2SK30A JFET replacement ?

[MartyMart]

Hi All,
Has anyone replaced one of these with another type? same bias/pinout ?
they are used in Ibanez tube screamers/OD855's etc etc.
Help would be great on this one.
Cheers, ~Marty~

[mikeb]

Some info I've found suggests that a 2N3819 would work (not sure about the pin out), and from there a MPF-102 (listed in a few places as a sub for the 2N3819) would work also. Note - I haven't done a comparison of the FET characteristics of these devices.

Edit: a J201 should work also. Let us know if you try these out and they work ok - or not!

Good luck!

Mike

[Marcos - Munky]

Just a question, for what you need them? Maybe we can help if you tell the project. They are most used in electronic switches like the Boss and Ibanez ones.

[MartyMart]

Thanks for the info guys, its a long story but i was simply trying to repair an Ibanez SD-9 and also a TS-9 some weeks ago.
Was having problems identifying the fault, bypass was giving me slight breakthrough of distortion and fx "on" was fine, i knew it was a "JFET" switching issue.
RS components (UK) gave me a replacement match of the 2SK30A as SC1815, which i fitted and got `NADA~  !!  confused ? so i tried another pair thinking they were bad........
Anyway just found out from Steve at smallbear that the SC1815 is a totally different thing and will never work !!       thanks RS !!!
Olaf Nobis at "Banzai effects" has original 2SK30A's in stock, so they're on the way. . . . . . .phew.
When you get the facts right, it helps a lot eh ?
I'm a good "modder" but dont have enough experience to identify a part error from a company as huge as RS  !!!!   M.

[Fret Wire]

How did you make out on your SD-1 bypass leakage?

[MartyMart]

Hey Fretwire, just waiting for the correct JFETS !
thats all it was, there were no other faults on the board, used audio probe and DMM, it all seemed fine, just wasted my time with the damm SC1815........!!  Bad information is disinformation :-)  aaaarrrrgghhhh ( as they used to say in those small war comics of yesteryear )
Marty.

OOPS!  sorry i'm confusing SD-1 with SD-9  !  DUH !
yeah i need to change those JFETS too ! there's still noise, but its an old one from 1985 so i'm not surprised ! sounds great though !
M.

[Fret Wire]

Too bad the 1k resistor trick didn't work. Many times it does, it's easy, and most people have 1k resistors around. Of course when it doesn't, you have to order jfets.

[MartyMart]

Yeah thats a neat trick, does it apply to other Boss goodies? or is it perculiar to the SD1?  I dont remember seeing a pair of resistors like that in others but . . . . . . .
M.

[puretube]

replacements for those FETs where discussed here, too:
http://diystompboxes.com/sboxforum/viewtopic.php?t=23064&postdays=0&postorder=asc&start=0