JPH0323705A - Equalizer amplifier circuit - Google Patents

Abstract

PURPOSE:To omit an electrolytic capacitor for coupling for cutting a DC voltage required for an input terminal and to prevent malfunction due to a defective electrolytic capacitor occurring by changing the input terminal to the one of GND reference input type. CONSTITUTION:In circuit configuration for an amplifier circuit A1, the input terminal A is changed to the one of GND reference input type, and the electrolytic capacitor for coupling for cutting the DC voltage required for the terminal A in a conventional circuit can be omitted. Therefore, an input circuit formed with of a seventh transistor Q7, a diode D1, and a constant current I4 performs the shiftup of the DC voltage for a normal sound signal inputted to the terminal A with a diode D7 via the emitter-follower operation of the Q7, and transmits a signal to the Q1 of the transistors Q1 and Q2 comprising a differential pair, and also, the base bias voltages of the Q1 and Q2 can be decided with the Q7 and the D1. In such a way, it is possible to prevent the malfunction due to the defect of the electrolytic capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video table recorder, and particularly to an equalizer amplification circuit used for normal audio reproduction processing.

[Conventional technology]

Conventionally, an equalizer amplifier circuit used for recording and reproducing normal audio of a video table recorder (hereinafter abbreviated as VTR) has an amplifier circuit A2 and a fourth amplifier circuit connected to the amplifier circuit input terminal A, as shown in FIG. Resistor R4, 12 capacitor C
2. Fourth capacitor C4, first, second, and third resistors R1, R2, and R3 connected between amplifier circuit input terminal B and amplifier circuit output terminal C, and first and third capacitors c1
, C3. To explain the operation, V
A normal audio signal magnetically recorded on a tape by a certain tank circuit from the TR's normal audio head and 02 is converted into an electrical signal and input to terminal A. here,
R4 is a damping resistor for the evening circuit, and c4
is a coupling electrolytic capacitor for cutting the DC potential of terminal A. The normal audio signal input to terminal A is transmitted to Rl, R2, R3 and C between terminals B and C of the amplifier circuit.
1, is amplified along the frequency characteristics, is output from terminal C, is input to a line amplification circuit, and is output from line out. Here, 03 is an electrolytic capacitor for cutting the DC potential of terminals B and C.

Next, the specific circuit structure and operation of the amplifier circuit A2 will be explained with reference to FIG. In FIG. 4, the normal audio signal input to terminal A is transmitted through the first and second transistor pair θ1, θ2, the third and fourth transistors θ3, θ4, and the tenth and eleventh resistors RI O, Rl 1 and constant current source,
It is amplified by a differential amplification circuit with a higher precision. Here, b is a stabilized constant voltage terminal, which is used to determine the base bias potential of the differential pair of θ1 and θ2. Also, the 12th
0° resistor R12 is a bias resistor. The normal audio signal is further amplified by a fifth transistor θ5 whose emitter terminal is connected to the power supply a and a common emitter amplifier circuit whose emitter is connected to the constant current source 2. It is output to output terminal C via the circuit. Here, CO is a capacitor for stopping oscillation in the amplifier circuit.

In the equalizer circuit used for the normal audio reproduction processing of the conventional VTR described above, due to the circuit structure of the amplifier circuit, a coupling electrolytic capacitor C4 for cutting DC potential is always required at the input terminal. If the electrolytic capacitor has defective leakage current characteristics, it has the disadvantage of malfunctioning. Furthermore, the use of electrolytic capacitors increases the cost of forming the equalizer amplifier circuit.

[Means to solve the problem]

The equalizer amplifier circuit used for normal audio reproduction processing of the VTR of the present invention includes an amplifier circuit including a GND reference input terminal, and first and second resistors connected in series between the output terminal and the feedback terminal of the amplifier circuit. and a first capacitor connected in parallel to the second resistor, a third resistor connected in series between the feedback terminal of the amplifier circuit and ground, and a third resistor connected in series between the third capacitor and the input terminal of the amplifier circuit and ground. and a fourth resistor and a second capacitor.

In this way, the coupling electrolytic capacitor can be omitted, and malfunctions due to defects in the electrolytic capacitor can be prevented.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, and parts equivalent to those in FIG. 3 showing a conventional example are designated by the same reference numerals. In the figure, the input terminal A in the circuit configuration of the amplifier circuit A1 is changed to a GND reference input type, thereby eliminating the need for the coupling electrolytic capacitor C4 for DC voltage cut, which was conventionally required at the terminal A. The other structural parts are the same as those in FIG. 3 and will be omitted.

The details of the changes to the amplifier circuit AI will be specifically explained with reference to FIG. Portions equivalent to those in FIG. 4, which shows a conventional example of an amplifier circuit, are designated by the same reference numerals. In the figure, a seventh transistor θ7 whose base terminal is connected to input terminal A and a diode D
1 and a constant current I4, the normal audio signal input to the terminal A is the normal audio signal θ7, and the input circuit shifts up the DC voltage at the diode D7 through the emitter follower operation of the transistor θ1 forming a differential pair. , θ2 to the base of θl, and the base bias voltages of θ1 and θ2 are determined by θ7 and D1. The other circuit configurations are the same as those shown in FIG. 4 and will be omitted.

〔Effect of the invention〕

As explained above, the present invention provides a G
By changing to the ND reference input type, the coupling electrolytic capacitor for DC voltage cut required at the input terminal can be omitted, which has the effect of eliminating malfunctions due to defects in the electrolytic capacitor. Furthermore, by omitting the electrolytic capacitor, it is possible to prevent an increase in cost for forming the equalizer amplifier circuit.

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the present invention, FIG. 2 is a specific example of the amplifier circuit A1 in FIG. 1, FIG. 3 is a conventional example, and FIG. 4 is a specific example of the amplifier circuit A2 in FIG. 3. It is a diagram. θ1, θ2, θ3, θ4jθ5, θ6, θ7...
・Transistor, DI...Diode, Il+
I2+Is, I4... Constant current source, Cl,
C2, C3, C4, Co... Capacitor, Rl
, R2, R3, R4, Rl O, Rl 1...
Resistor, a... Power supply, b... Stabilized constant voltage terminal, A... Input terminal of amplifier circuit, B
...Feedback terminal of the amplifier circuit, C...Output terminal of the amplifier circuit, Al, A2...Amplifier circuit.

Claims (1)

[Claims] an input terminal, a feedback terminal, an output terminal, first and second resistors connected in series between the output terminal and the feedback terminal 2, a first capacitor connected in parallel to the second resistor, and the feedback terminal. and a third resistor and a third capacitor connected in series between the input terminal and the ground, and a fourth resistor and a second capacitor connected in parallel between the input terminal and the ground. circuit.