John Curl's Blowtorch preamplifier part II - Page 2952 - diyAudio
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Old 19th November 2012, 06:41 AM   #29511
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Quote:
Originally Posted by Trevor White View Post
maybe it just avoids scrutiny !!
Blowtorch is a legend.
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Also how about the guru publish a design aimed at diyer's after all this is a diy forum
You don't know the secret of the happy hours to sold the parts.
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Last edited by Esperado; 19th November 2012 at 06:45 AM.
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Old 19th November 2012, 06:55 AM   #29512
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I wonder how many people, here, have even heard this mysterious unit ?
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Old 19th November 2012, 08:01 AM   #29513
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As far i'm in concern, this preamplifier is a master piece that:
- I have never seen.
- I have never listened to.
- I am not rich enough to even dream to buy.
- Is no more on the market
- His author refuse to show the schematic.
- His author refuse blind tests of it.
- Was build with mysterious and/or now obsoletes parts.
- Is build with perfect wires sensible to the current flow witch need to be burned out during 30 days on the coil and 30 more days after assembly (assembly process being sensible to the hours of the day).
- Is claimed by his author as one of the best of the world (if not the best).
- Is the matter of a thread of >= 1470 pages.

Can-you imagine the idea i can have about the intellectual sanity of my neighbors.
And mine, to keep posting on this thread, as well.
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Old 19th November 2012, 08:45 AM   #29514
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Originally Posted by bcarso View Post
Essentially, two issues: unavailable parts; likely need for a lot of hand-holding.
Du.uh! Not sure how JC translates this into good excuses for not posting a schematic ..

I'm sure there are enough true gurus here who can help find replacements for Unobtainium and provide alternative hand-holding ..

JC can sit on the sidelines & yell out, "Hot!", "Not even warm!" or "Cold!" as appropriate and as it suits his fancy. Brad & Scott will ply him with $zillion glasses of vino.

Last edited by kgrlee; 19th November 2012 at 08:52 AM.
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Old 19th November 2012, 09:40 AM   #29515
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Quote:
Originally Posted by Esperado View Post
I wonder how many people, here, have even heard this mysterious unit ?
I have. It seemed fine.

The schematic isn't that mysterious and can be pieced together from knowing the topologies that John generally uses, looking at the hints given, and a bit of common sense. The special thing about it lies in the stories about the materials used; beyond that, what you have is a solid, well-engineered preamp.
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Old 19th November 2012, 10:05 AM   #29516
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Originally Posted by Esperado View Post
I wonder how many people, here, have even heard this mysterious unit ?
thousands and thousands of posts by the so called guru and not one proposal for a diy project for the benefit of our less learned guests !! The excuses are totally absurd
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Old 19th November 2012, 10:14 AM   #29517
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Actually, there was. It's in a separate thread on discrete opamp design. Ended up with Scott Wurcer putting up some interesting designs.

If John doesn't want to post an explicit schematic, that's his right. He has said several times (and he's right) that if you can't puzzle out the schematic from what he's disclosed and the photos, you'd have little chance of getting the thing right even with an explicit schematic.
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Old 19th November 2012, 10:32 AM   #29518
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The hardest would be the case. The controls and sw,s I am sure you could get better ones today, provided you have the money. The connectors and the PCB material was also discusted a while back, and most likely you could get better ones ,or least similar quality. The topology as Sy said, can be pieced together. What is left are those rare fets. So the whole thing would be like a semi interesting puzzel. If you need a pre amplifier. I don't.
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Old 19th November 2012, 12:00 PM   #29519
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OK, and thanks SY (for once) for coming to my defense on this. For some reason, I have to take a number of 'cheap shots' every week, and I have to 'lump' it.
The design is a 4 quadrant, all fet, folded cascode, first used by Charles Hansen, but WITHOUT an output buffer. The unit is double servoed, and has no global feedback.
It is essentially a terminated (1K) balanced-in, balanced-out transconductance amplifier operating in rich Class A, at about +/- 30V, which is highly regulated.
At the time of my first refusal to publish the exact schematic, I was still finishing the units started by my former business partner, Bob Crump, and I still had one or two for sale ultimately, so I decided not to release the schematic at that time.
Now, that time has passed, and the parts difficulty has recently been reduced by Linear Systems. Now all you have to do is buy a bunch of complementary J-fets, pick only the highest Idss units, then get a very good match (at least 1ma) or better.
Any qualified design engineer can built their own circuit from this description. Some already have.
For the record, the exact schematic is not really the point of this exercise. It is the WAY that we put everything that we could think of into the Blowtorch, to make it as close to a 'straight wire with gain', as possible, AND we were successful.
I have given a number of circuits here that people could take, AND build.
For example the schematics for Parasound JC-2, and Parasound JC-3 are on this website, and the Levinson JC-2 and JC-3 power amp are here as well. Build those with my blessing.

Last edited by john curl; 19th November 2012 at 12:13 PM.
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Old 19th November 2012, 12:05 PM   #29520
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Miklos, I seriously doubt that BETTER passive or active components can be purchased today. The pots have doubled in price, the switches are mil spec. There have been no improvements (so far as I know) in this area.
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