John Curl's Blowtorch preamplifier part II - Page 2191 - diyAudio
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Old 31st March 2012, 10:50 AM   #21901
gk7 is offline gk7
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Quote:
Originally Posted by hitsware View Post
Yea ....... Center tap it to ground (0V)
No. Think it through, the sources of the upper half are at a positive potential compared to ground and the lower at negative. With the resistor in the middle each half acts like a current source for the other.
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Old 31st March 2012, 10:54 AM   #21902
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JC, isnt this patented by Analog devices ?? Maybe expired ?? Scott should know ??
I believe the design idea is by Gosser.
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Old 31st March 2012, 12:18 PM   #21903
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Originally Posted by johnferrier View Post
the resistor in the middle ?
What resistor? According to schematic posted by JC, those four in the middle are not even connected.
If they would, schematic would show dots connecting the respective lines - see my attachment.

Oops...

--------------
Five minutes later, voice of boss in the background: "Now, get me that (beep) guy responsible for this (beep) schematic. I want to see him NOW!"
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File Type: jpg not_connected.jpg (121.7 KB, 209 views)

Last edited by elektroj; 31st March 2012 at 12:39 PM.
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Old 31st March 2012, 12:22 PM   #21904
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Originally Posted by homemodder View Post
JC, isnt this patented by Analog devices ?? Maybe expired ?? Scott should know ??
I believe the design idea is by Gosser.
Wow you follow everything, thats the first thing I thought but Roy's circuit was all bipolar (makes a great RF diff-amp). I would have to carefully read the claims but as you say it might be expired.
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Old 31st March 2012, 12:33 PM   #21905
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elektroj

Maybe that's special notation to show were to put the dry solder joints that fail after the warranty expires.
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Old 31st March 2012, 12:34 PM   #21906
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To me this looks like two CFA's with the resistor network providing bias and feedback. The common mode reference is at the input no need to ground that point, maybe it's a test measurement point? Are those LED's to set the output bias, seems to be some local feedback too?
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Last edited by scott wurcer; 31st March 2012 at 12:42 PM.
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Old 31st March 2012, 12:37 PM   #21907
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Erno Borbely has a similar design without ground connection at the sources.
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Old 31st March 2012, 12:46 PM   #21908
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Originally Posted by johnferrier View Post
the resistor in the middle ?
JC asked what sets the current. Isn't it the middle resistor ?
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File Type: png middleR.png (24.9 KB, 202 views)
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Old 31st March 2012, 01:21 PM   #21909
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"Никогда не разговаривайте с неизвестными" Михаи́л Булга́ков

Wavebourn is there any more to the translation ?


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Last edited by johnferrier; 31st March 2012 at 01:45 PM.
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Old 31st March 2012, 01:35 PM   #21910
gk7 is offline gk7
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Originally Posted by johnferrier View Post
JC asked what sets the current. Isn't it the middle resistor ?
Yes, of course. With 2SK170V/2SJ74V it typically would be in the range 50-100 Ohm.
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