air core inductors

[Covenant]

Are air core inductors inferior to ferrite core ones? If so would replacing 4 of them in a T-amp improve SQ?

[Rare Bird]

Mundorf do some good Air-core Coils.. Nice thick wire is important..

Edit:sorry just realised you want them for an amp not speakarse!

[walpurgis]

I'd use air cored inductors where possible. Ferrite cored inductors are cheaper to make and I believe they can respond differently across the frequency range.

[Covenant]

That's interesting Geoff. I was reading a Google translation of an Italian T-amp forum where someone was saying the opposite. Mind you the translation was dire and I might have got the wrong end of the stick.

[NRG]

I wouldn't worry. Air core will tend to be larger and more expensive, very large and expensive at high inductance, ferrite core will saturate at some point but probably well above the power and frequency your amp is capable of.

[walpurgis]

very large and expensive at high inductance

I know. I used to build a lot of speaker crossovers and ended up winding my own inductors to keep costs down. Still dear though.

[istari_knight]

Ah this old chesnut! Its been done to death on diyaudio so I suggest doing a search there but this should get you started: http://www.diyaudio.com/forums/class-d/87789-design-output-inductor-class-d-amplifier.html

If you wanted to try some cheaply Arjen Helder sells them [you may have to request them] but you can clearly see what they look like fitted to his TA2020 board http://www.ebay.co.uk/itm/New-MKIII-Tripath-TA2020-PCB-25watt-Class-T-amplifier-/261199490671?pt=UK_MusicalInstr_Access_RL&hash=item3cd0b3ee6f

There is talk against toroid inductors because of their bad EMI performance at high frequencies but some prefer the sound... Suck it & see :)

[The Black Adder]

Well the smsl sa-s3 uses air cores.

[Covenant]

Well the smsl sa-s3 uses air cores.

That's what got me thinking about it Joe. Didn't realise it was such a contentious issue.

[The Black Adder]

It is, but I don't think there is a definitive answer, it's all about what sounds best to you. I tried air and ferrite cored ones in my crossovers. The result was air cored but some Tannoyists love ferrite even over high quality Mundorf Air cores.

[Covenant]

From a brief read it would seem that air cored inductors are more prone to electromagnetic radiation. Therefore there is a stronger argument for using a decent linear supply instead of a smps.
Yea or nay?

[The Black Adder]

.

[Reffc]

Hmmm, not sure about some of the answers being given really addressing the main issue which is distortion performance v's power. In general terms ferrite cored inductors perform less well when under extremes of power fed through them wrt distortion. Air cored inductors perform rather better but the downside is that they also take up more space and can be more expensive to produce.

Although air-cored ones are usually spec'd for things like high quality crossovers etc, truth is for the magnitude of the current they'll deal with in that application, there's little real benefit over ferrite cored inductors. I understand that steel cored are also better performing than pure ferrites wrt to lower distortion under power.

Suck it and see. You can of course buy a meter to measure inductance, buy the wire and wind your own.

[Covenant]

Cheers Paul,
I came across a thread on another forum about modifications to a t-amp where someone had put tin foil over his air core inductors to reduce RF interference. Do you think that is OTT?

[Reffc]

Cheers Paul,
I came across a thread on another forum about modifications to a t-amp where someone had put tin foil over his air core inductors to reduce RF interference. Do you think that is OTT?

Yes.;)


The casework should be doing a decent enough job. Inductors operating with line level or higher voltages appropriately positioned in circuit often need no further shielding. It's other components (including straight wire runs) in close proximity to the inductors which need shielding from the inductors and I could understand more easily if this was the reason for it within the T-amp.

[YNWaN]

Quite - the issue is that air-cored inductors do not have a ferrite core that can saturate so are theoretically more linear. However, they are also less efficient and so significantly more cable is needed to make them. As more cable is used, to construct an equivalent value air-core inductor, so the DC resistance increases -to achieve the same resistance a larger diameter of cable must be used. The end result is that air-core inductors with the same value and resistance as ferrite cored are very much larger - hence they tend to radiate more.

[Chris]

FWIW Peter Comeau prescribed one of each in the Xover kits for his World Audio speaker kits, both WD20T and WD25T floorstanders. Ferrite core for the bass circuit and air core for the treble if I remember rightly. I remember reading why but have of course forgotten. Will try and chase it up.

