Shure SM90 User Guide

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222 HARTREY AVE., EVANSTON, IL. 60204 U.S.A.

AREA CODE 312/866-2200 l CABLE: SHUREMlCRO

THE SOUND OF THE PROFESSlONALS

PROFESSIONAL PRODUCTS

the best location for any particular purpose or effect desired.

The carefully optimized design of the SM90 includes an entirely new cartridge, developed at Shure. The result is high output and extremely faithful sound reproduction across the entire audio frequency range. The supplied low-distortion, high-clipping-level preamplifier provides switch-selectable low-frequency Flat or Lo-Cut response for additional help in obtaining the best possible microphone signal even under difficult conditions.

The SM90 is powered either by two readily available 9-volt alkaline batteries (300 hours continuous battery

life) or by an 11-to-52 Vdc simplex (phantom) supply from broadcast, sound-reinforcement, or recording equipment.

The SM90 consists of a small, rugged, surfacemounted microphone finished in professional durable matte-black enamel; a 7.6m (25 ft) small diameter two-

conductor shielded interconnecting cable with two 3-socket miniature Switchcraft connectors; and a sturdy preamplifier assembly with battery compartment,

battery On/Off switch, green LED battery-condition in-

dicator, low-frequency Flat/Lo Cut switch, and standard 3-pin professional audio connector output.

GENERAL

The SM90 Microphone is designed specifically for surface-mounted applications. It is a professionalquality permanently-biased condenser microphone with a hemispherical pickup pattern (omnidirectional in the hemisphere above the mounting surface.)

The SM90 takes advantage of the well-known principle that, at a barrier or boundary, sound pressure doubles compared to its value if the boundary is removed. When placed sufficiently near the boundary surface, a microphone has effectively 6 dB higher sensitivity and approximately 3 dB greater rejection of random background noise.

Because of its high sensitivity and extremely flat frequency response, the SM90 can be used for distant pickup in circumstances where close miking would not be practical. The low-frequency cutoff switch in the preamplifier permits using the SM90 even in environments where low-frequency noise (e.g., from fans or air conditioners) would otherwise make distant pickup impossible. And the omnidirectional polar pattern of the SM90

means sound is picked up equally in the full 360° hemisphere around the microphone; there is no off-axis sound coloration or variation.

The SM90 can also be used for close pickup of an in-

dividual instrument, mounted, for instance, inside the

lid of a grand piano or on the floor next to a bass drum.

Experimentation and critical listening will demonstrate

Features:

l Wide flat frequency response for faithful sound

reproduction across the audio spectrum

Switch-selectable 12 dB/octave low-frequency cutoff

permits tailoring response to suit conditions

l Omnidirectional polar pattern for pickup in full

hemisphere surrounding microphone mounting sur-

face

l High sensitivity and high signal-to-noise ratio

l Very low distortion and high output clipping level

l Battery or simplex powering: uses standard 9-volt

alkaline batteries: accepts wide range of simplex

voltages - 11 to 52 Vdc

l Low susceptibility to RFI, electrostatic and electro-

magnetic hum

l Extremely rugged construction of both microphone

and preamplifier for outstanding reliability

l Low profile and matte black finish for unobtrusive

appearance on-camera or onstage; on floor, table, ceiling, wall, or lectern

l Usable over very wide range of temperature and

humidity

Printed in U.S.A.

Patent Pending

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SPECIFICATIONS

Type

Condenser (electret bias) for surface mounting

Frequency Response

20 to 20,000 Hz at 30° incidence to infinite surface (see Figure 1)

TYPICAL FREQUENCY RESPONSE

FIGURE 1

Polar Pattern

Omnidirectional in hemisphere above mounting surface

Output Impedance

Rated at 150 ohms (90 ohms actual) Recommended minimum load impedance: 800 ohms (May be used with loads as low as 150 ohms with reduced clipping level)

Output Level

at 30° incidence to flat surface)

Open Circuit Voltage . . . . . . . . . . . -66.0 dB (0.5 mV)

