PIREP: Garmin GMA340 impedance-matching audio cable

Back in April there was a thread in rec.aviation.ifr from a Garmin GMA340
audio panel owner who was questioning why the audio level of a plugged in
device was so low:

http://tinyurl.com/lvaap

Tom Borchert replied with a post that explained about the impedance-
mismatch and included instructions (from a fellow Cirrus pilot) on how to
build an impedance-matching cable from Radio Shack parts.

At the time I was able to overcome my GMA340's volume problem by using the
volume control on my MP3 player and satellite radio receiver so I really
didn't give much thought to buying or building a cable.

Just recently, however, I attempted to plug in a mobile DVD player's volume
cable and discovered that the highest volume setting still was not high
enough to be audible over the intercom. Initially I gave thought to
purchasing a cable from he

http://www.fremarllc.com/accessories/index.html

but the principle of paying as much for shipping, handling, and delivery
insurance as the price of the cable made me decide to try to build my own
using Tom's instructions. Here are the details:

6 foot stereo cable with male mini-plugs on both ends: US $6.00 at Target
2 Radio Shack audio transformers (8 ohm/1000 ohm): $2.99/each or $6.00/2
1 Project box (small plastic box to hold the transformers): $2.29

Total was about $16.00 with sales tax included. Total time to modify the
standard stereo cable by clipping the cable and soldering the audio
transformers properly took about 15 minutes.

What a difference the cable makes. If you are at all handy and have a
Garmin GMA340 audio panel and would like to use the external audio plug, I
strongly recommend building this cable. The improvement in audio level is
very dramatic.

Tom B, a belated thank you for posting the instructions.


--
Peter