GRADE

10
TLE-IA
ELECTRONIC PRODUCTS
ASSEMBLY AND SERVICING NCII
QUARTER 4 – WEEK 1, MODULE 1

AMPLIFIER
 LEARNING OBJECTIVES
TLE_IAESg10
LO 1. Operation of Amplifier
• Identify parts of amplifier circuits
• Determined the function/uses of audio amplifier

I INTRODUCTION
An electronic amplifier is a device that is used to increase the power, current,
or voltage of a signal. Amplifiers are used in music equipment, electronic devices such as
television and radio receivers, audio equipment, and computers to increase the amplitude of a
signal.

II MODULE CONTENT AMPLIFIER

How Does an Amplifier Work?
Amplifiers work by increasing a small input signal to deliver a larger output signal. Amps
in audio equipment take tiny electrical signals that contain musical frequencies and amplitudes
and increase their strength. When talking about power amps, this increases the power enough
to drive speakers back and forth to generate air pressure variations, also called waves.
It does this by taking power from a power supply and increasing the output to match the
(relatively low-power) input signal. This process invariably introduces
some noise and distortion into the signal; and the process cannot be 100% efficient at
increasing the gain without loss — amplifiers inherently will lose some energy in the form of
heat. The ideal amplifier can be described as “a straight wire with gain,” as the output would be
identical to the input, just greater.

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Audio Power Amplifier

An audio power amplifier is an electronic amplifier that amplifies low-power electronic

audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high
enough for driving loudspeakers or headphones.

Practical Power Amplifier Stages and Block Diagram

Practical power amplifier

Audio power amplifier is an amplifier which produces amplification of power between the
input and output. Theoretically every audio amplifier produces some amount of power
amplification, but in practical scenario every audio amplifier cannot be called a power amplifier. It
is the amount of power amplification that makes an amplifier power amplifier or not. A power
amplifier must produce a considerable amount of power amplification so as to drive a load.

Generally there is no fixed criteria for the output of a power amplifier even though some
designers say 50W RMS, some 20W RMS and some other guys 10W RMS. In practical sense
your power amplifier must have enough power output to drive the intended load. For an i-pad a
few hundred milli -watt amp will do a power amplifier while for a home theater system it might be
a few ten watt amplifier.

A simple RC coupled pre-amplifier makes considerable amount of voltage gain but it

cannot be considered as a power amplifier. When we connect a speaker to it we can hardly hear
anything because such an amplifier has very low current gain. Since power is the product of
voltage and current, such an amplifier has a low power gain and so it cannot drive a load like
speaker.

Power Amplifier Stages

A practical audio power amplifier must have dedicated circuits for producing voltage gain
and current gain. Sheer power is not the only factor that is considered while designing a practical
power amplifier. Special emphasis is given to factors like performance, reliability, ruggedness etc.
while designing a practical audio power amplifier. Different power amplifier stages are shown in
the block diagram below.10 EPAS Q 3 W8 M8 PAGE 2

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Voltage amplification Stage

The input signal to the amplifier from the source will be generally in the mill volt range and it is
very weak to drive the succeeding stages. The purpose of the voltage amplification stage is to
provide necessary voltage amplification to the input signal for the succeeding stages to process.
Usually the voltage amplification stage consists of two or more RC coupled Class A amplifiers.
These Class A amplifiers coupled together will make the necessary voltage gain.

Driver stage.

Driver stage is the stage that is standing between the voltage amplification stage and the
output stage. The output stage will usually have low input impedance and so the voltage
amplification stage cannot drive the output stage alone. The purpose of the driver stage is to
produce enough current gain in order to drive the output stage. Since there is sufficient current
gain, the driver stage produces considerable amount of power gain too.

Output stage.

