JB G Design and Development of JBG: An LM386-Based Audio Amplifier with Integrated Tone and Gain Controls In partial fulfillment of the requirements in Electronic Circuit Analysis and Design for the bachelor’s degree in Electronics Engineering Submitted by: Gutierrez, Joshua B. BSECE 2-1 Submitted to: Engr. John Carlo L. Espineli, ECT, RAOC ECEN70 Instructor May, 2024 Page | 1 Table of Contents I. Theory………………………………………………………………………………………….1 II. Background and Objectives……………………………………………… III. Materials and Tools IV. Diagrams V. Process and Construction VI. Project Output VII. References VIII. Appendices I. Theory In the contemporary realm of audio engineering, the pursuit of high-fidelity sound reproduction remains a central goal, driving innovation in the design and implementation of audio amplifiers. This thesis presents a comprehensive exploration of the design process and theoretical underpinnings of constructing an audio amplifier that not only amplifies sound but also offers users the capability to manipulate audio signals through advanced tone control mechanisms. Central to this study are four fundamental theories: Signal Amplification, Transistor Theory, Frequency Response, and Tone Control, which includes both Passive and Active Filters and Equalization techniques. Page | 2 The concept of Signal Amplification is foundational to the operation of audio amplifiers, providing the basic functionality of enhancing audio signal strength to levels suitable for driving various output devices like speakers and headphones. This amplification process is critical for the practical application of audio systems in environments ranging from intimate home settings to large-scale public audio distributions. Amplifiers are classified into different classes based on their operating characteristics, each with distinct advantages and trade-offs. One such class, the Class AB amplifier, strikes a balance between the efficiency of Class B and the linearity of Class A amplifiers. In the context of integrated circuits (ICs), devices like the LM386, often employed in Class AB configurations, offer a compact and efficient solution for small signal audio amplification tasks, combining the benefits of low power consumption with adequate performance. Transistor Theory is equally vital, serving as the backbone of modern electronic amplifiers. Transistors, whether bipolar or field-effect, play a pivotal role in the amplification process, acting as the active elements that control the flow of electrical currents under the influence of an input signal. In the realm of integrated circuits (ICs), devices like the LM386 are specifically engineered for small signal audio amplification, providing a compact and efficient solution for applications requiring low power consumption and space constraints. The LM386, a versatile and widely-used IC, exemplifies the principles of Transistor Theory by integrating multiple transistors, resistors, and capacitors into a single package, thereby simplifying circuit design and enhancing performance in small-scale audio amplification tasks. Further enhancing the complexity and utility of audio amplifiers is the consideration of Frequency Response. This characteristic defines how an amplifier handles different frequencies within an audio signal, ideally maintaining linear response across the audible spectrum to ensure sound is reproduced without coloration or loss of detail. The study of frequency response not only informs the design for fidelity but also impacts how an amplifier will interact with different audio sources and environments. Lastly, the thesis delves into the intricacies of Tone Control, facilitated by both passive and active filters and sophisticated equalization techniques. Tone control circuits allow users to shape the audio output by boosting or attenuating specific frequency Page | 3 bands, thereby optimizing sound quality to suit individual preferences or to compensate for acoustical anomalies in different listening environments. The design and implementation of these circuits involve a nuanced understanding of electronic filter design and the application of equalization, both of which play crucial roles in modern audio systems. Through detailed analysis and practical implementation, this thesis aims to bridge theoretical knowledge with real-world application, providing insights into the complex dynamics of audio