71
t h e m a i n a u d i o s i g n a l . M o d u l e # 2 i s a l o w p a s s f i l t e r w i t h g a i n . T h e o u t p u t s o f
t h e s e f i l t e r s a r e s u m m e d a t U 1 1 5 B . W h e n t h e g a i n , o f m o d u l e # 2 , i s s e t t o e q u a l
t h a t o f m o d u l e # 1 , t h e o v e r a l l r e s p o n s e o f t h e s y s t e m i s f l a t . B u t a s g a i n i s
i n c r e a s e d a t m o d u l e # 2 , t h e b o o s t e d l o w f r e q u e n c i e s w i l l o c c u r , i n t h e r e s p o n s e
o f a s h e l v i n g e q u a l i z e r , a l o n g t h e s l o p e o f t h e l o w p a s s f i l t e r . I f t h e m o d u l e s a r e
c o n f i g u r e d a s t h i r d o r d e r , t h e n t h e s h e l v i n g E Q w i l l f o l l o w a t h i r d o r d e r
r e s p o n s e . L i k e w i s e i f t h e m o d u l e s a r e c o n f i g u r e d a s s e c o n d o r d e r f i l t e r s . T h e
s t o c k c o n f i g u r a t i o n p r o v i d e s a t h i r d o r d e r b a s s e n h a n c e t h a t b e g i n s a r o u n d 1 0 5
H z .
S E L E C T A B L E M A T R I X N E T W O R K
U119A/B and the associated resistors create the L+R, L-R matrix for sum and difference processing.
Amplifier U119A/B is set for a gain factor of 0.5. When summing a left/right signal that consists of
full mono content, the summing action provides a 6dB increase in level. When this is coupled with a
gain stage of 0.5, unity gain of the stage is accomplished in full mono. This is done so that the gain
structure of the rest of the processing system can remain the same.
The output of U119A/B is routed to the berg jumpers that allow selection of discrete L/R or matrixed
L+R/L-R operation. When in the matrix configuration, the L+R signal occupies the left side
processing, and the L-R occupies the right side.
CROSS-OVER and DIGITAL PROCESSORS
C i r c u i t B o a r d s # 3 & # 6
Circuit boards #3 and #6 are essentially the same board. Board #3 handles the initial cross-over
network and provides the multiband leveling audio path. While #6 performs the limiting function and
provides a second cross-over, necessary only when the second path-point is utilized. Since the
technical description is similar, only the #3 board will be discussed. However, any small differences
between the two, will be referenced.
Wideband input audio appears, unbalanced, at pins 9 and 10 of J-1. Inputs for each individual band
will be described later. U202 and U205 form a phase linear bi-quad cross-over network. U203, U204,
and U206 are used to adjust the cross-over frequencies. The output of each band appears at the three
pin jumpers for each band. These jumpers select the input mode for each processor. In the first
position, the output of the cross-over is selected to feed the processor. This is the normal operation
mode for board #3. The second position selects the direct input to the processor. This configuration
allows direct input from a preceding processor section. This is the normal mode for board #6 where
direct audio is arriving to each limiter band directly from the preceding leveler band.
Whenever the second patch-point is used, the jumpers on board #6 would be set to the first position to
accept audio from the cross-over network on board #6. It should be noted that whenever the second
cross-over is utilized, the cross-over frequencies automatically match the cross-over points of the first
