SOLVED Noisy Spectrum Control In AION Andromeda (ODR-1) Build

[debrad]

I recently came back to my AionFX Andromeda build and noticed that the "Spectrum" control has some scratchy noise at each end of the rotation (for the record, I don't recall this issue happening in the past with this build). This is much more noticeable with a combination of high Volume and low Gain. It's only there as you turn the pot and you can't hear it if you are playing while adjusting. It sounds like the effect is amplifying the moving contact of the wiper on the track but only for a VERY short range at the beginning and end of the rotation (there is a slight pop/thump when the pot transitions to silence.

I have tried multiple replacements so the noise isn't coming from a dirty or damaged B25k pot and I reflowed the solder at the pot connections so there is good connectivity.

Is it possible that this scratch/thump is just a function of the Spectrum control amplifying certain frequencies (I'm thinking of the "scratch is normal" aspect of the SHO boost) or is it more likely that there is an issue somewhere in the build?

 

[debrad]

Schematic is here in case that helps:

https://forum.pedalpcb.com/attachments/schematic-png.34078/

 

[debrad]

Just to close the loop on this one in case anybody runs into the same issue with their Andromeda or Nobleman builds...

Folks on the Facebook pedal forums focused in on stray DC on the Spectrum pot that didn't seem to be an issue. I also took a look at a number of components in the Spectrum path, tried multiple B25k pots (along with an A25k pot), cleaned the board, reflowed my solder, and examined everything I could think of that might possibly impact this noise...all with no improvements.

On the verge of giving up, I decided to swap out the 2N5088 transistor in the Spectrum path...just in case...and, guess what? Yes, the noise was completely eliminated. I guess the original 2N5088 was either damaged or not soldered correctly so fixing whatever was wrong there solved my problem!!