6.0 AUDIO AMPLIFIER

Slide by Mohd Fairose

OBJECTIVE Understand principle of simple Audio

Amplifier Test the functionality of Audio Amplifier Troubleshoot simple Audio Amplifier Understand the principle of PA system Troubleshoot PA system unit

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6.0 AUDIO AMPLIFIER MENU

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AUDIO AMP VIDEO1AUDIO AMP VIDEO2PRINCIPLE OF AUDIO AMPLIFIER

AUDIO SYSTEM BLOCK DIAGRAMSCHEMATIC DIAGRAM OF AUDIO AMPLIFIERTEST THE FUNCTIONALITY

INPUT AND OUTPUTWAVEFORMTROUBLESHOOT AUDIO AMPLIFIERPRINCIPLE OF PA SYSTEM

PRINCIPLE OF SIMPLE AUDIO AMPLIFIER. Definition electronic amplifier that amplifies low-

power audio signals

between 20 - 20 000 Hz (level suitable for driving loudspeakers)

final stage in a typical audio playback chain.

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OBE Exercise

Discus in your group of what is the application of audio amplifier

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1

3

2Driver Amplifier

Audio / Power Amplifier

Pre Amplifier

I/P Transducer ex: mic, tape head etc.

Tone control – Bass, Volume, Treble

SpeakerAUDIO SYSTEM BLOCK DIAGRAM

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Transducer

converts one type of energy to another

energy types include electrical, mechanical, electromagnetic (including light), chemical and etc

CD/DVD Player, Tape, Radio AM/FM, Microphone, MP3 Player, IPod and etc

FUNCTION OF EACH BLOCKNextMenu

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Pre Amplifier prepares a small electrical signal for further

amplification or processing

often placed close to the sensor to reduce the effects of noise and interference

used to boost the signal strength without significantly degrading the signal-to-noise ratio (SNR)

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Tone control – Bass, Volume, Treble

equalize the sound produced on the speakers to match the original

Consist of Bass – low pass filter, Treble (high pass filter) and Volume (regulator)

basic principle of setting the tone is obtained by setting the value of R / C resonator in the filter circuit.

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Driver Amplifier

amplify signal from tone control

phase splitter & drive the power amplifier to operate.

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Audio/Power Amplifier

amplifying the regulatory signal from the tone circuit

vibrate the speaker membrane

main requirement is a low output impedance of 4-16 ohms and high efficiency.

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Speaker converts electrical signals into sound

signals

divided into three, namely the woofer (bass), Squeaker (middle), and the tweeter (high),subwoofer able to reproduce the audio signal below the woofer

Impedance of 4 ohm speakers, 8 ohms and 16 ohms.

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OBE Exercise

Discus in your group of what is the example of transducer What is the different between Bass

sound and Treble sound.

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SCHEMATIC DIAGRAM OF SIMPLE AUDIO AMPLIFIERPre- amp

uPC1032H low noise preamplifier

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When we want to use the signals from the tape head, magnetic needle, or a microphone as the input signal, then it must be through a network of small-signal amplifier

all input signal frequencies will be reinforced with multiples of the same magnitude.

In Figure 7.1 below shows a simple network of pre-amplifier. Equalizer network is determined by the values of R1, R2, R3, C2, C3, and C4 to adjust the value of Gain,A.

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Tone control

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Before the tone control circuit input, there is a transistor amplifier arranged with collector-base configuration feedback

Balance control located at the input transistors, the linear P2.

Bass voice is controlled by P3, whereas the treble voice operated by P4.

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Power amplifier (IC TA7230A)

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R14, R15, C24, and C25 at the input is a low pass filter network

C15 and C18 are used for input signal and arranged to prevent the voltage at on pins 3 and 8

C16 and C17 is a noun coefficients to the ac signal so that low-frequency sounds are not muted

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C19 is a bypass filter to the AF amplifier ripple voltage to it

Amplifier output is taken from pins 2 and 10 through capacitors C22 and C23, while power supply is supplied to the pin1 and 8.

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Power amplifier (IC LM386)

Bypass cap-avoid humming

Lowpass filter-adjust Bass

Coupling cap-block DC voltage (DC voltage can heat up and burn the speaker)

C1

C4

C3

C2

R1

R2

C1 and C2 known as bypass capacitor. It always applied at the voltage supplied to avoid humming noise.

C3 and R2 known as lowpass filter. It only let the low frequency pass. This also applied as a Bass sound controller.

C1 known as coupling capacitor. It block DC Voltage and only let AC Voltage through. DC can heat up and burn the speaker.

Power amplifier (IC LM386) operationV+

V-

npn

pnp

Power supply

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transformer center tap is used with the rating of 1A, 12-0-12 volts.

Diodes D1 and D2 serve as liters rectifier converts ac voltage the voltage dc and filtered by capacitor C26.

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C26 is supplied to the positive point of enforcement, at which point VCC.

Supply power to the network and pre-amplifier tone controls taken from points A and B after the voltage through the filter gyrator R17, C27, R18 and transistor BC 107.

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TEST THE FUNCTIONALITY OF AUDIO AMPLIFIER Use Audio generator and oscilloscope to

determine the voltage gain of the amplifier

Use multimeter to measure DC voltage

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INPUT AND OUTPUT WAVE FORM FOR EACH STAGE

Block Diagram of CRT Television

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TROUBLESHOOT SIMPLE AUDIO AMPLIFIER

Supply line variable voltage transformer (Variac) allows you

to make any power supply variable can be slowly increased while monitoring the

amplifier's output voltage (multimeter). Another useful test tool is a "lamp lead" - a

standard light bulb (usually 100W) wired in series with a mains lead (and properly insulated)

An amp with a short circuit fault will cause the lamp to glow at full brightness, but a normal load will cause the lamp to flash brightly for a moment, then settle down to a steady dull glow.

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Coupling component/signal line capacitive coupling is typically achieved

by placing a capacitor in series with the signal to be coupled.

In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked

Capacitive coupling is also known as AC coupling and the capacitor used for the purpose is known as a coupling or DC blocking capacitor.

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Biasing method of establishing predetermined

voltages and/or currents at various points

the point on the output characteristics that shows the direct current (DC), collector-emitter voltage (VCE), and the collector current (IC) with no input signal applied

The term is normally used in connection with devices such as transistors.

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Filtering electronic circuits which perform

signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both

high-pass, low-pass, bandpass,

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Distorted output

This diagram shows the behavior of a signal (made up of a square wave followed by a sine wave) as it is passed through various distorting functions.

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Distorted output The first trace (in black) shows the

input. It also shows the output from a non-distorting transfer function (straight line).

A high-pass filter (green trace) will distort the shape of a square wave by reducing its low frequency components. As the sine wave contains only one frequency, its shape is unaltered.

A low-pass filter (blue trace) will round the pulses by removing the high frequency components.

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A slightly non-linear transfer function (purple), this one is gently compressing as may be typical of a tube audio amplifier, will compress the peaks of the sine wave

A hard-clipping transfer function (red) will generate high order harmonics.

Parts of the transfer function are flat, which indicates that all information about the input signal has been lost in this region.

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PRINCIPLE OF PA SYSTEM Stage in PA system

Preamplifier

Equalizer/tone control

Driver Power Amplifier

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OBE Exercise.Discus in your group what is the purpose of

every stage below

Preamplifier

Equalizer/tone control

Driver

Power Amplifier.

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TO BE CONTINUED IN NEXT CHAPTER,…

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