Distortion in various core materials and geometries

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Is there any detailed information on what influences distortion in an inductor? There are several parameters
- ferrite vs. iron
- type of ferrite (zinc-manganese vs. ...)
- type of iron (silicon-doped vs. ..., tempered and glued metal sheets, sintered insulated powder, ...)
- geometry of the inductor

Clearly iron cores have a higher saturation level and hence lower distortion at very high power.

For everyday use we should be more concerned about low power. At Intertechnik (http://www.intertechnik.de/techtips/index.htm) they claim that some ferrites such as their high quality zinc-manganese are more linear aroung zero and hence offer lower distortion at low power than any iron material. The reasons are not explicitly given but seem to be linked to lower hysteresis and negligable eddy current losses.

On the other hand, the only coil I have ever seen with published typical values is the Intertechnik I-bar-core claimed to offer exceptionally low distortion of 0.01-0.05% typical 3rd harmonic at both low and high power. It's core seems to be the straight part of a C I transformer core. While the geometry might be favorable (low flux), the use of iron sheets rather than sintered iron powder or ferrite would be ideal at low power according to their own reasoning.

Anybody have links, experience, measurements?

Hi Eric,

I have an old article from the German magazine "Elrad" titled: "Klirrfaktor in Drosselspulen" .
They measured the distortion (k3) of various types of iron and ferrite inductors versus frequency and at different power levels (many nice graphs) with a Neutrik distortion analyzer.
Though it isn`t explained WHY there are differencies in distortion, might this be useful info for You??
Sure, this is exactly what I was looking for. Having the results and no theory is better than an unproven theory with no results...

Do you know the month and year? I have inherited a few dozen copies from my old job, but I think I would have noticed an article like that. If not, would you be willing to scan or xerox?

Eric (currently living in Aalen)
I do not know the month/year it`s a partial reprint (Sonderdruck)of Elrad Extra 7. That`s all I know.
Unfortunately my scanner still does not work with my PC (my brother didn`t have time to fix this).:(
If You want it now I can make pics with my digi camera.
In case You can wait a while, I can scan it for You when I´m at my brothers shop the next time but can`t say exactly when this will be.
I could email You either pics now (this weekend or so) or the scans (which are propably nicer) later ?
Your choice!
Christoph, just sent you an email about the article. I will post summary and conlusion once I have carefully read the article. Is there anything you could already summarize from memory?

From Audioasylum, I got the tip that there had been an article adressing exactly that problem in the now discontinued "Speaker Builder Magazine". At www.audioxpress.com, I found that in 1996, an article called "Quality issues in iron cores". Before I order a whole year of back issues (individual copies are no longer available), would anybody know about this article and whether it also compares various iron and ferrite materials?

The conclusions are somewhat to differentiated in order to summarize them. Moreover I don`t know how to properly translate the designations for the different inductor types as: Stiftkernspule, Glockenkernspule, Rollenkern, Sinterkern etc..
Maybe You know this better and can post the conclusions here with the right terminology.
Though in German, the article perhaps even would be nice for posting it in the Wiki?
I`m going to scan it - but it may take a while.
Distortion is caused by energy dissipation due to hysteresis, saturation and eddy currents. Anything that limits hysteresis and eddy currents and increases saturation (voltage) will reduce distortion.

Lamination and insulated ferrites limit eddy currents, large cores limit saturation and soft low carbon steel has very low hysteresis - I don't know what the properties of silicon steel are.

BTW, Ich studierte vor einigen Jahren in Oesterreich.
Gruss Gott! ;)
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