Shure SM94-LC User's Guide download pdf (Page 2)

Output Impedance

Rated at 150 Ω; 200 Ω actual

Recommended Minimum Load Impedance

800 Ω

Sensitivity (at 1,000 Hz)

Open Circuit Voltage: –49 dBV/Pa (3.5 mV) (phantom)

–50 dBV/Pa (3.2 mV) (battery) (1 Pa = 94dB SPL)

Output Clipping Level (1 kHz, 3% THD)

800-Ω Load–14 dBV (0.63 V) (phantom), 1% THD;

–23 dBV (0.71 V) (battery), 3% THD

Total Harmonic Distortion

< 0.25% (130 dB SPL at 250 Hz into 800 Ω load)

Maximum SPL

800 Ω Load: 141 dB (phantom), 123 dB (battery)

Hum Pickup

–3 dB equivalent SPL in a 1 millioersted field (60 Hz)

Output Noise (equivalent sound pressure levels;

measured with true rms voltmeter)

22 dB typical, A-weighted

25 dB typical, weighted per DIN 45 505

Dynamic Range

119 dB (phantom); 101 dB (battery) (maximum SPL,

2000–Ω load, to A–weighted noise level)

Signal-to-Noise Ratio

72 dB (IEC 651)* at 94 dB SPL

Overvoltage Protection

Maximum External Voltage Applied to Pins 2 and 3

with respect to Pin 1: +52Vdc

Reverse polarity protected to 75 Vdc

Polarity

Positive pressure on diaphragm produces positive

voltage on pin 2 relative to pin 3

Cartridge Capacitance

24 pF

Power

Phantom Operation

Supply Voltage: 11 to 52 Vdc, (+) pins 2 and 3

Current Drain: 1.0 to 1.2 mA max. at 52 Vdc

Battery Operation

Type: 1.5 V alkaline, AA size (NEDA 15A)

Life: Up to 5,000 hours with fresh battery

Environmental Conditions

Temperature:

Storage: . . . . . . . –29° to 74° C (–20° to 165° F)

Operating: –6.7° to 49° C (20° to 120° F)

Humidity:

Storage . . . . 0–95% relative humidity at room

temperature (72° to 80° F, 22° to 27° C)

Connector

XLR professional audio 3-Pin

Case

Steel and brass construction with gray finish and

stainless steel mesh grille

Dimensions

See Figure 3

OVERALL DIMENSIONS

FIGURE 3

Weight

Net 250 grams (8.8 oz) less battery

Packaged SM94-LC: 949.7 grams (2 Ib 1 1/2 oz)

Certification

Eligible to bear CE Marking. Conforms to European EMC Directive

89/336/EEC. Meets applicable tests and performance criteria in

European Standard EN55103 (1996) parts 1 and 2, for residential

(E1) and light industrial (E2) environments.

*S/N ratio is difference between microphone output at 94 dB SPL and

microphone self-noise A-weighted.

OPERATION

The SM94 is designed for phantom powering by a Shure PS1A

Power Supply, or by any microphone power supply providing 12 to

48 Vdc phantom voltage, or by any microphone mixer (such as the

Shure SCM262 and SCM268) with a phantom supply. In addition,

the SM94 can be powered by a single 1.5-volt AA alkaline battery.

The battery also serves as a backup in case of phantom power

failure. A new alkaline battery will provide up to 5,000 hours of

continuous microphone operation. Note that the microphone is

powered at all times during battery operation but there is no battery

drain during phantom-powered operation.

BATTERY OPERATION

Disconnect the microphone cable, and unscrew the SM94 handle,

turning counterclockwise (from top) until the handle is free of the

microphone body. Slide the handle away from the grille, exposing

the battery compartment. Insert a new battery (or replace the old

battery), observing the polarity marking in the compartment.

Slide the handle toward the grille, and tighten the handle by turning

it clockwise (from top).

WIND NOISE

Use the optional foam windscreen (A3WS) when using the SM94

outdoors on a windy day, indoors near strong air currents such as

air-moving equipment, or as a vocal microphone.

CIRCUIT DESCRIPTION

A block diagram of the SM94 is shown in Figure 4. The capacitor

cartridge is followed by an impedance converter stage. This stage

has an active load to obtain good load-driving capability with the

low battery voltage of 1.5 volts.

The audio signal is transformer-coupled for a balanced output to

the microphone connector. An active power supply circuit

1 2 3 4 5 6 7 8

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Shure SM94-LC User's Guide Page 2

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