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Old 31st August 2012, 03:41 PM   #1341
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I have considered this, but it may alter characteristic or intended sound of amp.
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Old 31st August 2012, 05:02 PM   #1342
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Old 31st August 2012, 08:05 PM   #1343
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Quote:
Originally Posted by Zen Mod View Post
why not ?



see ; +/-20V arbitrary - written for then actual chat

later I saw interesting idea too - called Hawksford buffer (second pic )

plain one is cascode voltage biass referenced to gnd , H. same referenced to sources - having as result that jfets are working in real constant voltage mode

search to read what's difference - lower output impedance , if I remember that well

didn't measured , didn't tried
The Hawksford circuit is what I am going to have driving the FE of my F6 and I have some questions. First concerns the Vref for the BJT. Based on history and whats out there, I was thinking that 5-6 LED's would be better, as this would put the Jfets in the 10V range that they seem to like. It would also allow them to be run at full Idss with no worries. Second; in Joachim's layout, he has a switch at the ground point of the LED's and Jfet sources. Is this meant to be a relay initiated thing? Third, based on Nelson and others comments, if matched Jfets were used, the source resistors could be dropped, correct. I have a place in the pcb to add an offset pot as a safety margin, but would like to go without it.

Edit: Great thing about the circuit is the fact that it can be built as per the original schematic with jumpers and then added to, testing along the way, and checking for improvements in either measurement or sound.
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File Type: jpg Hawksford buffer.jpg (3.9 KB, 300 views)
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Old 31st August 2012, 08:08 PM   #1344
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lazy Yank

give me proper pic

(just ignore that I have it somewhere in comp)
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File Type: gif smesna.gif (16.0 KB, 300 views)
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Old 31st August 2012, 08:09 PM   #1345
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Thought it would come over with quote. Still haven't learned anything.
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Old 31st August 2012, 08:11 PM   #1346
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open pic , collect link of it , then put it here with "insert pic" command
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Old 31st August 2012, 08:14 PM   #1347
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Its there in the original post now. Did it while you were making fun of me
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Old 31st August 2012, 08:27 PM   #1348
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Quote:
Originally Posted by buzzforb View Post
Its there in the original post now. Did it while you were making fun of me
Click the image to open in full size.
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Old 31st August 2012, 08:32 PM   #1349
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Quote:
Originally Posted by buzzforb View Post
The Hawksford circuit is what I am going to have driving the FE of my F6 and I have some questions. First concerns the Vref for the BJT. Based on history and whats out there, I was thinking that 5-6 LED's would be better, as this would put the Jfets in the 10V range that they seem to like. It would also allow them to be run at full Idss with no worries........
shortly - yes

Quote:
Originally Posted by buzzforb View Post
.... Second; in Joachim's layout, he has a switch at the ground point of the LED's and Jfet sources. Is this meant to be a relay initiated thing? ....
jumpers, switch , or whatever - make it one or another way ...... but make it switchable between both ways , to hear what's your bloody preference


Quote:
Originally Posted by buzzforb View Post
......Third, based on Nelson and others comments, if matched Jfets were used, the source resistors could be dropped, correct. I have a place in the pcb to add an offset pot as a safety margin, but would like to go without it.

.......
10R trimpot can't do any harm ; you can easily toss it out

Quote:
Originally Posted by buzzforb View Post
........

Edit: Great thing about the circuit is the fact that it can be built as per the original schematic with jumpers and then added to, testing along the way, and checking for improvements in either measurement or sound.

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Old 31st August 2012, 08:47 PM   #1350
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This will oscillate as presented - try putting some Gate stoppers on the Jfets.

Of course with a small amount of Source resistance on each, say 10 ohms,
and a lower supply voltage you can dump the cascoding altogether.



Can you say Beast With a Thousand Jfets?
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