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Thread: Jack Installations

  1. #1
    wireweinie's Avatar
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    Jack Installations

    For all you guys that know how to sort out audio, mic, and push to talk lines and connect them correctly, congratulations. For every one else, I'll try to explain mono vs stereo and mic audio and PTT connections.

    If everything went as planned, there should be two diagrams attached to this post. If it didn't go as planned, they should be attached to the NEXT post.

    Start by looking over the diagram titled 'Mono Jack Connections'. Mono audio is just what the name says, one channel of noise routed to both ear cups on your headphones. Single channel equals one wire. See the label 'Tip (phone audio)' that points to the single spring contact on the jack. On the jack itself, double check which solder tab corresponds to the contact. Now note the label 'Barrel (audio gnd)'. The solder tab for this is physically connected to the threaded barrel on the jack. Audio circuits are just another electrical circuit as in they need a positive and a negative. Positive is the phone audio and the ground is audio ground. You might hear them referred to as 'audio high' and 'audio low', but all the same. And NO!, the audio low is not, and should not, be tied to airframe ground (more on that later). On the headphone circuit at each position, you will only solder the audio high to the spring tab connection and the audio low to the ground connection and your done. Be sure to check the diagram for the model of intercom or radio that you are installing as there are two general ways that audio harnesses are fabricated.

    The first example is like PS Engineering. Their mono audio lines are called out to be two wires inside a braided shield. In this case the shield is just a shield. The braid is only connected to airframe ground, at the intercom, and the wires are connected to the jack as audio high and audio low.

    The second example is NAT (Northern Airborne Technologies) now rebranded as Anodyne. Their mono audio lines are called out to be a single wire inside a braided shield. In this system, the single wire is the audio high and the shield is pigtailed to the audio low tab, on the jack, and to a ground pin on the intercom.

    Both ways work just fine, but be sure your harness is constructed EXACTLY as the diagram calls out. Some units, such as the NAT systems will never work correctly if you use any shortcuts in fabrication.

    Now look at the diagram titled 'Stereo Jack Connections'. The only difference between mono and stereo audio is that there are now two 'audio high' and one 'audio low' connections. The two audio high wires will be connected to the tabs for the two spring contacts. The tip contact will be either left or right audio and the ring contact will be the other. Once again, check with the diagram for the exact model of intercom (there is no such thing as stereo audio in a com radio). The manufacturer will designate which contact is to be left or right audio. It's important to follow that as it can effect emergency audio and/or all audio if using a mono headset. I labeled the stereo and mono jack in this example diagram to give a visual of how similar the mono and stereo connections are.

    NOW. Go back to the diagram labeled 'Mono Jack Connections'. Look at the picture labeled 'Microphone'. Physically a microphone jack looks exactly like a stereo audio jack. The only difference is that the hole for the mic plug is smaller(.206") than the hole needed for a phone plug (mono and stereo phone plugs are the same diameter, .250"). In the case of a mic jack, the spring contact for the tip of the plug is for push to talk functions and the ring contact is for mic audio high. And of course the tab for the threaded barrel is for mic audio low. The wires for mic jacks can be called out just as stereo audio lines, i.e. two wires in a braided shield or three wires in a braided shield. Connect them exactly as the manufacturer calls out in the diagram.

    A note about PTT functions: Only 'pilot' and 'copilot' positions will have push to talk capabilities. Occasionally, you might find a system that allows an 'observer' position to have push to talk. It's important to connect the push to talk lines to each position, whether you think you need it or not. If you need to transmit from one of these positions in the future or if the installed PTT switch is broken, just plug in one of those curly cord type PTT switches. Passenger positions will not have push to talk capabilities so you'll need one less wire to each of those jacks. If you have a PTT switch in the yolk or on the stick, the best way to connect it into the system is to add one extra wire to the push to talk tab and the mic audio low tab. Route these two extra wires to the switch and solder them. When the switch is pushed, it creates a short between the push to talk tab and the mic audio low tab, which sets the intercom to 'transmit'.

    And finally, remember when I told you not to attache audio lows to airframe ground? The reason you don't do that is that the audio lows can pick up electrical noise from the airframe. Noise from pumps, lights, strobes, etc. When you install each jack into position, install fiber, isolation washers to insulate it from ground. The proper washers have a shoulder on one to keep the threaded barrel from touching the sides of the hole in the panel. This way the jack must go to ground through the audio low wire, all the way back to the intercom/radio.

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  2. #2
    wireweinie's Avatar
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    Sorry but the titles of the two pics didn't come through and I didn't notice till now. The one on the right should be titled 'Mono Jack connections' and the one on the left should be titled 'Stereo Jack Connections'.

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    hotrod180's Avatar
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    IMHO it's worth pointing out that my Sigtronics intercom diagram shows the mic jacks grounding back at the intercom,
    but the audio jacks grounding at the jack mounting itself.

    I've had to troubleshoot intercom issues at the back seat stations before,
    twice the problem(s) killed the audio to all the headsets whether the intercom was on or not.
    Each time, I'm not sure just what I did, but everything ended up working OK.
    I think there's a lot of voodoo involved with this avionics stuff.
    Cessna Skywagon-- accept no substitute!

  4. #4
    wireweinie's Avatar
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    Ugh. Don't say the 'S' word!

    Most *igtronics intercoms use a single amplifier for the headset audio. That means ALL headsets (mono) are connected to the same blue wire. If any jack has the audio high contact touch ground, it will short out ALL audio.

