Guide To Understanding Coil Whine!

[RobTapps]

First off lets start with some Techincal terms so you can better understand the components in your system that contain a "Coil" and create auditable noise.

Coils can be classified by the frequency of the current they are designed to operate with:

        Direct current or DC coils or electromagnets operate with a steady direct current in their windings
        Audio-frequency or AF coils, inductors or transformers operate with alternating currents in the audio frequency range, less than 20 kHz
        Radio-frequency or RF coils, inductors or transformers operate with alternating currents in the radio frequency range, above 20 kHz



Wiki Definitions

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Choke
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Choke (Electronics) In electronics, a choke is an inductor used to block higher-frequency alternating current (AC) in an electrical circuit, while passing lower-frequency or direct current (DC). A choke usually consists of a coil of insulated wire often wound on a magnetic core, although some consist of a donut-shaped "bead" of ferrite material strung on a wire. The choke's impedance increases with frequency. Its low electrical resistance passes both AC and DC with little power loss, but it can limit the amount of AC due to its reactance.
The name comes from blocking—“choking”—high frequencies while passing low frequencies. It is a functional name; the name “choke” is used if an inductor is used for blocking or decoupling higher frequencies, but is simply called an “inductor” if used in electronic filters or tuned circuits. Inductors designed for use as chokes are usually distinguished by not having the low-loss construction (high Q factor) required in inductors used in tuned circuits and filtering applications.

Types And Construction Chokes are divided into two broad classes – audio frequency chokes (AFC), those designed to block audio and power line frequencies while allowing DC to pass, and radio frequency chokes (RFC), designed to block radio frequencies while allowing audio and DC to pass.

Audio And Power Supply Filter Chokes Audio frequency (AF) chokes usually have ferromagnetic cores to increase their inductance. They are often constructed similarly to transformers, with laminated iron cores. A major use in the past was in power supplies to produce direct current (DC), where they were used in conjunction with large electrolytic capacitors as filters to remove the alternating current (AC) ripple at the output of rectifiers. A rectifier circuit designed for a choke-input filter may produce too much DC output voltage and subject the rectifier and filter capacitors to excessive in-rush and ripple currents if the inductor is removed. However, modern electrolytic capacitors with high ripple current ratings, and voltage regulators that remove more power supply ripple than chokes could, have eliminated heavy, bulky chokes from mains frequency power supplies. Smaller chokes are used in switching power supplies to remove the higher-frequency switching transients from the output (and sometimes from feeding back into the mains input); these often have toroidal ferrite cores.

RF Choke Chokes for higher frequencies often have iron powder or ferrite cores. They are often wound in complex patterns (basket winding) to reduce self-capacitance and proximity effect losses. Chokes for even higher frequencies have non-magnetic cores and low inductance. A modern form of choke used for eliminating digital RF noise from lines is the ferrite bead, a cylindrical or torus-shaped core of ferrite slipped over a wire. These are often seen on computer cables. A typical RF choke (RFC) value could be 2 millihenries.

Common Mode Chokes Common-mode chokes, where two coils are wound on a single core, are useful for prevention of electromagnetic interference (EMI) and radio frequency interference (RFI) from power supply lines and for prevention of malfunctioning of electronic equipment. They pass differential currents (equal but opposite), while blocking common-mode currents. Magnetic fields produced by differential-mode currents in the windings tend to cancel each other out; thus the choke presents little inductance or impedance to differential-mode currents. This also means the core will not saturate even for large differential-mode currents, and the maximum current rating is instead determined by the heating effect of the winding resistance. Common-mode currents, however, see a high impedance due to the combined inductance of the windings.

The wire or conductor which constitutes the coil is called the winding. The hole in the center of the coil is called the core area or magnetic axis. Each loop of wire is called a turn. In windings in which the turns touch, the wire must be insulated with a coating of nonconductive insulation such as plastic or enamel to prevent the current from passing between the wire turns. The winding is often wrapped around a coil form made of plastic or other material to hold it in place. The ends of the wire are brought out and attached to an external circuit. Windings may have additional electrical connections along their length; these are called taps. A winding which has a single tap in the center of its length is called center-tapped.
Coils can have more than one winding, insulated electrically from each other. When there are two or more windings around a common magnetic axis, the windings are said to be inductively coupled or magnetically coupled. A time-varying current through one winding will create a time-varying magnetic field which passes through the other winding, which will induce a time-varying voltage in the other windings. This is called a transformer.


