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Zen Mod
Official Court Jester
diyAudio Member

Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Quote:
 Originally Posted by vdi_nenna Ok, I understand. How do I find yfs? Datasheet gives a range or typical.
work first on Idss , think later of Yfs
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

 6th April 2019, 08:12 PM #42 EUVL   diyAudio Member   Join Date: Oct 2003 Datasheet gives you a graph of Yfs vs Id. You already have all the hints you need from my 2 links to build a high performance source follower with active parts. No need to use J113 or whatever else. There are no better N-JFETs than Toshiba, for me at least. Patrick __________________ xen-audio.com
 7th April 2019, 03:30 AM #43 vdi_nenna   diyAudio Member     Join Date: Oct 2000 Location: PA, USA Two very close matched 2sk170 at 9.76 mA gave a dc offset of .3v. __________________ I build, therefore I am. Do not create problems where there are none.
 7th April 2019, 06:38 AM #44 EUVL   diyAudio Member   Join Date: Oct 2003 Assume that you have shorted the input gate to Gnd, and your rail voltages are symmetrical to say 0.1V. Then something is likely to be wrong with your matching. If you have matched to 10µA under the same temperature, I expect your offset to be < 1mV. That is when you use Fig. 15c with Rs = 0. Patrick __________________ xen-audio.com
 7th April 2019, 10:42 AM #45 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain exact schematic needed before that , I can only presume that upper source resistor need to be trimmed for offset __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
 7th April 2019, 12:11 PM #46 vdi_nenna   diyAudio Member     Join Date: Oct 2000 Location: PA, USA I meant .3mV. Typing on phone late at night... I tried the formula for Rs, but getting values under 1 ohm. Not sure I'm doing it correctly. Maybe it's because the idss is under required Id? __________________ I build, therefore I am. Do not create problems where there are none. Last edited by vdi_nenna; 7th April 2019 at 12:15 PM.
 7th April 2019, 12:13 PM #47 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain ok , that's good checked cold/hot difference? __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
 7th April 2019, 03:21 PM #48 vdi_nenna   diyAudio Member     Join Date: Oct 2000 Location: PA, USA Started at .4 mV offset. After a couple of hours on, it's at around .9 to 1 mV dc offset. __________________ I build, therefore I am. Do not create problems where there are none.
 7th April 2019, 10:05 PM #49 vdi_nenna   diyAudio Member     Join Date: Oct 2000 Location: PA, USA After 4 hours, and turning on the DMM, still settles at .9mA. Goes from 1.1mA down to .9 after a few seconds. I'm using an 18 Ohm source resistor, because that's close to what the article use and thought it would be safe since I'm using 15v+/- source. I'm having trouble calculating the Rs value. __________________ I build, therefore I am. Do not create problems where there are none.
 7th April 2019, 10:07 PM #50 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain what's voltage across 18R __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

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