John Curl's Blowtorch preamplifier part II - Page 2725 - diyAudio
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Old 4th September 2012, 03:01 PM   #27241
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Quote:
Originally Posted by aeronautical View Post
is that because steel or ferric metal can be excited into being a magnet in the presence of a magnetic field...thereby fixing one problem and spawning others?
A ferromagnetic sheet won't have a linear BH curve. Whtn it is excited by a field on one side, the other side will see a permeability modulation. This can create harmonics which are a product of the two frequencies being shielded.

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Originally Posted by RNMarsh View Post
The research done on this came from Japan... I think I recall who/company but not sure. -Dick Marsh
It's currently a tenet of the EMC discipline.

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Originally Posted by john curl View Post
Richard is right. Of course, copper, silver, maybe Uranium might be OK. Can you afford it? I'll stick to aluminum.
Hey, maybe there's a 747 vertical stabilizer available out there on E bay. Maybe a group buy?? A sheet of aluminum foil over the uranium would stop the alpha particles.


jn
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Old 4th September 2012, 03:09 PM   #27242
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Aero, you should NOT try to make the Para JC-2, it already exists at a price point that it is cheaper to buy it, than waste your time building it. That's why I can show you the schematic of an existing product so openly. The JC-2 is an example of a relatively complex design, designed when jfets were cheap and available, that is NOT for amateurs.

In a different way, the CTC Blowtorch is MORE difficult, not because of the complexity, but in the excessive selection and matching of the jfets
.
However, all is not lost! You can build a clone version of the JC-80 line amp, and get virtually everything that you could get from the Para JC-2, just not the same distortion specs, AND not a balanced input, IN ITS PRESENT FORM. However, the Para JC-2 example can show you HOW to modify the JC-80 schematic to achieve balanced operation of both input and output, so you can be up-to-date, so to speak. The JC-80 'clones' sold on the internet are a 'heck of a deal', priced too cheap for me to even try to compete with. However, many subtle compromises have been made to do this, more like using VW parts to make a Porsche, and there will be a subtle difference, just not one that most people will ever notice. Only the crazy, rich people, with the world's best associated audio reproduction equipment would be able to note the difference.

I had this same experience with an automobile, 20 years ago. It was a few months after the firestorm wiped out my pocketbook, sports car (modified SAAB Sonett) and left me with a slightly old Honda Accord. What to do, I had been driving a sports car almost exclusively for the previous 27 years! Am I to forgo the joys of driving because I can't AFFORD a decent replacement? Well, I was given an offer of a Porsche 924, a special edition, with bigger tires and improved suspension, for an affordable amount. I bought it, and enthusiastically started out to 'improve' it. Bought all the manuals , books on engine design, etc. and attempted to make this 'bargain' into a race horse.

Well, after a couple of years of trying, I realized that I was at a 'dead-end'. The car would just NOT get any faster, because of the fundamental limitations of the VW based engine and associated components. About 8 years later, I was given an offer that I could not refuse, a MINT example of a Porsche 944, that succeeded the 924 by about 8 years or so. It wasn't that much more powerful, but it was more REFINED. And I drive it still, today. It is made of a majority of Porsche parts and my repair bills show this to be so. I guess that's what it takes, for 'refinement'. End of story.

Last edited by john curl; 4th September 2012 at 03:16 PM.
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Old 4th September 2012, 03:13 PM   #27243
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Well, what do you know? The industry forgoes ferromagnetic sheets to reduce distortion generation!
'-)
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Old 4th September 2012, 03:22 PM   #27244
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Originally Posted by john curl View Post
Well, what do you know? The industry forgoes ferromagnetic sheets to reduce distortion generation!
'-)
They have for decades.

Now at least, it is being supported by teaching.

I cannot state however, where the origional observations came from.

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Old 4th September 2012, 03:31 PM   #27245
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It sounds to me like a good example of Murphy's Law:
It doesn't matter.
It doesn't matter very much.
We invented it. '-)
Heck, Mark Levinson and I started with Mu-metal shielding, we just began to hear and measure the difference almost 40 years ago. Of course, we were 'crazy' to go to aluminum chassis, then! More expensive, less shielding. Even today, I am laughed at for the CTC Blowtorch's massive aluminum case (we couldn't afford silver), and asked why we didn't use steel?
Today, I suppose, our reasons are now in some book, somewhere, and not just in the obscure AES paper done on ferromagnetic shielding by the Japanese, decades ago.
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Old 4th September 2012, 03:36 PM   #27246
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Quote:
Originally Posted by jneutron View Post
They have for decades.

Now at least, it is being supported by teaching.

