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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 7th October 2012, 06:06 AM   #28001
john curl is offline john curl  United States
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There was a study done by a Japanese firm and it is somewhere in the AES papers. However, my personal experience shows me that a steel chassis can be audible. In fact, I had the Parasound JC-3 changed from steel to aluminum, where possible, and found an audible improvement. I do not know why this was so, but I would not release the JC-3, until we changed to aluminum. The JC-3 has been awarded an A rating, this is one of the reasons.
I realize that this seems strange, but sometimes we just don't know WHY something can make so much difference, because it can be virtually unmeasurable. I just follow my experience. Works for me.
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Old 7th October 2012, 09:06 AM   #28002
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I have very bad experience with steel enclosures in instrumentation for power (high-current) testing labs. It was absolutely necessary to avoid steel or mumetal and to use thick copper or aluminum. Of course, magnetic flux density and intensity of magnetic field was in orders higher than at home audio, but, on the other hand, signal level higher than the lowest audio signals.

For audio, I suspect even the phenomena like transformer magnetic flux coupled into steel metal enclosure. It is not only "low order" and in some cases the change of enclosure from steel to thick Al is measurable at the bottom line of the FFT analysis of the preamp output signal.
 
Old 7th October 2012, 09:13 AM   #28003
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I also have tried conductive plastics for audio, John. The result was not good. The unit was quite sensitive to placement with regards to another instruments. That means, placed on top or aside something that had a big transformer inside resulted in worse S/N and hum components audible and measurable. IMO conductive plastics might be used with consumer audio or mid-fi, but not with high end.
 
Old 7th October 2012, 12:51 PM   #28004
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Originally Posted by john curl View Post
I realize that this seems strange, but sometimes we just don't know WHY something can make so much difference, because it can be virtually unmeasurable. I just follow my experience. Works for me.
This is the nightmare world of fine tuning a complete system to get optimum sound. The first time I went down this road I burnt myself out with frustration, because I couldn't get a handle on what was going on. Later on, I learnt to pace my mod's: try something, let it settle down until I had a clear picture of what the long term benefits were, then move on to the next thing. It's taken years to get a decent understanding of what matters, and it's mostly none of the usual, obvious stuff.

The best measuring tools have always been my ears, I don't use any of the standard analysers and I'm certain I haven't lost out on anything by not having those on hand ...

Frank
 
Old 7th October 2012, 01:21 PM   #28005
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Of course, PMA, you are correct. However, to save a good deal of money invested in the case, I was wondering what is next best? Perhaps most of the added 'EMI' in our environments, today, is electrostatic or line induced. We could fix those sources without a heavy metal case, couldn't we?
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Old 7th October 2012, 02:16 PM   #28006
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I thought this thread was about high-end audio design
 
Old 7th October 2012, 03:13 PM   #28007
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Of course, PMA, you are correct. However, to save a good deal of money invested in the case, I was wondering what is next best? Perhaps most of the added 'EMI' in our environments, today, is electrostatic or line induced. We could fix those sources without a heavy metal case, couldn't we?
The scourge now mostly for the "low-end" is mandated switchmode a.c. adapters, to eliminate or reduce standby current drains from lossy double-bobbin transformers --- Balakrishnan's colorfully-named "energy vampires". The old adapters were bulky and inefficient, fairly strong magnetic field emitters, but had the virtue of low interwinding capacitance. And for the mag fields, distance helps a lot as the field falls off as the cube of the distance. Now, not only are the adapters themselves strong interference sources, generating mostly conducted high-frequency noise modulated by the mains and loading, but the coupling of junk from the line is much greater. And more and more junk is being dumped onto the mains.

In consumer electronics the convention of a relatively low capacitance coupling for the internal supplies or plain iron-copper external supply meant the whole shooting match tended to sit at about half of the mains voltage and move together. Hardly perfect, but if the electrical shielding were reasonable and the magnetic emitters positioned optimally and at some distance from pickup loops, you could get by. With the mandated switchers it becomes a lot harder. Or, before that, the referencing of some equipment (satellite stuff, computer sound cards) to the safety ground made things no longer move as one, and provoked line related noise.

All of the above can be dealt with in various ways, including balanced modes and very good common-mode chokes, but these are not that cheap and not without other potential penalties.
 
Old 7th October 2012, 06:00 PM   #28008
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by john curl View Post
There was a study done by a Japanese

The last time this “unmeasurable” effect has resurfaced in this thread, was only a month ago. See links below. (previous bursts of interest were with shielding of input x-formers and shielding of cartridge bodies, more than a year back)

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Originally Posted by john curl View Post
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Originally Posted by john curl View Post
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Originally Posted by aeronautical View Post
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Originally Posted by RNMarsh View Post
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Originally Posted by jneutron View Post
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Originally Posted by gpapag View Post
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Originally Posted by jneutron View Post
Do all questions still remain open? Come on people. There is enough of input (Jneutron has a multiple of times contributed on the issue) for realistic solutions.

FLEETWOOD MAC - Oh Well (1969 UK TV Performance) ~ HIGH QUALITY HQ ~ - YouTube

Are you looking for a housing of your preamplifier, that is a perfect electromagnetic shield to internal and external fields 0.1Hz –100THz, one which will also re-emit nothing back, 4 pi space, at any miniscule distance?

Your Jinni heard your (last) wish and noded “Yes Master. At no cost. Right now”.

Floop!

It has the shape of a ball. It is a hollow large ball.
Jinni laid in front of you the detailed engineering drawings.
The internal hollow space is as large as you wanted it to be.
The wall material has a varying electrical conductivity through it’s thickness, starting and ending at 0.000… IACS on both sides of the wall and in between increases to a value >>100, following a very wide, symmetrical, bell shape distribution.
It’s magnetic relative permeability follows the same distribution, starting from and ending to 1.000…, reaching in the middle of the wall thickness a value of some millions.
The thickness of the wall is >>1m.
There are no openings and no discontinuities of the wall material.


Now you only have to use it.


(silly) George
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Old 7th October 2012, 07:15 PM   #28009
john curl is offline john curl  United States
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George, what is the problem? I KNOW HOW to make good, relatively effective cases, BUT they are SO EXPENSIVE! They DOMINATE the building cost. Is this a good balance? I was hoping for some SHORTCUTS that might be almost as good, yet not cost anyway near as much.
However, the usual engineering solution would be to use a relatively thin steel case. BUT I will NOT use a steel case, because I can hear them when they are in physically close contact with my designs. I last tested this the the JC-3 phonostage design.
Now, let us go forward with some new approaches! Graphene? Silver foil?
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Old 7th October 2012, 07:46 PM   #28010
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Wood!
 

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