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

Dennis Hui

Paid Member
2002-08-27 7:19 pm
Toronto, Canada
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.
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.

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
More specifically, 60% to 80% of the Idss of the follower. Often, the CCS device
is chosen to have a higher Idss - the bottom position Jfet.

And for Umut1001, the store sells the LSK170 B grade for less than the Toshibas,
and it is a very close match which will work fine.
Hi.I just found 80pcs of J212 NOS National brand from my friend almost for free :D
It writes for audio amplifiers on datasheet and also low noise.
Have not received them yet but i simulated on multisim and it seems ok for DCB1 board.I will just add 330R resistors to their source and it seems it will be ok then.


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Paid Member
2003-06-12 7:04 pm
Maine USA
> i simulated on multisim and it seems ok

It is hard to get "not OK" results with that circuit and signal voltages much lower than supply voltage.

However 1Meg is an uncommonly "easy" load. Even a foot of coax is lower impedance than that. Hang a 10k load on the output and see how the THD changes. (It might not change much?) Also look at the relative 2nd 3rd 4th 5th... harmonics, because higher harmonics annoy the ear more.
If found genuine BF862 which do you prefer?
J113 or BF862? Which one will sound better ?
Is there anyone compared them?
Thanks and best regards
FWIW, I built my B1 just more than 3 years ago using BF862s as drop-in replacements for the 2SK170s without any source resistors. The BF862s were still stock items at RS at the time. I matched the Idss values to around 16mA if I remember correctly. We compared my B1 with a fellow forum member’s B1 with original 2SK170s and could not hear a difference. My B1 is still in my main system and used almost on a daily basis. Mine is running on a rail voltage of 16V, but up to 20V is ok for BF862.