I knew you'd think in that fashion.
You are confusing the direct measurement of electron movement with the coupling of a magnetic field caused by the movement. A hot wire does not produce external magnetic field more than 5 to 10 nanometers from the surface.
Interestingly enough, I pulled shot noise from a text. Granted, first edition was '59, second in '70.. Maybe Schwartz was confused...
Your definition of "good conductor" and mine are worlds apart. You live in the world of ampere per square mm, I live in the world of kiloampere per square mm and no electron-lattice interaction.
Read my previous post on "excess noise". Perhaps that will help you understand what I'm speaking of..
Cheers, John
Sorry, when you said shot noise I assumed you were talking about shot noise. Excess noise may also be present, of course, and scattering may well be a component of this. And thermal noise from all dissipation mechanisms.
As often on this site (and this thread), I wonder what all the fuss is about. We seem to have finally established that thermal noise is a significant (dominant, only?) contributor to transformer noise, and that this can be calculated by measuring the resistance at a particular frequency and estimating the temperature. This will be ambient for an input transformer - otherwise we would have to do separate calculations for windings, core and any other source of loss as they may have different temperatures.
If thinner laminations give lower Q and higher noise, then that is exactly what we would expect if eddies are a factor.
As often on this site (and this thread), I wonder what all the fuss is about. We seem to have finally established that thermal noise is a significant (dominant, only?) contributor to transformer noise, and that this can be calculated by measuring the resistance at a particular frequency and estimating the temperature. This will be ambient for an input transformer - otherwise we would have to do separate calculations for windings, core and any other source of loss as they may have different temperatures.
If thinner laminations give lower Q and higher noise, then that is exactly what we would expect if eddies are a factor.
Dave,
If a resistor, by itself, generates noise, presumably we can harvest that as energy. Where's the energy coming from? Would we cool down the universe when we would harvest it?
jan didden
No problem..I figured this is what was the sticking point..
It is what Schwartz called it in "Information Transmission, Modulation, and Noise..McGraw Hill, 1970. Page 512 on..
It is the dissipation mechanism of eddy currents that we've been discussing.
Well that's an entirely different question.
The fuss is because every person is an individual entity, living, breathing, and in need of being convinced that their opinion is not the correct one, and tht everybody MUST conform to (my) opinion...
That was an easy question...
At these power levels, actual temp is unimportant. An effective temp could be calculated, but I believe the effective resistance provides a better handle for building and designing..
What was asserted was that hf noise is somehow dependent on lamination thickness, and I attribute that to eddy current loss.
I believe you typo'd and meant if thicker lams..
Um, standard physics.
Do not confuse the magnetic coupling between the coil and core with thermal motion which does not produce a macroscopic magentic field.
The random thermal movement of electrons within the core do not create a magnetic field which the coils can see. As I stated, 5 to 10 nanometers from the surface, local magnetic fields are gone, integrated out.. That is below the surface oxides.
Cheers, John
If you could harvest the energy, then yes you would cool the resistor. This energy comes from whatever heated the resistor in the first place. Doing this would not cool the universe because the energy you extract will all end up as heat again eventually. Remember what thermodynamics says: you can't win, you can't even break even for long.
Almost any method you think of for harvesting the energy would end up being either inefficient, or putting just as much energy back. One possibility is to take another resistor of the same value, which just happens to be near absolute zero in temperature. (We will gloss over how much energy it took to cool it). Connect the two resistors together with wires which are good electrical conductors, but poor heat conductors (if you can find them). Then the hot resistor will cool, and the cold resistor will warm up. They will reach equilibrium at their original mean temperature. Don't hold your breath, as this may be a slow process unless they are very tiny in size. kT is not a lot of energy, unless you are trying to make a radio receiver or a phono pickup.
Almost any method you think of for harvesting the energy would end up being either inefficient, or putting just as much energy back. One possibility is to take another resistor of the same value, which just happens to be near absolute zero in temperature. (We will gloss over how much energy it took to cool it). Connect the two resistors together with wires which are good electrical conductors, but poor heat conductors (if you can find them). Then the hot resistor will cool, and the cold resistor will warm up. They will reach equilibrium at their original mean temperature. Don't hold your breath, as this may be a slow process unless they are very tiny in size. kT is not a lot of energy, unless you are trying to make a radio receiver or a phono pickup.
Sorry, yes "thicker lams".
Temperature does matter, unless we simply assume that all relevant items are at the same temperature. May be OK for a phono preamp, as they will be near ambient temp. However, we are used to calculating noise in voltage or power terms and for that you do need temperature.
I am not convinced that there is one-way coupling. You seem to have created a magnetic black hole! As I said, dissipation without fluctuation. A loss mechanism which generates no noise. I don't believe that.
Temperature does matter, unless we simply assume that all relevant items are at the same temperature. May be OK for a phono preamp, as they will be near ambient temp. However, we are used to calculating noise in voltage or power terms and for that you do need temperature.
I am not convinced that there is one-way coupling. You seem to have created a magnetic black hole! As I said, dissipation without fluctuation. A loss mechanism which generates no noise. I don't believe that.
