LM1875 PCB Layout: Design Considerations for High-Quality Audio Amplification


One of the most important parts of any audio system is the audio power amplifier, and this technology is constantly improving. This part amplify a feeble audio signal so it can run a speaker or other audio output device. This article aims to explore the intricate details surrounding audio power amplifiers. We will commence by providing an overview of their functionality and subsequently delve into their notable characteristics and applications in delivering exceptional sound quality.

Figure 1 LM1875 Audio Amplifier
Figure 1 LM1875 Audio Amplifier

First, we’ll define them, and then we’ll talk about their functions. An audio power amplifier is an electronic component that amplifies the intensity of audio impulses so that they may power loudspeakers. It is crucial to sound systems because it generates the power needed to power speakers and create audible sound. A sound system’s output level is inaudible to the human ear without an audio power amplifier. The LM1875 integrated circuit is widely utilized as a power amplifier for audio in a wide variety of devices. This monolithic power amplifier can provide up to 20 watts into an 8-ohm load with distortion of less than 0.03%. It can function on either a dual or single rail power source and is built with safeguards to ensure a long service life. It may also work in high-power audio amplifier designs with few supplementary components. The LM1875 only requires one power supply, making it perfect for portable devices that run on batteries.

Understanding the LM1875 Audio Amplifier IC

The LM1875 Audio Amplifier IC is widely used in various audio amplifier applications. This high-efficiency amplifier can send up to 30 watts of audio power into a load using a 25V supply. Amplifiers based on the LM1875 may be found in anything from home stereos and headphones to public address systems and instrument amplifiers. The LM1875 stands out for its high signal-to-noise ratio and low distortion. This is why it is ideal for any application with the highest possible sound reproduction quality.

Because of its broad frequency response range, the LM1875 can reproduce various audio frequencies. An amplifier circuit can be constructed with just a few more components and an LM1875 integrated circuit. The IC’s internal thermal shutdown safety circuit shields it from destructive overheating. As an added convenience, the LM1875 has a mute switch for temporarily silencing the amplifier’s output. LM1875 audio amplifier circuit design requires careful consideration of the supply voltage and current. To function correctly, the power source must generate the requisite current to run the amplifier, dependent on a voltage range 20V to 60V.

LM1875 Pin Configuration

Knowing the pinout and purpose of each IC’s terminals is crucial for its successful implementation. The LM1875 contains five pins, all of which are used for something.

Figure 2 LM1875 Pinout Configuration
Figure 2 LM1875 Pinout Configuration

The pinout diagram of the IC is as follows:

Non-Inverting Pin 1: It provides the input signal to the amplifier.

Inverting Input Pin 2: It provides the feedback signal to the amplifier.

Output Pin 3: It connects the amplifier to the speaker.

V- Pin 4: The amplifier’s negative power source comes here.

V+ Pin 5: Its job is to supply the amplifier with its positive power source.

LM1875 Integrated Circuit

The LM1875 integrated circuit is shown in the diagram. The amplifier includes built-in compensation, allowing it to achieve and sustain gains of at least ten without additional parts.

Figure 2 LM1875 Pinout Configuration
Figure 3 LM1875 IC Sample Circuit

This reduces complexity and saves money in the circuit. For the amplifier to be functional, the signals it amplifies must be of sufficient strength. Hence a steady gain of at least 10 is required.

LM1875 Amplifier circuit 20 watts

The LM1875 single and dual power supply operates on the same fundamental principle. In electronic circuits, using a single power supply can significantly impact the voltage division and biasing of the circuit. Specifically, when a single power supply is utilized, resistors R1 and R2 are employed for voltage division. Additionally, 1/2VCC is taken as the bias voltage and added to R3 to pin 1. This results in the output voltage changing up and down based on 1/2VCC. Then resistor R5, which serves the purpose of modifying the input impedance of the Arduino. It is also connected to capacitor C4 within IC1 in the amplifier section. C3 performs the filter function by reducing the amount of noise allowed to enter the system. The circuit’s gain may be adjusted by manipulating the feedback loop produced by resistors 7 and 8. C7 and R6 collaborate to redirect high-frequency noise toward the ground (GND), improving the overall sound quality generated by the system. In addition, C5 is the component in charge of connecting the signal to the load or output. Because of this connection, any leakage of DC voltage to the load is prevented or minimized, improving the sound quality.

