3. Introduction
•A compact disc, or CD, is an optical storage medium with
digital data recorded on it. The digital data can be in the
form of audio, video, or computer information. When the
CD is played, the information is read or detected by a tightly
focused light source called a LASER (thus the name optical
medium). This article will focus on audio compact discs,
which are used to play back recorded music.
•By the late 1970s, a common set of standards for the optical
storage discs had been developed by the joint efforts of Sony
and Philips.
•A consortium of 35 hardware manufacturers agreed to
adopt this standard in 1981 and the first compact discs and
compact disc players were introduced in the market in
1982.
4. What is a CD?
A compact disc is a thin, circular disc of metal and plastic
about 12cm (just over 4½ inches) in diameter.
It's actually made of three layers. Most of a CD is made
from a tough, brittle plastic called polycarbonate.
Sandwiched in the middle there is a thin layer of
aluminum. Finally, on top of the aluminum, is a protective
layer of lacquer. The first thing you notice about a CD is
that it is shiny on one side and dull on the other. The dull
side usually has a label on it telling you what's on the CD;
the shiny side is the important part. It's shiny so that a
laser beam can bounce off the disc and read the
information stored on it.
6. On one side of the disc the audio signals are recorded on
other side label ,indicating contents of the disc are
printed.
v Label side
Recording side or
Audio data
7. Size and capacity-
•Diameter- 4.75 inch(120mm)
•Whole to insert CD- 15mm
• Actual storage area- 33mm circular
• Disc thickness- 1.2mm
•A standard CD can store up to 74 minutes of data i.e.
audio information However, most CDs contain only
about 50 minutes of music, all of which is recorded on
only one side of the CD (the underside).
13. Lenses used in CD Player
1.Collimation Lens
2. Objective Lens
3. Concave Lens
4. Cylindrical lens
14. Collimation Lens
It is used to produce completely parallel beams of
LASER.
This lens together with objective lens is used to focus
the laser beam to the disc surface.
15. Objective Lens
•It is used to focus the LASER beam onto the CD
surface and to receive the reflected beam.
• It sharpens the beam and focus exactly at the
center of CD track using focus and tracking coil.
16. Concave Lens
•This concave lens is used to concentrate the beam
•Reflected back from the disc surface, on to the
photo-diode array.
•This lens is mainly used to improve the sensitivity
of the photo diode array.
17. Cylindrical lens
It is used to enable the reflected beam from the Cd
to assist in creating the necessary signal to make
sure that that focus of the laser beam on the
playing surface of the disc is maintained.
18. Drive motors in CD player
Types of drive motors used in CD player
1. Tray or loading motor
2. Disc, spindle or turntable motor
3. Slid , sled and feed motor
19. Tray or loading Motor
• It is also called carriage motor, moves tray in and
out for loading and unloading the disc.
• Usually plastic tray is driven by a plastic gear box
next to the play assembly.
• The tray of loading motor is controlled by a
loading driver IC and a signal from the system
control IC processor.
20. Slide, sled , feed motor
•It moves the optical pick- up assembly across the
disc from the inside to the outside rim of the CD ,
keeping the objective lens constantly in line with
the centre of the optical axis or track.
• The motor is gear driven to a rotating gear that
moves pick-up assembly up and down.
21. Spindle disc and turntable motor
•The spindle motor starts to rotate after the disc
has been loaded.
• the disc starts at approximately 500 RPM slows
down to approximately 200RPM.
22. Hi-Fi Amplifier
• Hi-Fi means High Fidelity.
• Fidelity means faithfulness.
• High fidelity reproduction is essentially sound
reproduction such that the most critical
person can listen without any distortion.
23. Hi-Fi Amplifier Characteristics
Stereo Amplifier becomes Hi-Fi amplifier if the
following requirements fulfilled-
1.Signal to noise ratio should be better than 50dB.
2.Frequency response should be flat within +-1dB.
3.The system should posses dynamic range of
atleast 8dB.
4.Non linear distortion should be less than 1%.
5.Stereophonic effect should be provided.
6. Environmental conditions should be such as to
eliminate the external noise in listening room.
24. Specifications of Hi-Fi Amplifier
1. Gain: voltage gain= 20log vo/vin(dB)
2. Bandwidth
3. Impedance
4. Distortion
i) Frequency distortion
ii) Phase Distortion
iii) Amplitude distortion
iv) Self oscillation distortion
25. Comparison of stereo and Hi-Fi
amplifier
Sr.No Stereo Amplifier Hi-Fi Amplifier
1 Less signal to noise ratio. Better signal to noise ratio.
2 Non-linear distortion occurs. Non-linear distortion not
more than input/output.
3 Equalizers not used. Equalizers used.
4 Two- way cross-over network
with gain control exist.
Three- way cross-over
network exist.
27. Block diagram of Hi-Fi amplifier
Left channel
Matching ckt.
Right channel
Pre-
Amplifier
Pre
amplifier
Equalizer
Equalizer
Power
amplifier
Matching
circuit
Power
Amplifier
Matching
Network
28. Controls available on Hi-Fi Aplifier
1. Balance , Blend and master gain control
2. Loudness control
3. Tone control
i)Bass control
ii) treble control
4.Quasi stereo switch
5. Mic in
6. Aux in
7.Earphone in
