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Thread: What is "coil whine" and what is that goopy stuff all over the inside of my PSU

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    Default What is "coil whine" and what is that goopy stuff all over the inside of my PSU

    DAILY, people in different forums ask "my PSU makes buzzing or humming noises. Is it defective?"

    EVERY OTHER DAY, people in different forums ask, "what's this white/gray/black goo all over my PSU? Did a cap just leak all over the inside of my PSU????

    First things first: Capacitors don't leak "goo". Capacitors vent a dry-ish, foamy liquid, and in very small amounts since a "wet" cap is made with paper soaked in an electrolyte and not a can filled with electrolyte as so many think.



    We'll get back to the goo later...

    The "coil whine" is simply the sound of electricity. Alternating current "alternates" at different frequencies. Your power supply is switching, chopping and changing the voltage of alternating current at very high frequencies a good deal before it's finally converted to DC. And some times, this switching frequency falls to a point where it's audible.

    From: https://en.wikipedia.org/wiki/Electr..._and_vibration

    Inductors

    In inductors, also called reactors or chokes, magnetic energy is stored in the airgap of the magnetic circuit, where large Maxwell forces apply. Resulting noise and vibrations depend on airgap material and magnetic circuit geometry.

    Transformers


    In transformers magnetic noise and vibrations are generated by several phenomena depending on the load case which include Laplace force on the windings, Maxwell forces in the joints of the laminations, and magnetostriction inside the laminated core.

    Capacitors


    Capacitors are also subject to large electrostatic forces. When the capacitor voltage/current waveform is not constant and contains time harmonics, some harmonic electric forces appear and acoustic noise can be generated. Ferroelectric capacitors also exhibit a piezoelectric effect that can be source of audible noise. This phenomenon is known as the "singing capacitor" effect.

    That leads us to the goo!



    The goo you see is just "RTV", a type of caulk. You can even buy it from Amazon: https://www.amazon.com/Clear-Electro...dp/B0063U2RT8/

    It's often applied to dampen vibration from alternating current, but is also widely used to keep "heavy" components from pulling off the PCB when the product is in transit so that the solder points aren't the only thing keeping the component attached to the PCB.



    Last edited by Jon Gerow; 06-10-2019 at 01:34 PM.

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    Quote Originally Posted by Jon Gerow View Post
    It's alternating at 50 to 60Hz which is way beyond human's scope of hearing.

    Humans can hear down to about 20Hz, and mains hum is easy to hear.

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    Quote Originally Posted by ashiekh View Post
    Humans can hear down to about 20Hz, and mains hum is easy to hear.
    Mains hum is not as simple as hearing the alternating current from the mains. You're not hearing your AC alternating at 50 to 60Hz when you hear mains hum.

    Mains hum can be from transformers or other inductors, magnetostriction, corona discharge, etc. changing the waveform. What I am saying is if you had an AC source without any component changing the wave form, you would not hear it.

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    I agree that higher harmonics make it easier to hear.

    Just wanted to question
    "50 to 60Hz which is way beyond human's scope of hearing"

    http://onlinetonegenerator.com/

    I can hear 20Hz sine-wave using the above (volume cranked all the way up)
    Last edited by ashiekh; 06-08-2019 at 10:44 PM.

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    For Hallowe'en one year 50y ago or so, my friend (we have known each other 65y) and I ran a speaker directly connected with "house" current (I know, dangerous; but we didn't know). We heard the sound loud and clear. I have since heard that noise in improperly grounded hifi equipment. Actually, you can hear it -- it's on the Woodstock soundtrack.
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    Quote Originally Posted by ashiekh View Post
    I can hear 20Hz using the above (volume cranked all the way up)
    You're not human.

    Quote Originally Posted by ehume View Post
    For Hallowe'en one year 50y ago or so, my friend (we have known each other 65y) and I ran a speaker directly connected with "house" current (I know, dangerous; but we didn't know). We heard the sound loud and clear. I have since heard that noise in improperly grounded hifi equipment. Actually, you can hear it -- it's on the Woodstock soundtrack.
    That's not exactly hearing it at 50 or 60Hz, though. DC power is 0Hz, but you can hook a 9V battery to a speaker and get a low hum.

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    Quote Originally Posted by ehume View Post
    I ran a speaker directly connected with "house" current

    And it survived?

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    Quote Originally Posted by Jon Gerow View Post
    You're not human.

    I think it is safer to do these experiments over speakers rather than headphones; using headphones I didn't feel so great.
    Last edited by ashiekh; 06-09-2019 at 11:05 AM.

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    Quote Originally Posted by ashiekh View Post
    And it survived?
    Yes. It was an old speaker in 1965, so I suspect it was "lofi."
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    Hearing down below 50-60Hz is not particularly uncommon - I can tell the difference between silence and 28Hz, even with notable background noise and my hearing is not particularly fantastic.

    According to https://www.audiocheck.net/testtones...distortion.php Humans cannot hear (much) below 20Hz, even with special gear.

    my testing was done with a pair of Audeze LCD2 with an Ifi Micro iDac 2, testing with my phone (iPhone Xr) causes significant distortion which causes sound to be hear-able below the usual human limit.
    Just some nerd from 'Straya

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