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SPA-3 STEREO PRECISION ATTENUATOR
I. DESCRIPTION
The SPA-3 is a stereo preci-
sion attenuator accessory
G
for use with DataPort-
O
equipped QSC amplifiers. It
mounts directly to the back
of two-channel CX, DCA, and
PL2 models, but it can be
O
used with the others
(PowerLight, ISA, and four-
channel
CX
or
DCA
amplifers) by using a
T
DataPort cable and a re-
mote mounting rack. Ampli-
o C
fiers from the ISA series
cannot power the SPA-3, so
it requires a 15-volt exter-
C
nal DC power supply when
used with one of them.
C
Signal
LED
Input
Stage
Up
Micro-
Down
½
controller
Shift
S
P
A
3 -
S
P
C E
F I
C I
T A
O I
N
S
E
N
R E
L A
N I
O F
R
M
T A
O I
N
p
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g n
e t
m
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a r
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u p
t t
p y
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c
a h
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l e
I
p n
t u
m i
p
d e
n a
e c
u
p t
t u
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p
d e
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x a
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u
m
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M
S
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a t l
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y D
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r
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v
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m
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o
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e
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a r
m
i m
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D
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R
S
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t t
n e
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o i t
( n
a e
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c
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S
g i
a n
p l
e r
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c n
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a e
h c
c
a h
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) l e
0
5 .
d
B
n i
i d
a c
o t
( r
a e
h c
c
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n n
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N
N
E
T C
O
R
S
I
p n
t u
D
a
a t
o P
t r
x E
e t
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l a
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r e
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R
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M
A
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E L
O
P
R E
T A
N I
G
P
A
R
A
A
e t t
u n
i t a
n o
y B
a p
s s
Digital
Potentio-
meter
Output
Stage
8.8.
2-Digit
7-Segment
Display
i D
e f f
e r
t n
l a i
8 2
4 .
t u
u p
l t
v e
) l e
>
1 +
V 5
@
3 <
0 0
m
A
v
a i
e
. t x
P
s u
b h
t t u
n o
s
w
t i
h c
s e
T
w
o
3
p -
n i
2
5 .
m
M
T E
R E
S
0
o t
To amplifier,
via DataPort
Block diagram of one channel of the SPA-3
2
0
7 –
° 0
C
a b
a l
c n
d e
t (
a r
s n
o f
m r
r e
b
l a
n a
i c
g n
o
i t p
Ω Ω Ω Ω Ω
Ω Ω Ω Ω Ω
k
b
l a
n a
e c
, d
4 1
7 .
k
n u
a b
a l
c n
d e
5 9 Ω Ω Ω Ω Ω
q ,
a u
- i s
a b
a l
c n
d e
+
8 1
d
B
u
e l
s s
h t
n a
1 -
0 0
d
r B
1
6 1
d
B
<
. 0
3 0
%
0 2
H
– z
0 2
k
H
, z
0 ±
2 .
d
B
0 5
d
B
m
n i
m i
u
m
> ;
0 6
d
B
t
p y
c i
l a
o p
w
e
j r
c a
, k
r o
o r f
m
a
m
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e i f
v r
a i
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: t n
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, t f i
U
2
d -
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o
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