1. Unit-II Audio Systems
-12 Marks

2. Course Outcome
Maintain Audio Systems

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.

5. Construction of Compact disc
Storage area
15mm mm
1.2mm
Disc thickness
50mm
116mm
120mm

6. v Label side Recording side or Audio data
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).

8. Material used

9. Block Diagram of CD Player

10. Components of CD Mechanism
CD pick-up assembly
CD Lens:
- Collimation Lens
- Concave Lens
- Objective Lens
- Cylindrical Lens
3. Drive motors
- Tray, loading motor
- Slide, sled, feed motor
- Spindle, disc, turntable motor
4. Gear system

11. Pick –Up assembly

12. Pick-up Assembly

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
Tray or loading motor
Disc, spindle or turntable motor
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
Gain: voltage gain= 20log vo/vin(dB)
Bandwidth
Impedance
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.

26. Block diagram of Hi-Fi amplifier

27. Block diagram of Hi-Fi amplifier
Left channel Matching ckt. Right channel
Matching circuit
Pre-
Amplifier
Equalizer
Power amplifier
L.S.
Pre amplifier
Equalizer
Power Amplifier
Matching Network
L.S.

28. Controls available on Hi-Fi Aplifier
Balance , Blend and master gain control
Loudness control
Tone control
i)Bass control
ii) treble control
4.Quasi stereo switch
5. Mic in
6. Aux in
7.Earphone in

29. Block diagram of MP3 Player

30. Block diagram of Flash MP3 Player

31. A Home theater