FirstWatt J2

[Syl20m]

Hi All,
thanks for your advises.

i have a quad of 2sk170 matched at 8,1mA and a quad of 2sj74 matched at 8,94ma, i ll keep them for another build then .
End i will try to get GR ones, or go for linear system ones.
thanks!

 

[Syl20m]

by the way would it be ok , if the sum of both k170 from R channel = sum of both K170 of L channel? instead of having all 4 mached .

thanks!

 

[Zen Mod]

yup

 

[Syl20m]

Thanks zen mode,

and same principle works for the sj74 in replacement of the 2sj109 ?

 

[JeffYoung]

Nope.

You want the two SJ74s matching within one channel, and the same for the other. Matching between channels is less of an issue.

Cheers,
Jeff.

 

[Syl20m]

thanks all,
so if i sum up :

for the Sk170:
sum of both k170 of R channel = sum of both K170 of L channel -> that is fine if no match Quad or Pairs in hands for R and for L channel !

For the Sj74:
matched pair for R channel , and mached pair for left channel -> is the way to go !

Cheers,

 

[Nelson Pass]

You want to have the two halves of the differential pair reasonably matched.

By this I mean that the parallel + input pair and the parallel - input pair want to
have a summed Idss within about 1 mA of each other. It is by no means critical,
as we are not looking for DC offset precision, and that's adjustable in any case.

Within each pair, it's nice to have some degree of matching, but again not essential.

For a project like this, obsession with precise matching is an esthetic choice.

 

[rothko]

Hi,
Is there any method to check that 2sj109 is genuine or fake?
I have got 2sj109 and 2sj74 from Aliexpress in cheap price.

 

[gadut]

Hi,
Is there any method to check that 2sj109 is genuine or fake?
I have got 2sj109 and 2sj74 from Aliexpress in cheap price.

cheap & aliexpress are not good signs

 

[mordikai]

Hi,
Is there any method to check that 2sj109 is genuine or fake?
I have got 2sj109 and 2sj74 from Aliexpress in cheap price.

you're probably good, proceed!
I get all my rare and desirable parts from aliexpress, I keep wondering when the rest of the world is gonna catch on.

 

[EUVL]

Check Idss and Vp and compare to datasheet.
http://www.linearsystems.com/lsdata/others/JFETs_The_New_Frontier_Part1_by_Erno_Bordely.pdf
Fig, 5.

Remember to reverse polarity for P-JFET.


Wish you LOTs of luck,
Patrick


PS I have yet to find a source in China for genuine 2SK170BLs and 2SJ74BLs for the last 3 years or so.

 

[rothko]

Thank you! Great paper for understanding JFET.

 

[twitchie]

@rothko, if you haven't caught on yet, it's almost guaranteed your Toshiba devices from Aliexpress are fake. Supply of genuine 2SJ109 and 2SJ74 Toshiba have dried up long ago unless you want to buy from known sources at about $10 USD for J74 or you can buy Linear Systems LSJ74 from the diyAudio store (or Linear systems).

If by some miracle you get your devices and they measure like real Toshiba jfets please let us all know and if they are fake please let us all know as well.

 

[TonyTecson]

i use this tester to verify components, this meter can identify depletion mosfets, and tells you if what you have is an enhancement type....

YouTube

 

[samoloko]

there seems to be confusing about Input differential pair for original J2 and schematic that Patrick proposed
original has x 2 quantity of j74 from Patrick schematic, etc parallel pair for + phase and parallel pair for - phase

 

[NicMac]

If anybody needs 2SK170 GR-grade I still have some matched quads up for sale (see link in my signature). Those <6 mA are gone, but there are some left which are pretty close.
Genuine Toshiba devices of course.

 

[EUVL]

They need 2SJ74GR for the J2.
Interest for genuine Toshiba 2SJ74BL curve tracer matched quads for J2

The 2SK170BL that were use in the FWJ2 is only as a CCS for the input LTP.
No need to match, only to trim for current.


Patrick



Patrick

 

[thompsontechs]

Love this J2, running it out of the PC to Singxer and HoloSpring Kitsune to DIs and they are singing even built for 8R running around 6R probably dropping to 4R.



Near field 80db half volume from PC



It's the little amp that could!

 

[thompsontechs]

Awesome J2

Love this J2, running it out of the PC to Singxer and HoloSpring Kitsune to DIs and they are singing even built for 8R running around 6R probably dropping to 4R.



Near field 80db half volume from PC



It's the little amp that could...


Thanks Papa the best sound, I've heard to date!

 

[vdi_nenna]

Wicked.