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Old 01-31-2017, 06:13 PM
GalinHdz's Avatar
GalinHdz GalinHdz is offline
Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,280
Default Cheap DIY Audio Adapter

I have a nice video camera which has an external audio input jack that I want to connect to the rear seat intercom jacks and record in flight conversation. But the camera audio system is 8ohms while the airplane audio panel is 600ohms. If you connect them together without some kind of impedance matching, recorded audio gets very distorted and might even damage the airplane audio panel. Being the cheapskate that I am I decided to put what little EE knowledge I still have to good use so I designed and built an inexpensive 8ohm to 600ohm audio adapter. My audio panel is mono while my camera is stereo so I went with a 1/4" mono plug and a 1/8" stereo plug. It is just a simple resistor voltage divider and I got all the parts at my local Radio Shack. If your audio panel is stereo, use a 1/4" stereo plug instead of a mono plug and use two resistor voltage dividers each one connected to each one of the stereo (L / R) channels.

The resistors are 1/4w (1M Ohm / 100K Ohm) and are so small they fit inside the 1/4" male mono plug.

This is how it is all wired up:

I have used it several times and the recorded audio quality is excellent. It took about 1hr to build and I spent less than $15 for all the parts.

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Last edited by GalinHdz : 02-03-2017 at 02:56 PM.
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Old 02-01-2017, 09:54 AM
Veetail88's Avatar
Veetail88 Veetail88 is offline
Join Date: Oct 2008
Location: Hales Corners, WI
Posts: 1,016

Thanks for posting this. Without that knowledge, I made up a connector like that without the impedance consideration to hook my GMA240 to a Garmin Verb. Pretty sure that's what fried one of the channels on the crew circuit on the audio panel and I've been too cheap to pay the $250 to send it to Garmin for repair.
Jesse Bentley
N229Z - RV-8 - Flying - Livin' the dream!
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