Figure 4 LM1875 Audio Amplifier 20 watts circuit
Figure 4 LM1875 Audio Amplifier 20 watts circuit

Obtaining the highest possible dynamic range is essential for various uses. The system will be able to record all signals without losing quality. This is especially significant in signal-sensitive applications like audio and video processing. In order to guarantee that a wide variety of signals are recorded, it is required to fine-tune the system’s settings, such as the gain and the signal-to-noise ratio. This maximizes the system’s dynamic range, which permits the most accurate signal processing.

Figure 5 LM1875 Audio Amplifier 20 watts circuit PCB Display
Figure 5 LM1875 Audio Amplifier 20 watts circuit PCB Display

LM1875 Amplifier circuit 30 watts

Delivering over 30 watts of power is possible using an 8-load and 30V supply. Even if no load is connected to the LM1875, it must always be used with a heat sink. This is because the LM1875 can generate a substantial quantity of heat during operation, which, if not properly dissipated, can cause damage to the device. To ensure the safe and dependable operation of the LM1875, it is always advised to use a heat absorber. When employing a heat sink, it is presumed that its thermal resistance is 1°C/W and that no insulator is present. In this scenario, the surrounding temperature is 25 degrees Celsius.

Figure 6 LM1875 Audio Amplifier 30 watts circuit
Figure 6 LM1875 Audio Amplifier 30 watts circuit

Features of LM1875

The LM1875 can run on various supply voltages, making it suitable for various applications. It also has a high maximum input offset voltage. Furthermore, it features a maximum input offset voltage, the highest voltage difference between the input signals, allowing for precise amplification.

  • The LM1875 has protections in place to preventdamage from overloading or overheating. These protections and improvements make the component more long-lasting.
  • The LM1875 is made to work with breadboards, which are used for quickly prototyping electrical circuits, and has a rapid slew rate. This means it can accurately and efficiently amplify the input signal despite any fluctuations.
  • The LM1875 produces nothing in the way of harmonic distortion noise, which is the undesirable byproduct of amplification that occurs at higher frequencies than necessary. This guarantees high-fidelity replicationby maintaining the integrity of the input signal in the output.
  • THANKS TO ITS HIGH OUTPUT CURRENT CAPABILITIES AND POWER RATING. The LM1875 can drive various loads, from speakers to headphones. In addition, it has a power rating specifying how much energy it can process without deteriorating efficiency.
  • The LM1875 is specified to operate reliably within a specific operating temperaturerange and withstand a particular load. This temperature window protects against instability and poor performance from harsh conditions. In addition, the range of allowable load resistance values for the component is detailed.
  • The LM1875 has a power bandwidth, a frequency range it can amplify without degrading the stated amount of power, and an open-loop gain. It also possesses an open-loop gain, representing the amplification factor without external feedback. These features determine the component’s amplification capabilities in different frequency ranges.
  • The LM1875 is available in different package types, which refer to the physical form of the component. The package type can vary based on size, pin configuration, and mounting options. Choosing the appropriate package type ensures compatibility with the intended application and ease of integration into the overall circuit design.

Importance of PCB Layout for LM1875 Performance

How a printed circuit board (PCB) is designed plays a crucial role in the performance of the LM1875 audio amplifier. Let us explore the impact of PCB layout on signal integrity and overall performance, as well as the benefits of a well-designed PCB layout.

