two fet stage, one trimmer...can be done?

[dschwartz]

hi all:
i´m planning to design a fet distortion, but don´t want to use a trimpot for each stage.

If the fets are properly matched, can i use 1 trim for all of them? should i still use drain resistors?

[nooneknows]

a minibooster like configuration is autobiasing (and I think it's sounds better) if you wanto get rid of trimmers

[wampcat1]

You don't have to use trimmers once you figure out what resistance your trim pot is using (providing it's biasing correctly). I use 15k's in place of the trim for fairchild j201's. Works great.
bw

[mojotron]

The beauty of the multiple trim pots is that you can tweak and tune the asymmetry of each stage. A mini-booster autobiasing idea will work, but you will not be able to tweak it and a cheap trimmer can be about the same cost as a 2nd JFET depending on the JFETs you use.

[d95err]

Use sockets so you can easily try differernt fixed resistors.

[dschwartz]

hmm personally, i dont like autobiasing.. and needs like 3 more resistors so is the same space used by trimmers..

the 15K idea sounds good..mixed with sockets for fets... but i still wanna tweak the bias a little...

i´ll make some simulations on livewire to see....

[frankclarke]

You can change the bias on a minibooster.

[Gus]

If you are going to DESIGN a Fet circuit why would you need a trimmer(s)

[squidsquad]

I guess this ain't 2 stage...but it popped into my head....a fun easy build.

http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html

SyRuPP

(2/3's down)

[mojo_hand]

If you know what the value's going to be (like the mention of 15K and J201s, above) you can do that, if you've tested your FET, done a little math, and know what to expect.  When I don't know what to expect, I just get it set right using the trim pot on a breadboard, then check the resistance of the pot & replace it with a fixed resistor.  Lower noise, cheaper, just an all-round better solution.  And I never run out of trim pots.