12
MODIIB STEREO PROCESSOR
and RIGHT PRE terminals on the rear panel. You
should read between 700 to 714 mV AC at these test
points.
If this is a two projector system, change over from
Projector 1 to Projector 2 by grounding the CHNG-
OVER terminal on the back panel. Then repeat the
above A chain calibration steps for the second projec-
tor.
SURROUND NULL:
Turn off switch #2 (to the left) on the Meter Card.
Now, turn on switch #3 (to the right) which makes the
bottom LED array the NULL reading. Select the
STEREO A button on the Format Card. Adjust the
SURROUND NULL trimpot on the Matrix Card until
a minimum number of LED’s are lit on the bottom
LED array of the Meter Card. A good null is when
only two or three LED’s are lit. This setting is crucial
because a good null means minimum crosstalk in the
surround channel. For normal operation, leave switch-
es #2 & #5 on (to the right), and all others off.
The most likely cause of difficulty in obtaining a good
null is the azimuth alignment of the optical sound
lens. This is a very critical soundhead adjustment if
you expect to get the best performance.
BYPASS:
Run a film soundtrack. Listen to the CENTER channel
on the booth monitor. Switch from Normal to Backup
(the switch on the Format Card) and adjust the backup
level pot on the Mono Card to achieve equal levels
while switching from Normal mode to Backup mode.
This completes the A Chain and BYPASS calibrations.
B CHAIN CALIBRATION
The B chain calibration is generally considered to be
the signal path from the processor’s master fader to
the speakers. This signal path includes the equalizers
and output stage. Before continuing with the B Chain
calibration, check the wiring of all auditorium speak-
ers to make sure the phase is correct. The “SMART EZ
Phase Checker” is a perfect unit for verifying proper
phase of speakers.
PRELIMINARY:
It is desirable to have a SMART PINK NOISE GENER-
ATOR CARD and an EXTENDER CARD for perform-
ing the calibration and testing of the MODIIB. Note:
Make sure the SMART Pink Noise Generator Card has
the following minor modification: There must be a
jumper wire between pins 4 & 5 of the edge connector
as viewed from the component side. This allows the
Surround switch to simultaneously feed pink noise to
both Left and Right Surround channels. A future ver-
sion of the Pink Noise Generator card will have sepa-
rate Left and Right Surround switches.
The PINK NOISE card may be plugged directly in
without the extender card if the metal cover is
removed from the Pink Noise Card. However, it is
easier if the extender card is used with the PINK
NOISE card. The PINK NOISE card plugs into the
MATRIX CARD position for setting house EQ levels
and sub-bass levels. The PINK NOISE CARD has
seven switches. Make sure the bottom switch is in the
NORMAL position. The top six switches are used to
turn individual channels on and off. These channel
switches are three position, with center position being
off, the top position giving an in-phase signal and the
bottom position giving an out-of-phase signal. There is
a built-in high quality pink noise source which feeds
these switches.
If a Pink Noise Card is not available for the MODIIB
calibration, then an external pink noise source may be
used instead. Feed the external pink noise source into
the DIGITAL INPUTS on the rear DB25 input connec-
tor of the MODIIB for the following checks. Set the
pink noise source level for .55 volts RMS. You must
use an analog meter to measure this voltage level.
Special Note: If you will be installing an external digi-
tal decoder, do so AFTER setting house levels. See the
DIGITAL LEVEL SETTINGS at the end of the B
CHAIN CALIBRATION section for more information.
For the following procedures, select STEREO A by
pushing the appropriate button on the Format Card.
Also, set the FILM LEVEL fader to the one o’clock
The optional extender card can be used with the Pink Noise
Card to calibrate the MODIIC. This allows easier access to
the Pink Noise Card.
