High noise level after installing HDX800

[Taigajoe]

Hello,

I substituted D700 with HDX800. After setting up HDX800 I checked the audio connection and were disappointed how much more noise produce the HDX800 in compare to D700.

The Dynon audio is connected to an audio mixer AP-60 from Flightdata. I shorted left+right audio output of Dynon together and connected them to an input of AP-60. The shield is connected to GND of AP-60 only. Audio GND pin 30 is connected to GND of AP-60. The output of AP-60 is connected to aux-input of Becker AR6201 radio. The headset is an ANR Bose A20. This installation worked for several years.

The situation with HDX800:
When I switch on the radio and the headset - I hear nearly nothing - it is absolutely silent.
When I switch on HDX800 there is no change during booting. Short before the booting voice speaks - the disturbing noise started!
The level of the noise is independent of the level setting of master volume of Dynon.

Even the noise of D700 was not so nice but in compare to HDX800 it was so much better!

I am thinking to install an noise filter...

Have anyone any suggestions?

Thank you!

Best regards
Taigajoe

 

[maartenversteeg]

There is a suggestion from Dynon to add an additional grounding wire from the Dynon display, but I don't remember where that was listed

 

[Taigajoe]

Thanks. I think you mean this: ....To minimize noise, ensure that your SkyView audio ground and intercom or audio panel ground are directly connected together, even though they nominally share a common ground via other aircraft wiring (audio ground is pin 30 on the D37)...
It is written in the installing guide.

I made this connection. It reduced the noise a little bit. But the noise level is still absolutly disturbing - and I had save the money for ANR headsets...
With D700 it was much less noise.

 

[Rhino]

I'm curious why the audio is going from the mixer to the radio, instead of from the radio to the mixer. That could be part of the problem.

Normally I'd say turn the radio off to isolate the problem, but it appears you have your headphones connected to the radio instead of the mixer.

You might try disconnecting pin 13 or 31 on the Skyview to make sure the two different channels aren't interfering with each other, but I doubt that's the issue.

All audio grounds and shields should terminate in the same location. I would suggest using the AP-60 for this, since you don't appear to have either an intercom or an audio panel. Something like this.

I'd also have the radio output go to an input on the mixer, and have the headphones get audio out from the mixer. That would look like this.

 

[Rhino]

It appears Flight Data Systems agrees with me. Just found this on their web site:

"All Com radios must be routed through the AP-60. The output of the AP-60 must go directly to your headphones or to the radio input of an intercom. Sending the output of the AP-60 to the audio input of your radio may not work properly and is not recommended."

That is likely your problem, or at least a big part of it

FAQ's — FLIGHT DATA SYSTEMS

www.fdatasystems.com

 

[Rhino]

And please let us know what the fix ends up being, so others here can benefit from it in the future.

 

[Taigajoe]

Thank you Rhino for your comments!

I installed the former D700 about 10 years ago and connected it to the AP-60 and the output of the AP-60 I connected to AF-AUX-INPUT of the combined Intercom/radio AR4201 and later to AR6201.
The other channels of AP-60 are used for Garmin, TRX-1500 etc.
These installation worked nearly perfect regarding audio quality with less noise. I mean in the air you did not hear this little noise from D700.

I have exactly this installation. The AF-aux-input is pin 4 of AR6201. The only excemption is: The audio GND from Dynon to AP60 GND is not shielded. Could this be the problem???? I do not think so.

The reason to install AP-60 between different audio sources and the intercom/radio was: In case of audio trouble with different audio sources I can easy switch off the AF-aux-Input of the AR6201 and all audio sources are disconnected with one step.
The other reason is: I think the reliability of the AR6201 is higher then of the AP60 (until now I had no problem with AP-60!). If I would connect the radio-output to the AP60 and the headphones to AP60 and the AP60 will stop working - than I would loose the radio communication in the air.

When I substituted the D700 with HDX800 I did not change anything in the installation and I got disturbing noise. I disconnected all other audio sources from AP-60 and switched on HDX800: After booting the noise appears again.

