Members amp_surgeon Posted June 25, 2011 Members Share Posted June 25, 2011 We can't diagnose the problem by listening to a clip. You're going to have to do a little work here. Have you tried running it with the speaker out of the cabinet like both Phil and I suggested? Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted June 25, 2011 Share Posted June 25, 2011 Tried the link to the clip on two different days now - both times, I get a "it seems you don't belong here" error message. Go back and re-read amp_surgeon's troubleshooting suggestions (I missed that earlier, or I would have just quoted it with a "This" added - good post! ). Get the speaker out of the amp and see if the problem goes away. If it doesn't, then it's either the speaker, or something wrong with the amp itself. Most likely, the speaker... but that's based on your description. Like I said, the link didn't work for me, and I have no idea what it sounds like. But if the problem goes away, it's most likely due to the speaker vibrations causing something else on the amp or cabinet to sympathetically resonate. If you decouple the speaker from the amp and cabinet, the noise goes away because you've removed the source of the vibration. Tighten up the amp chassis and cab and the problem usually goes away. Unless the issue is with the speaker, or its mounting. Which we've already told you how to test. Or maybe it's a preamp tube that's on the edge of being microphonic, and when you crank it up, it's giving you a weird sound. Check out erksin's suggestions on things that might be vibrating. It's just a process of trial, error and elimination. Check everything that could be causing the problem until you locate what is causing it. Start with the likely stuff, and the tests that tell you the most first. Like taking the speaker out of the amp and listening to it when they're connected only by the speaker cable. Oh, one thing that really works well, but you need to do it with the levels reasonably low... a stethoscope. Really. Be careful (don't hurt your ears!), but they can be a BIG help in trying to track down the source of a vibration problem. Link to comment Share on other sites More sharing options...
Members 11 Gauge Posted June 25, 2011 Members Share Posted June 25, 2011 Oh, one thing that really works well, but you need to do it with the levels reasonably low... a stethoscope. Really. If you don't have the bones for a "proper" one, a piece of small diameter hose (NOT garden hose, but fuel line or something) makes for a good "hillbilly stethoscope." I used one for years for diagnosing engine noises - isolating valve tapping, connecting rod noises, even EFI problems. It's amazing what you can isolate with one. Link to comment Share on other sites More sharing options...
Members JMR Posted June 25, 2011 Author Members Share Posted June 25, 2011 Thanks guys! http://dl.dropbox.com/u/33345922/jmr%27s%20amp%20problem.mp3 this link should work! Link to comment Share on other sites More sharing options...
Members falseswipe Posted June 25, 2011 Members Share Posted June 25, 2011 I had a problem with buzz/rattle a while back and eventually found that it was actually the wall outlet cover behind my amp that was making such a loud racket when hit with low frequencies. It's a longshot, but maybe this applies to you? Link to comment Share on other sites More sharing options...
Members Jules-RM Posted June 25, 2011 Members Share Posted June 25, 2011 Heh, similar thing. I was pissing around using a speaker cab, then changing the tubes... I finally traced it to the plastic surround in the overhead lights. It's always good to keep a spare set of tubes on hand anyway. I'd get another set, and if it doesn't end up being that, then just put em away until you need them. Link to comment Share on other sites More sharing options...
Members The Great Waldo Pepper Posted June 25, 2011 Members Share Posted June 25, 2011 Take the speaker out of the amp - thus decoupling it from any source of mechanical vibration. Connect the amp and speaker with a long (10' or so) speaker cable. If the vibration goes away, it's possibly in the amp (tubes, baffle board, etc.), and not the speaker. If the noise is still there and definitely coming out of the speaker, you may have a rubbing voice coil - just because the speaker doesn't have a visible "tear" in the cone doesn't mean it is healthy... You said it first! Link to comment Share on other sites More sharing options...
Members andreas Posted June 25, 2011 Members Share Posted June 25, 2011 Indeed - a rubbing voice coil is not something you can visually see. It's easiest to detect with the speaker in the cab (so it sits in the "playing" position) - simply push (carefully) on the speaker cone to make it move in/out. If you hear a rubbing sound, that's the problem. Link to comment Share on other sites More sharing options...
Members juri Posted June 25, 2011 Members Share Posted June 25, 2011 Sounds like a bad tube to me (like it's misfiring), I say try replacing the tubes first. You can have someone else play your amp and then you look at the tubes while he's playing my guess is you might see the tube in question move with the noise. Another thing you can do is tap the tubes with a wooden chopstick and listen to see if one of them is micro phonic or not. Link to comment Share on other sites More sharing options...
Members JMR Posted June 25, 2011 Author Members Share Posted June 25, 2011 Alright, just checked that and one of my preamp tubes is very microphonic and one or two of my power tubes is microphonic. The speaker checks out - no rubbing sound. Link to comment Share on other sites More sharing options...
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