The PCB layout greatly influences the integrity of the electrical signals within the LM1875 amplifier circuit. Proper placement and routing of components, traces, and ground planes are essential to minimize noise, distortion, and interference. A poorly designed layout can introduce unwanted coupling, crosstalk, or excessive parasitic capacitance and inductance, degrading the audio signal quality. These issues can result in reduced dynamic range, increased distortion, and diminished audio fidelity.

Several factors contribute to better LM1875 performance with a well-designed PCB layout:

  • A well-designed PCB layout avoids signal deteriorationand maintains audio signal integrity by carefully considering the component location and trace routing. This allows for more pure and authentic sound transmission.
  • Careful planning aids in isolating delicate analog and digital components, reducingthe impact of EMI and RFI. This results in less background noise and better overall audio quality.
  • The LM1875 amplifier, while operating, can produce heat. Thus, it is essential to keep it cool. A well-designed PCB layout will include heat sinks, thermal vias, and copper poursto disperse and dissipate heat effectively. So long as the amplifier stays within its acceptable operating temperature range, it will not experience any performance or reliability difficulties due to overheating.
  • An organized and optimized PCB layout facilitates smoother assembly and testing Components are logically arranged, making it easier for technicians to follow assembly instructions and perform accurate tests, reducing the likelihood of errors or faults.
  • A well-designed PCB layout takes into account future modifications or enhancements. It allows for easier upgrades or expansion of the LM1875 amplifier, enabling users to adapt the circuit to changing requirements without significant redesign or rework.

Key Considerations for LM1875 PCB Layout Design

The performance and dependability of an LM1875 audio amplifier rely on various factors that must be considered when building a PCB layout. Here are a few things to keep in mind:

  1. Separation and positioning of components:

The location of critical components should be carefully considered while building the layout for the LM1875 PCB. The LM1875 amplifier chip, capacitors for input and output, feedback resistors, and components for a power supply are all necessary. Parasitic effects can be reduced, and signal distortion avoided by positioning these parts nearby.

  1. Heat Sink:

The LM1875 amplifier produces heat when running. Thus, planning for thermal control in the PCB layout is essential by strategically placing a heatsink. A heatsink’s effectiveness in dissipating heat is directly proportional to its location. For best results, place the heatsink close to the LM1875 chip to reduce the thermal resistance between them. Heat can also be dissipated with the help of sufficient spacing and thermal vias.

  1. Power and grounding considerations:

One of the most important aspects of audio circuit functionality and noise reduction is the grounding. A ground plane should be used so the electrical current has a low-impedance path back to its source. The ground plane should be soldered to the LM1875 and additional ground locations on a separate PCB layer. A “star grounding” approach should be used to reduce ground loops and noise, in which all ground connections converge on a central location.

  1. Capacitors Decoupling:

To ensure a clean and reliable power supply for the LM1875 and any other integrated circuits, decoupling capacitors should be positioned as near to the ICs as feasible. These capacitors serve as a steady voltage reference for the amplifier while filtering out high-frequency noise. High-frequency power supply noise can be further reduced by using low-pass filters.

  1. Coordination of signal paths and trace lengths:

Trace length matching techniques are crucial for high-speed circuits to ensure signal integrity and avoid timing problems. An audio circuit’s input and feedback traces are two examples of signals that must arrive simultaneously and have identical trace lengths. Equalizing trace lengths requires modifying the routing path or employing serpentine patterns.

  1. Things to think about when assembling a PCB:

First, the circuit’s complexity and the available area should determine the PCB stack-up number of layers. A multilayer PCB allows for greater routing freedom and lessens the likelihood of signal interference. Although a two-layer PCB may be adequate for the LM1875 circuit, extra layers may be required for power and ground planes.

Correctly allocating signal and power planes is crucial to maintaining signal quality and ensuring even power distribution. Power and ground planes should be routed internally, while signal traces should be routed on the top and bottom levels. Voltage losses are minimized, and overall circuit performance is enhanced by using power planes. Capacitors used for decoupling should be carefully positioned between power and ground planes to reduce inductance and maximize decoupling efficiency. By considering these critical considerations for the LM1875 PCB layout design, you can optimize the performance of the amplifier circuit, reduce noise and interference, and ensure the proper functionality of the audio system.

