audio output to king KMA24

[peteD]

I want to connect my pilotaware audio output to my KMA audio panel, which has 500ohm input impedance.
I believe the 2B has a much lower output impedance which i presume is why it is very quiet.
Looking for advice as to how to deal with this please? can I use a transformer or do I need an amplifier? recommendations please!
Thanks

[Paul_Sengupta]

For audio impedance, if the output has a low impedance, it means it can drive a larger current. If the input impedance is high then it means it doesn't need a large current. The volume is determined by voltage levels. A transformer might help. Turning the volume up on the input might help unless it's already at its highest. An amplifier will almost definitely help, though there should be one in the audio panel. Any music output device putting out audio into headphones will normally have an impedance of 4-16 ohms, so for a music input the Pi should look similar to any music player.

[Admin]

Hi Pete

Ahaaa, I saw a similar thread on the euroga forum :-)

The connector is a TRRS style connector, I am surprised it is not powerful enough to drive the audio through an intercom.

Do you know what voltage levels the KMA is expecting, I am sure we can dig out specs on the RPi voltage output levels
edit:
so googling - it is apparently line level
https://www.raspberrypi.org/forums/viewtopic.php?t=181379

thx
Lee

[peteD]

Paul, thanks, that was my understanding from my rudimentary knowledge of electronics.

Lee, yes, wasn't any response here but pleased you're all back now! ;-)

The pilotaware drives my lightspeed headset phone input just fine, so no problems with the output.

However,  the KMA is expecting to see the sort of output than comes from an aircraft radio to drive an aircraft headset(500 ohm impedance), and to this end I have connected my handheld radio headphone output to the KMA which also works fine!

So I presume the KMA requires more than line level.

I was hoping a transformer might work(given the high impedance input) but am at the limit of my knowledge here!

I did see an audio transformer 600ohm(primary):50ohm(secondary) somewhere and wondered if there was any reason it couldn't be used the other way round......or am i barking up the wrong tree?

[PaulSS]

Would something like the LM386 amp work?

I have absolutely no idea what I'm talking about but have just bought one of these to construct an audio mixer.....thanks Moffrestorer 

The LM386 amp that I've bought has an adjustable 'volume' output i.e. voltage, so it might be what you need.

Something like this (many more available from China but this is a UK supplier): https://www.ebay.co.uk/itm/LM386-DC-5V-12V-Mini-Micro-Audio-Amplifier-Module-Board-Mono-AMP-Module-HIFI-L20/142868452981?hash=item21439f9675:g:un4AAOSw5GZbSxGx:rk:4:pf:0

[peteD]

Think we have an answer, see:
https://www.euroga.org/forums/maintenance-avionics/9985-pilotaware-audio-into-king-kma-24?page=3#post_193305
Post 24
Thanks all!