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
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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.
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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
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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
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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
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
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
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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
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c. Schematic Diagram for Power Amplification Stage
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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
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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.
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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)
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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)
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Figure 9 & 10. Connecting the Main Board and the Control Panel
Figure 11 & 12. Finalized connection for initial testing
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Figure 13 & 14. Mounted Passive Tone Control circuit in the Main Board
Figure 15 & 16. Finalized connections for final testing
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Figure 17 & 18. The Volume-Gain Control Panel (Left), Main Circuit Board (Right)
Figure 19 & 20. Back Panel Preparation
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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)
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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)
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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.
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VIII.
Appendices
A. LM386 Datasheet
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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
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
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.
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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.
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