I thought I had it!!!

"Man, I make a lot of money on Boogie problems!"

Baconator said:

So I was pretty certain that I had properly diagnosed the problem with my Mark IIC+ as mentioned in this thread: http://guitarscanada.com/Board/showthread.php?t=4255
I picked up a speaker from a fellow forumite and the same problem existed - albeit with a slightly different tone. I tried rotating a new preamp tube through all of the positions and had already tried different power tubes. Once again I tried connecting the amp to a 15" cab I have and the problem disappeared again. I don't have any other guitar cabs to try this with so and I'm frankly flummoxed as to how the amp would sound fine through a 15" cab but not through the combo speaker even when swapped out unless it's the speaker wire/plug. The only thing I can compare the sound to is a really scary sounding fuzz pedal with everything dimed and it fizzles with the decay of the note.

I'm going crazy here and will have to bring it over to someone who has other cabs to try it out with to see what happens. I'm going nuts over this and I guess I will have to take it into a tech, but if there's something else I can try first I'm all ears.

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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.

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!

Wild Bill, all I can say is :bow:

I haven't tried anything you've suggested yet, but suggestion number 2 definitely makes sense and I suppose number 3 is a possibility too. If I called you up and played the amp for you over the phone I'm 99% certain you'd agree with me - it definitely does sound like a loose connection issue - the fizziness of the sound tells me it ain't no loose cabinet. The loose connection theory also makes sense in that the noise actually seemed worse with the new speaker and I'm guessing this is because the speaker I installed has no (excuse my ignorance) 'dampening' material or gasket around the metal flange (hopefully you get the picture). The Boogie's speaker is front-mounted as opposed to many (most?) combos and the speaker has nothing between the metal of the speaker and the baffle which, I would imagine, could easily make the vibration of the circuit boards much worse.

It was the last thing on my mind last night as I was thinking about the noise, but what should I do about the lack of a gasket?

I've got a TPC wipe (contact cleaner) and will try the effect loop first since it's so easy to try. If it is just a matter of resoldering anything suspect I think I can take a stab at it. My soldering is actually getting prettu good after building four of the BYOC pedals . Don't worry - I wouldn't dare do this without some assistance from a friend of mine that knows all about discharging the filter caps!

Hmm . . . on second thought, I'll try bribing him with a case (or two) of beer to do it :tongue:.

Once again, thanks so much for your insights. Even if they prove to be wrong (although I doubt it) I appreciate the time you put into typing out your response.:food-smiley-004: :thanks5qx:

"Pay it forward."

Baconator said:

It was the last thing on my mind last night as I was thinking about the noise, but what should I do about the lack of a gasket?

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Nothing! If the speaker was designed without one then go ahead and mount it. A gasket is not going to fix the problem anyway.

Baconator said:

Hmm . . . on second thought, I'll try bribing him with a case (or two) of beer to do it :tongue:.

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More gets done in this world for beer than the entire federal budget! :tongue:

Baconator said:

Once again, thanks so much for your insights. Even if they prove to be wrong (although I doubt it) I appreciate the time you put into typing out your response.

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Glad to help, Mr. B. If we're lucky my suggestions will cure it. If not, well they had to be tried anyway. When you get a real spooky amp problem sometimes trying to hard to analyze the problem doesn't get you anywhere. You just have to wade in and try things step by step. That way you keep eliminating possibilities until the real culprit is flushed out.

It's hard for players to understand amp repairing, sometimes. If you've never sniffed solder yourself there's a tendency to think it's like fixing cars or other things mechanical. Cars can be spooky too but usually the problem is obvious. If the brake pads are worn out or the axle is broken you can see it!

Electronic parts normally do NOT burn up when they fail! You open up the amp and everything looks perfectly fine! You have to take voltage measurements and then sit back and try to figure out what would cause a measurement to be screwy. Once in a while I get a player who wants a firm estimate over the phone. How the heck could anyone do this? Only a psychic could tell what's involved with a dead engine without even popping the hood!

