JPH0136346Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial field to which the invention pertains) This invention relates to an expansion circuit for an audio amplifier.

(Prior art) As shown in Fig. 5, the conventional expansion circuit uses a bridge T-type RC filter circuit in the feedback circuit β ₂ of the feedback circuit tuning method selection amplifier, and keeps the tuning frequency _p of the filter circuit constant. was variable manually.

(Purpose of the invention) This invention is an audio amplifier that can be used in an audio amplifier to create a kind of audible sense of presence that has not existed before by developing the conventional expansion circuit described above. The purpose is to provide an expansion circuit for an amplifier.

(Structure, operation, and effect of the invention) As explained in the block diagram of FIG. 1, the audio amplifier expansion circuit of this invention consists of a bridge T-type RC filter circuit 2 using a voltage-controlled variable capacitance circuit 3 as a bridge capacitance element. is used in the feedback circuit β ₁ of the feedback circuit tuning method selection amplifier 1 to detect low frequency components of the input signal e _i , for example, frequency components of about 1 KHz or less,
This configuration is characterized in that it is controlled by a rectified DC voltage _ed .

The DC voltage e _d is determined by a voltage doubler rectifier circuit R including a buffer amplifier A ₂ , a bandpass filter/amplifier A ₃ in the frequency band of 10Hz to 1KHz, and diodes D ₁ and D ₂ as shown in the embodiment in FIG. , is obtained as the output voltage of the control voltage generating circuit 4 consisting of a time constant circuit T including a resistor R ₃ and a capacitor C ₃ , and is inputted to the control terminal C of the feedback circuit β ₁ . This DC voltage e _d is
This voltage is similar to the envelope of a signal with a frequency band of 10Hz to 1KHz, and is proportional to the amplitude of the low frequency component signal.

In the case where _the feedback _{circuit β1} is _{the embodiment} shown _{in FIG .} = _R2
=R, C ₁ =C, then a _p =1+C/2C _x ...(1) Therefore, there is a relationship between the tuning frequency _p and the amplification degree a _p of the amplifier A ₁ at this time as follows: a _p =1+(√2πCR _p ) ² ...(3).

Equation (3) shows that as the resonant frequency _p increases, the amplification degree a _p also increases, and conversely, as the resonant frequency _p decreases, the amplification degree a _p approaches 1.

When the audio amplifier expansion circuit of this invention is used in a two-channel stereo amplifier and incorporated into a stereo device as shown in FIG. 3, the following effects are produced. As the low frequency component signal level of the music signal gradually increases, the DC voltage e _d gradually increases, and the tuning frequency of the feedback circuit tuning method selection amplifiers 1 and 1' controlled by this DC voltage e _d
p , ′ _p , and the amplification degrees a _p , a′ _p at the tuning frequencies _p , ′ _p gradually increase. Conversely, as the signal level of the low frequency component gradually decreases, the DC voltage e _d gradually decreases, and along with this, the tuning frequencies _p , ′ _p and the amplification degrees a _p , a′ _p gradually decrease. When listening to reproduced sound in such a state, the listener will experience not only the stereo effect of the conventional two-channel stereo system, but also a certain kind of feeling as if the sound is approaching from a distance, or as if it is receding from the distance. You can feel the realism of the sound, and the powerful dynamic effect that seems to be approaching the bass reproduction.

[Brief explanation of the drawing]

Figure 1 is a block diagram explaining this idea, Figure 2
The figure is a circuit block diagram showing an embodiment of this invention, Fig. 3 is a circuit block diagram showing another embodiment, Fig. 4 is a characteristic diagram of the embodiment, and Fig. 5 is a circuit block diagram showing a conventional example. be. A ₁ , A ₂ ... Both amplifiers, A ₃ ... Band pass filter and amplifier, R ... Rectifier circuit, T ... Time constant circuit, β ₁ , β ₂ ... Both feedback circuit, 1 ... Feedback Circuit tuning method selection amplifier, 2...Voltage controlled variable capacitance circuit.

Claims (1)

[Scope of utility model registration request] A bridge T-type RC filter circuit using a voltage-controlled variable capacitance circuit as a bridge capacitance element was used in the feedback circuit of a feedback circuit tuning method selective amplifier, and the low frequency component of the input signal was controlled by a rectified DC voltage. An audio amplifier expansion circuit characterized by the following.