JPS6132843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier device in which negative feedback is provided from a speaker input terminal to an amplifier for driving a speaker.

In general, in component-type playback equipment, when connecting a speaker drive amplifier and a speaker, the connection cord becomes long, and the quality of the playback sound is affected by the characteristics of this connection cord, which has recently become a problem. Conventional amplifiers that drive speakers provide negative voltage feedback from the output end, making the output impedance extremely small. Normally, in a high-performance amplifier, the value of this output impedance is, for example, 0.1Ω or less in the audible band. This is necessary in order to drive the speaker's voice coil in faithful proportion to the amplifier's output signal. In other words, since the voice coil of the speaker is the source of subharmonics, cross-modulation wave distortion, and harmonic distortion components generated by the speaker, this is absorbed by the output impedance of the amplifier, and the voice coil is used as the speaker. This is to sufficiently damp the distortion generated in the

Furthermore, in a multi-way speaker system, the speaker system is designed to minimize the mutual influence of distortion between each channel, including distortion generated by the branching circuit inserted between the input terminal and the voice coil. It is desirable that the drive source impedance at the common input terminal is sufficiently small.

However, in conventional amplifier devices, although the output impedance of the amplifier is sufficiently small, the impedance of the connection cord connecting the amplifier and the speaker is added to the output impedance of the amplifier, reducing the above-mentioned effects.

FIG. 1 shows a connection state between a speaker driving amplifier and a speaker in a conventional amplifier device.

That is, the signal from the signal line 1 is applied to a negative feedback amplifier 4 composed of an amplifier 2 and a negative feedback circuit 3, and the output of this negative feedback amplifier 4 is connected to a speaker 6 via a connection cord 5.

Here, the amplification degree of the amplifier 2 when the negative feedback circuit 3 is not provided is A, the output impedance of this amplifier 2 is r, and the output impedance of the negative feedback amplifier 4 is r, when the transfer characteristic of the negative feedback circuit 3 is β. _NF
is r _NF = r ₀ /1+Aβ. Therefore, the drive source impedance Z _NFC when looking from the input terminal of the speaker 6 to the negative feedback amplifier 4 side is Z _NFC = r _NF + Z _C (however, Z _C is the impedance of connection code 5 ) becomes. By the way, the output impedance r _NF of the negative feedback amplifier 4 is 0.1Ω or less as mentioned above, and the impedance Z _C of the connection cord 5 is usually about 0.1 to 0.5Ω for a connection cord of several meters, although it depends on the length. many. Furthermore, the characteristic impedance Z _C of the normal type connection cord 5 is 10 to several 100 Ω, and the output end impedance of the negative feedback amplifier 4 is close to a short-circuit state, and when looking at the negative feedback amplifier 4 side from the input terminal of the speaker 6, the connection The characteristic impedance of code 5 becomes an inductive impedance, which increases as the frequency increases. This value is generally much larger than the output impedance _rNF of the negative feedback amplifier 4, as shown in FIG. 2, for example. Therefore, the damping effect of the speaker is significantly influenced by the characteristics of the connection cord.

The present invention provides an amplifier device that can provide negative feedback from the speaker input terminal so that the influence of the speaker connection cord can be ignored.

An embodiment of the present invention will be described in detail below with reference to FIG.

In FIG. 3, the signal source 10 has an input terminal a on the hot side and an input terminal b on the reference potential point side of a negative feedback amplifier 13 composed of an amplifier 11 and a feedback circuit 12.
The input terminal a is connected to one input terminal of the amplifier 11, and the input terminal b is connected to the negative feedback circuit 12. One output terminal of the amplifier 11 is connected to an output terminal a' on the hot side, and the other to an input terminal b' on the reference potential point side. Connect the speaker 1 from these output terminals a' and b' via the connection cord 14.
It is connected to input terminals C and D of 5. These input terminals C and D are connected to the feedback terminal a'' on the hot side of the negative feedback circuit 12 and the feedback terminal b'' on the reference potential point side via the connection cord 16 for negative feedback, and these negative feedback terminals a ", b" are connected to the input side of the negative feedback circuit 12. The output side of this negative feedback circuit 12 is connected to the other input side of the amplifier 11. Further, a resistor R1 is inserted between the output terminal a' of the amplifier 11 and the feedback terminal a'' of the negative feedback circuit 12.Furthermore, a resistor _R1 is inserted between the output terminal b' of the amplifier 11 and the feedback terminal b'' of the negative feedback circuit 12. A resistor _R2 is inserted between them.

