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Kamis, 16 Februari 2012

CD PLAYER


CD PLAYER

Many of the advanced technologies of the reference series sa-7s1 are now at work in this premium player. For example, it uses the exclusive-to-marantz dynamic digital filtering technology, which makes standard CDs sound as incredible as SACDs. There are three filter characteristic to cater for different testes. The unit offer fully balanced signal handling on short symmetrical discrete circuit architecture and theHDAM-SA2 high-speed amplifier module. The internal high precision clock keeps jitter at the lowest possible level. The rigid double-layer chassis minimizes vibration. Extensive copper plating and system-block shielding keeps the signal as clean as possible. In addition, you get balanced XLR; gold-plated RCA output terminals and a low-noise LCD. All of which means that you can enjoy sustained signal integrity, original sound stage reproduction, unsurpassed rhythmic intensity, and an unparalleled quality of dynamic and peace.


The most widespread laser applications are unambiguously the optical data storage system such as CD, DVD and nowadays blue-ray disc (BD). The CD was originally designed for storage and playing back music and was later extended to the CD-ROM for computer storage. Most optical drives operate on the principle of detecting changes in the intensity of light that is reflected by the media surface. The data information is printed as so-called pits onto the reflective surface of the media. The limitation of the storage capacity is the wave length of the laser light. Light of the shorter wavelength can be focused better thus allowing higher storage density. Within this course the data detection, the control loop for the riding laser head and other components of an optical drive will be demonstrated using the open frame CD player. The optical technique to read data remains the same regardless of whether a CD, a DVD or a BD is used.

Examples of investigations
Reading assembly: a laser beam of 780 nm wavelength in focused on the CD by means of lenses L1 and L2. The spot size on the reflective layer is about 0.6. the light returning from the CD is reflected by the polarizing beam splitter cube (BD) due to the action of the quarter wave plat (QWP) and is imaged on the position sensitive sensor (PSD).
Detection of pits: once the laser beam hits a pit, a changes in reflected light intensity occurs due to partial scattering and destructive interference between the incoming and outgoing laser beam. The pit length or the time duration within the light level determines whether the data is interpreted as 0’s and 1’s of binary data. The analogue intensity variations can be observed by means of an oscilloscope.
Laser beam positioning: to keep the beam focus on the rotating disc the focusing lens (L2) can be moved vertically by means of a coil in response to an error signal. A cylindrical lens (L3) projects s round spot only when the beam is correctly focused. A position sensitive detector (PSD) can determine whether the images of the focus is round. If it is not the case in generates an appropriate focusing error signal. An additional control loop ensures that the reading head follows the data track on the CD. All error signals can be displayed by means of an oscilloscope.    



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