John Curl's Blowtorch preamplifier part II

[jcx]

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???

...

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

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]

 

[Steve Eddy]

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?

se

 

[scott wurcer]

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.

 

[john curl]

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.

 

[scott wurcer]

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.

 

[Steve Eddy]

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?

se

 

[jneutron]

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

 

[Steve Eddy]

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

 

[jneutron]

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.

 

[john curl]

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.

 

[SY]

There ya go, second hand recount of a conversation where no-one but you knows what in particular was discussed and confirmed. Better than analysis or evidence.

 

[simon7000]

There ya go, second hand recount of a conversation where no-one but you knows what in particular was discussed and confirmed. Better than analysis or evidence.

SY, SY, SY...

This got interesting, based on technical opinions. The issue is minor and reasonably well discussed. If you don't believe J.C. that is not a technical issue. You can either confirm it, or disprove the content of the call, but personal issues really don't belong here.

ES

 

[SY]

You are correct, and my apologies if the tone was offensive.

 

[Pano]

JCX, you need some practice with the quote tag. The info is in the help file. BB code help
I've fixed your post.

 

[scott wurcer]

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.

I'm not sure you are following our debate.

 

[john curl]

Of course, I apologize. I was concerned with lamination thickness, and its effect on ultimate transformer importance. Whatever the rest of you were debating was 'off-topic' as far as I am concerned. I am trying to discuss low noise audio design, and deviation from this topic, should have been dealt with by others, I should think. What does everyone else think?

 

[mrfeedback]

Layer winding of audio transformers causes electrical resonance.....bundle winding helps to cure the resonance problem.

Eric.

 

[john curl]

All input transformers resonate.

 

[Steve Eddy]

Of course, I apologize. I was concerned with lamination thickness, and its effect on ultimate transformer importance. Whatever the rest of you were debating was 'off-topic' as far as I am concerned. I am trying to discuss low noise audio design, and deviation from this topic, should have been dealt with by others, I should think. What does everyone else think?

I think it's kind of pointless unless you can quantify it.

se

 

[mrfeedback]

All input transformers resonate.

Yes.
Bundle winding reduces the Q.

Eric.