By the way, the resistors R ₁ and R ₂ are connected to the negative feedback circuit 1.
2, that is, the impedance Z〓 when looking at the negative feedback circuit 12 from between the feedback terminals a'' and b'', and the output terminals a', b' of the amplifier 11 and the feedback terminals a'', The value should be sufficiently larger than the impedance Z _a ′ _b ′ and Z _a ″ _b ″ when looking at the load side from b″. That is, Zβ≫R ₁ ≫Z _a ′ _b ′, Zβ≫R ₂
≫Z _a ″ _b ″. Considering that the impedance of a normal speaker system is around several ohms and the characteristic impedance _Z〓O of the connection cord 14 is around several tens of ohms, resistances R ₁ and R ₂ of around several tens of ohms are sufficient to satisfy the above conditions. .

The operation will be explained based on the above configuration and conditions.

First, assuming that the connection cord 16 is not connected to the feedback terminals a'' and b'', the negative feedback circuit 12 has a resistance R ₁ that is sufficiently smaller than the impedance Z of the negative feedback circuit 12 compared to the configuration shown in FIG. , R ₂ has been inserted. Resistance R ₁ in this case and
R ₂ has an impedance that is sufficiently smaller than that of the negative feedback circuit 12, and the negative feedback circuit is essentially a voltage detection circuit due to its purpose, and the impedance Z〓 of the negative feedback circuit viewed from the negative feedback terminals a'' and b'' is sufficiently high. Therefore, almost no signal current flows. Therefore, the negative feedback constant β does not change much compared to the case where the resistances R ₁ and R ₂ are zero.

However, in a normal amplifier, the input terminal b, the feedback terminal a'', and the output terminal b'' are at a common ground potential, but in the case of the circuit configuration of the present invention, the input terminal b, the feedback terminal b'', which is the reference potential point, and the output terminal The reference potential point of terminal b' is isolated by resistor _R2 .
However, since the resistance R ₂ is sufficiently small compared to the coupling impedance between externally connected devices via a power transformer, etc., the connection to the housing is possible at each reference potential point of input terminal b, feedback terminal b'', and output terminal b'. There is no practical problem with either of these methods.Also, when connecting cord 16 is used, the reference potential points of output terminal b' and feedback terminal b'' are connected with low impedance, which may cause inconvenience. There isn't. In this way, connect the connection cord 1 from the input terminals C and D of the speaker 15.
A switch or an inter-terminal connector (not shown) may be provided to short-circuit the resistors R ₁ and R ₂ when R 6 is not connected.

Next, a case where the input terminals C and D of the speaker 15 are connected to the feedback terminals a'' and b'' via the connection cord 16 will be explained.

Since the impedance Z _a ″ b ″ when looking at the speaker 15 from the feedback terminals a″, _b ″ is sufficiently small compared to the resistances R ₁ , R ₂ , the voltage generated at the input terminals C, D remains unchanged at the feedback terminals a″, b″. The signal is applied to the feedback circuit 12 and negative feedback is provided from the input terminals C and D of the speaker 15. Further, the resistors R ₁ and R ₂ have a sufficiently larger impedance than the connection cord 14 that supplies power to the speaker 15, and almost no current flows through the connection cord 16 for negative feedback. Therefore, no voltage drop occurs due to the connection cord 16.

In this way, the resistors R ₁ and R ₂ perform decoupling between the negative feedback circuit 12 and the output circuit consisting of the amplifier 11, the connection cord 14, and the speaker 15, and also when the connection cord 16 is not connected, the amplifier 11
This function maintains the same amount of negative feedback and prevents abnormal increases in gain. Furthermore, the resistor R ₂ also has the role of coupling the input terminal b, which is the ground, of the amplifier 11 and the output terminal b ^- so that they do not become floating.

