John Curl's Blowtorch preamplifier part II

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#33,487
RNMarsh said:
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
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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
 
#33,488
jcx said:
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
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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
 
#33,489
Esperado said:
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.
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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
 
#33,491
Sounds familiar ...

What drives me nuts is getting the right focal length for seeing the damn thing I'm trying to work out. I don't "do glasses" so I have an assortment of cheap, plastic spec's to provide the right power for the occasion. The right power is often just not quite right enough, and then in the heat of the moment I step on the last one I was using, that I took off a moment before ... 🙁

Frank
 
#33,492
jneutron said:
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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yes, of course. The circuitry was 50K-100K in and low Z out configuration. Note that at the time, the measurment resolution wasnt what it is today. I dont recall all the gory details -- just the summary conclusion..... routing wires against the chassis was (is?) popular. Keep from lashing wires against a steel chassis bottom etc and keep a distance of an inch or more and you are good. Or, just use aluminium. -Thx RNMarsh
 
#33,493
fas42 said:
Sounds familiar ...

What drives me nuts is getting the right focal length for seeing the damn thing I'm trying to work out. I don't "do glasses" so I have an assortment of cheap, plastic spec's to provide the right power for the occasion. The right power is often just not quite right enough, and then in the heat of the moment I step on the last one I was using, that I took off a moment before ... 🙁

Frank
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I'm using one of those visor-type magnifiers lately. The one I got has a built-in lamp and three levels of magnification. It's not bad, and leaves both hands free. As long as things don't get a whole lot smaller I can do sloppy breadboarding with SM parts.
 
#33,494
john curl said:
Max, I think your question on the sonic differences between steel and aluminum is valid, but I don't have any evidence to prove it directly, except my experience.....I try to suggest to others what I have found over decades of designing audio products....Now, I just specify aluminum, because it sounds better in listening comparisons.
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John - thanks
Nelson, Richard, others - thanks, all good info.

Dan.

A wise man learns by the mistakes of others, a fool by his own - Latin Proverb.
11 Wise Lessons - Essential Wisdom for Life | Personal Development
 
#33,495
What bothers me is that "standard" texts for amplifier, etc, design don't mention this at all - can't see anything in Duncan or Cordell. So, only insiders know of these important "tricks", and the divide remains, between a very small number of people who can get everything right, and those that can't ...

Frank
 
#33,499
fas42 said:
What bothers me is that "standard" texts for amplifier, etc, design don't mention this at all - can't see anything in Duncan or Cordell. So, only insiders know of these important "tricks", and the divide remains, between a very small number of people who can get everything right, and those that can't ...

Frank
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I have noted sonic changes by shifting internal cables well away from chassis steel.
Eons ago there was a tweak called the VPI brick - a timber box enclosing I believe transformer laminations. There are varying views of optimal placement and sonic effects.
I have placed a standard clay house brick on top of my cd player in the past and the added mass altered the sound. Rotating the brick 180* further altered the sound 😱

Dan.
 
#33,500
fas42 said:
Sounds familiar ...

What drives me nuts is getting the right focal length for seeing the damn thing I'm trying to work out. I don't "do glasses" so I have an assortment of cheap, plastic spec's to provide the right power for the occasion. The right power is often just not quite right enough, and then in the heat of the moment I step on the last one I was using, that I took off a moment before ... 🙁

Frank
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Haha. I have a library of those two-dollar shp specs also....works for me !.

Dan.
 
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