3.
Net Weight
Microphone: 280 g (9.9 oz) less cable
ILP-1 Preamplifier: 170 g (6 oz)
LOCATION
To maintain the flattest possible low-frequency re-
sponse and the best rejection of random background noise,
choose a flat surface as large as possible on which to locate
the SM91A. The surface can be a floor, wall, ceiling or table.
Too small a mounting surface causes a low-frequency
rolloff beginning at the frequency whose wavelength is com-
parable to the size of the surface. The rolloff continues at a
rate of about 3 dB per octave until it reaches a plateau ap-
proximately 6 dB lower than the mid- and high-frequency re-
sponse. In a similar fashion, too small a mounting surface
decreases the rejection of low-frequency background noise.
MOUNTING
The SM91A can be permanently mounted to a lectern,
tabletop, floor, ceiling, or wall using two No. 6 screws lo-
cated 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.
MOUNTING CLAMPS, PREAMPLIFIER
FIGURE 4
The supplied mounting clamps are intended to hold the
preamplifier in place in permanent installations (see Figure
3). Use either one or two clamps depending on location and
application. To avoid ground loops and hum, avoid ground-
ing the microphone preamplifier housing to metal building
structures. The ILP-1 preamplifier can also be plugged di-
rectly into a flush mounted connector if desired.
INTERCONNECTING CABLE
One 7.6 m (25 ft) cable is supplied for connecting the
SM91A Microphone to the ILP-1 Preamplifier. To retain ac-
cess to the controls located in the preamplifier, it is some-
times desirable for the units to be located a greater dis-
tance apart. Up to 15 m (50 ft) of additional cable can be
used between the SM91A Microphone and ILP-1 Pream-
plifier with no loss in response or output.
CLEANING
When the microphone is located in a dusty environ-
ment, 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.
DISASSEMBLING AND REASSEMBLING THE ILP-1
1.
At the XLR-3 end of the preamplifier, turn the slotted
head setscrew fully inward (counterclockwise), and
use a long-nose pliers to withdraw the connector from
the case.
2.
Unsolder the three lead wires from the XLR-3 board.
3.
Remove all four Phillips-head screws from the ILP-1
case (three on the switch side, one on the back).
4.
Grasp the end cap and withdraw the cap assembly, pc
board assembly, and connecting wires and jacks from
the case.
REASSEMBLY
1.
Make sure the pc board is seated in the slot of the end-
cap and that no wires are pinched.
2.
With the XLR-3 connecting wires foremost, feed the
endcap-board assembly into the case. Again, take
care not to pinch the wires connecting the board to the
endcap.
3.
Rotate the assembly until the four holes for Phillips
screws line up with the holes in the case.
4.
Replace the four Phillips screws.
5.
Resolder the three lead wires to the back of the XLR-3
board as shown below.
RED
BLUE
BLACK
2
3
1
WIRING TO XLR-3 PC BOARD TERMINALS
FIGURE 5
6.
Replace the XLR-3 board-connector assembly in the
case lining up the key in the connector with the slot in
the case. Take care not to engage the butterfly-
shaped ground contact in the key slot as it will prevent
seating the connector properly.
7.
Insert the connector fully in the case until the slotted
setscrew can be seen in the case hole; tighten the set-
screw firmly by turning it clockwise.
