Ampeg SVT 3 PRO crackling and popping

[Davis]

Hey everyone. I have had an ampeg SVT 3 PRO for about 4 years. I am noticing when I play that once and a while the signal crackles and pops then cuts out for about 30 seconds, then floats back for another few seconds then clips again. While it is crackling the peak LED is flashing. I have replaced all my tubes (they needed changing anyway) and the problem is still there. I noticed the amp is quite warm when this happens. The air blowing out of the vent is also quite warm.

I was thinking maybe some biasing needed to be done, but the signal generally sounds decent when its not crackling and popping. Ive spent too much time over the board pulling my hair out, and need another opinion. If anyone can offer some wisdom on this problem, that would be amazing!

[Mark Black]

Due to the intermittent nature of the symptoms my first thought is cracking solder joints - most especially at multipin board interconnect headers, but also at any component which is PCB and also chassis or heatsink-mounted (jacks, switches, controls, LED's, power transistors, etc.). Any component which is large or produces heat can be involved as well, and there can be other spots which just got a bit "missed" during the wave-solder process.

I base this on previous experience with SVT-3 PRO as well as other modern Ampeg amps. The factory soldering is not great and about 3-5 years of heat-cycling & gigging is when the problems start to show up.

Of course there can be other issues as well, but my feeling is that until you retouch the solder joints at those areas you can end up needlessly chasing intermittent problems for a long time.

My personal preference is to scrutinize the aforementioned areas with a magnifier lamp and if I find any cracked (or just suspicious) joints I start going after all of the "usual suspects" while at the same time scanning for any others in less usual spots.

I liken this approach to replacing the plugs, rotor, & cap (plus points & condenser in the old days) first during an automobile tune-up. At least you know what it's NOT.

Best of luck!

[Davis]

Thanks a lot! Im on my way this afternoon to our jam space for an intense interrogation session with my amp.

[jmaf]

My personal preference is to scrutinize the aforementioned areas with a magnifier lamp and if I find any cracked (or just suspicious) joints I start going after all of the "usual suspects" while at the same time scanning for any others in less usual spots.

Poking around with the ubiquitous chinese chopstick is my favorite in case the magnifier lens doesn't reveal anything.

As taught by Gerald Weber I keep chopsticks on all the benches.

Another suggestion: tubes! Crackling can mean bad tube too... Good luck!

EDIT: Maybe it's obvious but I made this mistake once: use dry WOOD chopsticks! First time I did this I used a wet used pair that I thought I had dried 100%...not a good idea. Get a few new ones still wrapped in paper envelopes from some china fast food place.

[DivAud]

Sounds like the person who suggested inspecting the solder connections either works in a MI repair shop or owns one. I would follow the logic there, intermittent problems with this amp are almost always caused by poor solder joints or cracks. Resoldering all the controls, connectors, jacks, heavy objects soldered on the PC board, and or hotspots on the board will at least rule this out as a failure, and will probably fix this amp.

If you are not comfortable doing this, take it to a shop that has a good reputation and have it serviced. If you accidentally leave a solder bridge on this amp while resoldereing it, it could cost you !!!!!!