As is clear from the operation explained above, the impedance Z _C of the connection cord 14 is connected to the output impedance before negative feedback from the input terminals C and D of the speaker 15.
will be added. Therefore, the impedance seen from the input terminals C and D of the speaker 15 toward the negative feedback amplifier 13 is r _NF =r+Z _C /1+Aβ, and the impedance of the connection cord 14 is reduced to 1/1+Aβ.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 and 5. Components that are the same as those in FIG. 3 are given the same reference numerals, and their explanation will be omitted.

First, in FIG. 4, the negative feedback circuit 12 is divided, and one part is fed negative feedback from the output terminal a' of the amplifier 11, and the other part is fed negative feedback from the input terminals C and D of the speaker 15. In this case, the amount of negative feedback from the input terminals C and D of the speaker 15 and the amount of negative feedback from the amplifier 11 can be distributed as appropriate. If the amount of negative feedback is distributed in this way, the impedance reduction rate of the connection cord 14 that connects the speaker 15 will be reduced, but the characteristics of the connection cord 14, such as the transfer phase characteristics, etc. Feedback is effective when a stable state cannot be obtained.

Figure 5 shows the so-called BTL (Balanced
This is an example of application to an amplifier connected to Transless. That is, two amplifiers operating with opposite polarity to each other.
Only the hot sides of negative feedback circuits β ₁ and β ₂ of A ₁ and A ₂ are decoupled from the load impedance by resistors R and R', respectively, and taken out as feedback terminals a″b″. Further, the hot sides of amplifiers A ₁ and A ₂ are designated as output terminals a' and b'.

In the case of a BTL amplifier configured in this way, since the output is a balanced type, there is no reference potential point on the output side, so there is no need to decouple the reference potential points between the input and output as shown in Figure 3, which is extremely advantageous. be.

[Brief explanation of the drawing]

Figure 1 is a circuit configuration diagram showing a conventional amplifier, Figure 2 is a characteristic diagram showing the output impedance of the amplifier and the impedance of the speaker connection cord as seen from the speaker terminal with respect to the frequency of the conventional amplifier, and Figure 3 is a diagram of the present invention. FIGS. 4 and 5 are circuit diagrams showing one embodiment of the amplifier device of the invention, and FIGS. 4 and 5 are circuit diagrams showing other embodiments of the invention. 11...Amplifier, R ₁ R ₂ ...Resistor, 12...Negative feedback circuit, 16...Connection cord, a'', b''...Feedback terminal.

Claims (1)

[Claims] 1. A first and a second input terminal to which an input signal is applied, and a first of these first and second input terminals.
an amplifier having a first input terminal connected to the input terminal of the amplifier and a second input terminal; first and second output terminals through which a load current of the amplifier circulates; and a negative feedback circuit connected in series between the output terminal of the amplifier and the second input terminal of the amplifier, the first output terminal and the negative feedback circuit. a first feedback terminal connected through a resistor between the two, and a first feedback terminal derived from a connection point between the resistor and the negative feedback circuit, and a second output terminal connected to the second input terminal through a resistor; and a second feedback terminal derived from the connection point of this resistor and the second input terminal, and a second feedback terminal derived from the input terminal of the speaker connected from the first and second output terminals via the connection cord. An amplifier device characterized in that it is connected to the first and second feedback terminals, respectively, by connection cords. 2 first and second input terminals to which input signals are applied, and the first of these first and second input terminals;
an amplifier having a first input terminal connected to the input terminal of the amplifier and a second input terminal; first and second output terminals through which a load current of the amplifier circulates; and a negative feedback circuit connected in series between the output terminal of the amplifier, the second input terminal, and the second input terminal of the amplifier, the first feedback derived from the negative feedback circuit; a second output terminal connected to the second input terminal via a resistor, and derived from a connection point between the resistor and the second input terminal.
feedback terminals, and the input terminals of the speakers connected from the first and second output terminals via connection cords are connected to the first and second feedback terminals, respectively, by separate connection cords. An amplifying device characterized by: