I am one of the many awaiting that day when J2 schematic is released....no hurry, just to be prepared. I have the outputs safely stashed away, and was thinking of other needed parts to throw in stash.
Reading 6 moons review, I found this circuit tidbit: "The input stage uses parallel Toshiba 2SK170 and 2SJ109 JFETs for both the current source and the differential input." This got me itchy to make sure I have sufficient parts on hand in my Toshiba parts stash.
Does this above statement quoted from 6moons mean that for each channel I need (2) 2sk170 matched to not only each other, but to the 2SJ109, or does this mean to a pair of 2SJ109s? AND, since I have no 2SJ109 at all, I will need to substitute a pair of Toshiba J74 for each?
In short how many of which matched to which?
Last question, is there a suggested idss needed, or is BL version 7-8 or so good to go?
Thanks for any assistance to my preparations, it is much appreciated.
Russellc
Reading 6 moons review, I found this circuit tidbit: "The input stage uses parallel Toshiba 2SK170 and 2SJ109 JFETs for both the current source and the differential input." This got me itchy to make sure I have sufficient parts on hand in my Toshiba parts stash.
Does this above statement quoted from 6moons mean that for each channel I need (2) 2sk170 matched to not only each other, but to the 2SJ109, or does this mean to a pair of 2SJ109s? AND, since I have no 2SJ109 at all, I will need to substitute a pair of Toshiba J74 for each?
In short how many of which matched to which?
Last question, is there a suggested idss needed, or is BL version 7-8 or so good to go?
Thanks for any assistance to my preparations, it is much appreciated.
Russellc
probably wiser to leave answer to Pa , but anyway ..... though of him enjoying in evening's glass of wine and not interrupting to type something ...... 
BL , 7-8-9mA Idss is fine for everything
you'll need 2 pairs of 2SJ74BL for input LTP and one pair of 2SK170BL for CCS above it
damn clever Mithrandir :
speaking of LTP , you need JFets A and A' as first pair , B and B' JFets as second pair
then , you form positive input side of LTP from JFets A+B in parallel , and you form negative input side of LTP from JFets A'+B' in parallel .
similar applies for CCS above LTP , wishing to have same current CCS-es in both channels ; say that you have two pairs of 2SK170BL , with slightly different Idss.
Mark them as C JFet and C' JFet as first pair , D JFet and D' JFet as second pair.
Use C+D JFets in parallel for L channel (above LTP) CCS ; use C'+D' JFets in parallel for R channel (above LTP) CCS.
Cheers , Pa
BL , 7-8-9mA Idss is fine for everything
you'll need 2 pairs of 2SJ74BL for input LTP and one pair of 2SK170BL for CCS above it
damn clever Mithrandir :
speaking of LTP , you need JFets A and A' as first pair , B and B' JFets as second pair
then , you form positive input side of LTP from JFets A+B in parallel , and you form negative input side of LTP from JFets A'+B' in parallel .
similar applies for CCS above LTP , wishing to have same current CCS-es in both channels ; say that you have two pairs of 2SK170BL , with slightly different Idss.
Mark them as C JFet and C' JFet as first pair , D JFet and D' JFet as second pair.
Use C+D JFets in parallel for L channel (above LTP) CCS ; use C'+D' JFets in parallel for R channel (above LTP) CCS.
Cheers , Pa
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probably wiser to leave answer to Pa , but anyway ..... though of him enjoying in evening's glass of wine and not interrupting to type something ......
BL , 7-8-9mA Idss is fine for everything
you'll need 2 pairs of 2SJ74BL for input LTP and one pair of 2SK170BL for CCS above it
damn clever Mithrandir :
speaking of LTP , you need JFets A and A' as first pair , B and B' JFets as second pair
then , you form positive input side of LTP from JFets A+B in parallel , and you form negative input side of LTP from JFets A'+B' in parallel .
similar applies for CCS above LTP , wishing to have same current CCS-es in both channels ; say that you have two pairs of 2SK170BL , with slightly different Idss.
Mark them as C JFet and C' JFet as first pair , D JFet and D' JFet as second pair.
Use C+D JFets in parallel for L channel (above LTP) CCS ; use C'+D' JFets in parallel for R channel (above LTP) CCS.
Cheers , Pa
This:
"you'll need 2 pairs of 2SJ74BL for input LTP and one pair of 2SK170BL for CCS above it"
for EACH channel, right? The 170 sets do not need to match with the J74s?
Sorry if answer already implied and Im not quick enough to have caught it
I can get all 4 2SJ74BL matched if necessary, (for better sleep if nothing else) needed for each channel, and pair of 2SK170BL to match them as well. Or again do the 74s not need to match idss of 170s?
Thanks for info to help!
Russellc
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yeah ....... {4pcs of 2SJ74BL and 2 pcs of 2SK170BL}/channel
as I wrote about their function , it is clear - no need for matching SJ to SK , and with staying in mentioned Idss range for all of them , it's guaranteed that CCS is in proper relation with LTP
so sum will be {4 pairs of 2SJ and 2 pairs of 2SK} for stereo
hope I'm clearer now
as I wrote about their function , it is clear - no need for matching SJ to SK , and with staying in mentioned Idss range for all of them , it's guaranteed that CCS is in proper relation with LTP
so sum will be {4 pairs of 2SJ and 2 pairs of 2SK} for stereo
hope I'm clearer now
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You were plenty clear to start, me, I can mess up anvil with rubber hammer, especially ordering parts! Thanks for simplifying down to where even I most likely wont mess up!
