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Saturday, April 16, 2016

Magnetic Cores for Audio

As manufacturer of transformers, we can run away from magnetic cores. Magnetic cores are made of combinations of characteristics and properties. We we use mostly are the soft magnetic core materials, or so called electrical steels. Deep understanding of the electrical and magnetic properties will enable us to produce the end product with the right specifications.

We would need a big huge textbook to cover all the fundamental aspects of magnetic materials. We would only glide through the surface in blogs of course, for a general idea and high level understanding. What we focused on are those in lamination form, wound or stacked magnetic cores, for transformers used, primarily at mains frequency (50-60Hz) or at audio frequency (20-20kHz, or more!). 

We usually call cores for such application silicon steel, or SiFe, or iron silicon alloys. A lot of people call them silicon steel, or electrical steel. The magnetic properties / characteristics make them well suited for power or audio frequency usages. 

Core Loss

Primarily, a lot of the classification of silicon steels are by core loss. Core loss is usually the most important factor for us choosing a particular silicon steel for a certain application. Core loss is the electrical power loss in the form of heat in the core when subjected to AC magnetic force. 

There are several types of core loss, or a sum of all the different losses - hysteresis loss, eddy current loss within individual lamination, and inter-lamination.

We used to have so many types of grading since we have many steel manufacturers all over the world. The one I use the most is Z-prefix, commonly used in Japan and Asia, like the most common Z11 wit 0.35mm lamination. There is another standard, using M-prefix by USA (American Iron and Steel Institute) to grade the core loss. 

Grades

AISI grades the silicon steel by M-prefix followed by a number. M = magnetic material. Number = grade of the core, and also the relative core losses of grades within a class. The Number was a representative of the core loss of that grade but it was no longer applicable in modern days due to advancement of the silicon steel properties. 

Classes

Silicon steel are categorized into several classes generally. The classes are based on the primary magnetic properties of the material, the form, and the differences between the grades of the materials produced. 

Non-grain-oriented
Magnetic properties are same in any direction of magnetization in the plane of the material.

Grain-oriented
Magnetic properties are strongly oriented with respect to the direction of the rolling/annealing. The rolling/annealing process produces a crystal structure that are grains aligned so that the magnetic properties are far more superior in the rolling direction. 

Non-grain-oriented: M15, M19, M22, M27, M36, M-43, M-45, M47
Grain oriented: M2, M3, M4, M6

To be continued... 

16/4/2016
J&K Audio Design

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* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.

* Our product lines are always improving and increasing. If you do not see what you want, contact us!

* Please email for volume discounts, distributor and OEM pricing.

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