amplifier design. By integrating these key theories, the project not only seeks to build an amplifier that meets professional audio standards but also enhances user interaction through effective tone control strategies, thereby pushing the boundaries of what is achievable in the domain of audio technology. II. Background and Objectives Audio amplifiers play a crucial role in the electronics and audio industries, serving as essential components for enhancing sound quality and volume. Their primary function is to amplify low-power audio signals to a level suitable for driving loudspeakers, thereby making them audible to listeners. Over the years, the evolution and sophistication of audio amplifier technology have led to improvements in sound clarity, power efficiency, and overall audio performance. Amplifiers can be broadly categorized by their "class," which primarily refers to their design and operational characteristics, particularly how the amplifier handles the input signal within the output stage. The most common classes include Class A, Class B, Class AB, and Class D, each with its distinct operational principles and applications. Class A amplifiers, for example, are known for their exceptional linearity and low signal distortion but are relatively inefficient in terms of power consumption. Conversely, Class D amplifiers offer high efficiency and are often used in portable and space-constrained applications, albeit typically at the expense of increased signal distortion and complexity. The design and implementation of audio amplifiers heavily utilize various semiconductor technologies, notably Bipolar Junction Transistors (BJTs), Field-Effect Transistors (FETs), and Integrated Circuits (ICs). BJTs are valued for their ability to Page | 4 amplify weak electric signals and are often used in applications requiring high linearity, making them suitable for audio amplification in hi-fi systems. FETs, characterized by their voltage-controlled resistance, offer distinct advantages in terms of higher input impedance and lower noise, which is particularly beneficial in high-fidelity or sensitive audio applications. Integrated Circuits (ICs) represent a more modern approach in audio amplifier design, encapsulating multiple amplifier components into single packages. This integration facilitates smaller, more cost-effective designs with easier implementation and generally good performance, making IC-based amplifiers very popular in consumer electronic products such as mobile phones, television sets, and portable music players. Other technologies also play a role in the advancement of audio amplifier design. These include innovations in digital signal processing (DSP), which allows for the precise control of audio signals, and the development of new materials and manufacturing techniques that enhance the performance and durability of audio components. The study of audio amplifiers encompasses a multidisciplinary approach involving electronics, materials science, and acoustics, among other fields. Understanding the principles, applications, and evolving technologies of audio amplifiers is essential for the continued enhancement of audio quality and efficiency in various applications, from professional sound engineering to everyday consumer electronics. This background serves as a foundation for exploring the current trends, challenges, and future directions in the development of audio amplifier technologies. Furthermore, this project has the following objectives: To design an audio amplifier that adheres to Transistor Theory and other fundamental electronic and communication principles, To develop a functional audio amplifier utilizing the LM386 Integrated Circuit, To engineer an amplifier equipped with user-adjustable controls for volume, tone (equalization), and gain, To produce an aesthetically pleasing and versatile device that meets user requirements, and more importantly Page | 5 To gain proficiency in signal amplification processes and frequency filtration techniques, allowing for customizable bandwidth modification according to user preferences. III. Materials and Tools Component Quantity Circuit Board Components 10kΩ Potentiometers 2 100kΩ Potentiometers 2 3.5mm Adaptor Socket 1 10Ω Resistors 1 1kΩ Resistor 1 2kΩ Resistors 2 6.8kΩ Resistor 1 10kΩ Resistor 1 100kΩ Resistor 1 0.1uF Metalized Film Capacitor 2 0.1uF Polyester Film Capacitor 2 