General jfet power problem

[mnordbye]

I've recently had a hard time getting 4,5V to my new builds, from a standard 9V supply that i always use. I use 100K trimpots (tried others also), but the power at the FET (J201s mainly) never gets down to less than about 8,3V. I've tried it on the breadboard too, but same there. Also tried using resistors, had to go all the way to 1M to get it to 4,57V. What can be wrong here? I've had a hard time building lately, due to this..

Any help appreciated.

[MohiZ]

Maybe the JFET isn't conducting, and there's too little drain current. Check the connections. Do you have the problem on a particular build or all of them?

[mnordbye]

I've tested different JFETs. Nothing changes.

I've just noticed that the 1M pulldown resistor at the start of the circuit is actually not 1M, it's 1K! Can this be the error here?

[alanlan]

You need to change the pull down resistor anyway, but it could be that your source resistor is too high which will result in a lower nominal drain current (ID).  You would then have to use a larger drain resistor to pull down the drain to the required voltage.

[darron]

when you get the 4.5v to the bias, does the circuit act as it normally should?

what i might suggest that WILL give you the voltage you need, is to tie one outside end of your pot (100k or 500k) to positive and the other to negative, then have the voltage you want coming off the middle wiper. the trimmer will then give you an almost full range sweep of voltage with what you want being somewhere in the middle.

see how that goes?