They would either be classified and unless you work on the specific program you wouldn't know about them or they are not classified and you know about them. As John knows about them they cant be classified, or someone is breaking their security clearance, that is somthing the US dosn't like. A lot of this stuff is covered under ITAR, which is a PITA.
Ah, I missed that. My response: your mother wore combat boots..
Part of my interest in low inductance resistors stems from trying to measure phase response of magnets. To do so requires absolute accuracy in measuring the current as it varies with time. This requires a resistor with two qualities:
1. As little inductance as is physically possible, and 2. no loop to trap external field.
1. All resistors will have an inductance associated with it. At any frequency, the endpoint reactance of the resistor is the sum of the IR drop and L dI/dt. The IR drop is what is desired to measure, the L dI/dt is the error. It is also 90 degrees out of phase when the resistor is driven with a sine.
Once you have eliminated the simple inductive things, like a wirewound element and magnetic lead materials, you have only the current centroid (the center of the distributed current in space) to work with. Now, all you can do is try to cancel the magnetic field of the resistor's current. You can bring the return path of the current as close as possible, my earlier suggestion on using braid over the resistor to bring the return current over the body is the best one could do for an existing resistor. Or, you could create a resistor which has the return current passing through the primary current. The earlier picture had 20 ten ohm resistors in parallel between two flat plates, one half ohm total, and then another 20 ten ohm resistors interleaved between the first 20. Another half ohm, wired in series to give a 1 ohm resistor.
This construct has the current centroids passing through each other. Externally, the magnetic field is pretty much gone. Internally, most of it is also cancelled.. For this resistor topology, the inductance can be calculated using massive parallelism of inductors because they essentially cancel one another. (while not absolutely accurate, it is quite close.) The simple calculation
don't worry, no calculus involved... )A wire pair has inductance of approximately 200 nH per foot. My resistors are 1/4 inch long. Each pair has ~200/48 nanohenries, or 4.2 nH. I have 20 pairs in this resistor, so the equivalent inductance is 4.2nH/20, or 210 picohenries.
Using 3 pieces of one sided perf board and 40 1/4 watt mondo cheap metal film resistors from digikey (P/N P10.0CACT-ND), I now have a 1 ohm, 210 picohenry resistor. (1 microhenry is 10e-6, 1 nanohenry is 10e-9, 1 picohenry is 10e-12), my resistor has an inductance of 2 times 10e-10 henries.
Since the voltage is IR + L dI/dt, what is the error?
At a current slew rate of 1 ampere per microsecond (dI/dt of 10e6), my resistor has an error of 2 times 10e-10 times 10e6, or 2 times 10e-4 volts, 200 microvolts.
At 1 ampere per nanosecond, it will have an error of 200 millivolts.
If you need lower errors, you simply increase the number of resistors.
A normal resistor, if you returned the current right alongside it, would have about 5 nanohenries inductance, or 5 times 10e-9. The errors scale accordingly.If you choose NOT to return the current next to the resistor, you will see much higher inductances.
2. If you use the resistor as a current viewing resistor (the essence of a resistor ladder divider), you have the additional problem of preventing pickup of external fields, like the current path to and from the resistor. My resistor eliminates that, note the twisted pair pickup leads vs the power ones.
For example, my SWTPC's have the gain set via a 2.2k,100 ohm feedback divider. If I make the first part of my resistor using 20 pieces of 2k resistors, and the second part using 44k resistors, I have eliminated any dI/dt errors of the divider network in the feedback.
jn
edit: the tiger 250 is 3db down at 400Khz.. and output v of 70 volts, ladder current of 30 milliamps.
If the feedback ladder has a microhenry of inductance associated with the 100 ohm resistor, a full power slew of 1 uSec will give a ladder slew dI/dt of 3 * 10e4, inductive error of 30 millivolts added to 3 volts of IR drop, 10% inductive error. At 10 usec 70 volt slew, 1% inductive error (both at full scale out). Remember, the inductive term is rate dependent, the percentage error calcs I'm doing here is based only on full scale, a 10 usec slew to 7 volts gives 10% error.
Remember folks, math isnt one of my strong points, let me know if anybody finds errors...found two, will run outta edit time..
pps..I used this puppy (the tiger 250) for a 10 uSec slew to 40 volts into a 4 ohm non inductive load fed by 6 pieces of cat5e 15 feet long paralleled as a t-line of 4 ohms, so I know the tiger can do at least that..
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Same here, and they do hear nuances of performance and instrument quality that I could not begin to hear. I expect the same old excuses will be made.
I suppose this construct could be used to minimize a speaker cable inductance, but in that case the capacitance would be maximized?
Yes, and yes.
