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Thread: PC Coil Whine & the PSU

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    Default PC Coil Whine & the PSU

    Hey all! So I was researching coil whine and came across this thread on EVGA's forums where not one but two different people solved coil whine issues from three different GPUs by simply changing the power supply.

    My understanding was that coil whine was caused by the copper wire vibrating, so how could swapping the PSU change the power characteristics sufficiently to alleviate the problem? Can anyone help me understand this, and give an idea as to how reliable a solution this might be in reality?

    As indicated in the thread some individuals have received multiple replacement GPU's that had coil whine, and it has been an extremely common complaint for years regarding GPUs where even the RMA replacements exhibit coil whine. But if a PSU replacement fixed it then it is starting to sound like GPU/mainboard makers might want to start recommending replacing the PSU to solve coil whine issues?

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    Quote Originally Posted by Kougar View Post
    Can anyone help me understand this, and give an idea as to how reliable a solution this might be in reality?
    That's a tricky question, because coil whine always involves the relationships between PSU, GPU and mobo, so unless you have enough expertise and instrumentations, very often trying to solve it is just a lengthy trial and error procedure.

    From the average user perspective, first of all you have to pinpoint from where the coil whine comes.

    Whether the coil whine comes actually from the PSU, as many times seen on latest Seasonic-based PSUs, swapping the PSU with a proper working one should definitely solve the issue (so the whine was due to a defective PSU).

    Otherwise, whether it's from the GPU, you should check from reliable sources whether the PSU may have some sub-par behaviour at ripple and transient load response, as an excessive stress on graphics power circuitry might start the issue.
    If that were the case, then swapping the PSU with a better performing one might solve the issue.
    On the other hand, whether the original power supply were correctly functioning and it had a fine behaviour, then the graphics itself should be the real culprit, and therefore a PSU replacement should not have any positive effect (it may worth to note that sometimes even a high quality but defective PSU could give similar issues but, as an average user, you can't be sure about which of the two parts were actually defective!).

    As a third option, the whine may actually come from the mobo, adding more complexity to the whole scenario.

    Eventually, sometimes the specific parts involved are just incompatible for some misterious reasons: and that's were an average use like me usually give it up.

    Anyway, any real computer builder should have at least a spare, well known, reliable, high quality and possibly powerful PSU *just* for back-up/troubleshooting purposes: even if that's not a proper rule of thumb, that's what I've learnt in my experience, since my first DFI board a while ago.

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    Copying my own post from TPU:

    Coil whine usually doesn't affect either the PSU's or the components' operation, at least not to a measurable degree, since the resonant frequencies are typically such that they're easily damped in other components, such as capacitors and other filter coils. I believe all manufacturers are actually aware of this issue, and are doing what they can to deal with it, most of the time.

    Namely, there are three ways coil whine will develop. There's "self-whine" to which every coil under the Sun is susceptible (including various types of transformers) by it's very nature, and there's resonant/induced whine, which is a byproduct of resonance between VRMs on the motherboard and/or the graphics card, and the PSU's coil(s) and/or transformer(s). Let me elaborate further:

    As the current passes through a coil, it creates a magnetic field, which in turn induces a current in the coil such that it tends to cancel out the change in the initial current. So if there's a constant 1A through a coil, then it jumps to 1.1A, the change in magnetic field will induce a current of -0.1A (meaning 0.1A in the opposite direction), restoring the net flow to 1A. This is how coils remove unwanted ripple/noise from the DC output of a PSU, or a DC input into a VRM.

    Both the length of the coiling wire and the coil loop diameter are parts of the inductance equation, and are a variable just like the inductance is, and not constants. Well, theoretically they are constants for a given coil when it's effective inductance is calculated, but in real world, where approximations amount to a wrong result, the coil will shrink and expand under the influence of magnetostriction.

    Self-whine or coil noise can be twofold - physical and electrical.

    Physically, high frequency switching used in PSUs (50-150 kHz) will make the coil vibrate (from all the rapidly succeeding shrinking and expanding) at a lesser frequency, typically from one quarter to one eight of the switching frequency. This is sometimes well inside the audible range (~20 Hz - ~20 kHz, typically 30 - 18k). The lower frequency vibrations are a consequence of the finite velocity of current (rather, electrons) and the finite speed of expansion/shrinkage propagation through the coil. Not only that, but both the wire and the core are shrinking/expanding, and at a different rate and amplitude, so until everything aligns properly (rate and speed of shape change with the rate of propagation of the deformations), there will be no audible vibrations. This is part of the story.