Resistance Temco causes a problem here..stainless isn't too bad, it has almost the same value at 4.5 Kelvin as at room.
And 4.5K requires 1 kilowatt of refridgeration power for every watt dissipated. 1.88 K requires double that..
If anybody can find a good electrical but bad thermal conductor, I know a few facilities that will buy TONS of it.
Cheers, John
The coupling between coil and core is two way. It is Ampere's law/Faraday's law.
And that is magnetic coupling.
Heating the core does not create a magnetic field that will couple to the coil.
Driving the coil will cause dissipation within the core via eddies.
No, that is what you are interpreting.
Ah, now here is the interesting point..
The loop currents which are eddies must circulate within a material which does indeed dissipate exactly like a resistor, as it has bulk resistivity. They are created by flux rate of change which create loop voltages.
Loop voltages will cause a loop current within a bulk material. That loop current is going through a resistor.
The loop current causes a bucking flux, it's nature is to try to exclude the driving field from the material (lenz's law)
Variation of that loop current as a result of the "excessive noise" of that bulk material will cause variation of the bucking flux.
That is the (my) postulated source of the hf noise John C. speaks of.
edit: AND, I claim that (1)..the overall dissipation effect can be found by measurement of the two terminals to determine the effective series resistance of the system, and that (2)..THAT effective resistance at any frequency will correlate directly to the amount of noise generated at a specific frequency, (3), measuement of system Q will also correlate directly to generated noise at specific drive frequencies, and last but not least...(4), I hate you for forcing me to continually state that I am in total agreement with John Curl.....
Cheers, John
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In any case, eddy current losses DO generate noise that is added into the signal. It happens most at higher frequencies, so a careful designer will not have little if any audible component.
For the record, the Q of a professional tape head used by Ampex, at least until 1970, was less than 2 at 20KHz. Kind of lousy, in hindsight. This was due to the 6 mil lamination thickness that was the most practical to make for many years. Switching to 2 mils, increased the Q at 20KHz, and, of course, all lower frequencies, and you can hear the difference, if you are young enough to have extended high frequency sensitivity.
For the record, the Q of a professional tape head used by Ampex, at least until 1970, was less than 2 at 20KHz. Kind of lousy, in hindsight. This was due to the 6 mil lamination thickness that was the most practical to make for many years. Switching to 2 mils, increased the Q at 20KHz, and, of course, all lower frequencies, and you can hear the difference, if you are young enough to have extended high frequency sensitivity.
Maybe I can; however I doubt if it is necessary.
This morning I checked a 1:10 step up wound on a cobalt amorphous toroidal core, a "standard" item which make my customers happy enough
Bandwidth was OK, core saturation is out of the picture (occurred with 50 mV RMS input level (!!) at 8 Hz).
Pretty soon I can measure harmonic and IM distortion (FFT).
Primary DCR 0.52 ohm; secondary DCR 32 ohm.
OK, I buy that. Cores are not chosen for their good resistance properties, so excess noise could be an issue.
Regarding thermal noise from the core, I think neither of us is able to convince the other that he is wrong. One last try, then I will shut up. If heat can be dissipated in eddy currents, but not be a source of thermal noise, then you may have invented a perpetual motion heat pump. Connect a resistor to a winding. The thermal noise from this resistor will (very slowly!) heat up the core, but it won't come out again according to you (assume perfect thermal insulation). In electrical terms, where in the circuit is this heat being dissipated? Is there a reflected resistance in the winding circuit? If not, where is the power dissipated - it can't just disappear. If so, what temperature is this resistance - it must be zero if it generates no thermal energy itself.
Regarding thermal noise from the core, I think neither of us is able to convince the other that he is wrong. One last try, then I will shut up. If heat can be dissipated in eddy currents, but not be a source of thermal noise, then you may have invented a perpetual motion heat pump. Connect a resistor to a winding. The thermal noise from this resistor will (very slowly!) heat up the core, but it won't come out again according to you (assume perfect thermal insulation). In electrical terms, where in the circuit is this heat being dissipated? Is there a reflected resistance in the winding circuit? If not, where is the power dissipated - it can't just disappear. If so, what temperature is this resistance - it must be zero if it generates no thermal energy itself.
But you have not yet been able to quantify that noise. How does it compare to the noise due to winding resistance? I mean, if it ends up that it's pretty much swamped by winding resistance, is there really much point in worrying about it?
se
Even when distortion would be there I am pretty sure you would not notice it when listening to music... if you have the feeling "to have to live with the distortion" you might never enjoy listening to reproduced music in the first place because distortion is always there; I'd really feel sorry for you..
You are turning things around: I did not ask you to do some testing; you came up yourself with distortion measurments of two different step up transformers and I merely asked you at which input level you had performed these test just to check if core saturation might play a role.
Aren't we talking multiple thousand dollars pre amps here?
A good quality input transformer is a great investment I would say.
Apology accepted, but to avoid irritation try to use the forum tools (quote); it is not that difficult.
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