Output stage is the stage that is connected to the loudspeaker. The output stage gives
further improvement to the power gain and transfers this power to the loud speaker with
minimum loss. Push-pull arrangement consisting of two transistors is often employed in this
stage. Efficiency and impedance matching are the two important parameters considered while
designing this stage.
Push-pull arrangement is a very common type of output configuration used in power amplifiers.
In push-pull arrangement a pair of active devices (transistors) alternatively source or sink the
load current. Advantages of push-pull configuration over single transistor output are better
efficiency, higher power output, cancellation of even harmonics, cancellation of DC current at the
output etc.

Power amplifier stages in a real circuit.

Circuit diagram of a three stage practical audio power amplifier is shown in the figure below.

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 Small signal transistor Q1 and its associated components form the voltage amplification
stage. R1 and R2 are biasing resistors of Q1. C4 is the input coupling capacitor which blocks DC
components from the input signal. Resistor R7 limits the current through the biasing network. C1
is a filter capacitor. Output of the voltage amplification stage is taken from the collector of Q1.

Medium power transistor Q2 forms the driver stage. Output of the voltage amplification
stage is directly coupled to the base of Q2. Output of the driver stage is taken from the base of
Q2.

Dedicated power transistor Q3 and Q4 wired in the push-pull mode forms the output stage.
Collector of Q2 is connected to the base of Q3 and emitter of Q2 is connected to the base of Q4.
Audio output is taken from the emitter-base junction of the output transistors.

Audio circuit
Audio Circuits are used to process and manipulate audio signals as required by the
application. It is a combination of Audio Amplifiers, Audio mixers, Audio Frequency control and
other similar circuits that involve audio signal handling.

Tone control circuit

In their most basic form, tone control circuits attenuate the high or low frequencies of
the signal. This is called treble or bass "cut". The simplest tone control circuits are
passive circuits which utilize only resistors and capacitors or inductors.
Tone control is a type of equalization used to make specific pitches or "frequencies" in
an audio signal softer or louder. It allows a listener to adjust the tone of the sound produced by
an audio system to their liking, for example to compensate for inadequate bass response of
loudspeakers or earphones, tonal qualities of the room, or hearing impairment. A tone control
circuit is an electronic circuit that consists of a network of filters which modify the signal before it
is fed to speakers, headphones or recording devices by way of an amplifier. Tone controls are
found on many sound systems: radios, portable music players, boom boxes, public address
systems, and musical instrument amplifiers.
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 Schematic Diagram of Tone Control Circuit Actual Components

Equalizer
An equalizer (also called an “EQ”) is an audio filter that isolates certain frequencies and either
boosts them, lowers them, or leaves them unchanged. Equalizers are found on a wide array of
electronic devices.

Graphic Equalizer 5 Band Schematic Diagram Actual components

SOMETHING TO THINK ABOUT

III ACTIVITY 1 Self Check

Direction. Chose the letter of the best answer. Write your answer on a piece of paper.
____ 1. The process of increasing the volume of sound, especially using an amplifier,
A. Amplification C. Rectification
B. Conversion D. Detection10
____ 2. An electronic device that can increase the power of a signal (a time-varying voltage or
current). A. Amplifier C. Converter
B. Rectifier D. Transformer
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____ 3. The process of changing alternating current voltage to direct current voltage.
A. Amplification C. Conversion
B. Rectification D. Transformation
____ 4. An electronic device use to convert alternating current to direct current.
A. Amplifier C. Converter
B. Rectifier D. Transformer
____ 5. A term used to describe any sound or noise that is within a range the human ear is
capable of hearing.
A. Audio C. Video
B. Signal D. Wave
____ 6. Technical term, referring to sound coming from a recording, transmission or electronic
device.
A. Audio C. Video
B. Signal D. Wave
____ 7. Are transducers that convert electromagnetic waves into sound waves.
A. Amplifier C. Converter
B. Barrier D. Speaker
____ 8. A transducer – that converts sound into an electrical signal.
A. Amplifier C. Converter
B. Microphone D. Speaker
____ 9. What is the unit used in measuring sound?
A. ampere C. coulomb
B. hertz D. Decibels (dB)
____ 10. Audio means sound, while video means _________.
A. TV C. camera
B. photo D. Picture
ACTIVITY 2: Direction: Match column A with column B. Write only the letters of your
answer.
COLUMN A COLUMN B

