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Old 10th March 2011, 07:25 PM   #10981
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Originally Posted by scott wurcer View Post

ED - Why don't you throw a "transformed" resistor into your bridge like when you got all those sidebands on the carbon one.

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Scott,

I'll put that on the list of interesting experiments. I will ask for samples at the next AES I make it to.

Of course with my luck at getting the results I was not expecting you would give me a hard time when I report it caused ripples in the gravity waves.

ES
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Old 10th March 2011, 07:42 PM   #10982
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Originally Posted by john curl View Post
Scott, if tape heads have problems with lamination thickness, then input transformers will as well.
But what exactly is the "problem"?

You say it's an increase in high frequency noise, but can't point to anything in the literature regarding this.

Eddy currents in the laminations result in an effective decrease in permeability but I'm not sure I see how that produces noise.

Quote:
This is why I have gone through all this time and effort to acquaint people with eddy current loss and noise increase.
All you've done is point to articles that don't say anything about eddy current loss as it relate to noise increase.

se
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Old 10th March 2011, 07:48 PM   #10983
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Originally Posted by simon7000 View Post
Scott,

I'll put that on the list of interesting experiments. I will ask for samples at the next AES I make it to.

Of course with my luck at getting the results I was not expecting you would give me a hard time when I report it caused ripples in the gravity waves.

ES
I would only complain about scalar waves.
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Old 10th March 2011, 08:14 PM   #10984
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Originally Posted by scott wurcer View Post
I would only complain about scalar waves.
Let's see you mention Schumann resonance and understand that it is a possible source of free energy for real. All you need is a big enough collector or a really low power load. But scalar waves are too hard to accept.

I won't even go into the conspiracy preventing gravitational reduction technology, even when natural gravitation examples such as tornados are around us. Everyone knows anti gravity is only pursued by fools.

Scott,

I think the solution is clear, you have been spending too much time on the internet. The EMI from the data transfer devices has affected the zeta potential in your acetylcholine receptors.

I suggest you take a break and do something healthful, like opening a bottle of fine port wine, drinking it by a fire while reading a good hard bound paper book that is not about fantasy, science fiction, or religion.

ES
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Old 10th March 2011, 08:14 PM   #10985
gpapag is offline gpapag  Greece
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This is why I have gone through all this time and effort to acquaint people with eddy current loss and noise increase.
If I may, Your time and effort were spent to make a case (noise increase due to eddy current loss), which unfortunately you haven’t backed up with data yet.

Eddy current losses have been discussed and sited in many other forums here.
It is more than probable that people are acquainted with losses already.

http://ntrs.nasa.gov/archive/nasa/ca...1966001049.pdf
(especially eq. 41 &42)

Power losses in wound components
The bottom line is that eddy current loss is inversely proportional to the square of the number of laminations.

Regards
George
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Last edited by gpapag; 10th March 2011 at 08:21 PM.
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Old 10th March 2011, 08:23 PM   #10986
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The best dual Fet Opamp i found is the OPA1642. National has new ones too but i have not tryed them. The OPA627 is obsolete now. The substitute is the OPA827 but i like the ADA4627 even better but those are singles. The ADA4627 ( or ADA4637 ) is the best performing Fet Opamp so far athough it does not have the lowest noise. For the second stage it is fine. I also use it in INAs with the LME49990 at the input. The LME is a bipolar though.
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Old 10th March 2011, 08:44 PM   #10987
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Originally Posted by brianco View Post
What a studio was/is capable of and what they sometimes produced can be totally different 'things'. The particular studio I have in mind was one of the top international level studios in Britain. But that of course is not down to the studio management or permanent staff....it usually is down to the client and/or his producer.
Indeed.
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Old 10th March 2011, 10:09 PM   #10988
jcx is online now jcx  United States
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One must consider what an eddy current is, what the current loop paths are, and what happens to the magfield energy stored and released by the eddy currents. For example, if I place a 1/2 inch thick aluminum plate in the flux path, the aluminum will cause a lowering of the inductance by exclusion..(Lenz's law). The eddies within the aluminum are bucking the field, and when the driving field collapses, the energy stored within the aluminum will be dissipated. That dissipation is 90 degrees out of phase with the forcing field. This is a typical problem encountered in my line of work.

