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ply circuit regulates the phantom voltage, and the 1.5-volt
battery provides instantaneous backup in case the phan-
tom power supply fails. The regulator/reverse voltage pro-
tector provides built-in protection against miswired cables
and equipment.
TROUBLESHOOTING
Due to the circuit complexity of the SM94, only basic ser-
vicing is recommended. The following steps should be tak-
en if problems arise:
1. Check the power supply output voltage. For the Shure
PS1A, this should be 21.5, ±1.5 Vdc, open circuit.
2. Check the voltage on connector pins 2 and 3 (at back
of connector, with cable connector removed from shell,
but connected to microphone). The voltage at pins 2
and 3 with reference to pin 1 should be between 10 and
48 Vdc.
3. If the microphone does not work on phantom power,
battery operation may still be possible. Similarly, if bat-
tery operation is impaired, the SM94 may still operate
on phantom power. In either case, you should send the
microphone to an Authorized Shure Service Center at
your earliest opportunity.
CAPACITOR
IMPEDANCE CONVERTER
CARTRIDGE
WITH ACTIVE LOAD
BATTERY
FET
LF RESPONSE
FILTER
ARCHITECTS' SPECIFICATIONS
The microphone shall be a condenser microphone with
a frequency response of 40 to 16,000 Hz. It shall have a
cardioid directional characteristic, with cancellation at the
sides of 6 dB and a minimum cancellation at the rear of 15
dB at 1 kHz. The microphone shall have a rated output im-
pedance of 150 Ω for connection to microphone inputs of
150 Ω or higher. The open circuit voltage shall be –49 dBV/
Pa (3.5 mV) dB equals 1 volt per Pascal).
The overall dimensions shall be 190.5 mm (7–
length by 27.7 mm (1–
ameter shall be 24.1 mm (
grams (8.8 oz).
The microphone shall be capable of being powered by a
phantom power supply with an output of 11 to 52 Vdc, or by
a mixer, audio console or tape recorder capable of supply-
ing 11 to 52 Vdc, or by an internal 1.5–volt battery.
The microphone shall be a Shure Model SM94.
FURNISHED ACCESSORIES
Swivel Adapter
Carrying/Storage Bag
OPTIONAL ACCESSORIES
Phantom Power Supply
Switch–Selectable Attenuator
Isolation Mount
Windscreen
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.6 m (25 ft.) Cable
REPLACEMENT PARTS
Screen and Grille
CLASS A
COMPOUND
AMPLIFIER
REVERSE VOLTAGE
BLOCK DIAGRAM
FIGURE 4
3
3
/
in.) in diameter. The handle di-
32
15
/
in.) The weight shall be 250
16
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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. . . . . . . . . . . . . . . . . . . . . . . .
BALANCED
TRANSFORMER
RFI
FILTER
REGULATOR/
PROTECTOR
1
/
in.) in
2
A25D
26A13
PS1A
A15AS
A53M
A3WS
C25J
RK255G
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