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regulates the phantom voltage, and the 1.5-volt battery provides
instantaneous backup in case the phantom power supply fails. The
regulator/reverse voltage protector provides built-in protection
against miswired cables and equipment.
TROUBLESHOOTING
Due to the circuit complexity of the SM94, only basic servicing 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, battery
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 microphone to an Authorized
Shure Service Center at your earliest opportunity.
CAPACITOR
IMPEDANCE CONVERTER
CARTRIDGE
WITH ACTIVE LOAD
BATTERY
FET
LF RESPONSE
FILTER
BLOCK DIAGRAM
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 impedance 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 (7–1/2 in.) in length by
27.7 mm (1–3/32 in.) in diameter. The handle diameter shall be
24.1 mm (15/16 in.) The weight shall be 250 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 .................................................................. A25D
Carrying/Storage Bag ...................................................... 26A13
OPTIONAL ACCESSORIES
Phantom Power Supply.................................................... PS1A
Switch-Selectable Attenuator ........................................ A15AS
Isolation Mount ................................................................. A53M
Windscreen ..................................................................... A3WS
7.6 m (25 ft.) Cable .......................................................... C25J
REPLACEMENT PARTS
Screen and Grille ......................................................... RK255G
CLASS A
COMPOUND
AMPLIFIER
REVERSE VOLTAGE
FIGURE 4
3
BALANCED
TRANSFORMER
RFI
FILTER
REGULATOR/
PROTECTOR
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