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John Curl's Blowtorch preamplifier
John Curl's Blowtorch preamplifier
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Old 9th January 2006, 01:12 PM   #31
Terry Demol is offline Terry Demol  Australia
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Default Re: solid chunk of Al

Quote:
Originally posted by Elso Kwak


Does that improve the SOUND of the unit Terry????
Well I don't know Elso... I've never made a rack case with that form
of construction.

Perhaps you may try it and report back to us.

Cheers,

Terry
 
Old 9th January 2006, 02:05 PM   #32
jbaudiophile is offline jbaudiophile  France
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Wink CTC Blowtorch...

Hi, Jacco

Yes, the CTC Blowtorch is really a full machined aluminium block... with the back and top as exceptions.

Just see here :
http://www.tgaudio.com/pictures/Blow...erInterior.JPG

Machining marks are clearly visible on the left side panel, and the front inside corners are just "rounded". Ahem... The birdview just shows... the case bottom... Bob Crump emailed me that he wanted the maximum structural rigidity... and also to build a full Faraday cage....

The Teflon boards PCBs were also CNC routed... And "six nines" silver cables used... Sadly enough, the low pic resolution doesn't justice the CTC Blowtorch. But, as an evidence, only 40 Blowtorch were planned to build, so not any advertisment needed...

From the only "technical" papers I could read about it, the Teflon boards were mandatory because of a full open loop running, and the Line amplifier is (only ?) 350 Khz bandpass... Seems to me that it is complementary Jfets driving Mosfets in a folded cascode way... I read twice John Curl's early works with Matti Otala - about TIM distortion - as it seems to be a good starting point for understanding the whole design...

And guys : any paper (revues,...) or (preferably internal) pics to share with your European cousins on the Blowtorch ? Would be of interest for some of us (Darry, Jacco, and ... I). Thanks !
 
Old 9th January 2006, 07:20 PM   #33
Terry Demol is offline Terry Demol  Australia
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Default Re: CTC Blowtorch...

Quote:
Originally posted by jbaudiophile
Hi, Jacco

From the only "technical" papers I could read about it, the Teflon boards were mandatory because of a full open loop running, and the Line amplifier is (only ?) 350 Khz bandpass...


Open loop design .... I await the prescribed DIYA onslaught


Cheers,

Terry
 
Old 10th January 2006, 12:22 AM   #34
SY is offline SY  United States
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John Curl's Blowtorch preamplifier
Just chatted with JC. Yes, the case is indeed milled from a solid billet of aluminum. Pantograph lettering. $3000 manufacturer's cost for the case alone. All FET, no feedback, servoed. First stage is 4 quadrant comp diff, second is folded cascode using MOSFETs run at high current. Servo with roughly 1 sec time constant.

Input FETs are unobtanium from Toshiba. Feeder resistor in folded cascode is 5W Holco at 200 ohm.

I've been fortunate enough to see, touch, and hear one. Very nice. But I'll stick to tubes.
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Old 10th January 2006, 12:28 AM   #35
poobah is offline poobah  United States
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While such a bright photo, if you look closely enough, you can just make out the N-rays emmanating from radiused corners..
 
Old 10th January 2006, 01:11 AM   #36
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally posted by SY
$3000 manufacturer's cost for the case alone.
Jeeeeebus! What, were they paying some union laborer double overtime to chisel it out by hand?

Somebody got taken to the cleaners.

se
 
Old 10th January 2006, 02:29 AM   #37
SY is offline SY  United States
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John Curl's Blowtorch preamplifier
Nope, when John described the casework process to me, I estimated $1500 per case based on similar stuff I've spec'd with carved aluminum molds. He said, nope, it's $3k, but there's two cases. I asked, isn't that $1500 per case? A second or two of quiet and a, yeah, I guess that's right.
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Old 10th January 2006, 02:48 AM   #38
poobah is offline poobah  United States
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So... what do these jewels go for???
 
Old 10th January 2006, 03:17 AM   #39
niles is offline niles  United States
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if you have to ask . . . It depended on the configuration, you could have single ended or ballanced inputs and outputs or the vendetta phono. I think the base was about 12k and it went up from there.
 
Old 10th January 2006, 03:29 AM   #40
poobah is offline poobah  United States
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12K and up?

$500,000... (12K X 40 units)... good haul I 'spose. Good work if you can get it!
 

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