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How to Reduce Transformer Hum

Discussion in 'General Technical Questions and Answers' started by N0TZU, Aug 3, 2018.

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  1. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    I recently acquired a old Sorensen XT series dual 15 volt power supply. One of the two transformers has a significantly annoying magnetizing hum. I've checked that fasteners are tight, pushed an pulled on various hardware and other items, etc. and haven't been able to make much of an improvement.

    Any ideas?
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    It just hums because it doesn't know the words.

    Sometimes lifting the transformer off the chassis and using rubber or vinyl washers between the transformer and the chassis helps (assuming the issue is the hum being magnified by its mounting, which it often is).
    WB5YUZ and N0TZU like this.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    Does it run hot ? Under a load when not loaded down.

    WB2WIK's fix will work, If the transformer is not using the case as a heat sink.

    Some can be made quiet using a spray of clear acrylic.
    N0TZU likes this.
  4. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    Sometimes the fasteners and other hardware are too tight.

    Letting things "float" a little bit can often help reduce that darn annoying vibrating sound. lol

    Sometimes I install the transformer on the chassis and let it sit on top of some rubber washers to help dampen the sound.
    Last edited: Aug 4, 2018
    N0TZU likes this.
  5. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    The lacquer on the transformer laminations seems to be in good shape but I’ll check more carefully.

    It isn’t getting warm at idle and there’s no ripple issue with the supply so I don’t think there’s any sort of fault of the transformer or filter caps involved.

    I’ll try various hardware and isolation material “settings”.
  6. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    If it's not the laminations, the noise could be a rattling bobbin. Depending on construction, sometimes you can tap wood or plastic wedges to quiet a bobbin's movement. A little contact cement can help hold things still too.
    WR2E and N0TZU like this.
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    When I rewound a transformer (link) for an amplifier project, I noticed significant magnetostrictive noise ( A local transformer shoppe graciously vacuum-pressure impregnated it w/ a polyester compound. That helped A LOT. :)
    AI3V and N0TZU like this.
  8. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    The outfit I worked for always required VPI for all air cooled power transformers. I think it was the only way they could meet the noise specifications they also employed!
    During my years of specifying equipment and being involved in start-ups I was amazed at the number of transformer manufacturers that were in existence. Some good....some not so good.
    One of our clients insisted on using used transformers. I usually got involved after the used transformer failed during plant startup. When a plant is idle waiting on a replacement the pay got to be real good! Penny wise....pound foolish.
    KD5RJZ, N0TZU and WA7PRC like this.
  9. W5DXP

    W5DXP Ham Member QRZ Page

    My Astron hums loudly when I put it on the bottom shelf of my computer desk. When I put it anywhere else, it doesn't hum. That shelf seems to act like a resonant sounding board.
  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What was that?

    Can't hear you over that loud hum...
    KA9JLM likes this.

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