Printed in U.S.A. Copyright © 2001, Jensen Transformers, Inc.
5
SPDT switch if phantom power must be turned on and off frequently. Components
R13
and
C13
provide filtering to prevent “on-off” transients and to remove any residual noise from the phantom
power supply before it reaches the microphone input. Resistor
R14
discharges
C13
to ground if
the connections to
P1
are left open inadvertently. Resistors
R15
and
R16
provide the phantom
power to the microphone input and are precision matched to maintain balanced common mode
input impedances. Dipswitch positions
S1-1
,
S1-2
and
S1-3
allow the phantom power
connections to be either connected or completely disconnected from the microphone input. Under
normal circumstances, these three switches should be either all
ON
or all
OFF
.
2.1.4 Ground Lift Circuitry and Switches
Ground switching is provided for each individual input and output to allow maximum
flexibility in the grounding and termination of the splitter transformer shield connections.
Dipswitch
S1-4
controls whether
the microphone input shield is floating or connected to
ground through a low impedance network. Resistor
R12
provides a low impedance to ground at
low frequencies and capacitor
C12
provides a low impedance to ground at high frequencies when
S1-4
is in the default
ON
position.
This low impedance network is used, instead of a hard ground
connection, to limit circulating currents between devices that might potentially create a ground loop
problem.
Dipswitch position
S1-5
connects the isolated output winding shield of the microphone
splitter transformer to ground through low impedance networks consisting of
R11
and
C11
when
the switch is in the
ON
position. The default position of
S1-5
is
OFF
, to simulate a floating
microphone at the isolated output.
2.2 Power and Ground Wiring
2.2.1 Chassis and Groundplane Connections
The JT-MS-8N2 incorporates a groundplane on the top (component side) of the printed
circuit board to provide a very low impedance for the individual input and output ground dipswitch
connections. This groundplane is normally connected to the steel chassis plate by the default
jumper connection at
P10.
If alternate grounding connections are required for some reason, this
jumper may be moved to its alternate position, and the groundplane connection may be hard-
wired through the
GND
terminals on
J91
.
Wire sizes between 14 and 26 gauge, either stranded or
solid, may be used to make connections to the JT-MS-8N2. Stranded wire should be used if
connections will be subjected to repeated movement or vibration, to prevent breakage.
2.2.2 Phantom Power Supply Connections
The JT-MS-8N2 is designed to be used with a 48 Volt to 52 Volt phantom power supply.
Normally, a 48 Volt supply will work fine. In some cases though, when using microphones that
require the maximum 48 Volt power to be available for proper operation, the phantom power
supply may need to be adjusted to 52 Volts to overcome the slight drop in voltage that occurs
across the transient filtering network
consists of
R13
and
C13
.
A power supply with a floating (transformer isolated) secondary, such as a typical linear AC-
DC supply, should be used to
prevent creating any inadvertent paths to ground.
The positive
terminal of the power supply should be connected to the
48+
terminal of
J91.
The negative, or
common, terminal of the power supply should be connected to the
48C
terminal of
J91
. Parallel
through connections are provided on
J91
to facilitate “daisy-chaining” of the phantom power
connections when utilizing multiple JT-MS-8N2 assemblies.
Wire sizes between 14 and 26 gauge,
