Audio Testing

[Richard]

Hi all, I have installed the little amp that Lee pointed out on e bay. I can get good volume.  Testing in the hangar I am getting an annoying amount of interference.

Would the spare USB on PAW power a USB powered mini speaker like this one on eBay? May be worth a try?

http://www.ebay.co.uk/itm/181174656013

[rogerabc]

Hi Everyone,

I'm also looking to boost audio from PAW & iPad.
At present I have these wired in parallel with a Smart Ass airspeed speaker into my non adjustable intercom aux line (3 into 1).
They are all faintly audible but drowned out by the headset mics.
Would it be OK to feed all three through the same LM386 amp?
Has anyone found a better solution without the reported noise issues which I'm keen to avoid!
Grateful for any suggestions.

Roger

[Moffrestorer]

Hi Roger,

The iPad audio output is higher level than that from PAW. I realised this when about to join the LAA 70th tour, having left my mixer/amplifier at home, in error. The EasyVFR Nav program which I use has its own system of audible alerts triggered by PAW so I connected the iPad audio directly to the radio aux input, adjusted the iPad volume and all was fine for the subsequent flights. The alerts volume matched the level from the radio OK.

Personally I would be uncomfortable just connecting audio from different sources together, without a resistive mixer network to compensate for differing voltages. Once correctly combined, no problem with passing the combined audio through a single amplifier, LM386 or similar.

Regards,

Chris 

[Moffrestorer]

As an extension to the previous post, if you add a volume control to each audio input of the mixer/amplifier, you have an easy way to mute any audio should the alerts become overwhelming or a distraction, a facility Lee is being asked to implement for PAW at present.

Don't forget that if you are connecting to the audio jack of iPad or IPhone, it's best to purchase SLIM 3.5 mm plug cables (from eBay) as these fit better.

Regarding interference, I did detect a faint periodic clicking through the headphones when using the Maplin 1W amplifier, though in practice in the air it's undetectable!

Regards,

Chris

[rogerabc]

Thanks Chris,

So I probably need an adjustable, 3 channel resistive mixer, to balance the 3 outputs.
Is something suitable available ready made do you think or would it be soldering iron time?

Cheers,

Roger

[Richard]

Hi, May be something like this ?

http://www.aircraftspruce.com/catalog/avpages/gretzAudio_mixer.php

[Moffrestorer]

Or see the AP60 6 channel audio mixer from aircraft spruce at only 85$.

I ended up building mine (3 channel) for about £20 max including abs box, 3x 10K pots, knobs, some 1K resistors, a power socket for 12v input, 4x 3.5mm audio sockets; the amplifier kit from Maplins was £9 of that. Now I do have an LAA aircraft so if you have a CofA or need to be EASA compliant maybe something from Aircraft Spruce may be more appropriate.

I got the mixer circuit off t'internet posted by someone called Nighthawk. Details are on this or another audio thread somewhere on this forum. Alternatively, I could sketch out the circuit if anyone's interested.

It probably possible to find something already made up on eBay, but it might have 1/4" audio sockets and you need to match the supply voltage for your aircraft.

Chris

[rogerabc]

Thanks for the suggestions. I have made some progress but find myself, once again, wrestling with the mysteries of audio integration and hoping someone's advice can help me out.

I soldered up a resistive mixer & ebay amp which made my 3 audio devices nicely audible on a test flight during which I only monitored the VHF com. (There is a faint ticking noise when the iPad is charging)

This week I flew again & discovered that, when transmitting, my microphone sounds noisy & distorted (to me & also atc). De-powering the amp cures the problem.

Amplifier output goes to the intercom aux channel, not the comm, but of course the comm output does also go to the intercom.

The new problem only occurs when transmitting.

I will try reducing the amp gain & see if that helps but am otherwise unsure how to proceed.

Any advice most welcome.

Roger

[tnowak]

Roger,

I don't know what radio you have but I would have thought you would want to connect your audio amp to you radio's "ext audio in" rather than "intercom aux".
I suspect the impedance of your amp is affecting your radio's microphone circuit.

Or experiment with a series resistor between your amp output and "intercom aux" connection. Try 150 ohm and then up to 600 ohm.
Tony Nowak

[Moffrestorer]

Our Becker 8.33khz radio's integral intercom has a gain setting for the Auxiliary Input, via the menu system. I juggled with both this and the gain control of the mixer amp for best results. Sweet as a nut via intercom, and as far as I know TX comms unaffected, certainly sidetone sounds fine when transmitting. Used this input so that both occupants will hear the audio alerts.

Not sure if there is a separate "ext audio input". If there is, I suspect this audio could find its way onto your TX when the PTT is pressed!

Sounds as though you could be overloading the intercom so reducing amplifier gain should help, but still unclear how the amplifier can be causing distortion on the mic input. Presumably the amplifier output is decoupled (has a series capacitor on the output to stop any DC, something like 10uF minimum)?

[Moffrestorer]

Incidentally Roger, you didn't seem to notice any distortion on the first test flight, so is this a more recent problem? Could one of your audio sources have been unwittingly turned up to now cause this problem (though you would probably notice it being louder than the others).

The lowish level of the PAW audio output is the limiting factor so I would just start with this, adjusting intercom and mixer/amp gain (with individual channel volume pots set at max, if these are fitted) for satisfactory distortion free level into your headphones, as a "pre-set", then other sources can be adjusted to match. Then use channel pots to reduce or mute individual audios for flight, as required.

Regards,

Chris

[rogerabc]

Thanks Chris & Tony,
I will try your suggestions.
No distortion noted on first flight as there was no transmitting & it only occurs when I press the ptt.

Roger

[rogerabc]

Finally got my audio sources balanced & radio behaving - thanks to all who contributed advice.

I added a 10k potentiometer to the amplifier output & was able to dial out the distortion when transmitting.

Think I now need a mute switch for the PAW channel for use in the circuit & on the ground!

Cheers,

Roger

[exfirepro]

Hi Roger,

Lee made some changes recently in response to audio issues AlanG and I identified during testing some weeks ago in relation to FLARM and Bearingless Target Alerts. These have improved things significantly and are presumably incorporated in the new software due to be released later tonight (which I haven't had a chance to test run yet as I have been driving down to Telford all day).

Regards

Peter

[AlanG]

Hi All

I don't know if it's just finger trouble on my part but since updating to the latest software and trying both my units at home I seem unable to alter the volume setting and save it.
I can tap the volume control and select 10 (or any other number) and it apparently changes in the box alongside but pressing the test button sees no difference in the volume and when I then try to save this setting it just reverts to the default 5.  Even if I don't click save it reverts to 5 with the next refresh of the page.
Any ideas what I'm doing wrong.

Regards
Alan