John Curl's Blowtorch preamplifier part II - Page 5055 - diyAudio
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Old 14th April 2014, 09:01 AM   #50541
SY is offline SY  United States
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"A talented con man does not waste his time trying to convince knowledgeable skeptics. His job is to keep the true believers believing."

Rationality doesn't move merchandise.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 14th April 2014, 10:14 AM   #50542
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Originally Posted by RNMarsh View Post
No, it was me. It will take into account the cable balance characteristics and Zo of the source etc. It's really the best way --- do a system alignment.

Same for doing THD tests, freq response, noise, cross-talk etc -- check the complete systems from end-to-end.... not just one piece at a time. This is because it is what you are hearing -- the complete system playing music.

Yes, fully agreed.
Any experience with microphones to record A/B (ABX), end of system in room sound, and compare (Diffmaker, RMAA, Arta etc) ?.

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Old 14th April 2014, 10:15 AM   #50543
marce is offline marce  United Kingdom
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Originally Posted by fas42 View Post
If you care to look a little more carefully, marce, I'm quoting the term that Kindhornman used, in the post I was replying to ...

I will say one thing, I'm pleased that some people here are a long, long way away from the aeronautics industry - it would be a mighty scary thing going on a flight, otherwise ...
Like whom for instance...Its a bit of a throwaway generalisation with no defined targets.
Anyone with way out audiophile beliefs, or are you referring to us cynical ones who poo poo the way out subjective beliefs...
In my case you are pretty safe, I have only worked on boards for fighters not passenger aircraft.
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Old 14th April 2014, 11:37 AM   #50544
fas42 is offline fas42  Australia
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Basically saying it's frustrating to see a lack of interest in developing a methodology for ensuring that the final product, a complete audio system, performs to a certain standard - and can be relied upon to be consistent. The whole process of achieving good sound is so hit and miss, the tremendous variability in PA sound quality is as good an example of this as any - I don't know when I go to a show whether I will come out beaming, or curse the idiots who are hypnotised by the number of dials they can twiddle to screw up the sound ...
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Old 14th April 2014, 01:45 PM   #50545
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Originally Posted by jcx View Post
skin effect, lossy transmission lines, DA are usefully modeled as Linear Time Invariant - LTI systems don't produce any harmonics of the excitation frequencies.
Agreed. How is proximity effect induced resistance LTI? It follows dI/dt squared.

Originally Posted by gpapag View Post
Is this to confirm that a discrete amplifier’s bias compensation scheme based on temp sensing the intimate exterior of a power device is lagging at least by 1sec in response, while within a power op amp chip this time lag is ~ x1000 shorter?

It will depend on the scheme used to pick up the chip temp. IR has a sense fet where a cell buried within the matrix is used to monitor the die temp at the cell level. That is very fast compared to outside the package, and even fast compared to built on the chip but to the side.

If the sensor is on the chip but lateral to the power dissipator, there will be a lag based on the thermal diffusion velocity of the silicon.

Note that the thermal conductivity of silicon is also a function of temperature.

Originally Posted by keantoken View Post
JCX, Jneutron said skin/proximity effect caused a 2nd harmonic, and this seems to conflict with your statement.
JCX is assuming that proximity induced resistance increase is LTI. It is not.

Originally Posted by keantoken View Post
Is it that a thermal impulse spreading in a uniform material spreads as square root of time or something like this, and this is why TO92 thermal impedance tends to have a large 3db/oct region? And if true, that the higher slope in the 100uS region would be due to having a flat die, where one dimension of thermal expansion was effectively removed? And also, that a slope of less than 3db/oct would be caused by an interface from a less thermally conductive material to a more thermally conductive material?
It is very hard to characterize for several reasons.

The full surface of the die does not dissipate. The IR line is effectively about 30% of the die surface. Bipolars are better. Diodes are the best.

Silicon has a temp dependent thermal conductivity.

The temperature dependent parameter they use to monitor the junction temperature will start to recover the instant the dissipation has stopped, so how clean they settle to the sensing current is important.

Some assume incorrectly that the monitor parameter instantly reflects the junction temp.

And then there are the solders, the copper, the epoxy with the thermal masses and diffusion velocities all messing up the ideal.

The vendor numbers are great as a first pass, to get better than that is extremely difficult, and the resultant model change is of diminished returns.

Originally Posted by jcx View Post
I need to see his equations for an example physical arrangement and the calculation of the magnitude of the nonlinearity - he hasn't shown that or linked to a good example yet
Quite so. All the literature I find relating to switchmode supply inductors and transformers concentrate on characterization of the absolute value of the dissipation, rather than the nature of the resistor vs time.

Why don't you try this: get some small diameter coaxial cable with a braid shield. Make an air core inductor by coiling it nice and tight. Try for about 2 mH.

Measure the inductance vs frequency by using the braid only. You will find the region where the braid's Rs starts to climb. Measure it out to Rs=20 times the dc value.

Repeat this measurement using only the core wire. You will find that Rs will hold off its increase out to a higher frequency. The smaller diameter of the core resists proximity.

Now, for the actual test. Connect a power amp to the braid and core at one end of the coil. Return the power to the amp via the shield only. Sweep the sine from a low freq to the frequency where the Rs of the shield is 20 times the dc value.