    It also means that the more headsets are plugged in, the less volume you have. Also bad when connecting headsets with mismatched impedance (like a 300 ohm headset and a 600 ohm headset). Low volume again.

    If you insist on installing one of these things, use shielded wire and isolation washers. You'll avoid many noise issues.

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  5. #5
    Gordon Misch's Avatar
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    I tried unplugging the rear headset this afternoon and no change in front headset volume. SL30- radio and SPA-45 intercom.

    When the intercom is turned off, the radio volume is dramatically increased. Sidetone is distorted.

    Thoughts?

    Thank you much for your contributions!!
    Gordon

    N4328M KTDO
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  6. #6
    hotrod180's Avatar
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    Quote Originally Posted by wireweinie View Post
    ….Most *igtronics intercoms use a single amplifier for the headset audio. That means ALL headsets (mono) are connected to the same blue wire. If any jack has the audio high contact touch ground, it will short out ALL audio. It also means that the more headsets are plugged in, the less volume you have.....
    Had the short-em-all-out thing happen before--
    lots of head-scratching before I figured out that intercom station #3 was causing me to not hear radio at station #1.
    Fixed it by tinkering with it, twice or maybe 3 times now, but not sure exactly how I fixed it. Again, voodoo is likely involved.
    I have noticed that the com radio comes in a lot quieter at the copilot station, even with matching DC headsets.
    Not sure why, but since "copilot" seat is generally occupied by a passenger, not an FO or RIO, I'm not too worried about it.
    Cessna Skywagon-- accept no substitute!

  7. #7
    wireweinie's Avatar
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    Gordon,
    Do you have music plugged in? Is volume different with another headset (use a simple non noise cancelling headset for troubleshooting). Can you turn the volume down on the SL-30 and get rid of the distortion? Emergency jacks installed?

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  8. #8
    wireweinie's Avatar
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    Hotrod
    Do all your mic jacks function properly, is this just an audio problem? Do you have a single audio high wire on the #3 jack or do you have audio high and audio low wires both? Isolation washers installed?

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  9. #9
    Gordon Misch's Avatar
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    Quote Originally Posted by wireweinie View Post
    Gordon,
    Do you have music plugged in? Is volume different with another headset (use a simple non noise cancelling headset for troubleshooting). Can you turn the volume down on the SL-30 and get rid of the distortion? Emergency jacks installed?

    Web
    XM music is connected to the aux-in port, but the XM receiver is turned off.

    I don't own a non noise cancelling headset. The rear headset is Telex Stratus 50 and the front headset is zulu 2. I tried switching the Telex noise canceling function on and off, and it made no difference; same with the zulu.

    Yes, sidetone distortion decreases with the SL30 volume turned down. Radio reception is reasonably clear even at max volume.

    I don't know what you mean by "emergency jacks", but there are three pairs of jacks, one for front seat and two for back seat (PA-12). Only one of the back seat jacks has a headset plugged in; the other is open.

    Thank you
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  10. #10
    wireweinie's Avatar
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    Quote Originally Posted by Gordon Misch View Post
    XM music is connected to the aux-in port, but the XM receiver is turned off.

    I don't own a non noise cancelling headset. The rear headset is Telex Stratus 50 and the front headset is zulu 2. I tried switching the Telex noise canceling function on and off, and it made no difference; same with the zulu.

    Yes, sidetone distortion decreases with the SL30 volume turned down. Radio reception is reasonably clear even at max volume.

    I don't know what you mean by "emergency jacks", but there are three pairs of jacks, one for front seat and two for back seat (PA-12). Only one of the back seat jacks has a headset plugged in; the other is open.

    Thank you
    Borrow and old non noise canceling headset, unplug your XM, and try it again. If the volume still changes drastically you'll want to consider a different model/brand of intercom.

    Emergency jacks are placed in the audio, mic, and PTT lines that connect the intercom to the com radio. When you plug into the emergency jacks, you bypass the intercom and work the com radio directly. Should be in all installations as the are great troubleshooting aids.

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  11. #11
    hotrod180's Avatar
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    Quote Originally Posted by wireweinie View Post
    Hotrod Do all your mic jacks function properly, is this just an audio problem? Do you have a single audio high wire on the #3 jack or do you have audio high and audio low wires both? Isolation washers installed? Web
    Yes, audio problem only.
    Mic jacks work fine.
    And yes, single wire on the audio jack (dunno if it's "#3" or not).
    And no isolation washers on the aurdio jacks, as per Sig installation sinstructions.
    Jack is self-grounded.
    FWIW it's all working properly now.
    But it was before (until it wasn't)--
    like I said, voodoo.
    Cessna Skywagon-- accept no substitute!

  12. #12
    wireweinie's Avatar
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    Quote Originally Posted by hotrod180 View Post
    Yes, audio problem only.
    Mic jacks work fine.
    And yes, single wire on the audio jack (dunno if it's "#3" or not).
    And no isolation washers on the aurdio jacks, as per Sig installation sinstructions.
    Jack is self-grounded.
    FWIW it's all working properly now.
    But it was before (until it wasn't)--
    like I said, voodoo.
    It's a grounding issue with the jack. Since the 'S' people have installers attach the jack to airframe ground and don't use an audio low wire, that means the audio signal (very small) has to go to ground through the jack body and find it's way back to the intercom unit ground wire through all the corrosion and seams in the airframe.

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