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Old 11th March 2011, 08:52 PM   #11041
jcx is offline jcx  United States
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Originally Posted by jneutron View Post
I have coils on my desk which are made using 700 or so turns of 15 guage solid copper, and some made using equivalent guage litz. Measurement of both from 20 hz to 50 Khz clearly shows the equivalent series resistance of the solid goes nuts, exceeding 300 to 400 ohms at 20Khz.

Am I being told that both will have the exact same noise should I push 20 Khz 1 ampere into them?
not exactly MC xfmr candidates - and you conflate with a statement about typical signal level audio interconnects from SE's post
and somehow adopt my point as your objection???


...

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Actually, the entire core structure will indeed be setup such that it will couple to the windings. Buuuuuut....

Thermal molecular movement will be totally random in direction. There will be NO net carrier movement, therefore there will be no net fields generated at the macro level.

on average, long term, "net" /= measuring frequency dependant noise


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That was not the question I was discussing. I was discussing the distinguishing of the core via the primary (with no secondary load), but simply because the eddy losses will generate noise.
again you accept that core (and winding proximity/skin) eddies are coupled by mutual inductance to the windings but don't recognize the model validity of the secondary connected to a R??


Cheers, John[/QUOTE]

Last edited by jcx; 11th March 2011 at 09:21 PM.
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Old 11th March 2011, 08:55 PM   #11042
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My first thought would be no. The shorted coil would exhibit a current noise that would have to obey the same physics. The open circuit voltage noise would be due to the bulk R (there is no current i. e. no skin). Experiment No. 3 :0
Not sure I follow you here.

If we leave joule heating out of the equation for the moment, the only source of noise is thermal energy from the ambient room temperature, yes?

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Old 11th March 2011, 09:05 PM   #11043
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Not sure I follow you here.

If we leave joule heating out of the equation for the moment, the only source of noise is thermal energy from the ambient room temperature, yes?

se
Yup, a resistor has an open circuit voltage noise and a closed circuit current noise. I thought the skin effect would not effect the voltage noise, but I will have to think about that some more.
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Old 11th March 2011, 09:09 PM   #11044
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SE, you almost have it. Of course, the inductance drops a little, BUT not enough to track the radical departure in Q that the head (or transformer) will measure. I'm glad to see you thinking it through, however.
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Old 11th March 2011, 09:12 PM   #11045
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Originally Posted by jneutron View Post
I have coils on my desk which are made using 700 or so turns of 15 guage solid copper, and some made using equivalent guage litz. Measurement of both from 20 hz to 50 Khz clearly shows the equivalent series resistance of the solid goes nuts, exceeding 300 to 400 ohms at 20Khz.
I see you already have my experiment in hand. Using the virtual ground of a high speed op-amp to measure the current noise, the four noise spectra should have an answer.
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Old 11th March 2011, 09:34 PM   #11046
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SE, you almost have it. Of course, the inductance drops a little, BUT not enough to track the radical departure in Q that the head (or transformer) will measure.
Says who? Based on what exactly? Did you measure any transformers? What core material was being used in your measurements?

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Old 11th March 2011, 09:45 PM   #11047
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Gents,

A most enjoyable and thought provoking discussion. Honestly, one of the best I've had here..

One learns more through conveyance of differences in opinions.

I'll jump back in monday.

Cheers, John
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Old 11th March 2011, 09:48 PM   #11048
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Gents,

A most enjoyable and thought provoking discussion. Honestly, one of the best I've had here..

One learns more through conveyance of differences in opinions.

I'll jump back in monday.
Have a great weekend, John!

se
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Old 11th March 2011, 09:50 PM   #11049
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Yup, a resistor has an open circuit voltage noise and a closed circuit current noise. I thought the skin effect would not effect the voltage noise, but I will have to think about that some more.
The interesting part is, at frequency the wire effective resistance is higher. With DC currents, my solid conductor coils reads in the ohm range, while a 20 khz ac current makes it 300 ohms up. The litz is solidly the same across the bandwidth.

What about using a litz air core coil, pushed at 20Khz 1 ampere, with an analyzer on the terminals....then insert a piece of brass, aluminum, or copper to see if it's eddies cause the noise to change?

Cheers, John

ps...you too steve.
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Old 11th March 2011, 10:49 PM   #11050
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J.G. McKnight, personally, just conformed my understanding of eddy current losses and their contribution to reproduce noise increase at high frequencies. End of debate.
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