0 dB = 1V/µbar

Preamplifier Output Clipping Level

than 0.1% THD)

800 ohm load

150 ohm load

Maximum SPL (at 1,000 Hz, sound source at 30° incidence to flat surface)

800 ohm load

150 ohm load

Hum Pickup

-19 dB equivalent SPL in 1 m0e field (60 Hz)

Output Noise

20 dB SPL, A-weighted 23 dB SPL, weighted per DIN 45 405

Signal-to-Noise Ratio

74 dB re 94 dB SPL

Dynamic Range

121 dB

Phasing

Positive pressure on diaphragm produces positive voltage on pin 2 relative to pin 3 of preamplifier output connector

Power

Battery: Two 9 Vdc alkaline (NEMA 1604A),

approximately 300 hours continuous with fresh alkaline batteries

(at 1,000 Hz, measured with sound source

(at 1,000 Hz, less

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .

0 dBV (1.0V)

-13 dBV (0.22V)

141 dB 131 dB

Simplex

9 Vdc; 1.8 mA current drain; permissible to use simplex power with batteries in place or removed

Switches and Indicator

Two recessed slide switches and green LED indicator on top surface of preamplifier assembly

Battery On/Off Switch:

batteries or to use batteries as backup power in case of interruption to external power supply (no battery drain occurs as long as simplex voltage source is greater than total battery voltage). Move to Off to prevent battery drain when unit is not in use.

LED Indicator:

when switch is moved to On to indicate at least 8 hours of battery life remaining.

Flat/Lo Cut Switch:

rolloff below 30 Hz; in Lo Cut position, 12 dB/octave cutoff below 80 Hz (see Figure 1)

Cable

7.6m (25 ft) two-conductor shielded, small diameter, interconnecting cable with 3-socket miniature Switchcraft connector on each end to mate with microphone output connector and preamplifier input connector

Case

Microphone:

perforated steel grille with replaceable or cleanable fine mesh screen and foam pad wind/dirt barrier

Preamplifier:

Dimensions

See Figure 2

Environmental Conditions

Operating Temperature: -18° to 57°C (0° to

135°F) Storage Temperature: 168°F) Relative Humidity (Operating or Storage):

Net Weight

Microphone: 280 grams (9.9 oz) less cable Preamplifier:

Voltage:

OVERALL DIMENSIONS

11 to 52 Vdc, operational down to

Move to On to power from

Green LED flashes momentarily

In Flat position, 6 dB/octave

Matte black enamel die-cast base and

Matte black enamel die-cast aluminum

FIGURE 2

-29° to 74°C (-20° to

320 grams (11.3 oz) with batteries

0 to 95%

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LOCATION

To maintain the flattest possible low-frequency response and the best rejection of random background noise, choose a flat surface as large as possible on

which to locate the SM90. The surface can be a floor, wall, ceiling or table.

A small mounting surface causes a low-frequency

rolloff beginning at the frequency whose wavelength is comparable to the size of the surface. The rolloff continues at a rate of about 3 dB per octave until it reaches a plateau approximately 6 dB lower than the mid- and high-frequency response. In a similar fashion, a small mounting surface decreases the rejection of lowfrequency background noise.

MOUNTING

The SM90 can be permanently mounted to a lectern,

tabletop, floor, ceiling, or wall using two No. 6 screws located 50.1 mm (2 in.) apart. The location of two

keyhole slots in the base of the microphone is marked on the nameplate. Cut through the marked slots before sliding the base onto the screws.

To avoid ground loops and hum, avoid grounding the microphone preamplifier housing to metal building structures.

POWERING THE SM90

The SM90 can be powered by two internal 9-volt alkaline batteries or by an external simplex supply of 11 to 52 volts dc.

To use batteries, move the Battery On/Off switch to On. The green LED will indicate at least 8 hours of battery life remaining by flashing once when the switch is moved to On. If the LED does not flash, the batteries

should be replaced. A battery-powered SM90

preamplifier output can be connected to any balancedline low-impedance input.