2.2uF Tantalum Capacitor 2 220pF Ceramic Capacitor 1 1.5nF Ceramic Capacitor 1 15nF Ceramic Capacitor 1 10uF Electrolytic Capacitor 1 1000uF Electrolytic Capacitor 1 3300uF Electrolytic Capacitor 1 0.1uF Mylar Capacitor 1 JST Connectors Female and Male 4 M3 Hex Nut Spacer and Screw 4 5cmX7cm Universal Prototyping PCB 1 LM386 DIP IC 1 8P IC Socket 6 Peripherals and Output Indicators Wooden Casing 1 Wire Mesh 1 Knobs 4 3.5mm Audio Cable 1 Phone Stand 1 SPST Toggle Switch 1 91C4 Voltmeter 1 2.5V Blue LED 1 DC Power Jock Socket 1 Screws 2 4Ω 3W Full Range Speaker 1 8Ω 5W Mini Tweeter Speaker 1 Jumper Wires - Total Cost (₱) 20.00 22.00 9.00 10.00 2.00 2.00 2.00 5.50 2.00 18.00 8.00 40.00 2.50 2.50 2.50 2.00 25.00 25.00 8.00 30.00 24.00 35.00 15.00 6.00 220.00 30.00 20.00 99.00 30.00 15.00 75.00 1.00 10.00 2.00 60.00 50.00 20.00 Page | 6 Tools Hand Drill Screw Driver Scissor Cutter Wire Stripper Breadboard Wire Connectors Soldering Lead and Paste Ruler Equipment 12V DC Charger Soldering Iron OWON HDS2202S Handheld Oscilloscope Table 1. Table of Specification Overall Component Cost: ₱ 950.00 (Tools and Equipment expenses, as well as Indirect Costs were excluded) IV. Diagrams a. Block Diagram Power and Audio Input Pre-Amplifier Stage Power Amplification Speaker and Output Indicators b. Schematic Diagram for Pre-Amplifier Stage Page | 7 c. Schematic Diagram for Power Amplification Stage Page | 8 d. Schematic Diagram for Output Indicators Process and Construction V. i. Research, Planning, Material Selection and Acquisition The construction of the audio amplifier commenced with extensive research and careful design planning. A detailed schematic was developed to integrate the LM386 IC, including provisions for volume, tone, and gain controls. Reliable online resources were consulted to ensure accurate circuit configurations and component specifications. Using the online platform EasyEDA, the schematics were meticulously laid out. Following this, the selection of essential components, with particular attention to the material composition of capacitors, was conducted. These components were then acquired and subjected to thorough breadboard testing to validate their functionality and performance. ii. Testing and Circuit Assembly Using an oscilloscope, multitester, and function generator, the breadboard circuit was meticulously tested for potential noise issues. Following successful validation, the circuitry was transferred to a universal prototyping PCB, where it was carefully soldered into place. Additional tests were conducted to verify the safety and integrity of the connections, taking into account any design constraints. JST connectors were employed to link the main circuit board with the volume and gain controls, as well as to the output indicators, speakers, and power supply. After ensuring secure connections, hex nut Page | 9 spacers and screws were installed to provide robust stability when mounting the board within the casing. Also, the speakers were connected in parallel to obtain better sounding. iii. Enclosure Construction and Finishing Touches The preparation of the wooden casing was followed by drilling the required holes for the rotary knobs, switch, voltmeter, LED, and screws. Subsequently, the circuit board, speakers, along with the knobs, phone holder, and mesh wire cover, was installed and securely fastened using screws. The final step involved the aesthetic design of the casing, ensuring it not only protected the internal components but also enhanced the overall appearance of the amplifier. iv. Documentation Following the assembly, a comprehensive user manual was created. This manual includes photographs of the device, detailed instructions on how to operate it, and troubleshooting procedures to assist users in resolving any issues they may encounter. Page | 10 VI. Project Output Figure 1 & 2. Breadboard Testing (Left) with Passive Tone Control (Right) Figure 3 & 4. Breadboard Testing with finalized components (Left) and with Output Indicators (Right) Page | 11 Figure 5 & 6. Breadboard Testing Results with a sinusoidal signal (Left), with an actual audio (Right) Figure 7 & 8. PCB Installation top-view (Left), and bottom-view (Right) Page | 12 Figure 9 & 10. Connecting the Main Board and the Control Panel Figure 11 & 12. Finalized connection for initial testing Page | 13 Figure 13 & 14. Mounted Passive Tone Control circuit in the Main