Jfet preamp

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b2

Well-known member
Joined
May 26, 2005
Messages
135
Location
Loire Valley-France
Hi,

I'm working on the Fred Forssel JFet mike Preamp,and I'm searching a
replacement instead of the 2SJ74 and the 2SK170?

Does anyone knows if there's a equivalent of thoses transistors ?

Because,I've got problem to get the 2SJ74 and I want to matched them so I must take a lot in BL series .

Merci,beaucoup .

Merci.
 
First of all, these transistors are still available in large quantities (and perhaps even produced - only the dual ones ore discontinued IIRC).

Second, you might use the search function and you'll find a company which makes a replacement. bcarso mentioned the company a few times.

OK, I do it for you: www.linearsystems.com

Samuel
 
Unfortunately, they have no good substitutes. Lately, lintearsystems has become a second source for the 2SK170, but their parts are no more acessible than the Toshiba ones.
 
Thanks for the infos about Linearsystems,for the LSK170, it's seems to be hard to find JFet.Because, I try to find Thoses 2SJ74 and 2SK170 at Radiospares and they don't have.

For this time,I'going to see how I can buy them at Linearsystems!

Merci.
 
Another grey market supplier is Chips Technology Circuits in New Jersey. They have supplied SJ74's and SK170's. PM me for address and phone (they are a bit backward---no website!).

These parts are just so much better than the substitutes it is well worth the trouble to get them. US P-channel parts are pretty low performance although usable with great care and a lot of selection. If you need low pinchoff though you are SOL.

I don't think Linear Integrated Systems is interested in making P-channel subs, at least as yet.
 
[quote author="bcarso"]Another grey market supplier is Chips Technology Circuits in New Jersey. They have supplied SJ74's and SK170's. PM me for address and phone (they are a bit backward---no website!).

These parts are just so much better than the substitutes it is well worth the trouble to get them. US P-channel parts are pretty low performance although usable with great care and a lot of selection. If you need low pinchoff though you are SOL.

I don't think Linear Integrated Systems is interested in making P-channel subs, at least as yet.[/quote]YES!!

I'm just a poor French Audio Man and I couldn't by 1000000000 units of thoses 2SJ74 and 2SK170 ,I'm too small To be a big big of LInearsystems!
And I need,low quantities of thoses equivalents ,substitutes of 2SJ74 and 2SK170 so I'm interested!
It's only to build a PROTOTYPE and to see if it works as good as I suppose??????????
if it's great ,I'll send you a Bottle of French Wine!!!! if you like????
Can you please give me,the contact.
Thanks.

Merci.
 
[quote author="jrmintz"]I see there are a couple of different types. What are the best ones to get?[/quote]

Hi,
well I read a very very nice paper about DIY DOA by Nelson pass and the Fred forssel paper too.

In thoses paper,Fred Forssel Jfet preamp design with 2SJ74 and
2SK170 explained that for matching pair it will be more interesting to take
2SJ74 and 2SK170 in Bl serie....

So,MANY THANKS TO Fred Forssel and Nelson Pass!!

Voila.
 
[quote author="jrmintz"]I see there are a couple of different types. What are the best ones to get?[/quote]

Various schools of thought on that. The higher Idss codes are preferred unless the dissipation, temp dependent leakage current, and low frequency noise at those higher currents is enough worse to negate the advantages of lower midband noise and higher slew rate (the latter very circuit dependent). It's a fairly weak power law as far as mid-high freq noise, going as the 1/4 power of drain current ratio, about. Borbely et al. have written about this somewhere. [edit: thanks Samuel :grin: ]

The Idss codes are letters representing colors, typically going from Y (yellow) through GR, BL, V. Y is the lowest and V is the highest.

The pinchoff voltage typically is lower for lower Idss.

Interesting thing about these FETs: Even the V parts have such low pinchoff voltage that it is usually not possible to bias them at the nominal zero temperature coefficient operating point. That is, even at Idss, that is, zero volts gate-source and enough drain-source voltage to operate out of the "triode" region, the parts have a positive tempco of magnitude of drain current. So they are not as useful for some applications as other FETs, such as low temp drift constant current sources.
 
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