JFET's Trim-pot value

[alienas]

Hi,
for J201, the trim pots are usually 100k, but there are out of stock in 1/4" here, so do you know if a 50k would be enough? I have J201 from different sources, not tested yet...
Thanks

 

[temol]

What circuit? What's the source resistor value?

 

[alienas]

Boogie monster for instance, between 1k and 5k....

 

[temol]

With 9V supply 50k should be ok. Only with Q3 you get closer to 50k. Q1,2,4 - probably below 30k.
All of this assuming you have transistors with Vp around -0.7 to -0.8V.

 

[alienas]

Great thanks Temol^^

 

[alienas]

If the B+ is higher, for the same source resistor, how goes drain res?

 

[temol]

If you want to keep drain voltage @ 1/2 supply you have to increase value of the drain resistor.
Here's an example (Q1). From left to right:
9V supply, V drain = 1/2 supply,
24V supply - same R drain as above,
24v supply, V drain = 1/2 supply



But there's more. Sinewave @ Q1. Green - 9V supply, blue - 24V, no R adjustment, red - 24V, R adjusted.



Seems ok, right? But then there's first stage frequency response - not so right.
Colors as above


It would be necessary to recalculate each stage in order to keep frequency response similar.

 

[alienas]

Great thanks man!