Power ground versus audio ground

Discussion in 'Instruments / Avionics / Electrical System' started by Jaysmiths, Dec 19, 2013.

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  1. Dec 19, 2013 #1

    Jaysmiths

    Jaysmiths

    Jaysmiths

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    In reading the excellent responses to my post concerning shielding of various wires in the install of my FL760 and some information on the PS Engineering website concerning intercom install, I have a question concerning grounding of power (12-14v negative), the grounding of the wire shield itself, and the grounding of the audio signal in the mic and headphone.

    How do these inter-relate? Which if any need to be isolated? This entire area is truly mysterious to me.

    Thanks in advance for any light shed upon these dark realms.

    Jay
     
  2. Dec 20, 2013 #2

    djschwartz

    djschwartz

    djschwartz

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    Maybe this will help. I've posted it a couple of times before.
    View attachment GroundLoop.pdf
     
  3. Dec 20, 2013 #3

    N804RV

    N804RV

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    This blurb from PSE pretty much sums it up: " Radiated signals can be a factor when low level mic signals are bundled with current carrying
    power wires. Keep these cables separated."

    For many years, I susbscribed to the school of thought that the goal in audio shielding was to prevent the coupling of transient noises in to the input of any audio amplifier.

    There are basically 3 different conventions, any of them have been considered acceptable by manufacturers and are widely used in general aviation aircraft today. One is like Sigtronics, which doesn't really bother with shielding, they just collect all the mic audio common wires and terminate them together at a ground stud. Its important not to have any current carrying circuits grounded at this stud, because it can create a "ground loop" that can couple noise into the mic input.

    Another convention is the Bendix/King way of doing things, they terminate audio circuits through an internal audio common. Shield wires are collected and at one or more pins on the connector and is isolated internally before seeing a ground through the chassis ground.

    The 3rd way is the way PSE does it. They shield mic audio and headphone audio and terminate them with the external audio common at grounding stud that is specific for this purpose and kept away from current carrying circuits. PSE engineers seem to feel very strongly that headphone audio jacks should be isolated from the instrument panel by using the insulating washers like the ones provided with mic jacks.

    The best thing I can tell you to do, short of going back to school to study electronics, is to follow the manufacturer's instructions, and read some of the excellent stuff that other posters have linked to.
     
  4. Dec 22, 2013 #4

    cloudsurfer

    cloudsurfer

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    Altho for unmanned spacecraft a little something from the people that should know and explains some of the problems when you do it wrong. Also addresses the internal ground system of equipment. The manufacturers data is still number 1 when it comes to installation planning.
    https://standards.nasa.gov/documents/viewdoc/3314876/3314876‎
     
  5. Feb 2, 2014 #5

    PuertoRicoFlyer

    PuertoRicoFlyer

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    If no manufacturing recommendation is given then the easiest way to remember is: If you want to avoid interference from ESCAPING the wire (power cables) ground both sides of the shield. If you want to avoid interference from ENTERING the wire (signal cables) only ground the side closest to the equipment in question. :cool:
     

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