supplemental instructions for flightcom model 4dx
Information contained in the standard instructions is not repeated here, so
read these in conjunction with the standard instructions.
1. The Flightcom headsets are wired in a different manner than the basic
David Clark ("D.C.") headset. If you study the color diagram provided
(diagram showing green, red & black circuits) you will see that in most D.C.
headsets the audio (green) comes up from the main audio plug (enters the
left earcup), passes through the volume control, and then divides into two
leads, audio R and L, one going to each side. In the 4DX and 5DX models
however, you will find that the audio (+) leads (blue & yellow) go directly to
the speakers, and that the volume control is located on he audio ground
circuit. To install the ANR Adapter in these 2 Flightcom models, the wiring
must be altered slightly so that the volume control is located on the audio (+)
2. The only difference between the D.C. wiring & the FlightComm wiring is
this feature of the volume control operating on the ground circuit. It had its
advantages designed this way (permitted a stereo set with only 1 volume
control), but this arrangement will not work for the ANR Adapter because
these units use a common ground (for the audio and power system). If the
volume control were to remain on the ground circuit, the ANR Adapter
power system could not be fully grounded.
3. In order to correct this, the audio (+) leads should be disconnected (desoldered) from the original speakers. Since these are stereo headsets, there
are two audio(+) leads, R & L. These leads are blue and yellow and are
wired directly to the original audio speakers. (The audio (+) R leads attaches
to the crossover cable to provide audio to the right side, & should be
disconnected from the crossover cable at this time). These two leads should
now be joined into one lead (making the headset mono) and that lead should
pass through the volume control. After the audio (+) lead passes through the
volume control, it should divide into two leads, audio R & L, with one going
to each side.
Note: when disconnecting wires from the volume control, don't
disconnect any leads directly from the volume control terminal. Leaving
the original leads attached to the terminals & working with them "as is"
will be easier.
4. The only way to retain stereo is to add a 2nd volume control.
5. After disconnecting and rewiring as per above, the remainder of the
wiring job is per the standard instructions, that is, the audio (-) ground and
the 9v (-) ground join together to form a common ground, then divide
into two leads, one common ground for each side. Remember, the audio
(-) ground is the black wire which originally went directly from the volume
control down to the audio cable to the audio plug.
6. The 9v(+) lead is the simplest to prepare, it just divides into two leads and
one goes to each side.
7. The model 5DX has a printed circuit board in the left earcup. This p.c.
board is your boom mic amp & filter. We don't touch the boom-mic circuit
or any wiring attached to this p.c. board. This board takes up so much room
(depth) that it must be placed as deep into the earcup as possible. To do
this will require the removal of the foam insulation. After the insulation is
removed, adjust the board so that it lays all the way in the earcup. Now
replace the foam insulation. You should be able to fit all the original
insulation back in place.
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