Just finished a blues buster as part of a combo build. All the controls, pots and switch, are working except the gain pot. There is a varying amount of gain when the knob is turned but unlike, say a tube screamer there’s always a decent amount of gain present even at the bottom of the rotation.
I ran a jumper to C8 with good results and the gain pot is acting more like I would guess it should act. Is this correct? Sorry, although I have built about 60 DIY pedals, I have a very limited understanding of schematics. Thanks in advance for your help.
I think the video demo shows the type of tone I was able to achieve with a strat or les paul.
If using higher output pickups than that you will have less available cleans without rolling back the guitar volume.
Alternately I would visually recheck resistor values and reflow solder joints (some look suspect) and if you have an audio probe you could quickly find any trouble spots to focus on. The Guides Page has links to making one and using one.
go thru the circuit a component at a time, check voltages to ground on each side.. often the resulting disturbance is enough to show the problem component if you’re monitoring the circuit while checking voltages. anywhere that looks suspect, check it for a cold joint. it isn’t as hard as it seems, and can often quickly find the issue.
the gain pot isn’t supposed to go all the way to off, btw. look at the schematic and how the components connect. in order for it to go fully off, the ground pin of the pot has to go directly to ground, in this case its more of a variable resistance in the feedback loop of the opamp. different resistances will get different levels of gain. its common to see up to 1 meg pots in this application, but only if the circuit can support it.
that said, i found the gain pot came to life by replacing r6 , the 3.3k resistor, with a 1m one. more gain, nice sweep and seems to open up the tone some more. do this at your own risk, of course.