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MICROPHONE ClRCUlT MODlFlCATlON
The microphone circuit of the 4078 is normally open
when the microphone switch button is in the normal
position. The microphone switch of the 4078 may be
rewired to have a normally shorted microphone circuit.
To modify the Model 4078 for a normally shorted
microphone circuit, proceed as follows:
1.Remove the three No. 6 Phillips self-threading
screws from the back of the microphone case.
2.Separate the case front and back and remove the
microphone switch button.
3. Unsolder or clip the WHITE cable lead from the up-
per switch solder lug. See Figures 2 and 3.
4. Solder the WHITE cable lead to the lower terminal
lug (the lug with the YELLOW lead going to the
microphone cartridge). See Figures 2 and 3.
5.
Place the microphone switch button in the normal
position on the case front. Place the case back on
the case front and firmly press the cases together.
Fasten the case back to the case front with the
Phillips self-threading screws previously removed.
OPERATION
The 4078 will operate satisfactorily under all ordinary
conditions of humidity, heat, and cold. Dropping the
microphones or other severe mechanical shocks should
be avoided.
Output Level (at 1,000 Hz)
Open Circuit Voltage*
. . . . . . . . . . .
-33.0 dB (22 mV)
Power Level**.
. . . . . . . . . . . . . . . . . . . . . . . . -
52.0 dB
*O dB
=
1 volt per 100 microbars
**0 dB
=
1 milliwatt per 10 microbars
Impedance
Microphone rating impedance is 150 ohms (200 ohms
actual)
Load lmpedance Range
Minimum: 200 ohms
Recommended:
1000 ohms
Cable
1.8m (6 ft), 4-conductor, 2-conductor shielded, at-
tached, coiled cable
Case
Two-tone light gray and charcoal ARMO-DUR@
Dimensions
See Figure 5
UPPER LUG
LOWER LUG
REAR VIEW OF CHASSIS (CASE REMOVED)
FIGURE 3
.
SPECIFICATIONS
TY Pe
CONTROLLED MAGNETIC@
Frequency Response
300 to 4,000 Hz (see Figure 4)
OVERALL DIMENSIONS
FIGURE 5
Net Weight
312 grams (11 oz)
Packaged Weight
510 grams (1 Ib, 2 oz)
FURNISHED ACCESSORY
. . . . . . . . . . . . . . . . .
Mounting Bracket
(3
in kit).
RK6MB
REPLACEMENT PARTS
Cartridge
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99AL556
Cable
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
70A4107
Switch
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
90A3507
TYPICAL FREQUENCY RESPONSE
FIGURE
4
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