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Old 24th January 2013, 06:44 PM   #33481
RNMarsh is offline RNMarsh  United States
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First one to offer the pcb and BOM/parts gets my order. Thx-RNMarsh
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Old 24th January 2013, 06:50 PM   #33482
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Old 24th January 2013, 06:55 PM   #33483
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back when this thread only had one part I tried a AD797 sim

John Curl's Blowtorch preamplifier
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Old 24th January 2013, 07:30 PM   #33484
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The threshold of thd is about 2-3cm for steel.
Thanks for the precision Richard, it seems i was 1cm too optimistic.
Yes, it seems this thread is sometimes useful.
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Old 24th January 2013, 07:53 PM   #33485
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I would assume that the actual distance would be dependent on the impedance of the circuit as well. High impedance circuits will have lower magnetic fields, whereas low z one will have higher..

jn
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Old 24th January 2013, 08:44 PM   #33486
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Distance does help, IF you can create the distance.
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Old 24th January 2013, 09:07 PM   #33487
fas42 is offline fas42  Australia
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Originally Posted by RNMarsh View Post
The threshold of thd is about 2-3cm for steel. This was measured and reported on by researchers in Japan a looooong time ago. Thx-RNMarsh
Can anyone point to material researching other behaviours of pieces of iron or steel near audio relevant elements? Examples: a CD player with conventional steel case, large iron weight on top to reduce vibration; a speaker with usual treble driver on top, again with heavy iron weights on top to stabilise unit on supports. In both cases the sound was severely degraded ...

Frank
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Old 24th January 2013, 10:01 PM   #33488
gpapag is online now gpapag  Greece
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Hofer found some distoriton in his AP sine generator when the steel cover was put in place - the production fix was to add patch of Al sheet to the steel cover over the oscillator region

the Eddy Current "shielding" of the Al sheet knocks down the B reaching the steel

a inverted application of what Ott, others show for severe EMI shielding by layering high conductivity and high mu materials - the Eddy current in the conducive material "shields" (or reflects) anything more than a few skin depth in frequency content, the iron can short out lower frequency that gets through

so maybe audiophiles need to line their steel boxes with thick Al
True and copper would be more effective than aluminum on this.
But it works with HF.
Eddy current shielding needs at least 2, better 3 delta for shield thickness.
Visit the monogram that Richard kindly attached.
Detailed formulae have also been linked to.
As well as an old Bell paper that refers to calculation and measurement of distortion components due to magnetic hysteresis of steel.
The repetition period of visiting the same topic has become alarmingly short (age issue )

George
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Old 24th January 2013, 10:04 PM   #33489
gpapag is online now gpapag  Greece
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We have a very sadist proverb in France: "The best is the ennemy of the good".
It use to turn in circle in your brain each time you broke some near perfect stuff, trying to do better, mixed with a nice sample of your best insults.
Christophe
If you are referring to the driver I killed, it survived the modifications battle field. It died during measurements (Like:He fell from the stool in the bar and broke his neck).
Thanks to the profound stupidity of mine.

George
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Old 24th January 2013, 10:29 PM   #33490
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I envy you, George. With age, i begin to be so upset with all past bad experiences in electronic that i am virtually paralyzed, providing every gesture and its possible consequences before to begin a work. This does prevent nothing, of course, and certainly not Murphy.
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