Mini Booster Gain Control

[rockhorst]

Yes I did a search, and yes I got some info from it...But still my questions have not been fully answered   So here it goes:

I very much like the AMZ Mini-Booster. Usually, I build it without the source capacitor C6 of the first JFET, to lower the gain. I like how nicely clean it sounds then. However I would like to have the option of a little more grit. I tried this by substitutin a pot for R5 but this only gives a tiny amount of extra gain when maxed. Would adding the capacitor to the potwiper give a range from very clean to full grit? (see picture)



This is the gainstage from dragonfly's adaptation called the Golden Dragon. Looking forward to building it BTW.

From what I've found, the value of C6 is chosen to eliminate audible frequency roll off and doesn't matter for the amount of gain (as long as there is a capacitor). Is this correct?

[Davelectro]

It should work.

C6 is a bypass capacitor while C5 is the one filtering RF.

[rockhorst]

Okay, so that didn't work exactly   (notice that I didn't ground the pot in the previous diagram...come to think of it, that might've worked...?). I sorta figured it out now, but I still have some questions/doubts. The effect has been boxed, so I want to be pretty sure what to do, next time I open it up . I'll explain with the following adaptation of the original schematic:



Diagram A Standard mini booster JFET connections, no gain control

Diagram B The gain control I've implemented at the moment. Problem: noise when turning the pot (sorta like a wind sound and a SHO crackle). Especially as the pot gets to the end of its sweep, where the resistance approaches 0. It starts somewhere below the 'stock' resistor value of 1K. I guess this is to be expected, though I don't fully understand why. I'm happy with the gain range though, from almost completely clean to a nice gritty OD.

I'd like to remedy the noise the pot makes as it is turned, with the least number of modifications. I'm thinking of adding a 1K-ish resistor just before the pot, to ensure a minimum resistance. Would that kill the noise?

Diagram C Adaptation from gainstage of the AMZ MOSFET booster. Would this work (well) in the minibooster circuit?

If someone could either tell me which is the best solution or give me a deeper understanding of the JFET gain stage (or both), it would be greatly appreciated.

[Davelectro]

I think the gain pot on your first scheme must connect to ground (just as in Fuzz Face's fuzz control, for example).