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Sep 8 2020

NE5532 Audio Power Amplifier

I Introduction

The audio power amplifier is a key part of the audio system, which has been widely used in daily life and has strong practicability. However, there is still no suitable voice power amplifier in some occasions. Such as large classrooms for classes, medium-sized conference rooms for meetings, small square gatherings, and other occasions.

This blog introduces a simple and low-cost audio amplifier circuit based on NE5532. This circuit overcomes the problem of the high cost of professional equipment and the problem of insufficient power of low-end voice amplifiers on the market. Therefore, it has important research significance for satisfying actual study work.



I Introduction

II System Overall Design

III System Hardware Design

3.1 Band Pass Filter Circuit

3.2 Primary Power Amplification

3.3 Post-stage Power Amplification

3.4 DC Power Supply

3.5 Schematic Diagram and Physical Diagram

3.6 Test Data

IV Conclusion

II System Overall Design

The audio amplifier circuit is mainly composed of the following parts:

  • Band-pass filter circuit;
  • Primary power amplifier circuit;
  • Post-stage power amplifier circuit,
  • DC stabilized power supply;
  • ...

Its principle block diagram is shown as in Fig. 1.

circuit block diagram

Figure 1. Circuit Block Diagram

III System Hardware Design

3.1 Band Pass Filter Circuit

The main function of the band-pass filter circuit is to pre-process the audio signal. This can make it more in line with the requirements of the power amplifier circuit. The band-pass filter circuit uses resistors and capacitors to filter, the effect is stable and easy to debug. It is mainly composed of two parts: channel balance circuit and tone control circuit.

The concrete circuit is shown as in Fig. 2.

band pass filter circuitFigure 2. Band Pass Filter Circuit

3.1.1 Channel Balance Circuit

The sliding rheostat R1 in Figure 2 acts as an equalizer to balance the size of the left and right channels. The middle pin of the sliding rheostat is connected to the ground and a capacitor C1 is connected in parallel. The function of this capacitor is to filter out high frequency signals in high input audio.

3.1.2 Tone Control Circuit

The tone control circuit enables the listener to boost or attenuate certain frequency bands of the sound according to their needs. The multi-band tone circuit used in this blog. In this way, the incoming audio signal enters the middle, low, and high audio control circuit to adjust and then superimposes it into the power amplifier circuit. So that the corrected frequency response is more detailed and the effect is better.

(1) Treble Control

The rheostat R5 and surrounding components form a high-pitched tone circuit. Capacitor C3 can pass high-frequency signals. The treble signal increases when the rheostat slides up, and the treble signal decreases when it slides down.

(2) Midrange Control

The rheostat R8 and surrounding components constitute a mid-tone tuning circuit. Some high-frequency signals in the circuit are filtered out through components such as R7, C4, and R9. C5 can pass intermediate frequency signals in audio. The mid-audio signal increases when the rheostat R8 slides up, and the mid-audio signal decreases when it slides down.

(3) Bass Control

The rheostat R12 and surrounding components form a bass tuning circuit. The audio signal enters R12 to adjust its amplitude. Then, superimpose the adjusted treble and midrange into the power amplifier circuit. In this way, a complete high, middle and low tone circuit can be formed.

3.2 Primary Power Amplification

The primary power amplifier consists of NE5532. NE5532 is a high-performance low-noise dual op amp. It has good noise performance, excellent output drive capability and quite high small signal and power bandwidth. When NE5532 is used for audio amplification, the tone is warm and high fidelity. The circuit is shown in Figure 3.

  ne5532 circuit

Figure 3. Part of NE5532 Circuit

Here, the magnification is controlled by R14 and R15. Because there is a post-stage power amplification in the circuit, this stage is amplified to ensure sound quality. We set R14 as 1kΩ and R15 as 10kΩ, which is 10 times. R16 and C8 form a negative feedback circuit. Adjusting R16 and C8 in the circuit can make the sound quality softer, clearer, and more transparent. After repeated debugging, it can be determined that R16 is set to 1MΩ, and C8 is set to 33μF, which achieves their satisfactory results.

3.3 Post-stage Power Amplification

The post-stage power amplifier circuit is composed of two parts: a differential amplifier circuit and a composite tube amplifier circuit. Among them, the composite tube amplifier circuit uses high-power transistor 2N3055. The concrete circuit is shown as in Fig. 4.

 post stage power amplification

Figure 4.  Post-stage Power Amplification

3.4 DC Power Supply

This circuit turns the mains power into a unidirectional direct current through a bridge rectifier circuit. The pulsating component has to go through a filter circuit to become a smooth direct current. Finally, the circuit is stabilized into ±12V direct current through 7812 and 7912 voltage stabilizers and supplied to the load. The power circuit is shown as in Fig. 5.

dc power supply circuit

Figure 5. DC Power Supply Circuit

3.5 Schematic Diagram and Physical Diagram

The overall schematic diagram and physical diagram of the voice amplifier circuit are shown in Figure 6 and Figure 7.

ne5532 audio amplifier circuit

Figure 6. Overall Principle Diagram of Audio Amplifier Circuit

audio amplifierFigure 7. Audio Amplifier

3.6 Test Data

After our repeated debugging of the audio amplifier circuit, we finally achieved a relatively satisfactory effect. The test data is shown in Table 1.

Table 1. Test Data of Audio Amplifier Circuit

IV Conclusion

After theoretical analysis and practical testing, the audio amplifier circuit based on NE5532 is simple and stable, with a maximum output power of 40W. Compared with the current mainstream integrated circuit voice amplifier, it has the characteristics of low heat generation, good stability, low cost and high power. Therefore, it has better use value.

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