Burning Amplifier BA-1

[Dennis Hui]

You are using j109? If so, that's the wrong part. You are trying to replace
the 2sj109 (dual p channel jfet) with two j109, which is an n-channel jfet.
That won't work as-is.

 

[Zen Mod]

aha!

I was rushing today, so I understood question was about pinout arrangement - 2 x 2SJ74 instead of 2SJ109


silly ZM ...... Dennis got it .......

 

[Dennis Hui]

I also originally thought the question was about the pin out and was about to
write that it looked fine.

I looked at the photo more carefully and saw they are not toshibas.
Then I remember that j109 is an n-channel jfet...

 

[cubicincher]

Fairchild J109 not the same as Toshiba 2SJ109

I also thought in the beginning of my BA-1 build that I could use the Fairchild/OnSemi J109 (n-channel).

Was a 'little mistake'.
Then I had the luck to find a pair of original Toshiba J109BL.
Two JFETs (p-channel) in a single pack.
Greets Dirk

 

[cubicincher]

Again mistake. Toshiba 2SJ109BL
I am tired and not really concentrated.
Sorry!
Dirk

 

[cobar53]

Thank you

Thank you for the help. I recall seeing 2 single items occupying the space that the original dual Toshiba item did. I have seen the original for sale. Is this the only way to go, as the BOM says that it is not required? Wayne

 

[Zen Mod]

either one 2SJ109BL or a pair of 2SJ74BL or a pair of LSK74B

last ones - see in Store

 

[cubicincher]

to COBAR53

Hello COBAR53,


as ZenMod wrote you can replace the TOSHIBA 2SJ109 (BL-grade)
with

TOSHIBA 2SJ74 (BL-grade) pinout is: D-G-S
or
LINEAR SYSTEMS LSJ74 (BL-grade) pinout is: S-G-D!!!


I tried to make a sketch that hopefully explains how to insert two 2SJ74 or
two LSJ74 into the pcb instead of one TOSHIBA 2SJ109.
Observe the different pinout of 2SJ74 and LSJ74!
Check the pic. I hope i made no mistake.


Greets
Dirk

 

[cobar53]

Thank you

Thank you for the assistance. I will seek that method

 

[drjbf1]

I have just re-read the original BA1 article and notice that the front end schematic is different from what has been used here. The original is below and has the Out terminal connecting to the feedback network of the LTP instead of the feedback being local coming from the drain of Q203 as shown the the schematics in this thread.

My question is: if I wanted to employ global feedback over the local, will the original version of the schematic work?

 

[ItsAllInMyHead]

Hello COBAR53,


as ZenMod wrote you can replace the TOSHIBA 2SJ109 (BL-grade)
with

TOSHIBA 2SJ74 (BL-grade) pinout is: D-G-S
or
LINEAR SYSTEMS LSJ74 (BL-grade) pinout is: S-G-D!!!


I tried to make a sketch that hopefully explains how to insert two 2SJ74 or
two LSJ74 into the pcb instead of one TOSHIBA 2SJ109.
Observe the different pinout of 2SJ74 and LSJ74!
Check the pic. I hope i made no mistake.


Greets
Dirk

Hi Dirk!

Hope all is well. I have been confused about this for some time. I've accepted that I can't read a mechanical drawing properly (apparently I wasn't the only one confused). However, I believe that the pinout for the Toshiba and LS parts are the same. Thankfully, I caught my first error with some help before destroying parts. The stress from de-soldering the parts was enough to convince me to get one of those little testing thingamawhatsits that shows the pinouts. I installed my first set of genuine Toshibas incorrectly In all my following builds, I've used the same orientation / pinout for the parts with success... maybe just luck.

Someone with more experience than I should confirm definitively!!!! My only advice is to pause prior to implementing until a smarter brain chimes in. I'm often incorrect.

Here is a nice discussion that can explain more properly.

https://www.diyaudio.com/forums/the-diyaudio-store/243148-jfets-linear-systems-4.html#post4306123

Edited to add - I believe the pins when viewed from the "flat side facing you and pins down" is D-G-S for both left to right.

 

[cubicincher]

to ItsAllInMyHead

I am rechecking.


Greets
Dirk

 

[cubicincher]

to ItsAllInMyHead

Linear Systems datasheet says clearly 'from top'.


Toshiba datasheet shows pinout from 'legside' or bottom side?-I think



I am not 100% sure! I f I am back home, I will put those devices again in my

tester.
But I am not at home. Perhaps tomorrow.

 

[ItsAllInMyHead]

Hi Dirk,

To me, the LS data sheet is a bit more obvious. You are correct, that the lower rendering on the Toshiba data sheet is looking at the device from the bottom vs. the top. So, when it's "flipped over", you can see that the pinout is the same as the LS device, and is the same DGS configuration.

 

[cubicincher]

to ItsAllInMyHead

Yes, it's confusing!


I measured a Toshiba SJ74 and a Linear Systems LSJ74 with my older DCA75 and with the newer DCA75Pro.
Only the 'gate' can be detected. 'source' and 'drain' are called 'symmetrical'.
So: some more confusion.


Greets
Dirk

 

[cubicincher]

For me there is a difference, if you look from top or from bottom?



Greets
Dirk

 

[cubicincher]

Is my three-dimensional imagination confused?
Greets
Dirk

 

[ItsAllInMyHead]

See if this may help. Also... again... a wiser mind than mine should chime in.

 

[Zen Mod]

OK, I'm old and with bad attention level , but - what is a question ?

 

[Zen Mod]

......