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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 17th September 2019, 03:58 PM   #28971
hhoyt is offline hhoyt  United States
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John Curl's Blowtorch preamplifier part III
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Originally Posted by gerhard View Post
That does not even depend on matching. You can have huge SWR on a coax and no current outside...
regards, Gerhard
So true! If you terminate a 50 Ω transmission system with a isolated resistive load other than 50 Ω you will have a mismatch but no common-mode shield current on the coax feedline. However, if you terminate a transmission system with a radiator/antenna which shows an impedance imbalance between the radiator and counterpoise, or two halves of a dipole at the frequency you are operating, you will have external shield common-mode currents. This will be due to the imbalance current seeking an alternative path. Perversely, this imbalanced load can be properly matched and show low SWR, but the power is not all being radiated by the antenna, some is being radiated by the feedline!

A common-mode choke is one of the most neglected tools in both amateur and broadcast radio.

Back to ferrite speaker magnets, I think,...

Cheers!
Howie
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Old 17th September 2019, 04:47 PM   #28972
jneutron is offline jneutron  United States
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Finished the tests on the D205TI tweeter coil with brass, aluminum, and iron rings placed over the coil ID. The rings each were close to .250 inch thick, 2.05 +/- .002 inch ID.

Some really interesting results.

Top inductance scans.. as expected, the iron causes the system to have higher inductance, as it was a magnetic material, mu unknown. The top dark blue is the split iron ring, yellow is the full ring. Yellow is consistent with a front plate that is continuous and as a result, shows as a shorted turn. The dark blue, with the split, is no longer a shorted turn, and as is evident, inductance holds up better with frequency.

The orange is full aluminum ring, the grey is full brass ring. They both take a huge dive inductance wise starting from the getgo.

Also expected, the light blue and light green curves of the split aluminum and split brass do not dive as quickly inductance wise, as they no longer exclude field due to a shorted turn.
Of note, the split alum and brass do still show eddy losses, starting at 1000 hz. This is a consequence of a conductive material being brought into the time varying magnetic field, so it still reacts with eddy currents so as to exclude the field..hence lowering inductance.

The resistance is also interesting with a twist...
Yellow, full shorted turn iron ring, of course has the most dissipation, almost 2 ohms more at 20Khz. The iron split ring, dark blue, is better, roughly one ohm more than no ring at 20Khz. Indeed, cutting the iron ring halved the losses incurred by the ring.

What is really neat, is what happened to the aluminum and brass curves after they were split. above 20Khz, they exceeded the full ring dissipations. I expect that to be because with less field exclusion, more field was available to the bulk material as eddy generation loss. Given it's over 20Khz, I saw no reason to pursue this somewhat anomolous behavior.

From this data, specifically the iron full and split ring data, it would appear that breaking the circumferential conductivity of the faceplate will halve the shorted turn dissipative loss.

I also believe using a laminated faceplate structure will reduce the losses even further.

edit: second photo is tweeter with brass on it, iron front left, aluminum front right.

What these results suggest is the following...If one wishes to use a conductive ring as inductance control through xmax, the amount of inductance control can be tailored by the use of axial cuts in the structure. Not fully through the ring, but partials. By doing that, it will be possible to alter the behavior at higher frequencies, and dependent on voice coil position. (patent time again..)
jn
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File Type: jpg D205TI tests.jpg (543.2 KB, 362 views)
File Type: jpg d205TI tests photo.jpg (177.4 KB, 455 views)
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Last edited by jneutron; 17th September 2019 at 05:10 PM.
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Old 17th September 2019, 10:42 PM   #28973
RNMarsh is offline RNMarsh  United States
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can you show before and after ring cut on driver frequency response?

" " " " " " " " " " distortion?
-RNM

The ferrites which include iron powder mixed in are used for LF inductors. They can be conductive... often seen within a case or mold of insulated material.

I have very good success with ferrite formula #47. CM or DM coils for HF...... non conductive.

THx-RNMarsh
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Old 18th September 2019, 02:42 AM   #28974
jneutron is offline jneutron  United States
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I have shown before and after Ls/Rs for aluminum, brass, and iron. All are cut, so "before" measurements are now moot. My current plan is to figure out how to rebuild the visiton driver to sweep it with a front plate gap.

Beyond that, dvc build, test for tap coil differential, and make a new voice coil two inches diameter two layer with two layer tap coil to do many tests to see eddy dissipation, Lenz exclusion, shorted turn...interesting stuff.

Timeframe unfortunately is beyond your move date... Hope it goes well, look forward to hearing from you after you are settled in.

Jn
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Old 18th September 2019, 03:02 AM   #28975
1audio is offline 1audio  United States
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John Curl's Blowtorch preamplifier part III
Quote:
Originally Posted by jneutron View Post
What is really neat, is what happened to the aluminum and brass curves after they were split. above 20Khz, they exceeded the full ring dissipations. I expect that to be because with less field exclusion, more field was available to the bulk material as eddy generation loss. Given it's over 20Khz, I saw no reason to pursue this somewhat anomolous behavior.
jn
How much of the increase in resistance can be attributed to skin effect? I remember that was a component in LEAP's calculations for drivers. It also seems to be important for AC inductors operating in higher audio frequency range.
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Old 18th September 2019, 04:28 AM   #28976
jneutron is offline jneutron  United States
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None, zero, nada. I have very carefully included measurements of the voice coil up to 100 kHz, and it is basically flat.

No skin effect at one fifth the max freq of my tests. Normally, I prefer two orders of magnitude over desired freq, but I believe a factor of five is sufficient here.

I present fundamental measurements... I find that many "embellishments" lack the fundamentals. That is why I have done these measurements.
Jn
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Last edited by jneutron; 18th September 2019 at 04:34 AM.
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Old 18th September 2019, 02:31 PM   #28977
hhoyt is offline hhoyt  United States
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John Curl's Blowtorch preamplifier part III
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Originally Posted by jneutron View Post
...I present fundamental measurements... I find that many "embellishments" lack the fundamentals. That is why I have done these measurements.
Jn
Thank you...agreed +100...and did I mention thank you.

Howie
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Old 18th September 2019, 11:38 PM   #28978
elektroj is offline elektroj  Europe
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Thanks for the measurements, Jn!

Last edited by elektroj; 18th September 2019 at 11:40 PM.
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Old 19th September 2019, 01:09 PM   #28979
PMA is offline PMA  Europe
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Quote:
Originally Posted by Jakob2 View Post
It is still useful to remember that measurement with sine-waves (you know single-tone or pure-tone ) in the usual way (means using a distortion analyzer or voltmeter) is considered as so-called "steady state" measurement.
Is this considered a "steady state" measurement? You know, it uses a single-tone .
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Old 19th September 2019, 01:18 PM   #28980
vacuphile is offline vacuphile  Netherlands
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Pavel, this is not a single tone methinks. The on off points are impulses.
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Last edited by vacuphile; 19th September 2019 at 01:20 PM.
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