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Re: PP Iron for SE - repost of a 1996 rec.audio.tubes by "Paul"....

Posted by Steve Eddy on February 19, 2004 at 20:03:31

In Reply to: Re: PP Iron for SE - repost of a 1996 rec.audio.tubes by "Paul".... posted by dave slagle on February 19, 2004 at 08:29:56:

first we have to agree music is not sinusodal, then i have to ask so what if we are unipolar or AC... in the case of the pulse core, after a singlke pulse without the -Bdc applied, the core would remain at the +Br, but when the -Bdc is added the core then returns to the bias point rather than the Br.

It will no more return to the bias point than an unbiased transformer would return to 0,0.

The DC just introduces an offset.

but if we assume the loop momentarily ends up at a -Br point during a musical passsage, the bias point will demagnetize and remagnetize the core to the Bdc point.

No, it won't. The magnetic field due to the DC current never collapses. It magnetizes the core only once and that's it. After that, any magnetization or demagnetization of the core is brought about by the signal and everything else happens as usual but it happens about the Bdc point rather than about the 0,0 point.

there are a lot of "ifs" and assumptions in that statement. i don;t know if i woukld call it a fact (unless you assume) that Bmax=Bsat then i'll agree, but when Bmax is a fraction of Bsat wouldnt; be suprised to see the most linear part of the loop being somewhere other than (0,0) as an origin.

I haven't seen any instance where increasing DC current in the transformer increases its linearity. Except in the instance where a DC current in one winding is used to offset a DC current in the other winding.

yes, and whats more linear than air?

A vacuum. :)

Think about it though. Take one of your transformers and remove the core. Is it more linear without the core than it is with the core?

but above the knee of the loop the core is quite linear (your perm is very low, but thats a different issue)

Well sure. Once you saturate the core, it's not doing anything after that so it can't very well be nonlinear.

And yes, the permability drops and you have the equivalent of an air core transformer. But again, remove the core of one of your transformers and tell me how linear it is.

Without the high permeability of an unsaurated core, the coupling between the two windings drops considerably and distortion increases considerably as well. The primary inductace drops just as considerably and your low frequency response goes out the window.

it will be perfectly linear without the core, i think thats the point :-) your perm will be 1, but thats a different issue.

Let's see if it's perfectly linear without the core. Again, remove the cores of one of your transformers and see if it's at least AS linear as it was with the core.

sure it may be picking an nit, but i think its an important nit to understand. adding a magnetic core is adding nonlinearity, much of the time the increase in perm more that offsets any nonlinearity introduced by the core hence we see lots of iron cored (or nickel :-) outputs and very few air cored ones.

The increase in permeability also more than offsets the nonlinearity of piss-poor coupling. :)

se

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