HS-34 Audio Warning Output Issues

[jwachman]

Dear Dynon,

Here comes my diatribe and fault finding on an issue with the HS-34 Audio Warnings.

The setup. I have the HS-34 Audio output connected to an SPA-4 intercom. There is no seperate input for audio warnings, so I initially connected this to the common headset line. (You will see as you read - I have tried other connection points).

The problem - When the HS-34 is turned on the radio volume level drops by about 50%. My HS-34 and EMS happen to be connected to a seperate switch so I can turn them off with all other avionics on.

The audio warnings work fine. If I turn on the radio I can listen to various transmissions, all loud and clear. But when I turn on the HS-34, the radio audio level drops, and remains dropped, even when the warnings have finished.

It is like there is a continuous side-tone on the HS-34 output.

So onto the fault finding. I disconnected the HS-34 output. The radio volume returns to normal. If I connect the HS-34 to the left headphone output, the volume to that ear drops. Same to the right.
I connected a 250 ohm resistor, in series, this lowers the volume of the HS-34 warnings, and also reduces the impact on the volume of the radio.

If I connect the HS-34 to the same input to the intercom as the radio, it again drops the volume. This input location seems good, as it does stop the iPod sounds when warning tones are transmitted. This also indicates the intercom is working correctly.

So I purchased a Flight Data Systems - AP-60 Audio Mixer. Which mixes and amplifies up to six signals. When I connect the HS-34 output and radio to this and turn on the mixer, the HS-34 output causes a loud 'sream' which is only removed when I remove power from the mixer, or disconnect the HS-34 input to the mixer.

Conclusions: What appears to be happening is that the HS-34 audio output has a continuous sidetone. This side tone appears to cause a reduction in the volume of the radio. When I use the mixer it amplifies the sidetone, until it becomes a 'scream'.

Questions:

1. Have you got any idea whats going on?
2. Does the HS-34 produce a continuous sidetone on the Audio Warning output line.
3. Any other ideas?

Thanks

Jon :-/

 

[jakej]

FWIW and no offense but have you checked that the wire is indeed going to pin 25 ie it's a female Dsub ?

Jake J

 

[PhantomPholly]

Yeah, what Jakej said - the manual does say it, but when they say "female" they mean the connector on the HS34 not on the connector which attaches to it.  Ask me how I know...

For the volume cutting in half problem, I am wondering if you don't need a small resistor between the HS34 and the audio panel.  I use an intercom, not an audio panel, but I hooked up to the music input because that gets muted when there is an incoming radio call (HS34 alerts are repeated on screen, so you won't miss anything crucial).  The resistor should prevent any other source "leaking back" through the HS34.  Note that I don't really understand all of this, but a wiz helped me with my installation - see this diagram.

 

[dynonsupport]

First off, connecting the HS34 in parallel with any other audio source will cause exactly what you described with lower volumes. This is fully expected, and not unique to the HS34. All audio sources will compete in this way.

As you figured out, you need a mixer. It should work fine with the HS34. There are no "sidetones" coming from the HS34. Sidetone generally is applied to radios where they put a bit of your voice back on the headset so that you can hear yourself talk. It's not just a random tone on the output. The HS34 puts out no audio when it's not making sound.

What you have sounds like a ground loop. Are you sure that the HS34 and the mixer have good common grounds? Does the mixer need specific grounds for specific audio inputs?

I might ask the manufacturer of the mixer if they have heard of this issue. I promise you there is nothing coming out of the HS34 audio pin that sounds like you describe, so something else in the system is generating that interference.

 

[jwachman]

Thank you all for your replies.

I have now fixed the problem. I have added a 200 ohm resistor between the HS-34 output and the mixer. This has stopped the noise. I have been able to connect to the SPA-4S and adjusted the radio volume up on the SPA-4. So it is now nicely balanced.
For information this mixer has worked well with the SPA-4, as if I get an audio warning or radio call inbound the stereo music stops.

The system is jsut great. I'm now only waiting for the tank 3&4 fix to come out and all will be at 100%, till then 99% is pretty damn good.

Cheers from Oz.

 

[PhantomPholly]

Jon,

Does that mixer support Stereo inputs?

Did the diagram I posted help?  I cannot leave it where it is - if it is useful, perhaps Dynon would host it permanently?

I will happily "waive my rights to proprietary information" on this simple Visio diagram...