Home  Product Technical Articles   LM1875 Audio Power Amplifier Cricuit

LM1875 Audio Power Amplifier Cricuit

Author: Iggy
Date: 6 Apr 2022
 3554
audio amplifier

I Description

This blog introduces the power amplifier with NE5532 and LM1875T as the core components. The power amplifier we are discussing here is a high-fidelity two-channel stereo subwoofer power amplifier. Here, we will discuss its methods and procedures, schematic design, assembly and debugging, and speaker production. Hope this blog can provide a good reference for beginners.

lm1875

Figure 1. LM1875

Catalog

I Description

II LM1875T and NE5532 Overview

2.1 Power Amplifier LM1875T

2.2 Pre-amplification Component NE5532

III Composition of Power Supply

IV Assembly and Debugging Speaker

4.1 Electrical Inspection

4.2 Box Production

V In the End

FAQ

Ordering & Quantity

II LM1875T and NE5532 Overview

First, we introduce the core components that we will use. And then, the basic characteristics of these components. Audio power amplifier is generally composed of the following three parts: power supply, pre-amplifier and post-amplifier.

Here, we will use high-efficiency HI-FI power integrated chip LM1875T as the core original. LM1875T adopts a positive and negative 15V dual power supply, the left, and right channels work in OCL mode, and the bass works in BTL mode. As far as the characteristics of LM1875T are concerned, it has the characteristics of good sound quality, good frequency response, low cost and relatively simple circuit.

In addition, the pre-amplifier part uses the NE5532 integrated operational amplifier.

2.1 Power Amplifier LM1875T

LM1875T has excellent performance. Many luxury-looking active speakers, mid-range power amplifiers, and subwoofers on the market use LM1875T. The power amplifier circuit composed of LM1875T chip has the following characteristics:

  • The output power is large, the maximum power can reach about 20W;
  • The static current is small, the load capacity is strong, and the dynamic current is large, which can drive 4~8Ω speakers;
  • The circuit is simple, easy to manufacture and low cost;
  • With an internal protection circuit, it is a high-fidelity power amplifier component with stable performance.

The blog design of this article is a dual-channel stereo subwoofer power amplifier, but LM1875T is a mono-channel power amplifier integrated circuit, so the dual-channel OCL working mode uses one LM1875T for each channel. Since the bass works in BTL mode, we have to use two pieces.

LM1875T has 5 pins. They are positive power supply, negative power supply, positive input, reverse input, and output. The circuit is shown in Figure 2.

lm1875 applicationFigure 2. LM1875 Circuit

2.2 Pre-amplification Component NE5532

Before the power amplifier circuit, it is generally necessary to add a preamplifier. The purpose of this is to amplify the voltage of various input weak electrical signals. In order to ensure that the output electrical signal has high fidelity, the pre-amplifier is NE5532. NE5532 is a high-performance, low-noise, dual operational amplifier integrated circuit. Compared with many standard op amps, NE5532 has better sound performance, excellent output drive capability, relatively high small signal bandwidth, and large power supply voltage range. Therefore, it is very suitable for high-quality and professional audio equipment, instruments, control circuits and telephone channel amplifiers. When used for audio amplification, the tone is warm and high fidelity.

The functional block diagram of NE5532 is shown as in Fig. 3.

ne5532 functional block diagram

Figure 3. NE5532 Functional Block Diagram

III Composition of Power Supply

LM1875T adopts a positive and negative 15V dual power supply. The operating voltage of NE5532 is also ± 15V. We need to step down the mains power to 15V through a step-down transformer, then rectify it through the rectifier bridge KBL406, filter it through a large capacitor, and directly supply it to the power amplifier. In this way, larger output power is obtained. After 7815 and 7915, the regulated output ±15V is used as the power supply of the preamplifier NE5532. The composition of the power supply is shown in Figure 4.

