I just finished building Jake's Blue Magic. The circuit works fine, but I can't get the JFET drain voltage down to 4.7v as recommended with the 50K trimmer. The lowest I can get is about 5.6v. Any suggestions?
Also, any new suggestions as to capacitor values for the mid-boost switch? As with most threads I've read, the 530pf value doesn't seem to provide enough boost to hear any difference.
Any help would be appreciated.
Thanks, Russ
Which JFET did u use?
You could try a 100K trimmer?
Regards
RDV
The JFET is a J201, just as specified. In fact, I built it to GGG's parts specification exactly. That's why I can't understand why it won't bias correctly in its stock configuration.
Russ
Thank goodness you guys stay up as late at night as I do!
You could try a different J-Fet as there is a great deal of variance in them, or a 100K trimmer with the one you've got(assuming you didn't do any subs or make a mistake in parts placement). You could try a 1000pF cap & work your way up for the mid boost. It's good to socket certain components in these homebrew circuits, because the designer's tastes may differ greatly from your own.
HTH
RDV
Thanks Ricky Don,
I changed my J201 JFET out for another one, and with the bias pot at one extreme the voltage is down to 4.7v now.
Russ
It's amazing just how variable JFETs are. They are all over the map! That's why I almost always use trimpots on the drains on them things.