Bram Jacobse

Tinkering CD Players & Digital Audio

CDM 12

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The CDM 12.1 is a modular CD-mechanism, using a 2-stage, 3-spot system. It contains the following modules:

• a lightpen with holographic lightpath. (LDGU:Laser Diode and Grating Unit)

  • the actuator.
  • a disc motor assembly, containing a DC-motor with a turntable prepared for magnetical clamping
  • the frame with the sledge drive
  • the foil with the lasersupply

It is suited to be used in a wide variety of applica-tions, going from stand alone players for Midi and Mini systems to general Low End Hifi products.

To cope with this broad application range, the CDM 12.1 needs to be flexible:

  • suitable for 12 and 8 cm discs according to the CD standard.
  • limited size.
  • applicable in horizontal and vertical position.
  • wide temperature range.

Three beam tracking explained

The three beams of a CDM 12.1 are generated when the beam of the semiconductor laser (GaAl- As;which transmits invisible infrared light) trans- mits through the 3-beam grating on the top of the
LDGU (LDGU: Laser Diode and Grating Unit). The 3 beams are focused through the objective lens on the disc with central the main spot and on both sides the satellite spots (D1 and D5, also called R1 and R2) positioned 1/4 pitch off the track. With this configuration it is possible to de- termine the position of the main spot to the track.
(see fig. 1) The by the disc reflected spots are then transmit- ted through the objective lens and via the folding mirror towards the LDGU where the second gra- ting (Foucault grating) is deflecting the spots to
the detector diodes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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