new build troubleshoot

[yunger]

i changed r8,r9,r11 with measured, new, 1w carbon films. i also reflowed solder on all surrounding locations. no change in noise.
is there anything theoretically wrong with having a voltage divider in this location? i thought it was a common location, esp since r8 cuts the head off of really high frequencies.

[yunger]

do i even need to cut signal before the second triod? i don't have a scope nor experience to know where the amp is breaking up. i suspect that i am getting pure power tube distortion after reading about the nature of cathode biased el84s w/ no negative feedback. could i move the voltage divider after the second triode?

[yunger]

don't know if anyone is reading this (long thread) but, i put a 470pf across the plate resistor of v2 and noticed a reduction of what seemed to be a seperate, faint hiss. the noise i'm trying to kill is a much more overbearing wushhhhhhhhh.
maybe i should start a new thread for this issue.

[loudthud]

You don't have a whole lot of gain before the voltage divider. You might try removing the voltage divider but installing a resistor between pin 2 of the tone control and pin 3 of the volume pot. Something between 220K and 470K will get you back to the same amount of attenuation.

[yunger]

thanks loudthud. that sounds cool. i'll giv'er a try.

[yunger]

to close out this super long thread:
i ended up adding a temporary cap and vol pot between the preamp and pi. turns out the preamp is as clean as a whistle when maxed, so it is driving the pi and/or power amp into distortion. cutting the signal after the preamp also significantly drops noise. i think i'll find the right values that get me to a good balance of clean/crunch and be done with it. great learning experience. i'm grateful for all the help and patience here.

[Grun]

You could try reflowing solder joints. I've had bad/cold solder joints cause a little noise on one of my builds. I would reflow a section at a time with fresh solder and then listen to the amp.