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Transformer
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Transformer A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. Commonly, transformers are used to increase or decrease the voltages of alternating current in electric power applications.
A varying current in the transformer's primary winding creates a varying magnetic flux in the transformer core and a varying magnetic field impinging on the transformer's secondary winding. This varying magnetic field at the secondary winding induces a varying electromotive force (EMF) or voltage in the secondary winding. Making use of Faraday's Law in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within power networks.
Since the invention of the first constant potential transformer in 1885, transformers have become essential for the AC transmission, distribution, and utilization of electrical energy. A wide range of transformer designs is encountered in electronic and electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume to units interconnecting the power grid weighing hundreds of tons.



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Electromagnetic Windings
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Electromagnetic Windings An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix. Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in devices such as inductors, electromagnets, transformers, and sensor coils. Either an electric current is passed through the wire of the coil to generate a magnetic field, or conversely an external time-varying magnetic field through the interior of the coil generates an EMF (voltage) in the conductor.
A current through any conductor creates a circular magnetic field around the conductor due to Ampere's law. The advantage of using the coil shape is that it increases the strength of magnetic field produced by a given current. The magnetic fields generated by the separate turns of wire all pass through the center of the coil and add (superpose) to produce a strong field there. The more turns of wire, the stronger the field produced. Conversely, a changing external magnetic flux induces a voltage in a conductor such as a wire, due to Faraday's law of induction. The induced voltage can be increased by winding the wire into a coil, because the field lines intersect the circuit multiple times.
The direction of the magnetic field produced by a coil can be determined by the right hand grip rule. If the fingers of the right hand are wrapped around the magnetic core of a coil in the direction of conventional current through the wire, the thumb will point in the direction the magnetic field lines pass through the coil. The end of a magnetic core from which the field lines emerge is defined to be the North pole.
There are many different types of coils used in electric and electronic equipment.


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Inductors
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Inductors Inductors or reactors are coils which generate a magnetic field which interacts with the coil itself, to induce a back EMF which opposes changes in current through the coil. Inductors are used as circuit elements in electrical circuits, to temporarily store energy or resist changes in current. A few types:

Collection of RF inductors, showing techniques to reduce losses. The three top left and the ferrite loopstick or rod antenna, bottom, have basket windings.


        Tank coil - an inductor used in a tuned circuit
        Choke - an inductor used to block high frequency AC while allowing through low frequency AC.
        Loading coil - an inductor used to add inductance to an antenna, to make it resonant, or to a cable to prevent distortion of signals.
        Variometer - an adjustable inductor consisting of two coils in series, an outer stationary coil and a second one inside it which can be rotated so their magnetic axes are in the same direction or opposed.
        Flyback transformer - Although called a transformer, this is actually an inductor which serves to store energy in switching power supplies and horizontal deflection circuits for CRT televisions and monitors
        Saturable reactor - an iron-core inductor used to control AC power by varying the saturation of the core using a DC control voltage in an auxiliary winding.
        Inductive ballast - an inductor used in gas-discharge lamp circuits, such as fluorescent lamps, to limit the current through the lamp.


Types of inductors


Air core inductor Resonant oscillation transformer from a spark gap transmitter. Coupling can be adjusted by moving the top coil on the support rod. Shows high Q construction with spaced turns of large diameter tubing.
The term air core coil describes an inductor that does not use a magnetic core made of a ferromagnetic material. The term refers to coils wound on plastic, ceramic, or other nonmagnetic forms, as well as those that have only air inside the windings. Air core coils have lower inductance than ferromagnetic core coils, but are often used at high frequencies because they are free from energy losses called core losses that occur in ferromagnetic cores, which increase with frequency. A side effect that can occur in air core coils in which the winding is not rigidly supported on a form is 'microphony': mechanical vibration of the windings can cause variations in the inductance.


Radio frequency inductor Collection of RF inductors, showing techniques to reduce losses. The three top left and the ferrite loopstick or rod antenna, bottom, have basket windings.

