MGL Avionics User Forum

I have a question related to the connection of the sounds generated by the screen to send them to the headphones in the mx1.
According to the manual, the audio output is pin 20, I imagine that this will be the positive signal.
What would be the negative sign?
exist a wiring manual for the installation?

Thank you.

fritzi wrote: ↑Sun Mar 21, 2021 5:57 pm I have a question related to the connection of the sounds generated by the screen to send them to the headphones in the mx1.
According to the manual, the audio output is pin 20, I imagine that this will be the positive signal.
What would be the negative sign?
exist a wiring manual for the installation?

Thank you.

What are you connecting the audio signal to?
Adam at MichiganAvionics suggested that NOT connecting an audio ground signal gave him the best result. This requires, of course that both the MX1 and V16 (in my case) uses the same ground. I tried it both with the ground wire and without and noticed no difference. HOWEVER, I did have a lot of noise related to the MX1 processor (or something) so I had to install a voltage divider (two resistors) in order to clean up the audio.

I can post a diagram if you like.

brs wrote: ↑Sat Mar 27, 2021 4:33 pm Adam at MichiganAvionics suggested that NOT connecting an audio ground signal gave him the best result.

It should be noted that this was found on a bench-test environment, and is sometimes used as a troubleshooting step when diagnosing audio problems. Your mileage will vary here.

The voltage divider is necessary because the iEFIS units are designed to drive large audio loads (think cabin speaker) and as such, when connecting to a radio or audio panel has far too much power to be attenuated.

adamoconnor wrote: ↑Tue Mar 30, 2021 12:19 pm
The voltage divider is necessary because the iEFIS units are designed to drive large audio loads (think cabin speaker) and as such, when connecting to a radio or audio panel has far too much power to be attenuated.

Thanks Adam for this explanation. Knowing the "why" helps understand that what might seem like a fault is actually a design "necessity".

The Audio GND to the V16 is a bit confusing in that one (V16 I believe) has a dedicated marked "audio gnd" (going from memory here) yet the MX1 has an Audio out but not a specific Audio Gnd pin. So one is left with the question to add a wire (from the GND pins) to the MX1 or to eliminate (not install) a wire to the V16.

brs wrote: ↑Tue Mar 30, 2021 1:03 pm So one is left with the question to add a wire (from the GND pins) to the MX1 or to eliminate (not install) a wire to the V16.

The direct answer is that the ground on the V16 should meet the ground that goes into the MX1's connector in a splice a couple of inches behind the connector.

The MX1 references that ground for its audio output signal. By then referencing the V16's dedicated audio input ground to that same point, any differences in voltage (even a tenth of a volt difference in ground reference can cause big problems) are evened out. In small aircraft, especially in cases where grounds for all avionics are referenced to a common ground bus, this isn't usually a problem. Once we get into larger aircraft like twins or turbines, this becomes critical.

When I used to work on jets, grounding an item to a rib of the aircraft in the cockpit and another in the tail section would sometimes have half a volt difference. Then add to that 400Hz 115V AC Generators and wiring causing ripples, and suddenly you're chasing audio signal problems that you never knew could exist!