NJFETs for microphone amplifier.

[gentlevoice1]

Hi all,

I'm currently looking into suitable NJFETs for a microphone amplifier and hope you may help with some input as to which NJFETs may be suitable for connecting directly to the microphone capsule. I'm looking for a very linear, very low input capacitance, transconductance around 2 - 6 mS at ~ 3 - > 7 mA, NJFET. The ones I've found/tried out so far have been:

LSK 189
SK 222
BF 245C

I also have some 2SK170s & LSK170s that I will try out but I would be most interested in a tip on NJFETs that are considered "superb" for condenser capsule impedance conversion with a low capacitance microphone capsule ...

One such NJFET could be the 2N3819, however, I haven't found a place to source the ONSEMI version - which seems to have a much lower input capacitance than e.g. Fairchild's 2N3819. Anyone knows where to find the 2N3819 from ONSEMI in low amounts?

Thanks for any help - & a somewhat early, yet nevertheless, Merry Christmas to you ;-)

Jesper

 

[ln76d]

Try also 2n5457 and let me know what you think
There were TI 2n3819 on ebay in a small amount.

 

[gentlevoice1]

Try also 2n5457 and let me know what you think
There were TI 2n3819 on ebay in a small amount.

Hi - & thanks for the feedback. I'll try the 2N5457 as well then. In the meantime I also found the 2SK246GR, 2N4416 & MMBJ202 which (albeit a bit high in NF for the 2N4416 & another use I guess) could be interesting ... Might  there be other suggestions before I order some?

You mention 2N3819 from TI: I searched on the internet and they seem to have similar data as Fairchild's 2N3819 version - i.e. a bit higher capacitance than OnSemi's version. Do you consider them otherwise to be more interesting than the OnSemi version?

Cheers 

Jesper

 

[Khron]

Vishay/Siliconix J305's are also very low capacitance JFETs - Jim Williams of Rode used them in the (original) NT2 and possibly NT1, as well as recommended them for other mic mods / upgrades. 

They seem to be a few euros a piece on eBay

 

[ln76d]

You mention 2N3819 from TI: I searched on the internet and they seem to have similar data as Fairchild's 2N3819 version - i.e. a bit higher capacitance than OnSemi's version. Do you consider them otherwise to be more interesting than the OnSemi version?

Cheers 

Jesper

No, i don't know?!?
Doesn't Neumann used Texas version?
It's always Texas not Fairchild, so you can make comparision

2SK118 ("Condenser Microphone Applications")
http://pdf.datasheetcatalog.com/datasheet/toshiba/1026.pdf

2SK30 - used in many AKG microphones (0/O, Y, GR)
http://datasheet.octopart.com/2SK30A-Toshiba-datasheet-101654.pdf

BC264 - used by schoeps

 

[gentlevoice1]

@Khron & ln76d: Thank you both for your suggestions and comments ... Unless one the other members here comes up with a suggestion for a NJFET that is "indeed very interesting" I think I now have sufficient ideas to move on with some trials.

Thanks again for your tips & have a good weekend when you get to that 

Jesper

 

[midwayfair]

2SK30 is low capacitance. Get the GR bucket for gain a little closer to 2SK170; the other designations will be lower gain (which is fine if you're testing 2N3819).