User`s manual
2-20
There is also a pair of inputs which can be connected video projectors
etc. and which feed the Dolby decoder. This input can also be used for
background and intermission music.
The board also carries the driver circuitry for the Cat. No. 222A or Cat.
No. 222SR/A modules and the audio delay circuit for the surround
channel.
The Low frequency content of the front screen speaker signals is
separated and sent to a special output stage to drive a subwoofer if
required. If this signal is derived from optical sources, then it passes
thought a sliding band downward expander circuit which suppresses
very low frequency interference which can result from poor handling of
the film.
If the unit is to be used with a large amount of mono material, there is
a circuit which generates a pseudo-stereo output which tends to liven
up such sources and enhance the reproduction of music. This mode is
selected by a jumper on the main board.
Cat. No. 513 Equalization Board
The Cat. No. 513 board carries all the house equalizer controls for
adjusting the room response of the theater. There are seven 2/3 octave
bands which cover the frequencies which cause most difficulty in
loudspeaker systems. The bass and treble boost and cut controls are
parametric with adjustable turnover frequencies to compensate for both
the rate at which response tends to rise or fall and the corner frequency
where the tendency starts.
There are also simple three band surround equalizer sections and a two
pole filter for the subwoofer channel.
The main activity indicators are also on the front panel so that signal
activity on each channel can be checked.
The rest of the card is taken up with the controls for selecting the format
of the film to be shown or for selecting background music, etc.
Cat. No. 515 Stereo Surround Card (Optional)
The Cat. No. 515 is a small board that is mounted on the Cat. No. 511
main board when stereo surround operation is desired. It has voltage
controlled amplifiers and switching logic which control the source of
the stereo surround signal feed. In Formats 4 and 5, the source is the
motion picture matrix decoder on the main board, when format 60
(AUX) is selected, the source is the right surround input on the rear of
the unit. When the board is not fitted, the surround source is a 1:1 mix