I cannot state however, where the origional observations came from.

jn
It was certainly 20yrs. ago that I pointed it out to Martin Colloms. I'm sure it's been known for far longer. Maybe it's the steel nails in the floor that makes the wooden blocks work.
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Old 4th September 2012, 04:19 PM   #27247
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You know, Scott, you may have a point.
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Old 4th September 2012, 04:35 PM   #27248
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Quote:
Originally Posted by john curl View Post
Aero, you should NOT try to make the Para JC-2, it already exists at a price point that it is cheaper to buy it, than waste your time building it. That's why I can show you the schematic of an existing product so openly. The JC-2 is an example of a relatively complex design, designed when jfets were cheap and available, that is NOT for amateurs.
In a different way, the CTC Blowtorch is MORE difficult, not because of the complexity, but in the excessive selection and matching of the jfets.
However, all is not lost! You can build a clone version of the JC-80 line amp, and get virtually everything that you could get from the Para JC-2, just not the same distortion specs, AND not a balanced input, IN ITS PRESENT FORM. However, the Para JC-2 example can show you HOW to modify the JC-80 schematic to achieve balanced operation of both input and output, so you can be up-to-date, so to speak. The JC-80 'clones' sold on the internet are a 'heck of a deal', priced too cheap for me to even try to compete with. However, many subtle compromises have been made to do this, more like using VW parts to make a Porsche, and there will be a subtle difference, just not one that most people will ever notice. Only the crazy, rich people, with the world's best associated audio reproduction equipment would be able to note the difference.
I had this same experience with an automobile, 20 years ago. It was a few months after the firestorm wiped out my pocketbook, sports car (modified SAAB Sonett) and left me with a slightly old Honda Accord. What to do, I had been driving a sports car almost exclusively for the previous 27 years! Am I to forgo the joys of driving because I can't AFFORD a decent replacement? Well, I was given an offer of a Porsche 924, a special edition, with bigger tires and improved suspension, for an affordable amount. I bought it, and enthusiastically started out to 'improve' it. Bought all the manuals , books on engine design, etc. and attempted to make this 'bargain' into a race horse.
Well, after a couple of years of trying, I realized that I was at a 'dead-end'. The car would just NOT get any faster, because of the fundamental limitations of the VW based engine and associated components. About 8 years later, I was given an offer that I could not refuse, a MINT example of a Porsche 944, that succeeded the 924 by about 8 years or so. It wasn't that much more powerful, but it was more REFINED. And I drive it still, today. It is made of a majority of Porsche parts and my repair bills show this to be so. I guess that's what it takes, for 'refinement'. End of story.

Good Morning Mr. Curl,

I fully understand these dynamics you cite. Actually, I figured I would probably spend more than a finished product would cost of the same quality not to mention my time. I wanted to do this because I have such fond memories of the various electronics labs from college and later the fair number of projects I built for myself. I still listen to them now some 30 plus years later. I can close my eyes and still hear the music I listened to while at my bench with probes in my hands. Those are sweet memories for me and I always promised myself I would get back to it someday. I am here as a hobbiest. I am not in the electronics industry although I have the electronics education from many years ago. I would guess that most everyone on here has different reasons for being here; I have mine as I just intimated.

Anyway, that is what brought me here initially but let me tell you what I have found in the process. As you know, I made a fuss a while back about this thread being more of a chat room for sudio geeks than a thread to actually build anything, which is or course fine. But besprinkled among the coffee shop speak there is real genious here. You have to but read the last fifty or so posts and you find magnetic resonance theory, conductance, thermo-dynamics...real science.

What I ended up trying to do was to summon the team spirit among this group to work together. I made some rather direct appeals to a moderator to head up a project and lead the guys on this post to pool their knowlege and build something really special.

You guys could you know...you could design one for the ages. I think it would be fun and fulfilling.

As I mentioned, I have my own personal reasons which is getting back to something I loved and hopefully can make something for my kids, silly though some may find this. But along the way I recognized what an opportunity you guys have. I am something of a crusader if you haven't noticed.

So, to anyone who reads this, why not pool your knowlege and build something really special. Mr. Curl, you could keep us all out of trouble and I would even suggest that any patents that might come out of such a project would be yours. Perhaps a lasting legacy to cap off your already outstanding accomplishments.
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Old 4th September 2012, 04:45 PM   #27249
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Aero, you are still rather naive. I design new products all the time. I just don't PUBLISH them here.
Audio design of this quality does NOT need a committee to design it. In fact, that would ultimately compromise the final result.
Unfortunately, my BEST designs require matched jfets, that were once relatively cheap and available. Now, they are expensive and almost impossible to find (at the moment).
However, there is a 'loophole'. That is in the JC-80 clones on E-bay. They apparently sell the parts as well. That is the direction to go, IF you are serious. If that is not the direction for you, and you have reconsidered your options, I wish you well.
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Old 4th September 2012, 04:45 PM   #27250
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Originally Posted by aeronautical View Post

What I ended up trying to do was to summon the team spirit among this group to work together. I made some rather direct appeals to a moderator to head up a project and lead the guys on this post to pool their knowlege and build something really special.

You guys could you know...you could design one for the ages. I think it would be fun and fulfilling.
The task you are addressing is akin to herding cats (SY has already touched on troglodytes, who can be unmanageable as well). If you were to succeed, I recommend moving on to solving the 1000 year-old conflicts in the Middle East
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