Dolby Laboratories CP65 manual Optical Preamplifier Adjustments

4-6

A-Chain Alignment Procedures

b. Optical Preamplifier Adjustments

Step	Action	Indication
No.

1

2

3Cat. No.

240A

Proj. 1

GAIN Lt

hf

GAIN

Rt

hf

Lt tp

Lt

signal

present

Rt

Rt tp

GAIN Lt

hf

GAIN Rt

hf

Proj. 2 gnd

4-7

A-Chain Alignment Procedures

b. Optical Preamplifier Adjustments

Notes

Loosely install the stereo solar cell bracket on the projector. Position the bracket carefully until the surface of the cell is 1 mm from the film plane surface. Note that if this distance is exceeded, there will be crosstalk between the two optical stereo tracks. Check the image of the slit on the cell. The image should be a thin sharp line. The slit image should be as long as the cell, and positioned three-quarters of the way up the cell. Try to get the best compromise among all of these conditions and then tighten the cell bracket mounting screws.

Connect the cells to the correct CP65 input terminals via the terminal block, using a single “twisted pairs” shielded (screened) 4-conductor cable or two shielded 2-conductor cables. Connect the inner conductors to the projector input + and – terminals exactly as shown. Connect the shields only at the CP65 end. Note that the cell associated with the right channel is closest to the edge of the film.

Separate cells are used for each channel in reverse scan projectors. Both use identical red (high) and black (low) wires. A check will be made in Step 9 to determine the correct left and right placement.

On the Cat. No. 240A Optical Preamplifier Card

Turn all of the Proj 1 and Proj 2 gain potentiometers fully clockwise (CW).