JPS5917713A - Sound amplifier - Google Patents

Abstract

PURPOSE:To improve characteristics, by giving gains of extra-low band and DC to negative feedback of amplifiers and mxing anti-phase sound signal components of respective negative feedback circuits in a balanced sound amplifier. CONSTITUTION:Amplifying circuits 16-19 and 36-39 having gains only for DC and extra-low frequencies are inserted into negative feedback circuits of DC amplifiers 13 and 33 which can amplify the range from DC to sound band, and these DC amplifying circuits are so constituted that they are paired and correspond to respective poles of a balanced sound signal. Feedback signals of negative feedback circuits of amplifiers 13 and 33 are mixed with feedback inputs of respective amplifiers to obtain a prescribed amplification degree. Inferior parts of characteristics of amplifiers 13 and 33 are compensated with each other to improve characteristics in respect to the distortion rate and S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a balanced audio amplifier used for amplifying high quality audio signals.

Traditionally, this type of balanced amplifier uses transformers on the input and output sides, and the amplifier itself is unbalanced.
A balanced audio signal was converted to an unbalanced type by an input transformer (transformer), amplified by an unbalanced amplifier, and then converted again to a balanced type amplifier by a transformer (transformer).

However, in this case, when this amplifier is connected in series in multiple stages, the characteristics deteriorate due to the transformer (transformer), i.e., when the frequency characteristics deteriorate, the low frequency characteristics deteriorate, the distortion factor deteriorates, and the 8N ratio deteriorates. This method has the drawbacks of deterioration of the maximum audio signal margin and deterioration of the margin characteristics of the maximum audio signal.

Another conventional example is a balanced audio amplification circuit consisting of an amplifier circuit that amplifies at least from direct current to the audio band, and a feedback amplifier circuit that has a gain only for direct current, which is inserted into the negative feedback circuit of this amplifier circuit. An audio amplification circuit was formed by opposing each of the two audio signal paths. In this amplifier, each of the two internal amplifiers is an unbalanced amplifier independent with respect to the ground potential, and the degree of balance depends on the amplification degree of each amplifier. Correction for noise was lacking.

Figure 1 is a diagram showing the configuration of a conventional audio amplifier.
Referring to the figure, in the conventional example, balanced audio output terminals 11 and 12
．． Input transformer 13, load resistor 14, input coupling converter/
15, audio amplifier 16, resistors 17 and 18 that determine the amplification degree of the amplifier with a negative NiM lid, a capacitor 19 for eliminating loss of DC # return in order to perform 100-channel feedback of DC, output coupling capacitor 20, It consisted of an output transformer 21 and balanced audio outputs 22,23.

Incidentally, there is also an example in which the coupling capacitors 15 and 20 are omitted by using two positive and negative sources for the power supply, thereby increasing the fidelity. In FIG. 1, when there is a DC input from the outside by the transformer 13, the DC is completely cut off, and even if there is a DC component generated by the amplifier 16, the DC component is output to the outside by the transformer 21. I try not to let that happen. However, when this amplifier is used in series with thin films, the number of transformers required increases, resulting in deterioration of characteristics.

Figure 2 shows an example of a conventional audio amplifier that does not use a transformer.
2 and 32, main amplifiers 13 and 33. Negative feedback resistors 14 and 15 and 34 and 35 that determine amplification degree, DC amplifier 16
, 36. Negative feedback mixing resistors 17 and 37, resistors 18 and 38 to obtain a reference voltage to set the reference output of the DC amplifier to 0 volts, and the DC component from the output of the main amplifier to an extremely low level of several Hz or less. A low-pass filter that passes only the
(integrator circuit, etc.) 19 and 39 and balanced audio signal output terminals 20 and 40. The balanced audio amplifier shown in Figure 2 has one amplifier corresponding to the volume of the balanced audio signal, and each amplifier is independent and does not have complementary performance in terms of characteristics. .

Therefore, an object of the present invention is to provide an audio amplifier whose characteristics do not deteriorate even when connected in multiple stages and whose characteristics can be corrected within the amplifier.

According to the present invention, an amplifier circuit having an advantage only for DC and extremely low frequencies is inserted into the negative feedback circuit of a DC amplifier that can amplify from DC to the audio band, and two pairs of these DC amplifier circuits are connected. A predetermined amplification degree can be obtained by configuring the amplifier according to the volume of the balanced audio signal, and further mixing the feedback signal of the negative feedback circuit of each amplifier with the feedback input of each amplifier. , and by compensating for the inferior characteristics of each amplifier, the transformer (
A balanced audio output end with good characteristics in terms of υ distortion rate and 8N ratio can be obtained by using a balanced amplifier consisting of a set of two independent amplifiers with the transformer removed.

In the present invention, two audio amplifiers are used as a set, corresponding to the volume of the balanced audio signal, but each amplifier is not intended to amplify mutually opposite phase signals. Since the feedback input is also in reverse phase, by mixing the negative feedback signal opposite to this negative feedback input,
By obtaining a predetermined degree of amplification and compensating for the noise and signal distortion received from one side, the characteristics of a set of 3← balanced amplifiers can be improved.

Next, the present invention will be described in detail with reference to the drawings showing one embodiment of the present invention. FIG. 3 is a diagram showing an example of the present invention,
Balanced audio signal input terminals 11 and 31, load resistors 12 and 3
2. Main amplifiers 13 and 33, main amplifier feedback resistors 14 and 3
4. DC amplifiers 16 and 36, DC feedback mixing resistors 17 and 37, resistors 18 and 38 for obtaining a reference voltage to set the reference output of the DC amplifier to 0 volts, and the DC component from the output of the main amplifier to aHz. Mix the signals from the low-pass filters (integrator circuits) 19 and 39 that pass only the following very low frequencies, the balanced audio output terminals 20 and 40, and the feedback input terminal of the main amplifier that amplifies the two opposite-phase audio signals. and a resistor 1 which increases the amplification degree of each amplifier. If the resistor l in Fig. 3 is set to a value that is the sum of resistors 15 and 35 in Fig. 2, the same amplification can be obtained with the same constants as in Fig. 2, but this is because the id resistor 1 Both ends are of opposite polarity,
This is because the voltage of the audio signal across resistors 15 and 35 in FIG. 2 is twice as high. This resistor 1 causes the noise generated by the main amplifier.

Distortion characteristics are improved because the main amplifiers complement each other.

As explained above, the present invention divides the audio amplifier circuit into each of the two balanced audio circuits No. 1, and transforms the transmission signal by giving unnecessary ultra-low frequency and DC gain to the negative feedback of each amplifier. A balanced audio amplifier is obtained that does not use an amplifier, and the characteristics of the balanced audio amplifier can be further improved by mixing the opposite-phase audio signal components of the respective negative feedback circuits.

4. Brief explanation of the drawing 7
7 In Fig. 3, 11.31...Balanced audio signal input terminal, 12.32...Input load resistor, 13°33...Audio main amplifier, 14 .34・
... Negative feedback resistor, 16.36 ... DC amplifier, 17.37 ... Blood flow feedback mixing resistor, 18.38 ... DC potential Reference resistor, 19.
39...DC and very low frequency pass filter, 2
0.40...Balanced audio amplifier / Zukyu 2 Zuji 3 Figure

Claims (1)

[Claims] Two sets of audio circuits each consisting of an amplifier circuit that amplifies from the DC range to the audio band and a feedback circuit of the amplifier circuit that has a gain only in the DC range are provided corresponding to the two parallel audio input lines, and An audio amplifier characterized by comprising means for combining signals of the feedback circuit having mutually opposite phases.