    Electrically, as the coil loops are moving and the core changes shape, both travel inside a varying magnetic field, which causes additional self-induced currents to appear. These are mostly damped out by other filtering elements, due to their very low magnitude and their relatively high frequency, but sometimes they manage to get to an amplifier in a sound card, for example, and show up as audible noise in the sound (sub)system. Additionally, every coil is a (poor) antenna for high-frequency signals (voltage changes), and it radiates those signals out into wires and PCB traces. There they are induced back from electromagnetic emissions into current and possibly amplified as per above.

    The kicker is that physical noise can (and does, in larger inductors) cause electrical noise, and vice-versa. Further, any wire or other form of conductor (like a PCB trace) is also an inductor, albeit a poor one.

    Resonant whine can develop between any two oscillatory systems, which coils are all by themselves, as is practically any circuit that contains them. VRM circuits on motherboards, graphics cards, hard drives, etc. pretty much always contain at least one. In order to have an electrical oscillator, you need an inductor and a capacitor. All inductors are also (poor) capacitors, and this doesn't present a problem at low frequencies, because they "see" capacitors as open circuits. Self-capacitance is a problem at high frequencies, exactly the situations where you'd want to use coils in the first place... When two coupled coils (either connected via wires and traces or magnetically coupled, or when the EM radiation of one permeates the other) reach very similar electrical self-noise frequency, the parasitic signals they produce may be (and usually are) amplified exponentially. This can, in rare cases, actually pollute the DC input/output, and there are actual cases in practice. There are some Sirfa-made PSUs in which simply moving output wires away from a regulator coil makes the PSU output voltage significantly less noisy. I still consider this a rarity, though, and it can be solved by putting a simple EMI shield (a piece of isolated metal sheet) around the offending coil or between it and the "polluted" area.

    Coil whine can be lessened to an acceptable degree with a relatively simple fix. Just dampen the physical side of it by gluing or caulking down the coil, so that it's vibrations are absorbed. Another way is changing the current/voltage frequency, which is never easy, as it affects the electrical design of the device in question, or use a different coil. This could be a coil made of different materials, or of a different size, or even a different shape. I've seen coils made in the shape of the number 8 (or the infinity sign, if you need to be geeky about it), that produce significantly less noise than standard toroidal coils. I can't say how much this would add to the price, however. And let's not forget that transformers are, in effect, simply big-ass coils, and their whiny nature is much harder to deal with...

    As for why coil whine would develop in time, instead of right from the get-go, well... Perhaps the dampening glue/caulk "breaks in"? Or maybe the coils very slightly change their basic (at-rest) shape, such that their resonance pattern shifts into the audible range? Who knows, it's a very complex phenomenon.
    Careful what you wish for... You just might get it.

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    Quote Originally Posted by McSteel View Post
    Just dampen the physical side of it by gluing or caulking down the coil, so that it's vibrations are absorbed.
    Does that void the warranty, if any?


    Quote Originally Posted by McSteel View Post
    Another way is changing the current/voltage frequency, which is never easy, as it affects the electrical design of the device in question, or use a different coil.
    So, is that the reason why a different PSU or a different video card may actually work?

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    Yes, that would very much void the warranty, but it is a convenient method for PSUs that are already out of warranty. Coil whine may develop late into the PSU's life; and actually it's logical that it does - all the tape, glue and caulk loses some of the elasticity (needed to dampen vibrations) over time.

    Changing the PSU (even going for the exact same model even from the same production batch) can solve the coil whine problem because the coils used in the new unit may be wound tighter, glued/caulked down better, or the ripple/noise frequency may be just different enough for the vibrations to fall outside the human hearing range.
    Careful what you wish for... You just might get it.

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    Quote Originally Posted by quest for silence View Post
    Anyway, any real computer builder should have at least a spare, well known, reliable, high quality and possibly powerful PSU *just* for back-up/troubleshooting purposes: even if that's not a proper rule of thumb, that's what I've learnt in my experience, since my first DFI board a while ago.
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    Thanks guys for the explanations! I have a new appreciation for the complexities of electrical engineering... and more understanding as for why coil whine is still such a prevalent problem with GPUs in particular.

    Guess I will test it by hooking up a second PSU to just the GPU without taking the full system apart. I have a new Titan Black that depending on load type can generate a really loud, steady tonal whine which drives me up the wall. GPU RMA's are a waste of time and money, but more importantly the replacement card has a very high chance of exhibiting the same problem anyway.

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    Quote Originally Posted by Kougar View Post
    Guess I will test it by hooking up a second PSU to just the GPU without taking the full system apart.
    I don't know the Titan power distribution, but it *might* worth to test it even with a different mobo. Anyway, good luck in your troubleshooting.

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    Yeah, I'd like to but it's a Hydro model. Would be really messy to swap it for both PCs involved, doesn't help it uses different size fittings than my own desktop either.

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