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AF3400 audio alert and SL-40 comm on same input

O

oy-rvc

Member
I have an Advanced AF3400 with audio warnings that I want to run unmuted to my flightcom 403 intercom. Also I have an SL-40 that I want to run to the 403. Trouble is that the 403 only has one pin (21) to use as input. After searching the internet I could see that some are using a small preamp which supports multiple inputs. But really I dont want another active component (more than enough allready). So I came across a drawing showing that the outputs from EFIS, RADIO ect. can be mixed simply by using a 150 Ohm resistor and 10 uF capacitor in series with each line. Can anyone confirm this will work without doing any harm?

Regards
Christian Thygesen
Denmark
RV-8 QB - status: allmost ready for paint.
 
I tried that on my last Rocket and could not get it to work. On this build, I have one of Vern Little's audio mixer/amplifier units to run all the audio inputs into before sending them to the intercom. Slick little unit and I highly recommend it.
 
Thanks for reply Randy. I just tried it also with smaller and smaller resistors to see if it could work, but I will skip the idea also since it effect sound quality too much. I think going for an preamp is the only way.

I found this one - it looks like it will do the job.

http://www.fdatasystems.com/AP_60.htm

Regards
Christian Thygesen
Denmark
RV-8 QB - status: allmost ready for paint.
 
Christian
I have a Dynon D180, SL40, Zaon MRX, all tied to that single terminal on a Van's supplied harness for my Flightcom 403.
On my airplane's twin I have all that plus the SL30 Nav audio tied to that same terminal. It all works!
I'm sure someone is going to tell me the error of my ways, but 100 hrs on the plane with the additional SL30 audio and 70 hrs on my RV8 and no problems.
Actually a small issue in that the Dynon warning tone is not loud enough in flight, but I fixed that issue by just turning off all those annoying alarms anyway.:rolleyes:
Good Luck,

PS- I didn't use any resistors or capacitors in line.
 
Last edited:
I have all my audios going to the 403 also. AFS 3500, SL-30, Garmin 496. I used a terminal strip to tie them all together. John Stark told me to put a resistor in all of the audio outputs to equalize the volume. I will have to look up the rating and will post it. This setup works.
 
Stopped by the hangar on the way home. The resistor is a 220 ohm 1/4 watt.
As it was explained to me, by adding this resistor to each unswitched audio,
the difference in impedance of the audios is rendered insignificant which
equalizes the volume.
 
jthocker, Chino Tom. After reading that it can be done without a preamp I tried once again without the capacitors. After some playing around I finally got an acceptable solution. I does affect the sound a little as far as I can tell but I doubt that I will be able to hear the difference with the engine running. The key was also to find the correct volume settings between radio, efis and intercom. Thanks for input.

PS: will post picture of the completed instrument panel soon.

Regards
Christian Thygesen
Denmark
RV-8 QB - status: allmost ready for paint.
 
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