JBL Professional Series - Input Connections; Program Input; Microphone Input; Expander Input

Input
Connections
Program—
The
program
channels
are wired for
unbalanced
50,000-ohm
operation
and are
equipped
with both
screw
terminals
and
phone
jacks on
the rear panel. Either
of the
channels
can
be
converted
to
600-ohm bridging
input
by
removing
the
jumper
between
pins
2 and
8
(marked
by
white
dots) of
the
transformer
socket which
is
located on
the
chassis,
and
inserting
a
JBL
5196
plug-in
transformer.
Access
to
the
chassis
can
be
gained
by
removing
the top
cover
plate which
is
held
in place
by eight
sheet metal
screws.
Program
1
will
accept
the low level
output of
a
magnetic
phono
cartridge
if
the
jumper
between socket
pins
2 and
8
is
removed
and
a
model
5192 Phono Preamplifier
Module
is
inserted
in
its
place.
The
5192 connects
the phono
jacks
on
the
rear
panel
to
the
Program
1
preamplifier
circuit.
The
two
jacks,
marked
"Phono
Input,"
are paralleled
to
combine
the
signals
from
a
stereo
cartridge;
a
monaural
cartridge
can
be
plugged
into either of the
jacks.
Microphone—
The
microphone
channels
are each transformer
isolated
and
balanced for
50 to
600-ohm inputs.
Input con-
nections
are
made
through
female
XLR
connectors.
Pin 1
of
each
connector
is
ground and
pins
2 and 3 are the
balanced
input.
A high
level
input
that
would ordinarily
be connected to the
program
channels
may
be fed
to any
of
the microphone
inputs
if
external
loss
pads
are employed.
Under
these conditions,
microphone
channels
so used cannot be driven
beyond .5 volts
RMS
without
excessive
distortion.
A
high
level,
high
impedance program
source,
such as a tuner
or ceramic
phono
cartridge,
may be connected to
a
micro-
phone
channel
if
the
program
channels are
not available.
To
accomplish
this,
it is
necessary
to make a
pin adaptor to
replace
the
microphone
input transformer.
Connect
a
1
-micro-
farad
capacitor
across
pins
5
and
9
and connect
a
jumper
between
pins
1 and
3 of
the
adaptor. With the adaptor in
place,
input
impedance
will
be about
300,000
ohms, and pin
2
of
the
XLR
connector
will be connected
to ground.
The
peak
flasher
will
indicate
when
input voltage
is
too
high. This
modification
will
also
allow
use
of
a
high
impedance microphone.
Expander—
A five
pin
XLR
female
connector,
marked "Expander
Input,"
supplies
power
to a JBL 5308 8-channel expander
and
receives
the
mixed
signal from
the expander.
A
"Y" adaptor
can
be
fabricated
to
allow the
use
of
two
5308's.
The
Expander
Input
must
not
be
used to supply
power
to any
other accessory.
Output
Connections
The output
transformer
has
a split secondary
winding
to
permit
600-ohm or
dual
150/600-ohm
connections.
Balanced—
To achieve
a
600-ohm balanced
output,
terminals
2 and
3
on
the
rear
panel must
be strapped.
The output
connection
can
be made
at the male
XLR connector
pins
2 and
3
or
at screw
terminals
1 and
4 with
the
shield
connection
to
pin
1 of
the
connector or
at
the
terminal
marked
"GND."
600
n BAL
Shield
600-Ohm
Balanced
Output
For
150-ohm
output the
transformer
windings
may be
paral-
leled.
Starting
at the left
of the
terminal
strip,
strap
terminals
1 and
3
and
strap
terminal
2 to
terminal
4.
The
output
connection
can
then
be made
at terminals
1 and
4.
150-ohm Balanced
Output
4