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-   -   fetzer valve questions. (http://www.ultimate-guitar.com/forum/showthread.php?t=1566165)

T4ng3rine 10-03-2012 09:41 PM

fetzer valve questions.
 
I got a j201 JFET TRANSISTOR and I' ve decided to make a Fetzer Valve Preamp from ROG. Can I subtitute a fixed-value resistor to the trimpot in the schematic? If yes, What value...I'm gonna use a 12 wallwart to power the FV preamp and the power amp. Help please

end_citizen 10-03-2012 10:37 PM

You can use a resistor, but it is hard to know the right value. You could use a 100k pot temporarily wired in to the circuit. Find what works, and then put the right value in its place.

T4ng3rine 10-04-2012 04:10 AM

how do I wire the pot? Sorry still a noob at electronics.

end_citizen 10-04-2012 12:40 PM

Ignore the values in this image (I just used Google to pull something up).

http://www.gearslutz.com/board/atta...esistor-pot.jpg

Use a 100k pot, and the resistor should be about 4.7k. Once you have the pot to a spot that works, measure the resistance between the middle lug and the resistor. Then use the closest resistance value you have.

jenrg 10-04-2012 02:16 PM

Like already mentioned, it would be pretty much impossible to tell a resistor value that works without measuring. Jfets have so wide manufacturing tolerances that even if you'd find the right value for one particular Jfet, it wouldn't necessarily work even with another Jfet of the same type.


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