JPS5915311A - Sound reproducer - Google Patents

Abstract

PURPOSE:To obtain a negative feedback circuit having high accuracy and high stability, by providing a means which feeds back negatively only the distortion component that is generated by an output system including a speaker. CONSTITUTION:An input signal Vi supplied from a terminal 5 is amplified by a preamplifier 6 and supplied to a speaker 2 after receiving power amplification through a power amplifier 1. The driving current supplied to the speaker 2 is picked up by a microresistance 10 and supplied to a filter circuit 11 which has the characteristics opposite to the frequency characteristics of the speaker 2. The feedback signal V4 which is converted into flat frequency characteristics by the circuit 11 is supplied to the terminal at one side of an operational amplifier 14, and a signal V1 is supplied to the other terminal of the amplifier 14. Therefore V4proportional V1+beta is satisfied with the distortion beta generated by the amplifier 1 and the speaker 2. As a result, V5=V1-V1-beta is satisfied for the output V5 of the amplifier 14. Thus a signal V1 to be negatively fed back has only the distortion component beta.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sound reproduction device that is stable and extremely effective in preventing the failure of the entire sound reproduction system including speakers.

2. Description of the Related Art Conventionally, as a sound reproduction device that improves the overall design of a sound reproduction system including a speaker, for example, the one shown in FIG. 1 is known. The sound reproduction device shown in this figure is located at l11!
(By multiplying M F B, the human signal V1 is jt1
The speed component of the output of the speaker 2 is detected by the detection voice coil 3, and this detection signal is sent to the input side of the amplifier 10 via the feedback control circuit 4. This is designed to provide negative feedback.

However, the sound /Ii%1. shown in FIG.
In order to completely eliminate distortion, the reproducing device requires that the amplifier 1 has an open-loop gain as large as possible, and all detected signals containing distortion components must be negatively fed back. Since this is a system that uses multiple negative feedback, there is a problem that the amplification operation becomes unstable due to phase lag etc. (that is, it is likely to cause oscillation phenomena, etc.).Therefore, this type of 1f# reproducing device In practice, it is extremely difficult to reduce distortion by increasing feedback gain, and for this reason, it is currently used for limited purposes such as controlling low frequency characteristics.

This invention was made in view of the above circumstances, and its purpose is to be able to effectively cancel out distortion in the entire sound reproduction system including speakers, and to provide a method for amplifying operation. It is an object of the present invention to provide a sound reproduction device R that can be extremely stable without causing any adverse effects. The features of this invention include a load current detection circuit that detects the current flowing through the speaker, and a detection output 1 of this load current 1 current detection circuit.
A filter circuit is provided that applies and outputs a characteristic that compensates for the current detection characteristic of the load current detection circuit, and a first arithmetic circuit is used to compare the signal at the input end of the amplifier that drives the speaker with the signal at the input end of the amplifier that drives the speaker. The difference between the input signal 1 and the output of the filter circuit is calculated, and the input signal 1 is
The outputs of the arithmetic circuits are added together and supplied to the input terminal of the amplifier.Hereinafter, an embodiment of the sound reproduction device according to the present invention will be described in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of an embodiment of the present invention. In this figure, the input 1 input to the signal input terminal 5 is connected to the buffer amplifier 6 (thus amplified with a gain of +1), and then to the amplifier l via the resistor 7 ((IK)). The amplifier 1 is shown as an ideal gain amplifier with no distortion, and its output terminal is connected to one signal output terminal 8a. 1. Next, a speaker 2 is inserted between this signal output terminal 8a and the other signal output terminal 8b, but in this case, this speaker 2 is shown as an ideal speaker without distortion having an impedance zl. , this speaker 2 and MI
The total distortion d occurring in the actual amplifier 1 and 1 in J.
A virtual signal source 9 that outputs these two signal output terminals 8
The other signal output terminal 8b is connected to the speaker 2 in series between A and 8b. It is grounded via a detection resistor 10 (value Rs, which is the load current detection circuit in this invention).

Then, the voltage obtained from this (N output terminal 8bl) is M
The signal corresponding to the magnetic current of the speaker 2 is supplied to the input terminal of the filter circuit 11. This filter circuit 11 is connected to the speaker 21. The frequency characteristic of the current (this characteristic is determined by the impedance 'lx of speaker 2) and the transmission a characteristic 'r
(s), that is, the filter circuit has a transfer characteristic T(8) that compensates for the same frequency characteristic. On the other hand, the signal at the input terminal of the amplifier 1 is supplied to the input terminal of a buffer amplifier 12 having a gain of +1. The output terminal of this buffer amplifier 12 is a resistor 13a.

