Jfet bias question

[ildar]

Does the bias point of a jfet "drift" over time?
My Thunderchief was set properly at the drains when I built it  a bit more than a year ago. I never really used it much (though I love its sound), but last week I dug it out, popped in a new 9v, and it sounded farty and gatey. Do I need to rebias?

[burnt fingers]

Did you use tirmmers like the schematic suggests?  I'd double check those voltages again and look at the trimmers.

Scott

[petemoore]

  I seemed to notice that JFet circuits Drain node voltages "drifted' like you're saying.
  could be the trimpot 'moved' or something else changed...but at least what you've typed isn't a 'lone misnomer'...I know what you're talking about.

[brett]

Hi.
might be a poor solder, too.
For the extra few cents, sealed trimpots are a good investment.
cheers

[ildar]

I did use trimpots, the blue ones from Mouser.
The drains were all set at the time I built it, as I said. If one of the trimmers moved, would it affect the circuit like that? Since I didn't use it for quite some time, I'm wondering what could have changed?

[trevize]

it happened to me too

i realized that it was because i wasn't using a power supply adaptor but a battery. a bettery changes over time so the trim pot position should change over time.

bias your circuits with a good p.supply and always use that one! (or use a 78LXXX positive regulator in your circuits)