At high frequencies, particularly radio frequencies (RF), inductors have higher resistance and other losses. In addition to causing power loss, in resonant circuits this can reduce the Q factor of the circuit, broadening the bandwidth. In RF inductors, which are mostly air core types, specialized construction techniques are used to minimize these losses. The losses are due to these effects:
    Skin effect: The resistance of a wire to high frequency current is higher than its resistance to direct current because of skin effect. Radio frequency alternating current does not penetrate far into the body of a conductor but travels along its surface. Therefore, in a solid wire, most of the cross sectional area of the wire is not used to conduct the current, which is in a narrow annulus on the surface. This effect increases the resistance of the wire in the coil, which may already have a relatively high resistance due to its length and small diameter.
    Proximity effect: Another similar effect that also increases the resistance of the wire at high frequencies is proximity effect, which occurs in parallel wires that lie close to each other. The individual magnetic field of adjacent turns induces eddy currents in the wire of the coil, which causes the current in the conductor to be concentrated in a thin strip on the side near the adjacent wire. Like skin effect, this reduces the effective cross-sectional area of the wire conducting current, increasing its resistance.
    Dielectric losses: The high frequency electric field near the conductors in a tank coil can cause the motion of polar molecules in nearby insulating materials, dissipating energy as heat. So coils used for tuned circuits are often not wound on coil forms but are suspended in air, supported by narrow plastic or ceramic strips.
    Parasitic capacitance: The capacitance between individual wire turns of the coil, called parasitic capacitance, does not cause energy losses but can change the behavior of the coil. Each turn of the coil is at a slightly different potential, so the electric field between neighboring turns stores charge on the wire, so the coil acts as if it has a capacitor in parallel with it. At a high enough frequency this capacitance can resonate with the inductance of the coil forming a tuned circuit, causing the coil to become self-resonant.

High Q tank coil in a shortwave transmitter


(left) Spiderweb coil (right) Adjustable ferrite slug-tuned RF coil with basketweave winding and litz wire


To reduce parasitic capacitance and proximity effect, RF coils are constructed to avoid having many turns lying close together, parallel to one another. The windings of RF coils are often limited to a single layer, and the turns are spaced apart. To reduce resistance due to skin effect, in high-power inductors such as those used in transmitters the windings are sometimes made of a metal strip or tubing which has a larger surface area, and the surface is silver-plated.
    Basket-weave coils: To reduce proximity effect and parasitic capacitance, multilayer RF coils are wound in patterns in which successive turns are not parallel but crisscrossed at an angle; these are often called honeycomb or basket-weave coils. These are occasionally wound on a vertical insulating supports with dowels or slots, with the wire weaving in and out through the slots.
    Spiderweb coils: Another construction technique with similar advantages is flat spiral coils.These are often wound on a flat insulating support with radial spokes or slots, with the wire weaving in and out through the slots; these are called spiderweb coils. The form has an odd number of slots, so successive turns of the spiral lie on opposite sides of the form, increasing separation.
    Litz wire: To reduce skin effect losses, some coils are wound with a special type of radio frequency wire called litz wire. Instead of a single solid conductor, litz wire consists of several smaller wire strands that carry the current. Unlike ordinary stranded wire, the strands are insulated from each other, to prevent skin effect from forcing the current to the surface, and are twisted or braided together. The twist pattern ensures that each wire strand spends the same amount of its length on the outside of the wire bundle, so skin effect distributes the current equally between the strands, resulting in a larger cross-sectional conduction area than an equivalent single wire.


Ferromagnetic core inductor Ferromagnetic-core or iron-core inductors use a magnetic core made of a ferromagnetic or ferrimagnetic material such as iron or ferrite to increase the inductance. A magnetic core can increase the inductance of a coil by a factor of several thousand, by increasing the magnetic field due to its higher magnetic permeability. However the magnetic properties of the core material cause several side effects which alter the behavior of the inductor and require special construction:
    Core losses: A time-varying current in a ferromagnetic inductor, which causes a time-varying magnetic field in its core, causes energy losses in the core material that are dissipated as heat, due to two processes:
    Eddy currents: From Faraday's law of induction, the changing magnetic field can induce circulating loops of electric current in the conductive metal core. The energy in these currents is dissipated as heat in the resistance of the core material. The amount of energy lost increases with the area inside the loop of current.
    Hysteresis: Changing or reversing the magnetic field in the core also causes losses due to the motion of the tiny magnetic domains it is composed of. The energy loss is proportional to the area of the hysteresis loop in the BH graph of the core material. Materials with low coercivity have narrow hysteresis loops and so low hysteresis losses.