____ 1, An electronic amplifier that converts a weak A. Direct Current

electrical signal into an output signal strong
enough to be noise-tolerant. B. Picture
____ 2. The unit used in measuring sound. C. Pre-amplifier
____ 3. A device use to increase the amplitude of a Signal. D. Decibels (dB)
____ 4. The word video in electronic means ______. E. Amplifier
____ 5. The word audio means _______. F. Rectification
____ 6. The process of changing alternating current G. amplification
voltage to direct current voltage. H. speaker
____ 7. The process of increasing the volume of sound. I. microphone
____ 8. Are transducers that convert electromagnetic J. sound
waves into sound waves.
____ 9. . A transducer – that converts sound into an electrical signal.
____10. A type of current that flows in only one direction.
How Much Have You Learned?
III. SUMMATIVE ASSESSMENT Test I. Modified True or False
Directions: Write T if the statement is true and if false change the underlined word to make
the statement true. Use another sheet of paper for your answer.
10 EPAS Q4 W1 M1 PAGE 7
______ 1. Tone control is a type of equalization used to make specific pitches or "frequencies"
in an audio signal softer or louder.
______ 2. Equalizers are found on a wide array of electronic devices.
______ 3. An equalizer (also called an “EQ”) is an audio filter that isolates certain frequencies
and either boosts them, lowers them, or leaves them unchanged.
______ 4. In their most basic form, tone control circuits attenuate the high or low frequencies of
the signal.
______ 5. Output stage is the stage that is connected to the loudspeaker.
______ 6. Audio Circuits are used to process and manipulate audio signals as required by the
application.
______ 7. Driver stage is the stage that is standing between the voltage amplification stage and
the output stage.
______ 8. The input signal to the amplifier from the source will be generally in the mill volt range
and it is very weak to drive the succeeding stages.
______ 9. A practical audio power amplifier must have dedicated circuits for producing voltage
gain and current gain.
______ 10. A simple RC coupled pre-amplifier makes considerable amount of voltage gain but it
cannot be considered as a power amplifier.
TEST II. Direction. Chose the letter of the best answer. Write your answer on another piece
of paper.
____ 1. A term used to describe any sound or noise that is within a range the human ear is
capable of hearing.
A. Audio C. Video
B. Signal D. Wave
____ 2. Technical term, referring to sound coming from a recording, transmission or electronic
device.
A. Audio C. Video
B. Signal D. Wave
____ 3. Are transducers that convert electromagnetic waves into sound waves.
A. Amplifier C. Converter
B. Barrier D. Speaker
____ 4. A transducer – that converts sound into an electrical signal.
A. Amplifier C. Converter
B. Microphone D. Speaker
____ 5. What is the unit used in measuring sound?
A. ampere C. coulomb
B. hertz D. Decibels (dB)

TEST III. ESSAY QUESTION: (5 points each)

Direction: Answer briefly the given question and explain.
1. What is the importance of the Amplifier?
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
2. What is the used of the Equalizer circuit?
____________________________________________________________________________
____________________________________________________________________________

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 10. A 10. D
9. I 9. D
8. H 8. B
7. G 7. D
6. F 6. A
5. J 5. A
4. B 4. B
3. E 3. B
2. D 2. A
1. C 1. A
ACTIVITY 2 ACTIVITY 1

KEY ANSWERS

REFERENCES
Books
Ebalan, Ambrosio E. 1998. Technology and Home Economics BASIC ELECTRONICS I , Third
Year,
Phoenix Publishing House, Inc. : Quezon City, Philippines

Grob, Bernard. 1996. Basic Electronics , Seventh Edition, Glencoe/McGraw- Hill: 936 Eastwind
Drive
Westerville, OH 43081 , USA

On line
What is Amplifier?
https://www.google.com/search?rlz=1C1CHBD_enPH780PH780&biw=912&bih=636&sxsrf=ALe
Kk02A2

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