Russellc
as far I understand Papa's arrangement , it is logical to have 4-5mA per each JFet in LTP
which means CCS of 16-20mA
you can make it of toilet paper roll or of old lemon , I don't care ........ as long it is pushing said current with attitude of proper CCS
which means - you can use 4 of these GR wimpies, in parallel
which means CCS of 16-20mA
you can make it of toilet paper roll or of old lemon , I don't care ........ as long it is pushing said current with attitude of proper CCS
which means - you can use 4 of these GR wimpies, in parallel
The real J2 seems to have around 10mA CCS current for the four J74 or two J109.
My experience is that the CCS current value from the two or three parallel SK170 or 370 influences the sound in a big scale.
10-8mA summed current gives softer music, great stage. More CCS current gives a more dynamic sound, more highs. Too much current over 15mA starts to be to sharp, taking away flair and stage.
Nevertheless, some preferred the 8-10mA, some the 15mA.
May be the CCS needed for a good sound depends also on the two SS in the OS.
By changing only the places, upper and lower SS, the distortion pattern changed.
So it is possible that the CCS current is to be made in "harmony" with the SS in the OS.
This is really some work!
and
None of our clones sounded better than or similar to the original J2, long live Nelson!
My experience is that the CCS current value from the two or three parallel SK170 or 370 influences the sound in a big scale.
10-8mA summed current gives softer music, great stage. More CCS current gives a more dynamic sound, more highs. Too much current over 15mA starts to be to sharp, taking away flair and stage.
Nevertheless, some preferred the 8-10mA, some the 15mA.
May be the CCS needed for a good sound depends also on the two SS in the OS.
By changing only the places, upper and lower SS, the distortion pattern changed.
So it is possible that the CCS current is to be made in "harmony" with the SS in the OS.
This is really some work!
and
None of our clones sounded better than or similar to the original J2, long live Nelson!
generg, thank you for sharing so many experiments with the SS/LTP/Aleph/etal over the years.
Anybody have wisdom concerning increasing 100R gate resistor a little to smooth any edges or adjust the balance to taste? Asking before I dis-assemble my own Jango-ized version once again. I can't imagine how 15ma would sound, mine with 8ma (albeit 9610, 200Rs) is very dynamic already.
Anybody have wisdom concerning increasing 100R gate resistor a little to smooth any edges or adjust the balance to taste? Asking before I dis-assemble my own Jango-ized version once again. I can't imagine how 15ma would sound, mine with 8ma (albeit 9610, 200Rs) is very dynamic already.
Thanks for additional input, want to make sure correct pieces are saved...I thought the idss was for each piece, not total for the 2 pairs of J74! Guess I should have asked what should individual idss (for each piece) be for these J74s, and individual idss for each piece of 170? Whew! I little bit of knowledge is dangerous thing, and I'm stretching to have the little bit here....
Thanks again and now that I am asking correct question for proper INDIVIDUAL piece, so I get Total juice number correct for these toshiba goodies!
Like I said, Anvil can be destroyed by me with rubber hammer...
Much appreciated,
Russellc
Thanks again and now that I am asking correct question for proper INDIVIDUAL piece, so I get Total juice number correct for these toshiba goodies!
Like I said, Anvil can be destroyed by me with rubber hammer...
Much appreciated,
Russellc
when speaking of Idss , that's always for individual piece
you can count that Pa is always using those centered aroundish 8mA for signal ones ...... which is evident if you make dissipation analysis , let alone fact that he wrote something like that here and there
what's sum current of CCS hanging above input LTP , that's unknown to me ....... all those J2s ,ending in OPLDF , were badly damaged in transport and already butchered of JFets by Evil Postmen ...... though I saved pair or two of Semisouths
though - I like 5mA through each individual (signal) JFet , so why not condemning ya with my own spoil-ness
you can count that Pa is always using those centered aroundish 8mA for signal ones ...... which is evident if you make dissipation analysis , let alone fact that he wrote something like that here and there
what's sum current of CCS hanging above input LTP , that's unknown to me ....... all those J2s ,ending in OPLDF , were badly damaged in transport and already butchered of JFets by Evil Postmen ...... though I saved pair or two of Semisouths
though - I like 5mA through each individual (signal) JFet , so why not condemning ya with my own spoil-ness
I see no problem to augment the 100R to 150 or 220R. And indeed it makes a difference with the sound.
Get extra SS jfet for backup, and having more Toshiba jfets in your drawer is a nice inventory. i just ordered another 8pairs of that tiny jfet 8mA from alweit. I'm pretty sure that Papa will keep going to use this little angel (devil).
isn't there a post saying that even a F7 clone will beat J2 originalNone of our clones sounded better than or similar to the original J2, long live Nelson!
just kidding, maybe i read wrong number behind.
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