Advantages of the LM1875 Audio Amplifier

    1. The LM1875 is capable of producing high-quality sound reproduction with little distortion. It guarantees precise amplification of the source audio signal, yielding transparent, lifelike, and enveloping sound.
    2. Thanks to its excellent efficiency, this integrated amplifier can send much juice to your speakers without wasting much juice along the way. It makes the most efficient use of available electricity and generates the least waste heat.
    3. Thanks to its comprehensive frequency response, it can process a broad spectrum of audible frequencies. It amplifies bass and high frequencies well, creating a well-rounded and robust sound.
    4. It is simple to implement and operate, making it a good choice for amateur and professional audio engineers. It is easy to create and integrate because of its small footprint and lack of extra parts.
  1. Because it is compatible with a wide range of power supply voltages, it may be utilized in a variety of audio systems. As a result of its ability to function in both stereo and bridged modes, it is adaptable to the requirements of a wide variety of amplifier configurations and output levels.
  2. When it comes to audio amplification, this is a decision that is both reliable and economical. Its capability of combining several functionalities into a single chip contributes to a reduction in the cost of the system without compromising its overall performance.


The LM1875 audio amplifier has several uses outside of its standard function in audio systems. Because of its reliability and effectiveness, it is widely used in a wide range of audio applications. Here are a few illustrations:

Home Theater Systems: The LM1875 amplifier enhances the entire sound experience during movie nights or music playing by providing high-quality audio amplification for home theater installations.

Public Address Systems: The LM1875 amplifier is appropriate for public address systems used in auditoriums, conference rooms, and public areas due to its strong performance and ability to handle notable speakers.

Amplification of Musical Instruments: Musicians may use the LM1875 amplifier to amplify their musical instruments, such as guitars or keyboards, enabling them to play louder and more dynamically during rehearsals, concerts, or recording sessions.

DIY Audio Projects: Audiophiles often use the LM1875 amplifier in do-it-yourself (DIY) projects such as creating bespoke stereo systems, bookshelf speakers, and headphone amplifiers. As a result, they may design customized audio solutions with superb sound reproduction.

Cars Audio Systems: The LM1875 amplifier may be connected into vehicle audio installations to raise the audio output of car speakers, delivering better music quality and volume levels for a more pleasurable driving experience.

Audio Monitoring Systems: The LM1875 amplifier is utilized in professional recording studios and broadcasting venues for audio monitoring. It contributes to accurate and detailed sound reproduction, enabling sound engineers and producers to carefully monitor audio inputs.

Educational Labs: The LM1875 amplifier may be used in audio-related labs to teach concepts of sound amplification, audio signal processing, or even as part of student projects involving audio engineering in educational environments.


The LM1875 audio power amplifier integrated circuit (IC) is useful in a wide range of audio applications due to its many features and advantages. The low levels of distortion it produces and the efficient use of energy it requires make it a top pick for audio systems. Accurate amplification of a wide range of audible frequencies is made possible by the LM1875’s wide frequency response, leading to a full and enveloping sound. The IC’s ease of use makes it ideal for both novice and experienced audio technicians. It’s flexible since it works with different amplifier setups and can handle different voltages from power supplies.

The LM1875 is an attractive choice for audio amplification since it is both cheap and reliable. In home stereos, PA systems, and other uses, the LM1875 is invaluable for achieving high-quality sound reproduction. In addition, the LM1875 amplifier’s performance may be maximized and interference and noise can be reduced with careful planning of the PCB architecture. Maintaining audio signal integrity is possible by paying attention to issues including component positioning, temperature management, grounding, and trace routing. The LM1875 audio power amplifier IC is often regarded as the best available option for audio amplification because of its high output level, wide range of applications, and low cost.



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