Ampeg SVT 3 pro snapping and popping sounds

[xtian]

Follow-up: If I plug my signal into the Power Amp IN jack, I get the same cracking symptoms. AND, the TUBE GAIN control still makes it worse when clockwise.

The schematic would be a bonus, but I'm going to flip the PCB anyway and go to work. There are definitely more than one bad solder connection on this nasty old nag.

[xtian]

I flipped both PCBs and found half a dozen cold joints, including pin 1 on both ends of the main jumper that provides B+ to the power amp!

Still have the crackling. With a bit more chopsticking, I think I have found another cold joint I missed: C4 is really sensitive to wiggling. Gotta pull the board out again.

[xtian]

Yup, I missed cold joints on C4 in my visual inspection (on closer look, the cold joints were visible, no doubt about it). All issues solved, amp running well.

Bim, hope you get your problem sorted! My bet's on cold solder joints.

[MarkusBass]

Anyway, the schematics I've found (Index of /~kmg/files/schematics/ampeg/) do not show the TUBE GAIN circuit at all. I can't find it.
Anyone have a schematic that shows the TUBE GAIN circuit?

If you open the SVT-3_PRO.pdf file, the TUBE GAIN circuit is shown on the first page, top-left corner. Please take a look at Q1 transistor and J9 header. This is the TUBE GAIN circuit. Only the pot is missing. But I think it is just connected between the header and the ground.

Mark

[xtian]

Thanks for that, Mark!