# Marble Drive Bias



## PKRPedals (May 4, 2019)

Since I don't see anything in the build docs on biasing the fets, am I to assume that Q1, Q2, and Q5 are to be biased at 5v?
Thanks
Warren


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## Robert (May 4, 2019)

Bias at around 4.5V when in the 9V mode.


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## PKRPedals (May 4, 2019)

Thanks.
Warren


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## HamishR (Sep 29, 2019)

I have a heap of J201s i bought from Small Bear - Will this pedal definitely work with those or should I try 2N5457s or something?


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## PKRPedals (Sep 29, 2019)

I used the J201's and it sounds great. I'm sure 2n5457's will sound good also, I haven't tried them. Socket and try different ones to your taste.


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## HamishR (Sep 29, 2019)

Thanks!  I went with J201s because I don't like sockets for transistors.  I'll finish wiring it up tomorrow and see how my luck is!


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## zgrav (Sep 29, 2019)

Given the variations in some transistors, some folks use sockets and then lightly solder the transistors into the sockets after making sure they work as intended.


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## HamishR (Sep 30, 2019)

It's all together now and works.  The 201s biased easily (phew!) and all is as it should be.  Not a bad sounding OD.  I may tweak it to reduce the highs because it sure is bright.  As usual the board was easy to use and even survived my stupidly soldering the switch to the wrong side.


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## Chuck D. Bones (Oct 2, 2019)

Good to know I'm not the only one who has done that.

For future reference, JFETs can be screened prior to assembly.  The JFETs with the highest Vp will have the most headroom and gain.  With 9V power, we don't want Vp to be much greater than -3V.  Real J201s will be -1.5V or less.


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