Can anybody help me with vox ac30 cc2x?

[asaffi]

I know this is going to be complex, but...After a couple years of use without any problems, my vox ac30 cc2x begun to pop loudly, as if I was making popcorn. Took it to two well known repair shops, they found nothing, and I personally saw the amp working there with no issues. They told me that the problem was in my house electricity, could be the wiring or the lack of grounding. But the problem here is: 1: If it is my house's problem, why did it beguin to pop just after some years of use? and 2: Why did it make the same noises in all the places i took it after the repair shops? The places were modern houses and apartments, built with proper grounding and etc. Can someone give me some light on the subject?

[asaffi]

I know it's gonna be somewhat complex but...I bought this Vox AC30 CC2x like 7 years ago, brand new, with no issues until now. It beguins to pop loudly, after about 5 minutes that I turned it on. Took it to two well know repair shops, that found nothing wrong, and I personally could see it working properly there, no popping. They told me that the problem was in my house electricity wiring, probably because of the lack of grounding or something. But the questions are: #1: If it "my house's" fault, why did it begin to pop jus now; and #2: Why does it pop to any other place that I tested de amp, another houses and modern apartments, with modern electricity wiring, grounding, etc?

[Mick Bailey]

How old are the tubes? The output tubes and rectifier especially get a fairly hard time in these amps and can give the problems described, though the preamp tubes can also fail. When I get an amp in that exhibits this type of problem my first action is to replace the tubes with my 'bench set' which are a known-good test set. If this fixes the problem I then eliminate the problem area by substitution.

Mains wiring would be way down on my list for popping. A mains fault would show up right away as soon as the amp was operated - not just after it had been on for 5 minutes. My experience of wiring and grounding issues with the mains is that hum or buzz are the main problems that arise.

[asaffi]

I get it, but how come it just pops when it's turned on in some places, and not in others?

[trobbins]

Temperature, time and physical re-location/vibration history are all plausible reasons for that query. Swapping out all valves also may help wipe the socket contacts - there are just so many possibilities that you need to work through the simplest tests first that localise the fault.

[g1]

Also, cel phones can cause weird interference problems that might come and go depending on reception. May not be a likely cause, but easy enough to rule out by turning off your phone.

[Enzo]

My dad had a tropical fish tank. There was a small heater in it, and the thermostat had a noisy thermal switch. Every time it went on or off, a loud noise radiated through the power lines in the house. Came out my amp.

When you use it at home, do you also have pedals and things connected? And did you set it up at the service shop EXACTLY the same as at home?

And I have to ask, have we tried other guitars and other cords?

Do ANY of the controls affect the sound of the noises in ANY way?

[TomCarlos]

So if I read this correctly....

You have had this amp for some time and the popping just started to occur - so something in the amp has gone bad or changed.

You take it to other locations and the popping occurs - so this eliminates your house wiring but for safety purposes you should be using "grounded outlet."

The problem always happens after 5 minutes or so? So this means something is heating up and causing the problem.

It was suggested you try some different tubes. But before then, if you put on some gloves or use a towel, can you gently touch a tube and do a light wiggle to see if you can get the popping sound to happen?

A secondary test is to pull the chassis out and tap around the circuit. But we are not sure if you are comfortable doing that.

As Enzo suggested, did you try a different cable or guitar? And I would suggest, can you test the amp with NO cable or anything plugged into the amp? Just turn the amp on, volume levels down.

I believe this amp uses one GZ34 Rectifier tube, three12ax7 tubes, and the four EL84 output tubes. If you remove the first two preamp tubes, do you still get the popping?

The idea here is to see if you can establish a pattern of when the problem occurs.

Schematic for the vox ac30 cc2x