Board Figure 15 & 16. Finalized connections for final testing Page | 14 Figure 17 & 18. The Volume-Gain Control Panel (Left), Main Circuit Board (Right) Figure 19 & 20. Back Panel Preparation Page | 15 Figure 21 & 22. Mounted Power Socket and Output Indicators outside-view (Left), inside-view (Right) Figure 23 & 24. Front Panel Preparation (Left) and Installation of the Circuit Board and Peripherals (Right) Page | 16 Figure 25 & 26. Device partially done Figure 27 & 28. Finished Device corner-views Figure 29 & 30. Finished Device back-view (left) and bottom-view (right) Page | 17 Figure 31. Device in Upright Position (Intended for Phone Handling) VII. References ALPHA SOUND. (2023). Is doubling speakers +3DB or +6DB? what’s parallel and series wiring? Retrieved from https://www.youtube.com/watch?v=Om_1IYsqPWg Campbell, S. (2018). Build a great sounding audio amplifier (with Bass Boost) from the LM386. Retrieved from https://www.circuitbasics.com/build-a-great-soundingaudio-amplifier-with-bass-boost-from-the-lm386/?fbclid=IwAR2rADs5wgzVYSJ3AVrQalKhSJKCM7IgsNPHY29_OnDJfz7OlXdYgg2FOw Garaipoom, A. (2022). Passive Tone Control Circuit. Retrieved from https://www.eleccircuit.com/passive-tone-controlcircuit/?fbclid=IwAR09Jf7PGPm6I3RoEejXlbdo6doJDLXTvxRgcBzkHnRgjpxY CrBJHgE5YlI_aem_AcQyJmzA2izvw3lATEQCtgqutnL7xxSnY324AXyZbZ01_JARVJvU3p95sJqCbNsTnLQ5XZuAglrB_d2N9azTB3e Kulkarni, S. (2023). Audio amplifier with Tone Control. Retrieved from https://www.hackster.io/sohamkulkarni2309/audio-amplifier-with-tone-control8cf3c9 Texas Instruments. (2023). LM386 Datasheet. TI. Page | 18 VIII. Appendices A. LM386 Datasheet Page | 19 Page | 20 Page | 21 B. User Manual Model: JBG Audio Amplifier Table of Contents 1. Introduction 2. Safety Information 3. Package Contents 4. Product Overview 5. Setup Instructions 6. Operating Your Amplifier 7. Maintenance and Care 8. Troubleshooting 9. Technical Specifications 10. Warranty and Service Information 1. Introduction Congratulations on your purchase of the AMP-LM386TG, a high-quality audio amplifier designed for excellent sound amplification with customizable tone and gain settings. This manual provides all the necessary instructions to ensure optimal use of your amplifier. 2. Safety Information Electrical Safety: Always ensure the amplifier is off when not in use. Do not expose the amplifier to water or moisture. Handling: Handle the amplifier with care. Avoid dropping or impacting the unit. Repairs: Do not attempt to repair the amplifier yourself. Refer to a qualified technician for any service needs. 3. Package Contents Audio Amplifier Power Adapter User Manual Page | 22 3.5mm Audio Cable 4. Product Overview Front Panel: 3 1 1. Volume Control Knob 2. Bass Control Knob 5 3. Gain Control Knob 2 4 4. Treble Control Knob 5. Input Jack with cord Rear Panel: 6. Voltmeter 7. Power Switch 8. LED Power Indicator 7 9. Power Input 6 8 Right Panel: 9 10. Adjustable Phone Stand Top Panel: 11 10 11. Speakers 5. Setup Instructions 1. Place the Amplifier: Set the amplifier on a stable, flat surface free from excessive vibration. 2. Connect the Power Adapter: Plug the power adapter into the amplifier and then into a suitable wall outlet. 3. Connect the Audio Source: Plug the provided audio cable to the gadget of choice. 4. Mount device: Conveniently place your device (phone) on the provided phone case and enjoy! 6. Operating Your Amplifier 1. Power On: Switch on the amplifier using the power switch. 2. Adjusting Volume: Start with the volume low, and slowly increase it to the desired level. 3. Tone and Gain Settings: Adjust the tone and gain knobs to refine the sound according to your preferences. Page | 23 7. Maintenance and Care Keep the amplifier clean and dust-free with a soft, dry cloth. Avoid using harsh chemicals or solvents for cleaning. 8. Troubleshooting No Sound: Check all connections, ensure the amplifier is powered on, and the volume is set appropriately. Distortion: Lower the volume or gain if the sound is distorted. Intermittent Audio: Ensure cables are firmly connected and undamaged. 9. Technical Specifications Power Output: 4 Watts Frequency Response: 20 Hz - 20 kHz Input Sensitivity: 100 mV Power Supply: 12V DC 10. Warranty and Service Information The product comes with a one-year warranty covering manufacturing defects. For service inquiries or support, please contact our customer service department. Page | 24