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8th October 2012, 06:09 AM  #3591 
diyAudio Chief Moderator

P.S. If you can't find very good matches because just six, use the lesser IDSS one in a channel pair as the one with g,s pins going together in same node.

8th October 2012, 06:14 AM  #3592 
diyAudio Member
Join Date: May 2008

Hi
How much close we need to match jfet to put two in parallel in the B1 circuit ? Thanx Paul Last edited by tessier; 8th October 2012 at 06:44 AM. 
8th October 2012, 06:49 AM  #3593 
diyAudio Chief Moderator

Don't do it, its not a proper B1.
P.S. IDSS is only indicative of Vgs(off), Yfs, those are not exact in each die for even same ID. And then you got two different housings trying to follow in each position each other thermally and double the Ciss making it slower, leads and traces... no cigar, no real B1, you lose much more than in a GR B1. 
8th October 2012, 07:13 AM  #3594 
diyAudio Member
Join Date: May 2008

Hi
Ok, no paralleling. But anybody know how much more thd wen using 2SK170 with only 5 ma IDSS in the B1 ? Thanx Paul 
8th October 2012, 07:17 AM  #3595 
diyAudio Chief Moderator

Depends on signal level a lot too. Someone has got to make or simulate GR and BL B1 then FFT from min to max level so to speak in numbers.

8th October 2012, 07:29 AM  #3596 
diyAudio Member
Join Date: May 2008

Hi
I use Ltspice but the 2SK170 model do have a IDSS of 10ma .model J2sk170 NJF(Beta=59.86m Rs=4.151 Rd=4.151 Betatce=.5 Lambda=1.923m Vto=.5024 Vtotc=2.5m Cgd=20p M=.3805 Pb=.4746 Fc=.5 Cgs=25.48p Isr=84.77p Nr=2 Is=8.477p N=1 Xti=3 Alpha=10u Vk=100 Kf=111.3E18 Af=1) How can we change this model IDSS to 5 ma ? Thanx Paul 
8th October 2012, 07:37 AM  #3597 
diyAudio Chief Moderator

Lower Beta to 30m then Vto, until you will see 5mA for a k170 g,s shorted to gnd off a 9VDC source.

8th October 2012, 07:53 AM  #3598 
diyAudio Member
Join Date: May 2008

Hi
Here is the new model for the 2SK170GR, it have a IDSS of 5.04 ma. with a 9 volt dc source. .model J2sk170gr NJF(Beta=30m Rs=4.151 Rd=4.151 Betatce=.5 Lambda=1.923m Vto=.4274 Vtotc=2.5m Cgd=20p M=.3805 Pb=.4746 Fc=.5 Cgs=25.48p Isr=84.77p Nr=2 Is=8.477p N=1 Xti=3 Alpha=10u Vk=100 Kf=111.3E18 Af=1) Thanx Paul Last edited by tessier; 8th October 2012 at 07:55 AM. 
8th October 2012, 07:51 PM  #3599 
diyAudio Member
Join Date: May 2008

Hi
I've done Ltspice simulation of the B1 using those two model to compare. The BL type of 2sk170: .MODEL 2sk170 NJF (VTO=5.211e001 BETA=3.683e002 LAMBDA=4.829e003 IS=1.000e009, RD=0.000e+000 RS=0.000e+000 CGS=5.647e011 CGD=2.562e011 PB=4.860e+000 FC=0.5) The BR type of 2sk170: .MODEL 2sk170b NJF (VTO=4.911e001 BETA=1.983e002 LAMBDA=4.829e003 IS=1.000e009, RD=0.000e+000 RS=0.000e+000 CGS=5.647e011 CGD=2.562e011 PB=4.860e+000 FC=0.5) I simulated with a 1 volt 1 khz signal at the B1 circuit input. Adding a low pass filter capacitor at the input did cut a lot the thd of the BR type of 2sk170. Thanx Paul Last edited by tessier; 8th October 2012 at 07:57 PM. 
8th October 2012, 08:07 PM  #3600 
diyAudio Chief Moderator

With 24V supply its probably able to go near that as Vpp out max. What does with 2VRMS which is a typical digital source? Some go 3VRMS, what ever. Can you post the .asc so I get to see the details?

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