SOFTii Odd Volume/Treble Issue

[ThickMilkyGobs]

So I've finished a SOFTii build that works as expected, but I've got two odd issues:

1. If the treble knob is at 0, the pedal is silent

2. With a lot of gain and the stoner mode engaged, you get a splat-y tone when you dig into a note/chord

Audio Clip : https://voca.ro/jv6BZJFf0Dc

The transistors should be SMD MPF4393's, but I could be wrong, and I might try a set of 2n5457's later to see if anything changes.





I opted to not attach the DPDT for Stones/Stoner mode directly to the PCB, and used 6 long wires to connect it near the bottom of the enclosure. Could this be a possible source of problems?

I used to own a real Catalinbread SFT II, and it didn't have either of these... quirks. Anyone got any ideas? I can take some measurements of the transistors if need be.

 

[Robert]

If you have a DMM measure the resistance from Lug 1 of the Treble pot to ground.

Check the value of C7 and look for any shorts in that area... solder splash, stray wire strand, something touching the pot or PCB, etc.

It sounds like C7 is probably shorted to ground. This would cause the issue you're having with the Treble pot and could also affect the bias of Q5, causing the "splatty" sound.

 

[ThickMilkyGobs]

If you have a DMM measure the resistance from Lug 1 of the Treble pot to ground.

Check the value of C7 and look for any shorts in that area... solder splash, stray wire strand, something touching the pot or PCB, etc.

It sounds like C7 is probably shorted to ground. This would cause the issue you're having with the Treble pot and could also affect the bias of Q5, causing the "splatty" sound.

I took the guts out of the enclosure (going to rehouse it), and I checked C7's value and for shorts. It's the right value, and while I didn't see any solder splatter or stray wires, I did clean up the area anyway by lightly scraping away some flux near the solder joints with a sewing needle. It seems to function normally now! I'll update if I get issues when I rehouse it.