As I stated in general. What I pointed out is the eddies are 90 degrees out of phase with the driving current, and that the two HP4284A's I have been using will attribute this loss mechanism to added series resistance of the primary windings. This effect is more pronounced in my litz wound magnets. The mech guys initially designed the magnets with 1/4-24 stainless capscrews down the center of the air core winding, and the losses popped up as a frequency dependent series resistance..


When a conductive material is put into a time varying field, it will try to force exclusion of the field lines. That forcing is the eddy currents producing a magnetic field counter to the forcing field lines. Eddy currents within a conductor are still currents, and currents within a lossy conductor will produce noise. So your thinking that the currents do not couple back to the primary are seemingly good, but the noisy current does indeed produce a noisy bucking field.


As I initially stated, my HP4284A thinks the eddy losses are part of the series resistance of the coil. So, why would it believe that but yet audio signal circuitry wouldn't? I would think long and hard before accusing HP of being incorrect in a fundamental aspect of a piece of test equipment...


As frequency increases, the current density within the functional cross section of wire will quickly rise, increasing losses. Again, how does one distinguish the "out of phase" noise of the effect from the straightforward loss noise of the pure resistance. The noise will not correlate directly to the forcing current, so the only thing left to look for is a phase shift of the noise power envelope. Measuring that to fractions of a degree at mid to hf audio? Most CVR's can't even hold that kind of phase lag, so measurement will be loaded with error components..

…Agreed, it is not a given. However, the bucking field will be noisy as a result of the eddy current noise. How to measure, that's another story..



I see eddy noise generated proportionally to the derivative of signal current, which of course is 90 degrees lagging…

Cheers, John
my disagreement is with the "teleological" slant, apparent disregard of basic Linear (EM) systems theory fundamentals

mutual inductances, volume resistances, "just are", do not have a direction of causation, don't depend on human identified "source"

in a Linear model resistor noise is Not signal depedant - eddy currents are just the consequence of conductive materials/resistances coupled by mutual inductances
so "eddy current noise" would be the thermal noise of the resistances so coupled

as a linear passive transduction system a realistically complex Linear transformer is reversible - any currents with the same spatial distribution/components of "eddy current" from thermal noise in bulk resistive regions of core and conductor couple "back" to the transformer windings just as winding currents "induce" eddy currents
because of the distributed/continuous nature the coupling factors are complex valued and may even have fractional power frequency dependencies
lumped approximations require high order/many branch networks of mutual, leakage inductances, resistances

arguing from HP/Aligent's model that is so simplified that it can be silk screened on the instrument panel and only requires the 2 values of a single complex number is beside the point

the "eddy current noise" has to "be there" all of the time and should appear as frequency dependant noise at the transformer terminals - with or without applied signal - as a result of Linear EM theory

the Linear model predicts noise from “eddy current loss” in a transformer is Independent of signal level


of course magnetic core materials are far from Linear in their magnetic properties so there are many other level dependant mechanisms that could "modulate" the mutual inductances or contirbute signal dependant losses

at high enough signal levels self heating changes the “noise temperature” and values of the various R involved through their tempco – the core material resistance also could have “excess noise” and Vcoeff but since this noise its so hard to see in the 1st place these effects have to be really negligible – particularly in the presence of the expected orders of magnitude larger magnetic material nonlinearities

Last edited by jcx; 10th March 2011 at 10:22 PM.
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Old 10th March 2011, 10:39 PM   #10989
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the "eddy current noise" has to "be there" all of the time and should appear as frequency dependant noise at the transformer terminals - with or without applied signal - as a result of Linear EM theory
Which means that even a simple length of wire would also exhibit the same frequency dependent "eddy current noise," yes?

se
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Old 10th March 2011, 10:44 PM   #10990
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Just as a sidebar to the main discussion:
Will these alleged effects be important to transformers that handle larger signals, such as ~1V in a line level transfo? Or even 100+ volts in an OPT?
Or are they just tiny signal problems that affect moving coil and ribbon mic signal levels?
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