For both of these processes, the energy loss per cycle of alternating current is constant, so core losses increase linearly with frequency. Online core loss calculators[10] are available to calculate the energy loss. Using inputs such as input voltage, output voltage, output current, frequency, ambient temperature, and inductance these calculators can predict the losses of the inductors core and AC/DC based on the operating condition of the circuit being used.[11]
    Nonlinearity: If the current through a ferromagnetic core coil is high enough that the magnetic core saturates, the inductance will not remain constant but will change with the current through the device. This is called nonlinearity and results in distortion of the signal. For example, audio signals can suffer intermodulation distortion in saturated inductors. To prevent this, in linear circuits the current through iron core inductors must be limited below the saturation level. Some laminated cores have a narrow air gap in them for this purpose, and powdered iron cores have a distributed air gap. This allows higher levels of magnetic flux and thus higher currents through the inductor before it saturates.

A variety of types of ferrite core inductors and transformers



Laminated core inductor Low-frequency inductors are often made with laminated cores to prevent eddy currents, using construction similar to transformers. The core is made of stacks of thin steel sheets or laminations oriented parallel to the field, with an insulating coating on the surface. The insulation prevents eddy currents between the sheets, so any remaining currents must be within the cross sectional area of the individual laminations, reducing the area of the loop and thus reducing the energy losses greatly. The laminations are made of low-coercivity silicon steel, to reduce hysteresis losses.

Laminated iron core ballast inductor for a metal halide lamp



Ferrite-core inductor For higher frequencies, inductors are made with cores of ferrite. Ferrite is a ceramic ferrimagnetic material that is nonconductive, so eddy currents cannot flow within it. The formulation of ferrite is xxFe2O4 where xx represents various metals. For inductor cores soft ferrites are used, which have low coercivity and thus low hysteresis losses. Another similar material is powdered iron cemented with a binder.


Toroidal core inductor In an inductor wound on a straight rod-shaped core, the magnetic field lines emerging from one end of the core must pass through the air to reenter the core at the other end. This reduces the field, because much of the magnetic field path is in air rather than the higher permeability core material. A higher magnetic field and inductance can be achieved by forming the core in a closed magnetic circuit. The magnetic field lines form closed loops within the core without leaving the core material. The shape often used is a toroidal or doughnut-shaped ferrite core. Because of their symmetry, toroidal cores allow a minimum of the magnetic flux to escape outside the core (called leakage flux), so they radiate less electromagnetic interference than other shapes. Toroidal core coils are manufactured of various materials, primarily ferrite, powdered iron and laminated cores.

Toroidal inductor in the power supply of a wireless router




Choke A choke is designed specifically for blocking higher-frequency alternating current (AC) in an electrical circuit, while allowing lower frequency or DC current to pass. It usually consists of a coil of insulated wire often wound on a magnetic core, although some consist of a donut-shaped "bead" of ferrite material strung on a wire. Like other inductors, chokes resist changes to the current passing through them, and so alternating currents of higher frequency, which reverse direction rapidly, are resisted more than currents of lower frequency; the choke's impedance increases with frequency. Its low electrical resistance allows both AC and DC to pass with little power loss, but it can limit the amount of AC passing through it due to its reactance.
 

An MF or HF radio choke for tenths of an ampere, and a ferrite bead VHF choke for several amperes.

 

A Covered Choke Found in most PC parts today



Variable inductor Probably the most common type of variable inductor today is one with a moveable ferrite magnetic core, which can be slid or screwed in or out of the coil. Moving the core farther into the coil increases the permeability, increasing the magnetic field and the inductance. Many inductors used in radio applications (usually less than 100 MHz) use adjustable cores in order to tune such inductors to their desired value, since manufacturing processes have certain tolerances (inaccuracy). Sometimes such cores for frequencies above 100 MHz are made from highly conductive non-magnetic material such as aluminum. They decrease the inductance because the magnetic field must bypass them.
Air core inductors can use sliding contacts or multiple taps to increase or decrease the number of turns included in the circuit, to change the inductance. A type much used in the past but mostly obsolete today has a spring contact that can slide along the bare surface of the windings. The disadvantage of this type is that the contact usually short-circuits one or more turns. These turns act like a single-turn short-circuited transformer secondary winding; the large currents induced in them cause power losses.
A type of continuously variable air core inductor is the variometer. This consists of two coils with the same number of turns connected in series, one inside the other. The inner coil is mounted on a shaft so its axis can be turned with respect to the outer coil. When the two coils' axes are collinear, with the magnetic fields pointing in the same direction, the fields add and the inductance is maximum. When the inner coil is turned so its axis is at an angle with the outer, the mutual inductance between them is smaller so the total inductance is less. When the inner coil is turned 180° so the coils are collinear with their magnetic fields opposing, the two fields cancel each other and the inductance is very small. This type has the advantage that it is continuously variable over a wide range. It is used in antenna tuners and matching circuits to match low frequency transmitters to their antennas.
Another method to control the inductance without any moving parts requires an additional DC current bias winding which controls the permeability of an easily saturable core material. See Magnetic amplifier.

