Trim Pot Values: I made a whoopsie

[Lytt Effects]

Hey all,

I did some digging but didn’t find anything that addressed what I need help with.

I’m in the middle of a build of the Super 64 (JHS Superbolt), which has three J201 transistors along with three trim pots. Two of the trim pots on the parts list are listed at 100K, while the third is listed at 50K.

I flubbed up and accidentally orders 5K trim pots instead of 50K pots, so I’m in need of some information on how much the trim pot value matters here. I’m a bit of a novice when it comes to circuit design and schematics, so outside of knowing what value needs to go where, I’m a bit lost.

I have 100K trimmers on hand, as well as the 5K that I accidentally ordered. What would happen when using one of these in place of the 50K that is called for? I have other builds that call for 50K trimmers as well, so I will be ordering some anyway, but I’m curious as to why one of these is 50K while the other two are 100K, and what may happen when using a 100K or 5K versus the 50K. Any help would be greatly appreciated. Thanks!

(Attached schematic for reference)

 

[giovanni]

The transistors all have different source resistors, so the corresponding drain resistor has to be different in order to get the correct biasing.

Edit: and 5K would probably not allow you to bias that stage correctly.

 

[owlexifry]

idk if it's gonna help or be worthwhile, but FYI - you can turn a 100K trimpot into a 50K trimpot by putting a 100K resistor across pins 1 + 3

if you are able to find the ideal bias point (resistance of the trimpot) you could replace trimpot with a resistor of the same resistance.

although it's a hell of a lot easier to just use the correct part depends what you have more of - time to waste, or patience for the right part.