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John Curl's Blowtorch preamplifier
John Curl's Blowtorch preamplifier
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Old 2nd May 2006, 06:24 AM   #1091
Upupa Epops is offline Upupa Epops  Czech Republic
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Fan club or denomination of feedbackless amps, Patrick ? Now I understand, discussion is vain....
Old 2nd May 2006, 06:35 AM   #1092
john curl is offline john curl  United States
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Grey, I had the same experience with the Grateful Dead back in 1970-71. They originally used Ampex tube mixers and Mac tube power amps. They wanted me to help them update to solid state. Well, most of our efforts for the first few years was essentially a failure. Open loop tubes actually sounded better than my IC op amp designs. It wasn't until I read Otala's papers that I was able to make successful solid state products with high open loop bandwidth, high slew rate and reasonably low distortion that pleased the band. Later, Mark Levinson built and used these circuits for the JC-2 preamp.
Old 2nd May 2006, 06:38 AM   #1093
EUVL is offline EUVL  Europe
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> Fan club or denomination of feedbackless amps, Patrick ?

I have both in my chain, with or without global feedback.
And I have both versions built for my linestage.

Old 2nd May 2006, 01:30 PM   #1094
PMA is offline PMA  Europe
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John Curl's Blowtorch preamplifier
Nice article, proving that there is nothing like "pleasant distortion", "harmonic fullness" etc.

Old 2nd May 2006, 01:37 PM   #1095
GRollins is offline GRollins  United States
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Something I have found curious is that a solid state piece might take an open loop bandwidth of 200-300kHz to acheive similiar sonic qualities to a tube piece that has OL bandwidth of perhaps 75-100kHz. Granted, we're talking inherent differences between the circuits, but shooting from the hip I would say that, if anything, it should be the other way around, with the tube piece requiring greater bandwidth in order to push (coupling capacitor and/or transformer) phase shifts further out of the audible frequency range.
Got any ideas on that?

Old 2nd May 2006, 03:47 PM   #1096
john curl is offline john curl  United States
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Grey, this is a fairly narrow conclusion, but I would look at the effect of non-linear capacitance of the active devices for an answer. It is well known that transistors and fets have a lot of it, and this would be the primary limitation to open loop bandwidth. Less 'effective' capacitance means higher bandwidth.
Old 2nd May 2006, 03:50 PM   #1097
Geophysicist is offline Geophysicist  United States
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Default Blowtorch in Europe

Hi Folks,

I've enjoyed reading the thread. I have just acquired a Blowtorch, something I've coveted for some time - ever since I heard Bob Crump's unit at his home. Nothing that I have ever heard equals the musical honesty of this preamp.

Early on, I noticed that several folks had observed that there apparently were no Blowtorchs in Europe. Well, that MAY change. I'd estimate roughly 50:50 odds that there will be one in London this year - mine. This would be my second time working in the UK, and is something I'm hoping works out. We shall see. Regardless, just wanted you to know that those in the area towards the end of the year would be welcome to drop by if they wish.

Old 2nd May 2006, 09:17 PM   #1098
joho is offline joho  Netherlands
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Talking Blowtorch inspection team

Hi Mike,

Watch out for Sherlock Holmes and his magnifying glass!

Old 2nd May 2006, 09:38 PM   #1099
jbaudiophile is offline jbaudiophile  France
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Hi, Joho,

And just wait Dr Watson for autopsy...

Old 2nd May 2006, 11:41 PM   #1100
john curl is offline john curl  United States
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It is good to hear from someone who has actually listened to the blowtorch preamp and likes it.

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