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Old 10th March 2011, 02:55 AM   #10911
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Quote:
Originally Posted by hitsware View Post
with an ideal transformer
there is no voltage accross
the secondary without a load ?
No, there will be a voltage (see Faraday). But what's the point of a transformer if you've no load on the secondary?

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Old 10th March 2011, 03:17 AM   #10912
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I think here we're arguing at crossed purposes. I'm not of the view there's anything discontinuous going on. Just offering support for Mr. Neutron's thesis which you seemed to be disagreeing with.



I'd be as skeptical as you of such 'results'
My disagreement is a very fine point. You induce eddy currents and they dissipate heat so you have a loss that's OK. The claim that these eddy currents experience excess 1/f noise as in a carbon comp resistor and this loss is also coupled into your system is not a given.
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Old 10th March 2011, 03:26 AM   #10913
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My disagreement is a very fine point.
Yes, thanks for the clarification. The devil is most certainly in the detail.

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You induce eddy currents and they dissipate heat so you have a loss that's OK. The claim that these eddy currents experience excess 1/f noise as in a carbon comp resistor and this loss is also coupled into your system is not a given.
In the way I read Mr. Neutron, I don't see him making such a claim (that being about excess or 1/f noise). Just pointing out a signal dependent loss - one which you acknowledge already in accepting fractional f.
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Old 10th March 2011, 04:01 AM   #10914
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If anyone cares to read the AES papers made by Jay Knight during the 60's (when I worked with him) and the 70's, you will find that eddy current loss makes high frequency noise and this is dependent on the lamination thickness, typically 6 mil, back in the early 70's and earlier, 2 mil, later. 1 mil has long been possible, but it is very difficult to handle by the assemblers, I am told. It would be interesting what thickness the laminations are in the input transformers normally made today? Cheap ones may use 10 mil lams, extra good ones might use 2 mil lams, I would bet 4-6 mils for most of the professional models.
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Old 10th March 2011, 04:43 AM   #10915
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If anyone cares to read the AES papers made by Jay Knight during the 60's (when I worked with him) and the 70's, you will find that eddy current loss makes high frequency noise and this is dependent on the lamination thickness...
Do you mean Jay McKnight?

If so, which paper or papers specifically?

And was he writing about audio transformers or tape heads?

How significant is the noise and what lamination materials did he write about?

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Old 10th March 2011, 04:52 AM   #10916
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> But what's the point of a transformer if you've no load on the secondary?

I have utilized xfmr windings as inductors.
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Old 10th March 2011, 04:57 AM   #10917
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Not generally a good idea unless the currents are small. Given the typical primary inductance of a transformer runs into several Henries, what use do you find for such huge values?
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Old 10th March 2011, 04:58 AM   #10918
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> But what's the point of a transformer if you've no load on the secondary?

I have utilized xfmr windings as inductors.
So have I. But then it's no longer a transformer, is it?

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Old 10th March 2011, 05:06 AM   #10919
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But then it's no longer a transformer, is it?
Oooh se, its great when you get all philosophical Yes it is still a transformer ontologically, but no its not one existentially. Any help?
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Old 10th March 2011, 05:08 AM   #10920
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Not generally a good idea unless the currents are small. Given the typical primary inductance of a transformer runs into several Henries, what use do you find for such huge values?
I'm using 600:600 quadfilar line output transformers as center-tapped chokes in this headphone amp/preamp circuit.

Click the image to open in full size.

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