[Reffc]

FWIW Peter Comeau prescribed one of each in the Xover kits for his World Audio speaker kits, both WD20T and WD25T floorstanders. Ferrite core for the bass circuit and air core for the treble if I remember rightly. I remember reading why but have of course forgotten. Will try and chase it up.

In truth it shouldn't matter for the sort of current and frequencies that inductors are being tasked with handling in crossovers.

In theory, with iron cored inductors, higher currents and frequencies can lead to higher core losses, so perhaps the thinking was that reactive losses affect iron cored inductors more than air cored inductors if used for higher frequencies.:scratch:

I can't see this as being relevant in reality since the opposite is more likely to be true, ie LF circuits usually draw more current, that current dropping with increased frequency. That means that power draw is greater in the LF inductor, and since air cored inductors suffer less distortion with increased saturation, then I would have thought that an air cored inductor was more suited to LF applications. There is a "however" however :eyebrows:

For the sort of currents dealt with in loudspeaker crossovers inductors, if properly rated for the application, inductors should never reach the point of saturation. That leaves the only design advantage (that I can see) of using a ferrite cored inductor in the LF section is that it's radiated field of influence is smaller, and if dealing with higher currents, perhaps this is seen as more important for limiting interference with other components in the circuit.

[YNWaN]

Isn't the reason suggested that non-linearity tends to exhibit at higher frequencies and so less relevant for bass sections? Also, on a more pragmatic level, the values required for bass inductors would generally mean a blooming huge air-cored inductor.

[Reffc]

Isn't the reason suggested that non-linearity tends to exhibit at higher frequencies and so less relevant for bass sections? Also, on a more pragmatic level, the values required for bass inductors would generally mean a blooming huge air-cored inductor.

:lol: which is exactly what I ended up with.

Non linearity is exhibited at higher frequencies for several reasons one of which is skin effect but this comes into play way above the audible spectrum. The only other major cause of non linearity is core saturation and this is unlikely provided that the inductors are properly rated which they almost certainly will be.

[YNWaN]

Yep, I considered all air-inductors but ended up using them for the high freq and upper mid - ferrite cored for the lower mid and bass. Even though my crossovers are external and about the size of a sheet of A4, there just wouldn't have been enough room to make the other two inductors air-cored (and with questionable value).

[Chris]

Peter Comeau said this on the World Audio forum
"The problem with air cores is that you either put up with a higher DC resistance (DCR) for a small coil or have an enormous coil for the low DCR that a ferrite offers.

With a large air cored coil you have big problems with the magnetic and inductive field. The magnetic field will affect other coils in the vicinity, but the coil is also prone, via mutual inductance, to pick up any electrical radiation in and around the speaker.

When you offset these problems against the slight increase in peak distortion that a good ferrite offers you might just find that the ferrite core wins out.

These aspects change at high frequencies where the coils are small and the distortion from ferrites is more significant.

Sometimes the increase in DCR when changing from a ferrite to an air core is beneficial, for example if you are using a lightweight, high sensitivity driver in a cabinet that is designed to bolster the bass output through resonance. Here a higher resistance between amplifier and drive unit results in a lower damping factor, so the resonance is more 'loosely controlled' resulting in a higher subjective level of bass output. "

Dunno if this helps..

Chris

[Reffc]

It sort of makes sense right up to the point that he talks about distortion from ferrites "being more significant" at higher frequencies, which implies that distortion must be significant enough to be noteworthy and that simply is NOT the case as long as the ferrite inductor is properly rated. The distortion values are more usually almost completely insignificant where inductors are concerned for this application.

The coil is unlikely to pick up any mutual inductive interference from the speaker either at the distance the crossover usually is from the drive unit (in my case its just under a metre). It would only be an issue for much smaller boxes.

It is true that the radiation field from an air-cored inductor is more far reaching than for a smaller ferrite, but as long as the orientation is at right angles wrt the axis of the other inductors and spaced as close to the furthest corners of the board as possible, then it's rarely an issue of any real significance, depending of course on the actual spacing.

For those reasons, I don't entirely go along with his conclusions which are more generalisations and slightly misleading in that context.

[YNWaN]

I can only agree with all of that.