Mile McCallum wrote --
>While we have some avionics experts (?) on line, perhaps someone could point
>me at a solution to a problem I have: Narco 810, hooked up to a sigtronics
>portable i/c. Works OKish, but when you hit the transmit button, the volume
>triples...
I have a Narco COM 810 and the service manual, too. I know nothing about a
Sigtronics intercom, and not all are the same circuit-wise.
When you talk into an intercom, it amplifies the mike signal directly. When
you key the mike, intercoms usually pick off the audio from the comm unit,
which will be the sidetone,
which is independent of the volume knob setting on the 810.
You can check this by using the 810 without the IC. The sidetone on transmit
should be
the same as a comfortable level on normal received audio, or slightly higher.
If not, you must remove the 810 (a welding rod shoved way into the tiny hole
on
the right side of the faceplate pops it out). Remove the set screws in the
freq setting
knobs. These are not hex set screws, though, but star-type, which tool is
tough to find.
I hand-filed an allen wrench for mine. Assuming you get that far, remove the
black screws
on the side and the faceplate; a trimpot now exposed is the sidetone
adjustment. (recall two
trimpots are exposed, but one is accessible thru the faceplate and it's for
the dimmer).
Otherwise. it's an easy job for an avionics guy.
If the sidetone is OK, and the volume knob on the intercom affects normal
comm audio also, then try setting up the intercom without disturbing the
"normal" volume setting on the 810. If mic audio (intercom, not transmit) is
too low, its output may be too low, and you're compensating with increased IC
volume and reduced 810 output. If you can adjust mic output on your
microphone, try that. Some headsets and mics have a trimpot buried somewhere
for this purpose. This won't bother the 810, as it has an audio-leveling
circuit that can take up to
2 volts rms, which no mike can put out.
Next, I'd try a friends mic or headset for comparison.
Hope all this helps.
Fred Fillinger
Europa A063 (wings 60% done)
Mentor, Ohio, USA
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