Suitable jfet for an zero GNFB amp?

roender · 27th November 2008, 07:45 AM

Characteristics:

low noise
Yfs > 10mS
zero Ids (Vgs) drift with temperature at any current in the range of 2...8mA

There is such device?

h_a · 27th November 2008, 08:44 AM

2SK170/2SJ74
2SK369

However there's no data on temperature dependence of drain current in the datasheet.

Have fun, Hannes

EDIT: I just saw your RMI-amp uses the 2SK170; so what is your particular interest, the zero tempco for ID? I don't remember that spec in any jfet datasheet, but I only have the abbreviated pdfs.

john curl · 27th November 2008, 08:48 AM

I don't think this will have 0 tc Too much transconductance. You need about 0.7V bias voltage to get 0 tc, and a 170 will not get you there easily.

roender · 27th November 2008, 08:56 AM

Quote:

Originally posted by john curl
I don't think this will have 0 tc Too much transconductance. You need about 0.7V bias voltage to get 0 tc, and a 170 will not get you there easily.

Zero Tc for k170 is at 13...14mA but at this current is has very high transconductance and it not sound good.

bogdan_borko · 27th November 2008, 09:50 AM

Quote:

Originally posted by roender
Characteristics:

low noise
Yfs > 10mS
zero Ids (Vgs) drift with temperature at any current in the range of 2...8mA

There is such device?

I don`t think you`ll easily find a jfet like that.
btw. I`m working on non-global-feedback amplifier and I`m using 2SK170BL/2SJ74BL in the input stage but with servo incuded.

roender · 27th November 2008, 10:01 AM

Linear Systems j308/j309/j310 maybe?

homemodder · 27th November 2008, 11:03 AM

Roender, you have mail, let me know if it works out.

Lumba Ogir · 28th November 2008, 12:56 AM

Roender,

Quote:

zero Ids (Vgs) drift with temperature at any current in the range of 2...8mA There is such device?

There is not (on this planet).

AndrewT · 28th November 2008, 10:25 AM

Feucht wrote a paper on temp coef of Jfet.
I seem to recall he said the Vgs should be 800mV above Vpinchoff for closest to temp comp.
Then the CCS is set up to ensure it too has temp comp at the required current.

roender · 28th November 2008, 11:36 AM

Quote:

Originally posted by AndrewT

I seem to recall he said the Vgs should be 800mV above Vpinchoff for closest to temp comp.

VGS = VP + 0.63V for zero TC
http://www.tkhifi.com/div/Erno_Borbe..._articel_1.pdf

27th November 2008, 07:45 AM	#1
roender diyAudio Member Join Date: Sep 2006	Suitable jfet for an zero GNFB amp? Characteristics: low noise Yfs > 10mS zero Ids (Vgs) drift with temperature at any current in the range of 2...8mA There is such device?

27th November 2008, 08:44 AM	#2
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	2SK170/2SJ74 2SK369 However there's no data on temperature dependence of drain current in the datasheet. Have fun, Hannes EDIT: I just saw your RMI-amp uses the 2SK170; so what is your particular interest, the zero tempco for ID? I don't remember that spec in any jfet datasheet, but I only have the abbreviated pdfs. __________________ fresh matched IRFP240/IRFP9240 fets \|\| AlephJ/JX-kits F5 transistor kits \|\| Burning Amp BA-1/2/3 transistor kits

28th November 2008, 10:25 AM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Feucht wrote a paper on temp coef of Jfet. I seem to recall he said the Vgs should be 800mV above Vpinchoff for closest to temp comp. Then the CCS is set up to ensure it too has temp comp at the required current. __________________ regards Andrew T.

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27th November 2008, 08:48 AM	#3
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	I don't think this will have 0 tc Too much transconductance. You need about 0.7V bias voltage to get 0 tc, and a 170 will not get you there easily.

27th November 2008, 10:01 AM	#6
roender diyAudio Member Join Date: Sep 2006	Linear Systems j308/j309/j310 maybe?

27th November 2008, 11:03 AM	#7
homemodder diyAudio Member Join Date: May 2006	Roender, you have mail, let me know if it works out.

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