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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 23:30:59

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 21:06:11:

then what is he point of the application of a -Bdc in pulse core use?

I don't know. I'm not familiar with the technique and what the reasoning is behind it.

the use of the -Bdc is to combat remenance which is exactly the reason we never return to the (0,0) point.

Is it or is that just a guess on your part?

I don't see how the DC bias can combat remnance as the restorative force of the field produced by the DC doesn't get returned to the system in order to restore anything.

. i wish i could find some better references on it, but it is a documented practice, it just doesn't see widespread uses since an airgap just happens to be cheaper.

Well you haven't given any reference so far. :)

but what happens when the signal is removed?

Same thing that happens when the signal is removed from a non-biased core except where it ends up will be offset depending on how much of a bias there is.

with a Bdc point the core remains at that point. without the Bdc "reference" the core ends up at a point based on its previous history, it could be (0,1000) it could be (0, 10,000) it just moves about.

The core would only remain at the Bdc point if the Bdc point were such that the core always remained in saturation.

Tell me, where does the restorative force come from which brings the core back to the Bdc point once the signal is removed?

well can we agree that the nonlinear factor in a transformer (wrt the core) is the variability of the perm?

Well I guess it would have to be wouldn't it?

depends what you look at... i understand the simple answer, but that possibly overlooks the big picture.

What I'm looking at is non-linear distortion. So what "big picture" are you referring to which would have a transformer which has considerable non-linear distortion but does not distort?

very linear... but again that depends on the winding geometry, and we are talking mor about core behavior... two very different (but equally important) issues.

Ok. I agree that a core which always remains saturated would not cause distortion.

But so what? If the core's saturated, it's not going to behave anything like it would without it being saturated so what's the point?

depends what you look at... consider that many cores cease to be effective above a few khz so the perm is gone anyways.

But my system doesn't include speakers that are made up of nothing but a tweeter.

sure, but again we know that and take that into consideration when looking at the overall design... it has little to do with the concept at hand...

Ok...

what do you define as linear???

I define as linear that which is linear. Do we have to consult Webster's on that? If so, how 'bout this one:

"having or being a response or output that is directly proportional to the input."

and again it depends on the design. lets take a 1:1 bifilar tranformer and i'll say it will be much more linear without the core than with it.

Ok. But of what practial use would it be?

se

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