Acoustic signal amplifier

Abstract

This circuit provides a way to lower the output impedance before negative feedback in an acoustic signal amplifier for accurately driving dynamic speakers. [Solution] The circuit uses a common collector configuration for the amplifier's output stage, inserting a resistor between its input and ground, either DC or AC. By setting the resistance value of this resistor to a value sufficiently smaller than the product of the speaker impedance and the output stage's current amplification factor, it becomes possible to voltage-drive the speaker without negative feedback.

Description

Technical Field

[0001] The present invention relates to an acoustic signal amplifier.

Background Art

[0002] An acoustic signal amplifier using transistors is widely used to drive a dynamic speaker as part of an acoustic device. However, its characteristic evaluation (measurement) has been continuously performed with a resistive load since the era of vacuum tube amplifiers. When actually conducting a listening comparison in combination with a speaker, in many cases, the sound quality of a triode was preferred to that of a pentode. However, after transistors became common, it has not been much of a topic.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Generally, an amplifier uses negative feedback. In a resistive load, the characteristics before negative feedback are greatly improved by negative feedback. Therefore, in an amplifier using transistors, due to a large amount of negative feedback, the characteristics with a resistive load have been improved to an excessive extent and it has been considered that no further improvement is necessary. However, a dynamic speaker has resonance characteristics, and it has come to be questioned whether a design considering the responsiveness to resonance, that is, the damping characteristics, is not necessary. As a solution to this, it was devised to improve a general power amplifier circuit in which an emitter-grounded amplifier and a constant current load are connected to a complementary collector-grounded circuit to make the output impedance before negative feedback lower than the impedance of the speaker. The problem to be solved is that, in order to increase the amount of negative feedback, the previous stage (amplification stage) uses a constant current load. Therefore, although it is collector-grounded, the output impedance (before negative feedback) has become relatively high.

Means for Solving the Problems

[0004] This invention involves inserting a resistor, either directly or via a capacitor, from the connection point between the preceding amplification stage and the constant current load. By setting this resistor value to be sufficiently lower than the speaker impedance multiplied by the hfe (emitter-ground current amplification factor) of the common-collector stage transistor, the speaker load can be driven at a constant voltage without negative feedback. In some cases, this constant current load can be a current mirror circuit. [Effects of the Invention]

[0005] This effectively suppresses the resonance of dynamic speakers, enabling faithful sound reproduction. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 Conventional circuit diagram (example) [Figure 2] Figure 2 Designed Circuit Diagram RZ< <ZL x

[0007] Figure 1 is a circuit diagram (conventional circuit diagram) of the output stage and its preceding stage of a conventional audio signal amplifier. Figure 2 is an improved circuit diagram that implements the present invention in the conventional diagram. Here, ZL is the (nominal) impedance of the speaker, and the resistor RZ added by the present invention is set to a value sufficiently lower than the value obtained by multiplying the current amplification factor of the final stage transistors Q4 and Q6 or Q5 and Q7 by ZL.

Claims

[Claim 1] An acoustic signal amplifier in which the load of the common-emitter amplification stage is a constant-current circuit or a current mirror circuit, and the output of the amplification stage is used to drive a dynamic speaker with a common-collector amplification stage, characterized in that a resistor with a value sufficiently smaller than the current amplification factor multiple of the common-collector stage transistor of the load speaker impedance is inserted between the base input of the common-collector stage and ground, or between it and AC ground via a capacitor. 。

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