Audio Cabling Wire Lead Lengths

drone_pilot · #1 06-08-2015, 06:12 PM

I am using dual Dynon 10" displays complete with the Dynon Com and Intercom. I have a couple of questions for someone more experienced than I am. I am using a 3 conductor shielded cable for my headphone and MIC jacks. I know not to terminate the shield at these jacks but how much wire lead can I leave exposed without shielding to solder to the jacks?

Also, these same shielded cables go to to a 24 pin D Sub connector at my Dynon Intercom where the shields and some ground wires all connect to a common pin 1. Again, how much wire lead can I leave exposed without the shielding at this connector. Having to piggyback the shields to ground is going to consume a lot of space and I'm wondering if I can do this outside of the D-Sub connector's shell?

Any input is greatly appreciated!

BobTurner · #2 06-08-2015, 06:39 PM

This is not critical. An inch or two without the shield is unlikely to be an issue. Do keep all the wires (including one dedicated to ground, remember to insulate the jacks from the chassis) twisted together as much as possible.
At the D-sub (or whatever) connector it is common practice to solder the shield (support with shrink tubing) to a "pig tail", about 2" of wire, and then tie all the pigtails together under a designated grounding screw (or combine them into one if it's a D sub pin).

Raymo · #3 06-09-2015, 02:28 PM

You will need to strip back enough shielding to keep them outside the shell. They won't all fit inside, otherwise (ask me how I know).

I used solder splices on each shielded wire and inserted a 22 gauge black wire that pointed away from the connector. The black wires where then soldered together with pin 1 to one 18 gauge wire to the grounding block. Same for the ground wires (white, in my case) from the headset jacks. Heat shrink over the combined grounds makes them look nice.

The .250 jack can be wired with a shielded twisted pair, connecting the shield on the jack end to the barrel connector. The .210 jack needs the shielded trio, of course.

Robert Anglin · #4 06-10-2015, 07:15 AM

Bob is on the money here. All I have to add is that we found a way to make up these ends that can chain them together or as a single shield with ring crimp on the shielding ends. We just put in our C.A.N. , RS-232, RS-485, and audio and mice runs to a GMA-340. Most all of these are either 2 or 3 wire twisted shielded cables used for the Garmin G3X systems. What we did was strip back the outer case a good length say 6 inches or so. Push the shielding back like a chines finger. go down to the base where we had cut the outer-casing away. Open up the shielding with a snap-on O-ring pick and pull the wires and data tag threw that opening. We cut the data tag off and took the shielding, pulled it to get it flat and thin. Then twisted the shielding to get it into a thin round twist. We then took a peace of 1/16 shrink rap and cut it to length and put it over the shield. When we hade the shield covered we then put a peace of 3/16 shrink rap over the spot where the shield and the wires comes out of the outer casing. All we needed to do then was hold the made up end back of the back-shell and gage how long we wanted to cut the AWG-22 wires to let the spot where we had the shield coming out of the outer-casing be 1/2 to 1" behind the back-shell strain relief bar. Now that lose shield wire can have a ring crimp put on the end or two of them can be put in the same ring crimp and the ground bar or back plate of your audio panel will be easy to reach with that length of shield lead. Or you can cut them to a length you like. This is just another way to make it up with out using solder joints and seams to work for all three types of wiring, C.A.N., SR-, Audio, and Mice. We are in the middle of this install now so it will have to prove it's self out, but it dose look good to go.
Gust food for thought. Yours as always. R.E.A. III #80888

BobTurner · #5 06-10-2015, 11:23 AM

Quote:

Originally Posted by Raymo

The .250 jack can be wired with a shielded twisted pair, connecting the shield on the jack end to the barrel connector.

se.

Ground loops are like black magic.
Connecting the shield to the barrel connector works fine with engine off. Start the alternator, you may hear whine. Or maybe not for 8 months, after various airframe lap joints oxidize a bit.
This is a case of where an oz of prevention, now, may save a pound of headaches, later.