Pastel Preamp - low gain

[slowpogo]

I built the Pastel using the stock transistors. For my 2N6429s the hFE measures 725-750 so well within specs. However the gain level of the finished pedal is quite a bit lower than what I see in demos of the JHS Crayon.

In Crayon demos, with all knobs at noon you already have a very healthy distortion. With my build, I have to turn the gain knob close to 3 o'clock just to start hearing notable distortion. And the maximum gain does not gate nearly as much as the Crayon demos. However the distortion does sound exactly like the Crayon, just not nearly as much available.

I double-checked all my component values, everything is correct. I also tried several different J201s with no real difference. What might be going on?

 

[BuddytheReow]

Post some pics to be as transparent as possible. We might see something you don't

 

[slowpogo]

Think I solved it. I ended up putting 10k trimmer on R4, the Source leg of the J201. Turned out lowering the value to around 2.4k notably increased gain. Enough that any difference to the demos could be chalked up to pot tolerance.

JFETs seem really finicky this way. I had a similar issue when building a ssbs Mini clone, had to reduce a JFET resistor to get the bias knob range correct. I don't really understand how they work but it makes me wonder why JFET projects don't all have trimmers by default

 

[lowpitch]

Q1 is a unity gain buffer. A poorly chosen source resistor can negatively affect the output swing range of Q1 and thus provide less than unity gain, but there's a range of values that will work here and unless your J201s are out of spec or something else is going on, both 2.4k and 3.3k should be within that range. With that being said, if it works it works, so that's good