13b (both values are r) and are grounded in sequence through this wire,
The connection point between the resistors 13a and 13b is connected to the non-inverting input terminal of the operational amplifier 14. Further, the output terminal of the filter circuit 11 is connected to a resistor 13C213d (both values are 1 kHz).
), and the connection point of these resistors 13C113d is connected to the inverting input terminal of the operational amplifier 14. In this case, the portion consisting of the resistors 13a to 13d and the operational amplifier 14 converts the output voltage of the buffer amplifier 12 into the filter circuit 11.
Subtraction circuit 15 (first arithmetic circuit) that subtracts the output voltage of
It consists of Then, between the output terminal of the amplifier 14 and the input DHj of the amplifier 10, a magnetic current proportional to the voltage at the output terminal of the operational amplifier 14 is applied in the direction of the input terminal of the amplifier 1. A current source 16 (with mutual conductance gm) is inserted to direct the current to the buffer amplifier 6. In this case, the portion consisting of the current source 16 and the resistor 7 is connected to the output 1 of the buffer amplifier 6 ((, voltage; First, a voltage adder circuit 17 (second arithmetic circuit) which adds the output voltage of the operational amplifier 14 and supplies it to the input terminal of the amplifier 1 is configured.

Next, the operation of this embodiment with the above configuration will be explained. In the following explanation, the voltage of the signal at the input terminal of the amplifier 1 is defined as Vl + the voltage of the signal at the output terminal of the amplifier 1. 1 voltage is Vt, (I output terminal 13a
, the voltage between 8b is ■. , the voltage across the speaker 2 is Vt, the ML pressure of the signal at the signal output terminal 8b is v8 + the voltage of the signal at the output terminal of the filter circuit 11 is 4 + η, the signal voltage at the output terminal of the amplifier 14 is / The lW pressure is assumed to be ■.

First, when the input signal Vi is supplied to the signal input terminal 5f, the input signal vl of C is sent to the buffer amplifier 6°PI4 width amplifier 1.
The signals are sequentially amplified and supplied to the speaker 2. As a result, the speaker 2 is driven by the output of the amplifier 1, but in this case, the current flowing through the speaker 21 is
0, the voltage is detected as . By the way, since the impedance 22 of the speaker 2 has a characteristic that it becomes maximum at the lowest resonant frequency f0 of the same speaker 2, the voltage vs is equal to the lowest resonant frequency as shown by the curved line in FIG. Detection is performed according to characteristics such that the detection output is minimum at f0. this? B. The pressure v8 is supplied to the filter circuit 11 (this filter circuit 11
is a characteristic that compensates for the characteristic shown by curve B in Fig. 3, that is, a characteristic shown in Fig.
1l(s), the output terminal of this filter circuit 11 (obtained voltage v4) has a flat characteristic. A signal of the same voltage as the signal 1 at the input terminal of signal 1 is obtained. Therefore, if the signal levels of the signal vI and the signal 4 are equal, the calculation) Zeng 11I1. l vessel 1
The output terminal of 4 receives a signal V.

As a result of subtracting the signal 4 from A1, a signal V corresponding only to the distortion d is obtained. Ru. 71; The current source 16 causes a current to flow through the resistor 7 in accordance with this (No. 8 V), so the signal V is the input signal Vl j This signal V
, is the sum of the signals corresponding to .

In this case, since the current source 16 is in a floating state in terms of voltage when viewed from the resistor 7 side, the resistance value of the resistor 7 is 11. By changing g, the addition 3 (coefficient 3) when adding the signal corresponding to signal h*
IFI H Koyo 11. For example, if the addition coefficient of the pressure addition circuit 17 is set to an appropriate value, the amplifier 1 including the speaker 2 can be
It is possible to cancel out the distortion generated in each subsequent section extremely stably and completely, and the amplification operation is extremely stable, unlike the conventional method which requires a large amount of negative feedback A.

Next, the operation described above will be analyzed using mathematical formulas.

First, the voltage V/ in I between both ends of the speaker 2 is the sum of the distortion voltage d and the voltage v0 between the signal output terminals 8a and 8b, so V/=V, + d...・・・・・・・・・
...(1) holds true. Also, the appropriate pressure Vo and voltage V,
, between V3, =A・V, (1-K)- and -d...
...(2) There is a relationship. Therefore, from equation (2) and equation (2), V/=(A-V, +d)(1-K), ・-,,
, , +31, equation (8) is obtained. On the other hand, grn-R
Letting g be μ, V, =Vi 10μ・V, =vl-1-μ(V,-v4
)・141, and the intervening pressure v4 is as follows: V4 = T(s) −V, = T(s)・K(A ・V,
+ d ) ...--+51. Therefore, from these equations (4) and (6), the following relationship can be obtained. Here, T(S)・f(-A=1 ・・・・・・・・・・・・
・・・・・・・・・・・・・・・ When (7) is set, the above equation (6) becomes as follows. Therefore, substituting this equation (8) into the equation (3) above = (A・Vi+d(1-μ))(1-K) −...
-+91 is obtained. Here, if μ and K are returned to their original values, equation (9) becomes as follows. Therefore, the equivalent circuit of this embodiment becomes a circuit as shown in FIG. From this a1 formula, gm・几g
It can be seen that by setting =1, the signal component related to the distortion d can be completely removed from the voltage V/.

