Loud Pop When Going Into Standby on 5:50 - with Solution

[MattG]

I bought my Express 5:50 new about a year and few months ago. The last couple of weeks it has developed a loud Pop! when going into Standby. It does this with no guitar plugged in, on either channel, and the volume knobs rolled all the way to off. I've also unplugged the EFX loop. The amp is in the 50W setting. Now that I'm thinking about it, it seems the Pop! was always there when going into Standby when on the 5W setting, but never the 50W setting. I don't use the 5W setting much and figured it was due to the funky configuration of the power tubes in this setting.
The amp sounds wonderful and I don't notice anything else strange, except when switching into Standby.
I swapped out the power tubes. The problem remains, although I cannot vouch for the tubes I had on-hand; it's possible they have the same problem.
Any help/ideas is much appreciated.
Thanks!
Matt

 

[Newysurfer]

Well not being an amp tech I can't really help you Matt.
Except to say that I don't have any pops on my 5:50 - 5w or 50w.
I changed tubes 6 months ago and had no issues before or after

 

[MattG]

Update: I can now say that the tubes are not the cause of the problem. I bought a set of power tubes last night and it still goes Pop! quite loudly.

 

[vbf]

My 5:50 pops using the standby switch. I mic my amp at church so the pop is a bad thing. I don't use it but when I know the mic is off or we're between services. The pop is annoying but I think it has to do with the kind of switch it is. everything Mesa uses is high quality and built to last and the switches are no different. I have a feeling any type of switch would make some sort of noise. I agree that it's very likely not the tubes.

 

[Don]

My 5:50 doesn't pop. I'd suspect a resistor.

 

[soundchaser59]

My 5.25 doesn't ever make any sound when I go into or out of standby. But my other non-Mesa amp pops.

 

[MattG]

I thought I'd be a good Boogie Boarder and post my solution.
I spoke with Mesa support a few times and eventually decided to take my amp to a warranty service center. The amp tech looked through the amp and ... didn't find anything wrong. He agreed that the pop was not right, however, and ended up installing a capacitor across the Standby switch. The pop! is now gone.
So not exactly as satisfying as find the smoking gun, but the problem is now gone. He didn't tell me what cap he installed, but almost any high-voltage cap would work to dampen the spike.
So my guess is that it could still be the switch. He told me that he swapped the lugs between the Power and Standby switches to check this, but the results were the same. I guess he didn't see any signs of arcing. Not sure what else it could be.
So if you're in the San Diego area and need amp service, I would recommend Top Gear in La Mesa. He's got a sizable backlog of repairs so it could take a bit of time, but he does good work and seems quite thorough.

 

[a2dconverter]

Hey Matt..thanks for your info..

if your feeling brave, and happen to have your amp opened up, maybe you could take note or take a pic of the cap

seeya

Joe