JPS6329290Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the distortion factor of an amplifier having a load such as a speaker.

It has been known that when an electroacoustic transducer such as a speaker is driven by an amplifier, distortion occurs at the output end of the amplifier due to back electromotive force of the speaker. For this reason, by applying negative feedback,
Distortion at the output end of the amplifier is removed, but when driving a load such as a speaker that is located far from the amplifier, a long cord is used to connect it. For this reason, even if the distortion at the output end of the amplifier is improved, the distortion at the load end to which a speaker or the like is actually connected is not so improved.

For this reason, in the past, the voltage at the speaker input terminal was made to correspond to the amplifier input voltage by detecting the voltage drop occurring in the speaker cord and feeding back this voltage negatively to the input side of the amplifier. However, in this case, in order to detect the voltage generated in the speaker cord, a detection cord must be connected between the speaker input terminal and the amplifier, which has the disadvantage that the wiring of such cords becomes complicated. had.

In order to eliminate such drawbacks, an amplifier as shown in FIG. 1 has been considered. In the figure, amplifier 2
The first input terminal of is connected to input terminal 1, the output is connected to output terminal 5 via resistor 4 for detecting load current, and is also connected to the non-inverting input terminal of differential amplifier 3. The inverting input terminal of the amplifier 3 is connected to the output terminal 5, and the second input terminal of the amplifier 2 is connected to the output terminal of the differential amplifier 3. Output terminal 5 and ground terminal 6 are connected to input terminals 7 and 8 of speaker 11 via speaker cords 9 and 10, respectively.
connected to.

In the above configuration, it is assumed that the voltages applied to the first and second input terminals are added and amplified in the amplifier 2, and that the voltage applied to the input terminal 1 is ei, the gain of the amplifier 2 is A, and the difference is The gain of the dynamic amplifier 3 is α, the resistance value of the resistor 4 is γ, the load current is Io, the impedance of the speaker cords 9 and 10 is Z ₁ and Z ₂ , the impedance of the speaker 11 is Z _L , the output terminal 5 and the ground point 6 When _{e 0 is the voltage generated between 2} + Z _L ) I ₀ …(2) I ₀ =e _L /Z _L …(3) Calculating e _L using equations (1)(2)(3), e _L =ei・Z _L・A/Z ₁ +Z ₂ +Z _L +γ−α・γ・A …(4) Here, if Z ₁ +Z ₂ =γ(αA−1) …(5) then e _L becomes e _L =ei・A …(6) A voltage accurately proportional to the input signal ei is applied to the speaker 11 without being affected by the impedance of the speaker 11. Therefore, the amplification degrees of amplifier 2 and differential amplifier 3 are adjusted so as to satisfy equation (5).
You can adjust the resistance value of resistor 4 and resistor 4, but in actual adjustment, adjust the amplification level and value of each amplifier to minimize distortion at the speaker input terminal with the speaker connected according to the speaker cord used All you have to do is adjust the resistance value of the load current detection resistor.

The present invention aims to improve the distortion factor of a push-pull amplifier based on the above-mentioned principle, and will be described in detail below with reference to embodiments. FIG. 2 shows an embodiment of the present invention. In the figure, the same parts as in FIG.
through NPN and PNP transistors 13 and 1
4 and connected to the bases of transistors 13 and 1
The collector of 4 is connected to the power supplies +B and -B, and the emitter is connected to the output terminal 5 via resistors 15 and 16, and also to the non-inverting input terminal 21 of the differential amplifier 3 via resistors 17 and 18. be done. Since other parts are the same as those in FIG. 1, detailed explanation will be omitted.

In the above configuration, the voltage generated at the non-inverting input terminal 21 is the average value of both emitter voltages of the transistors 13 and 14, and corresponds to the output voltage of the amplifier 2 in the principle diagram of FIG. Further, since the resistors 15 and 16 correspond to the load current detecting resistor 4 in the embodiment of FIG. 1, the influence of the speaker 11 can be eliminated in the same manner as in the case of FIG.

Note that using a variable resistor as a resistor for detecting load current is very convenient in cases where the speaker cord is replaced.

Further, in the above description, the case where the load is a speaker has been explained, but the present invention is not limited to this, and is useful for use in general electroacoustic transducers that convert electrical output into acoustic output.

As described above, according to the present invention, it is possible to reduce distortion caused by load fluctuations in a push-pull amplifier with an extremely simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the principle of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 2 is an amplifier, 3 is a differential amplifier, 4 is a resistor,
9 and 10 are speaker cords, and 11 is a speaker.

Claims (1)

[Scope of utility model registration request] push-pull connected first and second transistors of mutually different conductivity types, each having an emitter resistor commonly connected to a load end; a pre-stage amplifier that applies a common signal to the bases of the first and second transistors; The emitter of the first transistor and the second
differentially amplify the output voltage at the connection point between the first and second resistors and the output voltage at the load end. and means for providing negative feedback to the preamplifier.