MOD 7a STEREO PROCESSOR
14
10 Observe the real time analyzer and focus the lens for
maximum high frequency output while maintaining the
best azimuth.
This is not easy, but it is one of the most critical adjustments
affecting the overall system performance and is often not
done as well as it should be.
11. Adjust the vertical and lateral alignment of the EX-
CITER LAMP for maximum output on both channels. This
is especially critical with a narrow slit optical lens because
there is a much smaller window for the light to pass
through.
12. Check the high frequency output on both channels and
make sure the response is the same on both channels
.
With a narrow slit optical lens, the response should be flat
within ± 3 dB to about 12 kHz with NO slit loss correction.
If not, this MUST be corrected before proceeding with the
next steps. It is not permissible to use slit loss correction to
correct poor high frequency response caused by misalign-
ment of the optical soundhead. An EXCITER LAMP out of
alignment, the barrel of the optical lens crooked, or oil in
the optical lens will all affect output and balance.
Slit Loss Correction
1. Run the Pink Noise side of C.A.T. #69 Test Film.
2. Observe the frequency response on your RTA which
should be still connected to the preamp testpoints.
2. Adjust the left and right slit loss correction trimpots on
the PREAMP for optimum flat high frequency response.
Do not over adjust the slit loss correction in an effort to
obtain extended response. This will result in an undesir-
able frequency response peak. While adjusting the slit loss
correction, aim for as flat a high frequency response as
possible. If one of the preamp channels is slightly worse
that the other , then adjust the better responding preamp to
match the lesser. This will ensure that the matrix steering
in the MOD 7a will be as accurate as possible.
Optical Preamp Calibration
1. Run a Dolby C.A.T. #69 Test Film, Dolby tone side.
2. Locate the preamp calibration switch (SW1) and LEDs
(LED1 and LED2) on the left hand side of the front of the
main circuit board.
3. Push SW1 to the left. This causes the LEDs to indicate
the status of the Left channel preamp level.
Make sure you are changed over to the correct projector by
observing the
CHANGEOVER
terminal on the back of the
MOD 7. If the pin is open, the system is in projector 1
mode, if it is grounded, the system is in projector 2 mode.
4. Adjust Projector 1 left channel gain control (L1) until
both LEDs are lit.
This is a critical adjustment. You may not be able to get
both LEDs on simultaneously. Try to get as close as
possible.
5. Repeat steps 1-4 for the right channel gain control (R1),
and for projector 2 left and right channel gain control (L2
and R2).
Left side potentiometers (Preamp, slit loss, hearing impaired,
and backup levels) and preamp calibration selector switch
Figure 7. Pink noise in X/Y mode on the oscilloscope.
Preamp Calibration LEDs