Measure the core's voltage to ground (shield return) using a 10 x probe to prevent loading. (you are measuring primary to secondary voltage difference with secondary unloaded.)

What's the waveform look like? It is the IR drop of the shield.

Scott knows this test design.

edit: I have the test schematic elsewhere, but no access to it at the moment. Any Q's, please ask.


Last edited by jneutron; 14th April 2014 at 01:50 PM.
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Old 14th April 2014, 02:13 PM   #50546
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Well Frank,
Let's see the last major projects I worked on were for the Apache Helicopter, Carson Presidential helicopter, Dessault Winglets for a retrofit, B-52 inlet duct replacement parts, all kinds of parts for older KC135 bonded panels that were no longer in production and a nice UAV program for the US Air Force made of carbon/ epoxy composites. Before that I had my own manufacturing and R&D company doing such things as medical devices, a touch screen project about 25 years ago, yes that long ago we were working on touch screen technology, solar panels and a nice solid fuel rocket. So I guess you could say I have been involved in both rocket science and medical device manufacturing among other things. I got a patent in waveguide design applications that covered materials application and mathematical design in 1976 so I have been involved with audio design for 37 years now. Some of what I am doing today I could patent but then I have to give away my design to everyone else to see, I would rather keep it as a trade secret and let others try and figure out what the hell I did and how I did it.

Though I have done some weird stuff, many things could be considered somewhat mundane today, but when I did them they were all outside of the norm. I have always had to push technology and materials applications into areas that I have been told haven't been done before. At the same time there has always been scientific method used to get to the end result, you can't just guess about these things, but you do need to use intuition in many instances and evolve those ideas to get to the final point. I would say the same happens in audio, you may have an idea that is outside the norm, but there is always some basis for trying something or an inkling of an idea that you would try. I have a pretty good idea that anything that John has done has come from some technical knowledge that he has learned along the way. That doesn't mean you don't try something nobody else has done but you have some idea of an outcome you are trying to create. Just stabbing around in the dark without any end result in mind doesn't often work. Unless you are working in a place like a Bell Labs where you really don't know what something you are going to try may do, basic research with unlimited discovery potential that is a rare thing. Most people don't do that type of science, only a few get that opportunity and audio isn't an area that you are just willy-nilly putinng electronic parts together with no knowledge of what might happen. We aren't inventing electricity and trying to invent a new way for ears to work, we have a pretty good idea how all this stuff works at this point. Developing new test equipment is rather rare in audio today, doesn't mean someone may not come up with a new tests protocol or stumble upon a new way to measure distortion that nobody thought of before.
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Old 14th April 2014, 02:23 PM   #50547
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Here's the test design.

It's setup so that there are no equipment ground problems, and there is no need for a differential measurement.

If you use too low an inductance value such that you have to go very high in frequency, then there will also be a capacitive coupling inherent in the dielectric of the coax to worry about. While that in itself is purely a linear coupling, it can confound the result simply because it is coupling a distributed primary voltage along the entire length of the winding. Nonetheless, if there is a proximity induced dI/dt squared effect, that will show up in the IR drop of the shield.

Attached Images
File Type: jpg proximity test of air core shield.jpg (94.1 KB, 141 views)

Last edited by jneutron; 14th April 2014 at 02:27 PM.
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Old 14th April 2014, 02:55 PM   #50548
KBK is offline KBK  Canada
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Originally Posted by john curl View Post
Thanks George for the paper. Looks very interesting.
Getting warmer.....

(JN cleared some of it up, a few posts back from this quote. The dissipation is local due to the lack of lattice constraint in a true fluid. As the system moves into disorder (signal cut), it is predominantly localized dissipation, which is what gave the non-standard pf measurements which do not correlate with norms of transmission equations and expectations)

Last edited by KBK; 14th April 2014 at 03:06 PM.
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Old 14th April 2014, 03:09 PM   #50549
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Originally Posted by KBK View Post
Getting warmer.....

(JN cleared some of it up, a few posts back from this quote. The dissipation is local due to the lack of lattice constraint in a true fluid. As the system moves into disorder (signal cut), it is predominantly localized dissipation, which is what gave the non-standard pf measurements which do not correlate with norms of transmission equations and expectations)
I am very clear in what I said, but am clueless as to what you just posted.

Did anybody else survive the explosion in the thesaurus factory?

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Old 14th April 2014, 03:15 PM   #50550
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Yes Marce, I come to the defense of my colleagues. Look at where you are? You are not on some thread trying to make the cheapest electronics possible, or something similar. Every time you comment, you tend to insult what I do for a living, and often, specifically what I both believe in and have invested money toward.
For example, I have a cable 'break-in' box designed by a colleague that is used by 100's of audiophiles out there. This 'box' was first commissioned by my deceased colleague, Bob Crump, the other` C in CTC, also the true father of the CTC Blowtorch preamp, who made cables independently, on the side, and INSISTED on break-in for ALL wires and audio equipment that we made. Each Blowtorch was broken-in for weeks before it was released, and the silver wire that it was wired with was both directionalized and broken-in for 30 days on the spool, before installation. Can you now understand what I have to 'put-up' with your criticisms?
"Condemnation without Examination is Prejudice"
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