A few troubleshooting questions; intermitten buzz

[mattelliott]

Hi all!

I have a Ceriatone OTS100 that I assembled and am having trouble with some buzz.

I built the amp almost a year ago, and recently while playing, I hear a tube "pop" and then there is intermitten buzz for a few seconds. The buzz then just cuts out; it doesnt fade out. Also, there is no rhyme or reason to the timing of it. I've just noticed that the tube pops then sure enough the buzz comes back.

I know that there is the always present hum that every tube amp has, but this buzz comes in on top of that.

If anyone can give me advice on what to do, it would be greatly appreciated. Thank you all, and I look forward to the responses.

-Matt

[Chuck H]

That's an odd symptom. How do you know it's a tube "popping"? Perhaps there is just a pop noise as the problem starts. By the description I would guess that a nieghbor is doing a wood shop project or something and the noise is getting into your signal chain. Any other symptoms or specific activities that cause the problem?

[mattelliott]

Chuck,

Thanks for the reply. Perhaps I wasnt clear on the sound, "pop" might be wrong. Its more of a "ping". Its not from the speaker however, its more mechanical. I can hear it from the backside of the amp.

I play with single coils, so I thought that could be the problem, but after switching to humbuckers, its still the same. The sound is heard best while an overdrive pedal is on, as then it is a lot louder. I keep a laptop in my room, as well as a LCD TV. I thought it could be radio frequencies, but it didn't amplify the usual beep or hum that I get on radio frequencies.

Also, I pondered the pedal chain. I troubleshot every pedal, first isolating it as the only pedal, then in conjuction with an OD.

Whats worse, is now that I've opened Pandora's box of "wait, is that it buzzing again?" I cant play it without worrying.

If you have any other ideas, I'd love to hear them.
Thanks!
-Matt

[olddawg]

Chuck,

Thanks for the reply. Perhaps I wasnt clear on the sound, "pop" might be wrong. Its more of a "ping". Its not from the speaker however, its more mechanical. I can hear it from the backside of the amp.

I play with single coils, so I thought that could be the problem, but after switching to humbuckers, its still the same. The sound is heard best while an overdrive pedal is on, as then it is a lot louder. I keep a laptop in my room, as well as a LCD TV. I thought it could be radio frequencies, but it didn't amplify the usual beep or hum that I get on radio frequencies.

Also, I pondered the pedal chain. I troubleshot every pedal, first isolating it as the only pedal, then in conjuction with an OD.

Whats worse, is now that I've opened Pandora's box of "wait, is that it buzzing again?" I cant play it without worrying.

If you have any other ideas, I'd love to hear them.
Thanks!
-Matt

Do you have access to a dummy load? You could then listen for mechanical noise while observing the amp. I suspect a heat expansion issue for the ping. For the buzz it could be tube rattle or the OT. If you have a bad load it could cause it with a resistive connection or partial short. Have you tried a different speaker cab and cable? Seriously, if you can use a dummy load you can stick your face in it with the pedals an amp dimed to see where it's coming from.

[mattelliott]

I dont have access to a dummy load, but I plan on building amps for some extra cash after I get out of college, so I can justify needing one.

Could tube rattle be the cause of intermitten buzz, I would think that it would buzz all the time if that was the case. Same with the OT. But I could be wrong. I also didnt think that the matched imedence speakers could cause so much trouble in the amp, after all, it is after the output.

Would the heat expansion do any serious damage to the amp? Ive noticed it still makes the ping sound while its cooling down also, if that helps.

I feel as though we are getting close, and I appreciate any input.
-Matt

Edit: Just took a look at cables, in case one may have gotten switched after a gig. Sure 'nuff, "live wire advantage instrument cable" in between the head and cab. I know it needs a speaker cable, but cant find mine, must have left it at practice spot. I'll replace it ASAP. But could this problem be because of the instrument cable? I've never seen such a big impact before...

[Chuck H]

Using an instrument cable shouldn't cause the problem you describe. What it could do is open up and leave your amp without a load (bad). You should NEVER run your speakers with an instrument cable. Especially with a 100 watt amp. If you don't have a speaker cable you should wait until you do before continuing.

I'm going with dawg here in that it's probably tube rattle. You probably need new power tubes. Try pulling the two inner power tubes and switching your impedance tap to half whatever your speaker load is. If the problem remains plug the two inners back in and pull the two outer power tubes. If one of these two procedures stops the problem you have a rattly tube. Don't forget to switch the impedance tap to the correct load when you put all the tubes back in.

[mattelliott]

Alright, ill be picking up another speaker cable today, and I agree that it shouldnt be the cause.

Along with tube rattle, could there be any other problems? Just to give you a better diagnosis, I do hear A LOT of rattling at higher volumes, I always assumed it was pictures on the walls or lightbulbs on the fan. I guess I feel like an idiot. Is there a surefire method to stop this if it is the problem?

Thanks again guys, yall are the reason there is still DIYers out there!
-Matt

[Chuck H]

Big bottles usually have to be REALLY worn out to rattle inside. Well, unless their Chinese. I've seen cheap chinese tubes rattle in less than a year.

It's not out of the question that there could be something else wrong. It could be that the wrong bias condition on one or all the sockets has caused the tube or tubes to wear prematurely. The bias should be checked when replacing tubes so a problem like this should reveal itself. There's been a rash of "matched" tubes being sold that don't match at all so I would check the current draw for each tube instead of the typical group reading.

As to replacing the tubes, read online reviews of available tubes. Any losers are usually identified pretty quickly. Don't go by the descriptions from the on line sellers or you'll just believe everything is wonderful.

[mattelliott]

Chuck,

Replaced the cable with a speaker cable. Also, I put the head cab on a table, and put the speaker cab across the room. Not noticing the buzz right now, but Im going to dime it for a few hours and wait to see what happens.

Sure, the neighbors will hate me, but if its the best interest of tube amps, I'll take the heat.

Is it possible that speaker cab resonance was causing all this trouble?

-Matt

[Chuck H]

The speaker vibration will exacerbate the problem. You might even get away with the long distance method your trying. But in the long run tubes behave somewhat mechanically to their electronic function so any microphonic tubes will be problematic.

[mattelliott]

I hear you on that. I have tried to rebias the tubes, and low and behold, they were way too hot. Also, I put the head back on the speaker cab, and the problem came back. The vibrations are definately the cause of the problem.

I have no doubt that at least one of the tubes are microphonic, which is a bummer, but I've been looking for a reason to try out something other than JJs.

Thank you all very much, your help has made a happy musician even happier.
-Matt