LM

Figure 4. Power Circuit

power amplifier circuit board

Figure 5. Power Amplifier Circuit Board

IV Assembly and Debugging Speaker

When starting the circuit installation, first check the circuit board against the circuit diagram. For example, check whether the main components are installed correctly, and whether the solder joints have missing soldering or false soldering. Then turn on the power to debug the circuit, and make speakers after the debugging is completed. The actual production is shown in Figure 6.

  Physical Shooting Pic

Figure 6. Physical Shooting Pic

 

4.1 Electrical Inspection

Use an AC signal generator to add a tiny sinusoidal signal to the signal input. Then, use the oscilloscope to measure the three output signals of the power amplifier board. At this time, observe whether the sine meets the requirements and whether the parameters in the test are relatively stable.

Then, connect two full-range speakers to the left and right channels, and connect a woofer to the bass output port. At this time, add the song signal to carefully check whether the three speakers are working properly and the sound is good. If the above steps are well expressed, then proceed to the next step.

4.2 Box Production

The key to making speakers is the selection, size and other steps. In the experiment, we used the laminates in the laboratory for splicing and assembly.

First, draw a sketch. The painting is divided on three different substrates, and then made into two parts respectively. After drilling, polishing, splicing and bonding, the completed circuit parts are installed in their respective parts.

Then, we divide the entire power amplifier into three parts. Two satellite speakers, as well as a woofer and power amplifier board. These three parts together form a complete 2.1 subwoofer power amplifier. Here, there is a place that needs special attention. When making the bass part of the cabinet, the impact of vibration should be fully considered. Therefore, we have to design damping components.

V In the End

After the installation is normal, connect the music signal source and listen to the music effect. The sound reproduced by this circuit has a strong sense of hierarchy, a clear sense of orientation, and an obvious sense of space and distance. In addition, the sound image orientation is clear, the width is outstanding, and the sound dynamic range is large, giving people a real feeling.

FAQ

  • What is the Maximum Input Offset Voltage of LM1875T?

15@±25V mV

 

  • What is the Output Type of LM1875T?

1 Channel Mono

 

  • What is the Output Signal Type of LM1875T? 

Single-Ended

 

  • What is the Case of LM1875T? 

TO220-NDH5D

 

  • What is the Output power of LM1875T?

25W

Related Articles

STM32F429IIT6 STMicroelectronics: Specification, Datasheet, Feature

Iggy 26 Mar 2022 3174

STM32F4 is a series of high-performance microcontrollers developed by ST (STMicroelectronics). It uses 90nm NVM technology and ART technology (Adaptive Real-Time Accelerator). The STM32F429xx device ...

Continue reading »

FDD5614P MOSFET: Pinout, Datasheet, Applications

Victoria 14 Nov 2022 1052

Catalog FDD5614P OverviewFDD5614P FeaturesFDD5614P PinoutFDD5614P ApplicationsFDD5614P CAD ModelsFDD5614P SpecificationFDD5614P ManufacturerFDD5614P DatasheetUsing Warnings FDD5614P Overvi...

Continue reading »

FT232RL IC: CAD Models, Datasheet, Features [Video&FAQ]

Lydia 31 Aug 2022 804

Catalog Product OverviewFT232RL Related Video IntroductionFT232RL CAD ModelsFT232RL Pin ConfigurationFT232RL Block DiagramFT232RL FeaturesFT232RL ApplicationsFT232RL DatasheetFT232RL SpecificationsFT...

Continue reading »

FDB045AN08A0 N-Channel PowerTrench® MOSFET Datasheet PDF Download

Irene 27 Apr 2022 917

Catalog FeaturesMOSFET Maximum RatingsThermal CharacteristicsPackage Marking and Ordering InformationElectrical CharacteristicsTypical CharacteristicsTest Circuits and WaveformsThermal Resistance vs....

Continue reading »

74LS04 HEX INVERTER

Mia 27 Jan 2022 9242

Description74LS04 contains six independent gates each of which performs the logic INVERT function. The output signals of the six inverters are opposite to the input signals. The inverter can reverse t...

Continue reading »

0 comment

Leave a Reply

Your email address will not be published.

 
 
   
 
Rating:

# 0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z