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B1 Buffer Jfets alternatives question
B1 Buffer Jfets alternatives question
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Old 20th January 2016, 09:04 AM   #1
Fatech is offline Fatech  Romania
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Default B1 Buffer Jfets alternatives question

Hello

What jfets alternatives are without modifying original setup? I try to simmulate in Electronic workbench with bf861B but i think spice model of bf861B is faulty...may i use j310 without modifications ?

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Mircea
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Old 20th January 2016, 11:41 AM   #2
MASantos is offline MASantos  Portugal
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the lsk170 is available at the diyaudio store, any reason why you wouldn't want to use those?
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Old 20th January 2016, 12:55 PM   #3
Fatech is offline Fatech  Romania
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its expensive compared with bf861 or bf862
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Old 20th January 2016, 01:44 PM   #4
Dennis Hui is offline Dennis Hui  Canada
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B1 Buffer Jfets alternatives question
Here's a spice model for BF862:

http://www.nxp.com/documents/spice_model/BF862.prm

Hope this works for you.

Dennis
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Old 21st January 2016, 09:39 PM   #5
Fatech is offline Fatech  Romania
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thanks
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Old 13th November 2019, 08:39 PM   #6
umut1001 is offline umut1001  Europe
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B1 Buffer Jfets alternatives question
Hi.Long time passed but i will build 3 B1 boards for myself at buffered PLLXO for my project and i have another 5pcs B1 buffer preamp PCBs for another projects.Is there any new and/or available Jfet for using on B1 buffer?
There are 8pcs of 2sk170bl per board and i sold my 2sk170bls many years ago and nothing left to me
And i do not want to buy these 2sk170bl at expensive price and also there are many fakes around.
I need 100pcs of JFETS for B1.I can make modification of SMD parts and it is better if there are leaded genuine parts around.(there are many BF862 sellers on ebay but i do not trust many of them)
Any suggestions?Maybe J111 ?
Thanks and regards
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Old 13th November 2019, 08:45 PM   #7
TungstenAudio is offline TungstenAudio  United States
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Perhaps the J113 will meet your needs. The latest version of the B1 Korg is shipped with matching sets of J113s and source resistors.
It is also worth mentioning that Linear Systems is making good quality LS170s in B grade. Much easier to find than the NOS Toshiba parts.
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Old 13th November 2019, 09:38 PM   #8
umut1001 is offline umut1001  Europe
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B1 Buffer Jfets alternatives question
Hi.Thank you for your answer.LSK parts are also expensive.I have many projects with B1 buffers and i do not want expensive parts.I am very happy i can find an alternative to 2sk170s.Should i connect 10R resistor to source of J113s after matching them?Thank you again.
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Old 13th November 2019, 09:53 PM   #9
Dennis Hui is offline Dennis Hui  Canada
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B1 Buffer Jfets alternatives question
The source resistor will depend on the Idss of your parts. Apparently even for j113
the Idss can be quite high. For example, in the ACP+ project for BAF, the selected j113
parts were paired with 125 ohm source resistors to get a current in the 10mA range.

Note also the pin assignment of j113 is different from the Toshibas.
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Old 13th November 2019, 10:50 PM   #10
TungstenAudio is offline TungstenAudio  United States
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Just as Dennis says.
More specifically, the source resistor is chosen to set the quiescent current through the JFet pair to about 60% to 80% of the Idss. First the JFets are matched as buffer pairs, then for corresponding stereo locations. In a buffer pair, the JFet with slightly higher Idss is used in the top position. The source resistors may be chosen to keep quiescent currents approximately the same, and may be adjusted over a range of values. (The pinch-off voltage of the JFets may also affect this, but this is above my level of understanding.)
There have been recent discussions in several threads, including the ACP+ thread, as well as the B1 Korg thread.
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