Inexpensive JFET Preamp

[Salas]

I was very surprised at the low idss range of the 2N5462.

Possibly fake parts?

 

[HKC]

Possibly fake parts?

salas I don't think they are. I ordered the parts from Mouser and they are within the idss specification but all of them at the lower range.
They were Fairchild JFets.

 

[Salas]

Do they have some IDSS class distinction like the GR,BL,V of Toshiba 2SK170 so you can order a specific IDSS range?

edit: I looked it up. No they don't. But they are made from enough manufacturers. So maybe one make with happier general IDSS can be spotted. This P-JFET has different (more) noise than 2N5459 N-JFET. That does not matter?

 

[lineup]

Yes, salas.

Different manufacturer may have some producing lines
that get some bit lower IDSS.
Another year, they may get higher IDSS.
It is not constant the quality of semiconductors produced.

 

[Josip_Del]

Can I just ask? Can I put 10uF on output instead of 5uF

 

[lineup]

Yes you can.
Problem can be when we take less than 5uF (4.7uF).
But more capacitance can even be good.
10uF will be just fine.

 

[Josip_Del]

And one more can I use 2N3819? I presume I can. But I ask smarter

 

[lineup]

I would not replace the 2N5459 with 2N3819.
Because they would not be a good match with the 2N5462.
We better keep using 2N5459 and 2N5462.
These were chosen to work well together.

You can try. And see if it works.
There will not be anything dangerous happen if you try 2N3819.
But it may not work good.

 

[Josip_Del]

And again one more. In the schematic Voltage + or - whatever is always connected on drain of jfet or? Thanks for 2N3819, that why I ask smarter

 

[Josip_Del]

Could someone tell me in that schematic which is D which is S. I presume S is the one closer to the mark of G.

 

[lineup]

Could someone tell me in that schematic which is D which is S.
I presume S is the one closer to the mark of G.

You presume correctly.
See my attached diagram.

 

[Josip_Del]

Thank again Lineup, now I have all the info

 

[jonusgrumby]

Good luck with the preamp.

I've had good luck with mine and it still works fine.

The drain and source are interchangeable on these parts, but hte other posts are correct. Changing the input capacitor is not a problem.

 

[Josip_Del]

The last one question? R1 is resistor or pot, can pot be 10K

 

[jonusgrumby]

It is a pot, the center terminal goes to the gate. Anything from 5K to 25K will be fine.

 

[Josip_Del]

Thanks jonusgrumby