In addition, the voltage Vz when gln・几g=1 is set.
As is clear from equation α1, the relationship between and voltage vi is such that distortion of opposite polarity is generated.Also, in order to satisfy the sales condition shown in equation (7) above, , the transfer characteristic l of the filter circuit 11
1l(s > must be set so that T(s) is usually set to be sufficiently smaller than zt, so T(s) is approximately equivalent to the impedance Z/ of speaker 2. Legend a
A bandpass filter or the like having a characteristic may be used.

As is clear from the above analysis, it is possible to completely eliminate distortion without increasing the open-loop gain of the circuit to infinity, and as a result, extremely stable operation can be obtained. I understand that it will happen.

Next, a specific circuit of the embodiment shown in FIG. 2 is shown in FIG. In this figure, parts corresponding to those in FIG. 2 are denoted by the same reference numerals.

! < In Figure 5, the input signal Vl is connected to the signal input terminal 5a,
In addition, the resistor 7 inserted between the output terminal of the buffer amplifier 6 and the input terminal of the amplifier L is composed of a variable resistor, and thereby the tonicity addition In order to adjust the addition coefficient in the circuit 171 (
It's happening. In addition, the speaker 21 is inserted between the signal output terminal 8a and 8. The resistor 28 represents the voice coil resistor, the coil 2b represents the inductance of the speaker, the capacitor 2C, the resistor 2d, and the coil 2e.
The parallel resonant circuit consisting of and shows the mechanical elements of the same speaker. In addition, in the addition circuit 17, resistors 19a and 19b (both values are 2), resistors 2oa and zob (both values are 2), and resistors 21a and 21
b, Zener diodes 22a, 22b, and PNP
) transistor 2387NPN) transistor 23b constitutes a current source 16.

Next, a specific circuit of the filter circuit 11 will be shown.

The filter circuit 11 shown in FIG.
, an amplifier circuit 25 that amplifies the voltage at the sliding terminal 24c of the variable resistor 24 with a gain of +3, a filter section 26 that inputs the output of this amplifier circuit 25, and amplifies the output of this filter section 26 with a gain of +1. In the filter section 26, when each resistance value 1t of the interlocking variable resistors 28 and 29 and each field λC of the capacitor 30 and 31 are set as follows, the input terminal 32 and The gain G (Jω) between the output terminal 33 and the sliding terminal 2 in the variable resistor 24
Resistance value a between 4e and each fixed terminal 24a, 24b,
Depending on the Q determined by the process, the songs in Figure 7 @A, B,
It is designed to change as shown in C. In this case, the gain G(Jω) is as follows, and the gain Q is as follows.

As is clear from the above description, according to the sound reproducing device according to the present invention, there is a current detection circuit that detects the current flowing through the speaker, and a current detection circuit that connects the same load to the detection output of the load current detection circuit. a first arithmetic circuit that calculates a difference between a signal at an input terminal of an amplifier that drives the speaker and an output signal of the filter circuit; and a second arithmetic circuit which adds the output signal of the first arithmetic circuit to the input signal and supplies the result to the input terminal of the amplifier.
111 m, the distortion generated in the amplifier, the connecting part between the amplifier and the speaker, and the output system including the speaker can be eliminated with extremely high accuracy and effectiveness by rebalancing only the minute signal corresponding to the distortion component. Moreover, it can be canceled without adversely affecting the amplification operation. Furthermore, in this case, since the snoring of the feedback distortion component can be set arbitrarily, it is also possible to adjust the degree of distortion reduction effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the configuration of a conventional sound reproduction device,
FIG. 2 is a circuit diagram showing the structure of a fabric example of this invention, and FIG. 3 is a circuit diagram showing the current detection characteristic of the speaker 2 and the transfer characteristic T(s) of the filter circuit 11 in the same example. 4 is an equivalent 0] circuit diagram of the same embodiment, FIG. 5 is a circuit diagram showing an example of a specific circuit of the same embodiment, and FIG. 6 is a circuit diagram of the same embodiment (
FIG. 7 is a circuit diagram showing an example of a specific circuit of the filter circuit ti in this case. 2 is a characteristic diagram showing the characteristics of a specific circuit of the filter circuit 11. FIG. 1...Amplifier, 2...Speaker, 5.
...Signal input terminal, lO...Load current detection circuit (current detection resistor), 11...Filter circuit,
15. River... first arithmetic circuit (subtraction circuit), 17...
...Second arithmetic circuit (voltage addition circuit). Applicant: Nippon Musical Instruments Manufacturing Co., Ltd.

Claims (1)

[Claims] An amplifier that drives a speaker, a load current detection circuit that detects the current flowing through the speaker, and a transfer characteristic that compensates for the current detection characteristics of the load current detection circuit, and inputs the detection output of the load current detection circuit. a first arithmetic circuit that calculates the difference between the output of this filter circuit and a signal at the input end of the amplifier; 1. A sound reproduction device comprising: a second arithmetic circuit that supplies data to an input terminal of the sound reproduction device.