As I said, I used 6 pieces of cat5e to make a 4 ohm t line, it drove a one meter long stripline made of two copper ribbons half inch wide separated by 1 mil kapton to the load, a bifilar heater embedded into a supercon magnet.
Seeing a 50usec wide heating pulse through all that into a 4 ohm NI load in liquid helium with 10 usec rise and fall and no overshoot or ripple was a beautiful thing..
The boundary for speaker cables will be the equation:
LC = 1034 DC. L in nH per foot, C in pf per foot. Typical dielectrics will be around 3.
The only caveat to low z speaker lines it the case where the speaker unloads below the open loop unity gain point of the amp. As the speaker unloads, the amp will see the capacitance. If the speaker could remain constant impedance beyond the amp open loop unity gainpoint, the amp will see only the characteristic impedance of the cable.
jn
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I think that problem has been addressed before!
At least one of the high end manufacturers uses networks to keep the input impedance flat. That way the loudspeakers tame some of the high end "artsy" amplifiers.
The call for comments on AES3 is open and the document may be found at http://www.aes.org/standards/comments/drafts/aes-2id-xxxx-cfc-120816.pdf
There are some interesting changes, but I'll see what the peanut gallery thinks.
There are some interesting changes, but I'll see what the peanut gallery thinks.
Allow me to say something important. There are 'facts' and there are 'corrections' to 'facts'. For example: If someone says: 'Musicians don't seem to care much about hi fi'.
Well the 'correction' might be: That's true, probably because musicians, especially classical musicians, use more of the left side of their brain to process music.
Now, I lived with several hundred classical musicians for a couple of years, as a faculty member. I got the fact that they could get most of what they needed from a table model radio. I was impressed! I even married one, a violinist, and she 'tolerated' my obsession with hi fi, but she thought the sound at the recording studio was much better.
However, another important woman later in my life was a hi fi nut. Her background was sociology, even though she had played in the college band.
She had her own hi fi store when I first met her, and she became a reviewer for TAS for a time. She was rare, but a true follower of hi end audio.
In any case, I hope that you realize that one person's 'fact' should not go unchallenged, if there is further evidence that changes the implication of the fact's significance.
If many of you question the 'facts' presented here, you can Google and get some very interesting info about some 'facts' discussed. For example: 'Try left brain right brain' or something similar and see what you get. For example, interesting tests are presented showing which side dominates in your case or a significant others. Enlightening.
Well the 'correction' might be: That's true, probably because musicians, especially classical musicians, use more of the left side of their brain to process music.
Now, I lived with several hundred classical musicians for a couple of years, as a faculty member. I got the fact that they could get most of what they needed from a table model radio. I was impressed! I even married one, a violinist, and she 'tolerated' my obsession with hi fi, but she thought the sound at the recording studio was much better.
However, another important woman later in my life was a hi fi nut. Her background was sociology, even though she had played in the college band.
She had her own hi fi store when I first met her, and she became a reviewer for TAS for a time. She was rare, but a true follower of hi end audio.
In any case, I hope that you realize that one person's 'fact' should not go unchallenged, if there is further evidence that changes the implication of the fact's significance.
If many of you question the 'facts' presented here, you can Google and get some very interesting info about some 'facts' discussed. For example: 'Try left brain right brain' or something similar and see what you get. For example, interesting tests are presented showing which side dominates in your case or a significant others. Enlightening.
You should see one of my latest designs! Paralleled fets, 50/channel, rows of resistors, some very expensive, all polystyrene caps, even in the power supply bypass. Big bucks!
Our biggest headache is that although the case may weight 50-90 lbs, the box manufacturer left too little space for reasonable size circuit boards. What a hassle!
Our biggest headache is that although the case may weight 50-90 lbs, the box manufacturer left too little space for reasonable size circuit boards. What a hassle!
A popular test of left-right brain dominance is the rotating figure. Google for it.
You either see it turning/rotating to the left or to the right. When i first saw it, it turned one way but then i started 'thinking' about it and the figure started turning the other direction. see if you can make it turn in either direction... switching from left to right brain. If you cant or if you are fixed in one direction of spin... that has implications for what you can percieve... which limits what you can understand -- there are fewer dots to connect to form a judgement.
We all go in and out of left-right thinking but mostly you dont control it conciously. When you can do it concciously, you can learn more and have greater insights and do so more quickly. I am sure it would affect what we percieve when listening, too.
-RNM
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Probably not what you wanted to see...
NeuroLogica Blog Left Brain – Right brain and the Spinning Girl
And - here's some more on the persistent beliefs in the left/right brain nonsense:
NeuroLogica Blog More Left Brain / Right Brain Nonsense
Cheers.
ZAP
NeuroLogica Blog More Left Brain / Right Brain Nonsense
Cheers.
ZAP
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