To use simplex power, connect the preamplifier output to a balanced-line microphone input supplying 11 to

52 Vdc simplex (phantom) power. The batteries may be

left in place while the unit is externally powered. There

will be no battery drain if the battery switch is turned Off, or as long as the simplex voltage exceeds the battery voltage with the battery switch On.

BATTERY INSTALLATION

To install batteries, remove the four screws in the cor-

ners of the preamplifier case. Lift off the case cover, ex-

posing the battery compartment. The use of O-volt alkaline batteries (NEMA 1604A or equivalent) is highly recommended. Two batteries are required; always replace batteries in pairs.

SM90 Microphone to its Preamplifer. To retain access to the controls located in the preamplifier, it is sometimes desirable for the units to be located a greater distance apart. Up to 15m (50 ft) of additional cable can be used between the SM90 Microphone and Preamplifier with no loss in response or output.

CLEANING

When the microphone is located in a dusty environment, periodic cleaning may be desirable. This can be easily accomplished by removing the Phillips-head screw on the grille, and lifting off the grille, the fine mesh screen, and the foam pad. Clean the fine stainless steel mesh screen by washing it in soapy water. Dry it thoroughly, and replace the foam pad, screen, and grille. Fasten firmly with the Phillips screw.

GUARANTEE

This Shure product is guaranteed in normal use to be

free from electrical and mechanical defects for a period of one year from date of purchase. Please retain proof of purchase date. This guarantee includes all parts and

labor. This guarantee is in lieu of any and all other

guarantees or warranties, express or implied, and there shall be no recovery for any consequential or incidental damages.

SHIPPING INSTRUCTIONS

Carefully repack the unit, have it insured, and return it

prepaid to:

Shure Brothers Incorporated Attention: Service Department 222 Hartrey Avenue

Evanston, Illinois 60204

If outside the United States, return the unit to your dealer or Authorized Shure Service Center for repair. The unit will be returned to you prepaid.

CONDENSER CARTRIDGE

IMPEDANCE 3-PIN MINIATURE

CONVERTER

CONNECTOR

CARTRIDGE

ASSEMBLY

long period of time.

INTERCONNECTING CABLE

One 7.6m (25 ft) cable is supplied for connecting the

MICROPHONE CIRCUIT DIAGRAM

FIGURE 3

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PREAMPLIFIER CIRCUIT DIAGRAM

REPLACEMENT PARTS LIST

PREAMPLIFIER PC BOARD

FIGURE 4 FIGURE 5

Reference Part Designation Number

90A8216

A2 R130

C102, 107, 108, 110

C103

86S628R

86AE629

C106 86W628R

D101, 102, 103, 105, 106 86A415R

D104

D107

86A8405 LED, Green None

86C429

L1, L2 80A253

MP1

MP2

65A8066

53A1879B

MP3 37A147

95A8077

95A247

Q101, 105 86A350

Q102, 103, 104 86A348

S101, 102

55A8031

51A286

C107

Commercial

Description

Printed Circuit Board Assembly

Microphone Cartridge & Impedance Converter

Capacitor, Electrolytic, 1 µF, 50 Wvdc

Alternate

None

Capacitor, Electrolytic, 33 µF, 16 Wvdc Mallory VTL33S25

Capacitor, Electrolytic, 15 µF, 63 Wvdc

Diode, Computer, 75V, 0.4A

None

TI, GE 1N4148

Diode, Current Regulator, 1.3 mA Motorola, Teledyne

1N5300

Ferrite Bead Ring

Battery Tray (Preamplifier)

Grille (Microphone)

Inner Screen (Microphone)

Stackpole 57-0180

None

Connector, Receptacle, 3-pin Miniature Switchcraft TB3M

Connector, Receptacle, 3-pin

Transistor, NPN

Switchcraft D3M

Motorola, National Semiconductor 2N5210

Transistor, PNP

Motorola, National Semiconductor 2N5087

Slide Switch, SPDT

Transformer

Cable and Connector Assembly

None

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