Audio Gremlin in my a/c

[Tiger]

I have an annoying problem which is preventing me from "semi-permanently" installing PAW in my group a/c, a Grumman Tiger.

I am using an RavPower 12v - USB power supply plugged into the aircraft's cig lighter. it was ordered as a high quality one and it feels nice and solid, so hopefully not Chinese crap.

I am also connecting the PAW audio to my audio panel, an GMA 340 with a dedicated 'music' input.

With these both connected a get a constant whining noise in my headset, which disappears as soon as I either:

- Disconnect the PAW audio, or
- Power PAW from a battery pack

I have tried to wrap both the USB power lead and the audio lead around a ferrite core to act as a choke, but that's not helping.

I am not 100% certain this is RFI from the power converter, or perhaps a ground loop caused by having two connections to the aircraft, but I am sure they'd all have a common ground, anyway.

One other thing to note is that the GMA 340 is certainly interpreting the whine as 'audio' coming in, because when I speak and the intercom is active, the whine stops, to then restart when I stop talking.

Any ideas on what I can try to isolate this?

[Seanhump]

Plug another set of iPhone type headphones into the PAW and see if the whine is still there ... if it is then it's pointing to the power source (or something else on the PAW)

Can you try a different power source to see if that's the common point .?

You could try to attached a ground to the audio cable shield .... though I'dve thought it'd get that from your audio panel.

I've been using mine whilst testing with a single earpiece (the computer skype type ones) plugged into the PAW and then into my ear under my headset (Bose X doesn't have an audio in though I believe there's a mod you can make using the pins on the unused earcup connector but that's a different story)

[Ian Melville]

Yes, some power adaptors can be very RFI noisy, which is why we recommend some particular products that have been proven good. I use a 2 USB port Anker product that had been recommended, however I understand that it is no longer available. I think there is mention of a single port version somewhere.

[Tiger]

Cheers both.

I have a few more tests to do tomorrow, and hopefully one or more will help:

1. As per Seanhump, check if the audio is clean from the PAW itself without plugging into the panel
2. Check if another music source is OK while the PAW is powered up
3. Try a different audio cable. The one I am using is VERY thin and probably not well sheilded
4. I've just found an audio isolator and wired some new ends to it. I will try that out. It will eliminate any ground loop type issues because there will be no electrical connection between the PAW and the Audio Panel.

With regard to the power supply, that is still suspect because the problem does disappear when I am not using the aircraft's power. I am ordering one of the recommended Anker ones to try as well.

[Keithvinning]

These are the power supplies to use

https://www.amazon.co.uk/Anker-PowerDrive-Charger-MultiProtect-Samsung-Black/dp/B00VH84L5E/ref=sr_1_7/259-1504511-5061341?s=telephone&ie=UTF8&qid=1513719913&sr=1-7&refinements=p_4%3AAnker

keith

[AlanG]

Hi

There's also the PowerDrive 5, which gives extra ports for tablets, phones etc.

https://www.amazon.co.uk/PowerDrive-5-Port-Charging-iPhone-Galaxy/dp/B00OUK0N26

Alan

[PaulSS]

Might be worth chucking one of these in the circuit. Doesn't cost much, eliminates one cause of the whine and won't do any harm to have no matter what.

https://www.ebay.co.uk/itm/MPOW-Ground-Loop-Noise-Isolator-F-Home-Audio-Car-Stereo-System-3-5mm-Aux-Cable/132250997700?hash=item1ecac613c4:g:0LIAAOSw4A5YsPJm

From a total novice, the whine noise sounds just like a couple of problems that have appeared on this forum in the past and both of those were resolved with a ground loop isolator.

[Tiger]

PaulSS, what you've linked to there is pretty much exactly what I am planning to test today, but in a much smaller form factor. If today's test works then I'll get that smaller one, so thanks for the link!

It's basically a 1:1 transformer, so a coil on each side, where audio in one coil induces the same audio in the other coil, without them being physically connected, so no ground loop.

Fingers crossed

[PaulSS]

The very best of luck    What you said kind of went way over my head but it did sound impressive. I'm just regurgitating the successes of a ground loop isolator with similar symptoms as yours, as described in other audio threads. One guy had a video of his noise and the isolator sorted that out. Another chap went through a bajillion bits of investigation, including taking half his radio apart (I exaggerate for effect) but the isolator sorted him out as well. Lets hope it works third time.

[Tiger]

Good news!

The isolator worked perfectly. No noise at all! My homemade one is a bit of a bodge so I'll certainly order one of the ones you linked to.

Yet to perform a proper flight test so unable to check if there is any RFI going on from the USB supply, but I feel like I'm half way there.

Cheers!

[PaulSS]