Me, I give "guesstimates" but make clear that they are NOT firm! I tell the player how much it will likely be if there are no surprises and if when I get inside the amp I discover something "scary" I stop and make a phone call to warn him and give him the option to keep going.

The nice thing is that there are so few good techs around that if I get an unreasonable customer I can play like Seinfeld's "Soup Nazi" and just tell him "No amp for you!" Those types I WANT going to a competitor! Best thing for me is for them to bother the competition and waste their time and money. I'm lucky to have developed a large group of customers that are also good people. I don't have to make them wait longer while trying to please someone who's demanding the impossible for the cheapest price.

A case of beer is a great price if you can arrange it! You're gonna quickly find that fixing your amp with this spooky problem will gobble up a lot of time. A professional would likely pare down his shop rate to give you a break but you're still looking at a lot of hours. Besides saving money you're getting some education. Learning about amps is always worthwhile! The next time someone is trying to sell you an amp you'll ask better questions. Like how much a PITA will a Boogie be to repair after the warranty is over and how much will that cost?

Since you can't get a good clean tone from most Boogies to save your soul most guys buy 'em for the crunch tones. The crunch channel circuit looks to me like a direct ripoff of Mike Soldano's SLO100. If you want just the crunch you can pick up a SLO for a lot less money than a Boogie and you'll pay less in repairs.

Me, I'd rather take an old JMP100 that has no master volume and set all the controls to 10! Go for that thick power amp distortion!

"Mississippi Queen", anyone?:rockon2:

Wild Bill said:

Like how much a PITA will a Boogie be to repair after the warranty is over and how much will that cost?

Since you can't get a good clean tone from most Boogies to save your soul most guys buy 'em for the crunch tones. The crunch channel circuit looks to me like a direct ripoff of Mike Soldano's SLO100. If you want just the crunch you can pick up a SLO for a lot less money than a Boogie and you'll pay less in repairs.

Me, I'd rather take an old JMP100 that has no master volume and set all the controls to 10! Go for that thick power amp distortion!

"Mississippi Queen", anyone?:rockon2:

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I got a great deal on the Boogie - enough so that as long as I don't end up paying more than $500-600 or so for the repair I can still sell it at a good profit at the prices they seem to be selling for. Mine's a Mark IIC+ circa '83-84 so I don't think Randall Smith stole the design from Mr. Soldano . I guess I'm a bit of an oddball, since I actually like the clean sound on the amp - it doesn't really do fender cleans and has no 'chime', but it works for me. I'd go for the Marshall too, but a) it would likely cost me about 3 times what I paid for the Boogie and b) I've never played a gig in which I could dime it as wonderful as it probably sounds. It's a great thing there's so many amps to choose from these days at such reasonable prices - at least until you get into the collector/ultra boutique markets. I've actually been talking with Scott from axeandyoushallreceive about possibly picking up a Mack amp - if they're as good as he says then for the price they're an insanely good deal.

Scottone said:

I'm sure that putting a high powered printed circuit board amp chassis in a compact combo cabinet seemed like a good idea at the time

Does the problem happen at all volume levels?

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Given the number of high powered cicuit board combos that still keep popping on the market it would appear as if the deluded thinking is still alive and kicking!

The problem only exists when I get the amp to (upper end) gig volumes. If I decided to build or buy a head shell for the amp and have a separate cab for the speaker (upon which I would obviously never place said amp head) I don't know if I'd ever hear that problem again. I had things turned up to 'loud, but not enought to really piss off the wife' levels tonight (i.e. at gig volume if you're playing in a really 'retentive' environment) and couldn't hear any problems. I think Bill nailed it on the head when he said it was related to vibrations, so now it's just a matter of finding out what's vibrating too much.

I had another friend of mine that used to work on guitar amps for a living that thought it might be something as simple as oxidized tube sockets. I'll try cranking things up again in the morning to wake up the kids - "GOOD MORNING VIET NAM!" :rockon2: God knows they've wakened me up enough times and will continue to do so for some years to come.