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Old 07-19-2013, 11:06 PM   #1
nox
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Question Why do some PSUs squeal / buzz / whine?

Why do some PSUs make a high pitched squeal / buzz / whine?

Is it always the transformer which makes the noise or can the capacitors also make the noise?

I've heard it referred to as "Capacitor Squeal" before, but then people say it's actually the transformer coils causing harmonic resonance because they're loose or the because the frequency is off.

Could a failing cap alter frequency & create harmonic resonance in a transformer?

If this is the case why do some PSUs that are brand new make squealing noises?

I've read accounts on different forums of even brand new high end PSUs like SS X series or Platinum having a high pitched squeal or ringing. Surely a brand new PSU wouldn't have failing capacitors.

I've also read posts where people say it can be dependent on the motherboard/video card(s)/hard drive(s) it's attached to. That the PSU could make a high pitched noise while connected to one setup but not another. Is there some sort of electric feedback involved where this could actually be the true?

The last hypothesis I've read about is the PSU getting "dirty power". That there's power noise in the outlet the PSU is plugged into. I'm not sure if a power conditioner would be practical in that case, especially with a high wattage PSU. Correct me if I'm wrong, but I don't think a UPS does any power conditioning; so most PSUs only have their own transient filtering to rely on.

But again, high end PSUs have still been known to have a squeal; & they usually have good transient filtering (compared to cheaper PSUs at least). It also wouldn't explain why the same person may not have squeal with another PSU.

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Old 07-20-2013, 02:53 AM   #2
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Default Re: Why do some PSUs squeal / buzz / whine?

New PSU buzzing = loose coil winding vibrating = manufacturing mistake.
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Old 07-20-2013, 05:44 AM   #3
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Default Re: Why do some PSUs squeal / buzz / whine?

New psu buzzing/squealing = bad engineering design OR bad parts

bad engineering design can include improper loading for the design being used. Bad parts can include variations between manufacturers.......engineer used parts made by one company but production models have parts made by another company.

And finally, I don't hear most squealing. As we age our high frequency hearing goes away. So if you don't like the squealing, just wait a while!
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Old 07-20-2013, 05:54 AM   #4
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Default Re: Why do some PSUs squeal / buzz / whine?

If they are designed to operate at an audiable frequency - which is extremely rare these days - then you will hear a squeal.

Other than that, if the psu has bad capacitors, or if there is a fault in the engineering of the psu, then it will have oscillations at lower frequencies, from being unstable.

The whine and hum you hear from transformers is made by magnetostriction, basically, the magnetic parts expanding and contracting ever so slightly. You can hear this in mains frequency transformers, as a hum sound.
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Old 07-20-2013, 02:23 PM   #5
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Default Re: Why do some PSUs squeal / buzz / whine?

What you are hearing is the transformer laminations. The metal plates are not bound tight enough when rivited together.
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Old 07-20-2013, 03:24 PM   #6
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Default Re: Why do some PSUs squeal / buzz / whine?

Quote:
Originally Posted by Ltank View Post
What you are hearing is the transformer laminations. The metal plates are not bound tight enough when rivited together.
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Switch mode PSU don't have metal laminations. Most noise is caused by either bad fan bearings or toroids operating at resonant frequencies.
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Old 07-20-2013, 07:43 PM   #7
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Default Re: Why do some PSUs squeal / buzz / whine?

Quote:
Originally Posted by Evil Lurker View Post
Most noise is caused by either bad fan bearings or toroids operating at resonant frequencies.
Yeah... they call it "coil whine" for a reason.
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Old 07-21-2013, 12:11 AM   #8
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Default Re: Why do some PSUs squeal / buzz / whine?

When I removed the capacitor (sometimes with a resistor in series) between the Reference and Cathode of a TL431 feedback element during a test, the power supply (and the TL431) oscillates with a sound from the magnetics.
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Old 07-21-2013, 04:53 AM   #9
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Default Re: Why do some PSUs squeal / buzz / whine?

Quote:
Originally Posted by japlytic View Post
When I removed the capacitor (sometimes with a resistor in series) between the Reference and Cathode of a TL431 feedback element during a test, the power supply (and the TL431) oscillates with a sound from the magnetics.
That capacitor is for compensation, and when the PSU isn't compensated, it gets unstable and has oscillations at lower audible frequencies.
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Old 07-21-2013, 07:16 AM   #10
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Default Re: Why do some PSUs squeal / buzz / whine?

Quote:
Originally Posted by ben7 View Post
That capacitor is for compensation, and when the PSU isn't compensated, it gets unstable and has oscillations at lower audible frequencies.
once again.......bad design OR improper loading
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Old 07-21-2013, 08:35 AM   #11
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Default Re: Why do some PSUs squeal / buzz / whine?

Strangely, I had a PC PSU that seems to buzz at AC mains frequency!

And/or the case would buzz at what seemed to be the AC frequency!
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