"Man, I make a lot of money on Boogie problems!"
One is that you have a cabinet problem. If the glue is letting go along a seam or there's a crack in the wood you can get a rattle that is resonant to a certain note. You may have to take the chassis out of the cabinet and tap along all the seams with a small mallet to find it. With any speaker cabinet perhaps the most important thing is stiffness, or rigidity. If you look inside a Marshall 4-12 notice how they have a piece of wood that pins the front speaker baffle board to the back of the cabinet. If your combo has been banged, dropped or just old enough that the glue is failing you may have a mechanical vibration problem.
The other possibility is that you have a flaky solder joint or two inside the amp. Boogies have a printed circuit board jam packed with parts. Like most boards once the amp gets older and past warranty the heating and cooling of the tubes has flexed the solder points with expansion and contraction. They can start to go intermittent. If the joint is just barely making contact then vibration can cause the connection to "buzz" with a note. When you run an extension speaker it's far away enough that it won't pass vibration on to the chassis.
The way to diagnose it is to open up the amp and prop it up so you can see the innards. Make sure you don't have the amp resting on the tubes! Use pieces of wood or something to make sure the tubes are hanging in the air. Hook up a speaker and turn the amp on. When it's warmed up take a wooden dowel or some kind of non-conducting material and gently tap the circuit board while listening for noises in the speaker.
DO NOT USE A PENCIL! The pencil lead is a great conductor and the voltage can travel up the pencil and bite you!
If it is a bad solder problem you'll hear noises when you tap. Unfortunately, usually you can't isolate it 'cuz the vibration goes through the whole board no matter where you tap. This is where a tech would flip the board over and touch up every solder joint he can see. In most Boogies, getting the board flipped over is good for an hour's time right there. They are really a PITA to work on!
Actually, I just thought of a third possibility but it's really a long shot. The effects channel usually works with shorting jacks, so that with nothing plugged into the effects jacks the signal goes through the shorting contacts to the power amp. Jacks can build up a thin oxide on their contacts over the years that makes the contact a bit dicey. You can check this one really quickly! Just take a guitar type patch cord and jumper the effects in/out jacks. This takes the shorting contacts out and the signal passes through the patch cord. If the problem goes away then some contact cleaner squirted into the jacks should fix things. Plug the cord into the jack a few times with some extra cleaner squirts to make sure you hit the contacts. Also, if you do this from inside the amp you get a much better angle on the shorting contacts. Wouldn't hurt to clean the channel guitar input jacks while you're at it.
That's all that comes to mind. Good luck and hope some of this is useful!
Mr. B, if the problem is ONLY with running the built-in combo speaker and you've swapped out the combo speaker then there are only 2 causes left, at least that I can see.Baconator said:
One is that you have a cabinet problem. If the glue is letting go along a seam or there's a crack in the wood you can get a rattle that is resonant to a certain note. You may have to take the chassis out of the cabinet and tap along all the seams with a small mallet to find it. With any speaker cabinet perhaps the most important thing is stiffness, or rigidity. If you look inside a Marshall 4-12 notice how they have a piece of wood that pins the front speaker baffle board to the back of the cabinet. If your combo has been banged, dropped or just old enough that the glue is failing you may have a mechanical vibration problem.
The other possibility is that you have a flaky solder joint or two inside the amp. Boogies have a printed circuit board jam packed with parts. Like most boards once the amp gets older and past warranty the heating and cooling of the tubes has flexed the solder points with expansion and contraction. They can start to go intermittent. If the joint is just barely making contact then vibration can cause the connection to "buzz" with a note. When you run an extension speaker it's far away enough that it won't pass vibration on to the chassis.
The way to diagnose it is to open up the amp and prop it up so you can see the innards. Make sure you don't have the amp resting on the tubes! Use pieces of wood or something to make sure the tubes are hanging in the air. Hook up a speaker and turn the amp on. When it's warmed up take a wooden dowel or some kind of non-conducting material and gently tap the circuit board while listening for noises in the speaker.
DO NOT USE A PENCIL! The pencil lead is a great conductor and the voltage can travel up the pencil and bite you!
If it is a bad solder problem you'll hear noises when you tap. Unfortunately, usually you can't isolate it 'cuz the vibration goes through the whole board no matter where you tap. This is where a tech would flip the board over and touch up every solder joint he can see. In most Boogies, getting the board flipped over is good for an hour's time right there. They are really a PITA to work on!
Actually, I just thought of a third possibility but it's really a long shot. The effects channel usually works with shorting jacks, so that with nothing plugged into the effects jacks the signal goes through the shorting contacts to the power amp. Jacks can build up a thin oxide on their contacts over the years that makes the contact a bit dicey. You can check this one really quickly! Just take a guitar type patch cord and jumper the effects in/out jacks. This takes the shorting contacts out and the signal passes through the patch cord. If the problem goes away then some contact cleaner squirted into the jacks should fix things. Plug the cord into the jack a few times with some extra cleaner squirts to make sure you hit the contacts. Also, if you do this from inside the amp you get a much better angle on the shorting contacts. Wouldn't hurt to clean the channel guitar input jacks while you're at it.
That's all that comes to mind. Good luck and hope some of this is useful!