JFET suitable for new design

[Ranchu32]

Hi guys... sorry for the slightly off topic question...

We've been discussing the merits of using a JFET as the input transistor in a conventional 3 stage Class B design.

http://www.diyaudio.com/forums/soli...fier-based-rod-elliot-p3a-36.html#post3917178

Are there any modern day replacements for the venerable 2SK170 (either through hole or surface mount) with suitable specs (e.g. generous gate-drain voltage) that are widely available?

 

[EUVL]

2SK209 (SMD version of 2SK117), LSK170, BF862, 2SK3557-6, 2SK2394-5, -6, ......
Plenty of choices for N-JFETs, especially in SMD.


Patrick

 

[Zen Mod]

LSK170 in Store

 

[EUVL]

For new design no need to be restricted to 2SK170 or LSK170.
Can be easily designed around.

2SK209 is an excellent part, and available from Mouser, etc.


Patrick

 

[29285]

There are some Sanyo types as well. I think Sanyo has been acquired by ON-semi meanwhile.

 

[EUVL]

There are some Sanyo types as well. I think Sanyo has been acquired by ON-semi meanwhile.

"2SK3557-6, 2SK2394-5, -6, ......" are all Sanyo (On Semi).


Patrick

 

[jcarr]

As I have written elsewhere, the Japanese manufacturer Isahaya Denshi still makes several types of P and N JFETs, in both leaded and smd packages.

J-FET(FIELD-EFFECT TRANSISTOR):SMD TYPE

J-FET(FIELD-EFFECT TRANSISTOR):LEAD FRAME TYPE

kind regards, jonathan carr

 

[Ranchu32]

Thanks Patrick. The 2sk209 looks interesting and is available from my local distributer - RS electronics. The Vgds on the others is too low to be useful in a power amp.

 

[AndrewT]

RS UK stock 2sk209Y
100 off for £19.80 + vat.

Unfortunately no GR and no BL.

 

[Ranchu32]

Very good point Andrew. Digikey had ample stocks of the BL rank transistors but I was hoping to avoid the high shipping costs.

 

[EUVL]

You can cascode the others to use in high voltage applications.
As I do all the time.


Patrick

 

[Ranchu32]

Understood, but I'd rather keep it simple unless there's a compelling reason to do otherwise.

 

[cochleus]

"Are there any modern day replacements for the venerable 2SK170"

Zen Mod gave the right answer in post #3. LSK170 (Linear Systems) is right here in the store, and is a direct replacement for 2SK170. 😎

 

[Algar_emi]

What would be the P-CH equivalent of the 2sk209?

 

[wrenchone]

I saw lots of interesting new jfet prospects the last time I searched the Mouser catalog, esp if surface mount is no longer taboo. There are some interesting prospects in small signal depletion mode mosfets as well - my current favorite is the Infineon BSS159. It comes in a surface mount package (SOT-23), but the Vgs part to part is pretty close, so I've been using siome in my current projects without doing any rigorous selection. The preamp board I'm currently using in my living room has them in two of its gain stages.

 

[wrenchone]

Oh, and one alternative to using N-channel and P-Channel devices is to play with current mirrors and an N-Channel differential input stage. One amp concept using that setup is shown in the "Le Mutant" thread in the Pass forum. It sounds pretty swell, but its swellness may in part due to the fact that by nature and design it is always in Class A mode. Discusson is welcome there.

 

[Sky63]

It is interesting - audio community is looking for more linear output transistor – SiC JFet, Mosfet, VFet, depletion, enhanced mode etc. But for input stages we are still using classic old low noise jfet`s. What about better linearity for input transistors? Small depletion mosfet`s are available as mentioned by wrenchone. Has somebody experience with this? Is here some benefit for sound?

 

[Bigun]

Perhaps? - It is usually the output stage linearity that limits us - because of the large currents driving the need to push the devices further up their characteristic curves. The input stage is easy to linearize with local feedback too. And for those who live in warm climes, Class AB is the name of the game and output linearity is clearly the challenge.