplifier op via the capacitor C1 and the input resistor group R□.

The input resistance group R1 includes a fixed resistance R1-2 and a variable resistor VR1 connected in series with respect to the input signal, and further includes fixed resistances R1-□, R1 that can be connected in parallel with the variable resistance VR1.
-2. Contains R1-3.

One of the resistors R, . . . , R, 2 and R1-3 is selected by the switch S and connected in parallel with the variable resistor VR1.

The output terminal of the operational amplifier op is connected to 1 through the feedback resistor group R2.
The feedback resistor group R1 is connected to the input terminal, and includes fixed resistors R2-4 connected in series with each other and fixed resistors R, .

2, including R.

One of the resistors R2HR221 and R2-3 is selected by the switch S2 and connected in parallel with the variable resistor VR2.

The output terminal of the operational amplifier OP is also connected to the output terminal OUT via a resistor R4 and also to the other input terminal of the operational amplifier OP.

A capacitor C2 and a resistor group R3 are connected between the output terminal -0LJT and ground.

The resistance group R3 includes fixed resistances R3-1 connected in series with each other.
and a variable resistor R3, and further includes fixed resistors R3t and R3-29R33 that can be connected in parallel with the variable resistor VR3.

Resistor R3-□? R3-2 and R3-3 are switch S3
The configuration is such that one is selected and connected in parallel with the variable resistor VR3.

In such a configuration, assuming that C1=C2=C and R=R2=1/R for the sake of simplicity, the gain G in FIG. 1 can be obtained as shown in the following equation.

S = jω, ω210 = 1/C2・R2 and = R
2/R4.

Therefore ω. =2rrf, the gain Gv at Gv=/
(2-k), and the selectivity Q is Q=1/ (2
−k).

Therefore, Q is determined by k, that is, resistors R2 and R1, and ω.

That is, the resonant frequency f. It can be seen that is determined by C and R.

In other words, in the equalizer circuit in Figure 1,
The selectivity Q is determined by the resistance A2t R4, and the resonant frequency f
.

can be independently varied by the resistors R1 and R3.

Therefore, as shown in the figure, the variable resistor VR2 of the feedback resistor group R2 is used to vary the selectivity Q, and the resonant frequency f.

In order to vary the input resistor group R□ and the resistor group R3, variable resistors VR1 and VH2 are used, respectively.

FIG. 2 shows Q and j in the equalizer circuit of FIG.
.

The solid line shows the standard characteristic, the dashed line shows the characteristic when VH2 is varied, and the dotted line shows the characteristic when VRl and VH2 are varied. are shown respectively.

Furthermore, by using the switches S□ to S3 to switch the fixed resistances according to the tape type, it is possible to perform optimal equalizer adjustment.

Further, an appropriate buffer amplifier (not shown) can be further provided at the output OUT as necessary.

FIG. 3 shows another embodiment of the present invention, in which the input signal IN is applied to one of the operational amplifiers OP via an input resistor R5.

The output OUT of the amplifier OP is a variable resistor R2 which is a feedback resistor.
It is applied to one person's power through a circuit, and is fed back to other inputs through a series connection circuit of a capacitor C1 and a variable resistor R.

A capacitor C2 and a variable resistor R3 are connected in parallel between the input and ground.

Even in such a configuration, R1: R3-1 is used for simplicity.
/R9C1=C2=C, then ω210=1/C2R
2, Q=1/(2-R2/R5), and therefore the resonant frequency f.

can be adjusted independently by R1 and R3, and the selectivity Q can be adjusted independently by R2 and R5.

Therefore, as shown in FIG. 3, the resistance R2 is made variable to obtain Q, and the resistances R1 and R3 are made variable to obtain f.

are adjusted respectively.

Furthermore, as shown in FIG. 1, it is of course possible to provide a tape selector switch for switching depending on the type of tape so that fixed resistors connected in parallel to these variable resistors can be selectively switched.

As described in detail above, according to the recording equalizer circuit of the present invention, the bandpass active filter using an operational amplifier is
, and Q are configured to be adjusted individually by varying the impedance value, for example, the resistance value of the passive element, so the high and mid ranges in the recording equalizer circuit can be adjusted independently, which was previously considered difficult. This allows good recording compensation to be achieved.

Furthermore, there is no need to use a large coil and the I
Since a C (integrated circuit) operational amplifier can be used, the circuit can be made smaller and lower in price.

In addition, since the variable impedance element can be a semi-fixed VR, adjustment is easy, and there are also advantages such as the VR can be attached to the front panel of the device and can be adjusted freely by the user. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram of another embodiment of the present invention. Explanation of symbols of main parts, OP... operational amplifier,
R...Resistance, VR...Variable resistance, C...
...Capacitor.

Claims (2)

[Scope of utility model registration request] (1) An equalizer circuit for a tape recorder, comprising an operational amplifier and first and second feedback circuits respectively provided between the output of the operational amplifier and a pair of inputs of the operational amplifier, A passive element that determines the feedback amount of the first feedback circuit is made variable to control frequency selectivity, and a passive element that determines the feedback amount of at least the second feedback circuit is made variable to freely control the resonance frequency. Features an equalizer circuit. (2) The equalizer circuit according to claim 1, wherein the passive element is a variable resistor.