12
gain. Make sure that all other B-chain calibration adjust-
ments have been made prior to adjusting the digital input
levels on the External Input/NR Switching Card (see special
note in the PRELIMINARY section of the B CHAIN CALI-
BRATION).
A CHAIN CALIBRATION:
PRELIMINARY:
1. Clean soundhead optics, exciter lamp, optical lens and
solar cell before attempting a soundhead alignment.
2. Set exciter lamp voltage for at least 80% of rated voltage.
BXM 9 volt 4 amp — 7.2 volts
BXN 10 volt 5 amp — 8 volts
Most foreign 6.3 volt 4 amp — 5 volts
3. Make sure film/cell spacing is approximately 1mm with
the slit image striking the top one-third of solar cell.
4. Connect scope and real time analyzer to the left and right
preamp outputs on the rear terminals of the MOD V, or at
the test points (mini-banana jacks) on the front panel dis-
play board.
5. Locate gain controls on 300 Preamp Card. Turn gain
controls fully clockwise.
6. Turn the MASTER FILM FADER all the way down to
avoid excessive noises in the auditorium
for the next steps.
SOUNDHEAD ALIGNMENT:
1. Play a S.M.P.T.E. Buzz Track loop.
Adjust the lateral film guide assembly or
exciter lamp assembly. Monitor the pre-
amp signals with the oscilloscope. Adjust
for minimum signal on the left and right
channels. Refer to specific instructions in
the projector soundhead manual. Minor
variations in alignment procedure depend
on the individual mechanical design of the soundhead.
2. Play CAT.# 97 Stereo Cell Alignment Film. Move solar
cell laterally and vertically until you have achieved mini-
mum crosstalk between channels (see above right).
3. Repeat steps 1 and 2 until no further improvement can be
obtained.
4. Play Pink Noise side of CAT.# 69 Test Film. Switch
scope to X/Y Mode. Adjust soundhead optical lens azimuth
for narrowest diagonal trace. 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.
5. Adjust the vertical and lateral alignment of the EXCITER
LAMP for maximum output on both channels. This is espe-
cially critical with a narrow slit optical lens because there is
a much smaller “window” for the light to pass through.
6. Check the high frequency output on both channels. Make
sure the response is the same on both channels. With a nar-
row 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 misalignment of
the optical soundhead. An EXCITER LAMP out of align-
ment, the barrel of the optical lens crooked, or oil in the
optical lens will all affect output and balance.
OPTICAL PREAMP CALIBRATION:
Run the pink noise side of the CAT. # 69 loop. Observe the
frequency response on your RTA which is still connected to
the preamp testpoints. Adjust the left and right slit loss cor-
rection trimpots on the PREAMP CARD 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 undesirable frequency response peak.
Note: 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 than the other, then adjust the bet-
ter responding preamp to match the lesser. This will ensure
that the matrix steering in the MOD V will be as accurate as
possible.
While running the Dolby CAT. # 69 loop, tone side.
Observe the preamp calibration LED’s on the front panel
display board. These LED’s are located near the right front
of the display board, component side. Adjust the LEFT and
RIGHT trimpots on the PREAMP CARD until both LED’s
Low crosstalk between channels.
The preamp calibration LED’s