(left) Inductor with a threaded ferrite slug (visible at top) that can be turned to move it into or out of the coil. 4.2 cm high. (right) A variometer used in radio receivers in the 1920s.


A "roller coil", an adjustable air-core RF inductor used in the tuned circuits of radio transmitters. One of the contacts to the coil is made by the small grooved wheel, which rides on the wire. Turning the shaft rotates the coil, moving the contact wheel up or down the coil, allowing more or fewer turns of the coil into the circuit, to change the inductance.

 

 

Section 2


Q&A

Q: Why do these components containing "Coils" make noise?
A: They make noise due to "resinance" of the windings vibrating at an extremely high frequncy, this is caused by electricity. for example if you stand next to a power plant you will hear an audible "HUM" coming from the transformers. This is the "Windings" vibrating. This is "Coil Whine" only on a massive scale.

Q: Is it just components containing a "Coil" that create noise?
A: The correct answer is NO, there are other components in your electronic device that may also cause noise such as capacitors that are about to fail. It can be hard to distinguish weather or not it is a "capacitor" or a "coil" making these spounds.

Q: How can I tell if the problem is "true coil whine" or a "capacitor about to fail"?
A: First I suggest that you check the tops of your capacitors to ensure they are not discolored or "bulging". I will include a picture below this answer so you can be sure!


Q: Can I fix or get rid of "Coil Whine"?
A: YES YOU CAN!(Most of the time) by coating the "Coil" in question in wax, epoxy, shoegoo or silicone this will effectivly absorb any high frequency vibrations from the "Coil" in question. A lot of MISINFORMED people will tell you otherwise saying "you gotta deal with it", when infact they are just inept.


Fixing the issue

Now as there are MANY different types of coils this may be different for each one.

1: Use a straw to your ear to isolate what component is causing the noise.

2a: For NON ENCLOSED COILS - just put a dab of shoegoo or silicone on the windings and let it dry prior to powering the unit on.

2b: For ENSLOSED COILS - these are a lot more of a pain, some can have covers that can be removed, others have the covers "molded" over the coils from the factory. for the removable covers gently pry them off and coat the windings the same as the "uncovered coils". For Molded coils you will need to get creative and use a syringe and some melted wax, or epoxy to inject the enclosed coil. PLEASE BE AWARE THAT THIS IS TO BE DONE AT YOUR OWN RISK!

 

References
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Choke (Electronics) - https://en.wikipedia.org/wiki/Choke_%28electronics%29

Transformers - https://en.wikipedia.org/wiki/Transformer

Electromagnetic Windings - https://en.wikipedia.org/wiki/Electromagnetic_coil

Inductors - https://en.wikipedia.org/wiki/Inductor



-End

[sirtoby]

Why the repost?

[RobTapps]

Why the repost?

didnt think of making it a tutorial until some one PM'd me lol so I Moved it here, the other threads were deleted.

[Bloodyvalley]

Why the repost?

Other posts were removed for an unknown reason

 

also OP, can you please make a TL;DR version?

[sirtoby]

didnt think of making it a tutorial until some one PM'd me lol so I Moved it here, the other threads were deleted.

ok, I just wondered, because I came across this thread earlier today. Good article btw.

[RobTapps]

Other posts were removed for an unknown reason

 

also OP, can you please make a TL;DR version?

by tldr i assume you mean too long didn't read, if that is in fact what you meant then... NO I can not as this is all relevant information relating to understanding coil whine and its causes. if you are too lazy to read it then that's your problem and you are just gonna have to figure it out on your own.

 

 

 

ok, I just wondered, because I came across this thread earlier today. Good article btw.

Thanks man took a while. and there is still information to add