I did not read this information from Flight Data Systems:
"All Com radios must be routed through the AP-60. The output of the AP-60 must go directly to your headphones or to the radio input of an intercom. Sending the output of the AP-60 to the audio input of your radio may not work properly and is not recommended."

I mean this sentence "The output of the AP-60 must go directly to your headphones or to the radio input of an intercom. " says, that the output of AP60 can be connected to the input of an intercom. I have no separate intercom - it is included in AR6201. And the AF-aux-input will be connected to the internal intercom.

Anyway. First I will separate Dynon audio left and right and will pray that the noise will disappear (but I do not believe it...).

 

[Rhino]

It's possible that not shielding the ground wire from the Skyview is your problem. Your original post said you did have noise with the D700, just not as much. Just try to make sure the shielding isn't grounded at both ends of any of your audio cables, and are all only grounded to one place, preferably the AP-60.

I think the way you have the AP-60 wired to the radio is more likely your problem, or at least a portion of it. You have a mixer inputting to a mixer, and quite possibly a line level input to a destination that isn't designed for that. What pin on the AR6201 does pin 1 on the AP-60 go to?

 

[Taigajoe]

Today I separated Dynon audio left+right with no success regarding noise reduction. It doesn't matter which audio line I connected to the AP60 - the noise kept it's level.

All audio cable shields are grounded on one end only.

Next step: I will shield the ground wire. If this is not successful then I will connect the audio output direct to AR6201AF-aux-input.

Pin 1 of AP60 is connected to AF-aux-input pin 4 of AR6201.

Please cross your fingers - I am afraid that the audio ouput of the Dynon has a problem....

 

[Taigajoe]

Hi Rhino - thank you for crossing your fingers -you are the winner!

At the first step today I reconnected audio left+right again and shielded the ground connection from Dynon to AP60 - with no change regarding noise level.

At the second step I connected Dynon audio direct to AR6201 AF-aux-input (without AP60) and the noise disappeared!!!

That means - as you said - the AP60 is at the wrong place. And it means also that I flew several hundred hours with a wrong installation and did not recognise it.
But I do not really understand why it doesn't matter where to install the audio mixer....

Anyway - now I have a lot of work with rewire many connections.

But I am happy that the HDX800 has no defect! I was very close to install the D700 again....

Thank you Rhino!

 

[Rhino]

You might have an impedance mismatch. There are no specs that I can find for the AP-60, but it looks like it's designed to output like a dynamic or electret microphone. Pin 4 on the 6201 isn't for a radio input. It's for aux audio, which is likely a line level input. Before you go completely rewiring everything, you might try swapping the input to the 6201 from pin 4 to pin 5. If that doesn't work, try pin 9. Neither one may work, but if one does, the fix will be a whole lot easier than rewiring your entire system.

Then again, your AP-60 may simply be bad. I hope not.

 

[Taigajoe]

Thanks for your explaination! I will take it into consideration.
Pin 5 instead 4 sounds plausible. But pin 9 is marked with NC?!

 

[Rhino]

The 6200 series install manual I have shows pin 9 is MIKE_STD2_HI. That should nominally have impedance centered around 600 ohms.

 

[Rhino]

I should also note that an impedance mismatch probably isn't the problem. That usually just affects the volume, not cause noise. I was just fishing for a way to not make you rewire everything.

 

[Taigajoe]

In different versions of manual for 6201 I could not find a MIKE_STD2_HI.
Pin 9 is not connected - see attached file.

 

[Rhino]

That's weird. The install manual for the 6200 series says pin 9 is MIKE_STD2_HI, but the older 6201 manual doesn't.

It's only a guess, but maybe the early versions didn't have a Mic 2. If that's the case, they really should have made that clear.

Just skip pin 9 for now. As I said before, this probably isn't an impedance mismatch, so this is sort of a shot in the dark anyway. I was just trying to think of anything that might avoid rewiring your system.

 

[Rhino]

By the way, what pin is your microphone hooked to?

 

[Rhino]

Looking more closely at the manual, you could also try pin 18.

 

[bartonnel03]

hi