Son of ben q1, why use a trimmer?

[Locrian99]

Wouldnt it just make sense to make r5 12k. Is there any real reason not to so this?

 

[Robert]

As with any JFET in this configuration, it'll likely need to be tweaked depending on the parameters of your specific JFET.

That's much easier with a trim pot.

According to Benson all three JFET drains should be biased to 4.0VDC, I've updated the documentation to reflect this. It's worth noting that Q1 has been measured at around 5.0V on multiple originals, so as always, tweaking by ear will likely be necessary.

 

[Locrian99]

As with any JFET in this configuration, it'll likely need to be tweaked depending on the parameters of your specific JFET.

That's much easier with a trim pot.

According to Benson all three JFET drains should be biased to 4.0VDC, I've updated the documentation to reflect this. It's worth noting that Q1 has been measured at around 5.0V on multiple originals, so as always, tweaking by ear will likely be necessary

Alright. Yea the set the trimmer to 2k just seemed bizarre every time i did it. Like why not just put a 12k here and save 20 cents and the hassle

 

[AsaSenger]

Gives flexibility to tweak JFET bias points. Fixed resistors like 12k can simplify the design, JFETs can have significant variations in their characteristics, meaning fixed resistors may not achieve the ideal drain voltage (around 4.0VDC).

Raft Wars​