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The audio signal is transformer–coupled for a balanced
output to the microphone connector. An active power supply
circuit regulates the phantom voltage, and the 1.5–volt bat-
tery provides instantaneous backup in case the phantom
power supply fails. The regularor/reverse voltage protector
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 taken
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, bat-
tery operation may still be possible. Similarly, if battery
operation is impaired, the SM94 may still operate on
phantom power. In either case, you should send the mi-
crophone to an Authorized Shure Service Center at your
earliest opportunity.
ARCHITECTS' SPECIFICATIONS
The microphone shall be a condenser microphone with a
frequency response of 40 to 16,000 Hz. It shall have a cardi-
oid 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 impedance
CAPACITOR
IMPEDANCE CONVERTER
CARTRIDGE
FET
WITH ACTIVE LOAD
BATTERY
of 150 Ω for connection to microphone inputs of 150 Ω or
higher. The open circuit voltage shall be –69 dB (0.30 mV)
to dB equals 1 volt per microbar).
The overall dimensions shall be 190.5 mm (7–
length by 27.7 mm (1–
eter 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 supplying
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
For additional service or parts information, please contact
the Shure Service Department at 1–800–516–2525. Out-
side the United States, please contact your authorized
Shure Service Center.
CLASS A
LF RESPONSE
COMPOUND
FILTER
AMPLIFIER
BLOCK DIAGRAM
FIGURE 4
3
3
/
in.) in diameter. The handle diam-
32
15
/
in.) The weight shall be 250
16
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BALANCED
TRANSFORMER
RFI
FILTER
REGULATOR/
REVERSE VOLTAGE
PROTECTOR
www.audiovias.com
1
/
in.) in
2
A25D
26A13
PS1A
A15AS
A53M
A3WS
C25J
RK255G
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