My New mark IV has developed a bad buzz.

[brianf]

My New Mark IV has developed a bad buzz.

It only happens on certain notes but it is a cab buzz. I took the casters off to make sure it was not them.

When I hit the offending notes and it starts to buzz, just resting my foot in the middle of the cab near the handle stops the buzz.

Even just a gentle press helps. It tried both tightening up the chassis and handle screws and even tried loosening them off a bit but the buzz is still there.

The amp is a wood version. Any ideas how to fix before I haul it back to the dealer for warrenty.

brianf

 

[Boogiebabies]

Are you playing on solid surface? If you are in an upstairs room, it could be a sypathetic vibration from your room. Try isolating it from the floor and see if it still buzzes. All of my stuff is in a bonus room above my garage. I have to use Auralex Gramma isolation risers to prevent the big buzz on certain cabinets. If I dont, they vibrate and rattle the whole room.

 

[brianf]

It's the amp for sure. It's in my music room which is buzz free. The floor is concrete with berber carpeting over it. It is the amp cabinet. I have the chassis screws loosened right off now and the buzz is gone. I'll find some dense thin rubber weather stripping type stuff to put around the edge of the chassis tomorrow at Home Depot and tighten it back up.

Room buzzes are funny though. I thought my Deluxe Reverb had a cabinet buzz a couple of years ago. For the life of me I could not find it.

I took it outside and no buzz. Back down to the basement and buzz.

It was a loose screw in a wall electrical outlet


brianf

 

[Boogiebabies]

Make sure the fan screws are tight and the speaker screws as well. I dont have any idea of what else could be rattling. Wiggle the transformers to make sure they are not dangling.

 

[Brewski]

Also make sure that none of the metallic insulation has come loose. That occasionally happens and could cause a buzz. Make sure that there is nothing hitting your speaker cones. Oh also, check to make sure that the center of your speaker doesn't have any rips or is coming loose in any way.

 

[brianf]

Ok. I got it fixed. I had my son playing it and I was poking around holding this and that and just trying to find the cause. I was determined it was either a tube or tube socket rattling. Then I thought since it was less of a buzz when I sat on it, it had to be the chassis rattling. I stuck a guitar pick between the chassis and the bubinga and it was gone!!!!!!!

I then loosened off all 4 chassis screws so the chassis was lowered from the wood about 1/2 inch. I took some black electric wire insulation off a piece of wire. About 6 inches long. I tucked it in the gap, cranked the chassis screws back up, cranked up the amp and its all gone!!!!


Thanks for the input though guys!!!


brianf

 

[twally]

Congrat's on finding the problem and simple but effective fix.


TW

 

[jimdodson]

I have a similar rattle happening in my Mark IV widebody combo. I'm going to get someone to play through it while I try to track it down. Before I do that, is there anything I should worry about touching while the amp is on - for fear of heat and/or electrical shock?

-Jim

 

[Russ]

Yeah, be careful of the tubes because they get hot. Also be careful not to touch anything inside the chassis or you'll get zapped and possibly die. For real. It is ok to touch the chassis itself but do not touch any electrical component inside. It would be a good idea to have dry hands and not sweat either. There should be nothing that that would shock you outside of the amp's chassis. It is just the unprotected internals that will get you. Normally you would never see them if you never loosened the chassis mounting screws.

brianf-
You can use some weatherstrip foam for something that is easily replaceable and that will self adhere to the top chassis flange thereby reducing the risk of anything falling into your chassis someday. To install it and change it I would power down and unplug your amp then slide the chassis out to install it. Just be careful not to tear it off as you reinstall it but it should stay put with just the sticky backing.

As a precaution, when I migrated my amp's chassis from a head cabinet to a combo cabinet I had some weatherstrip foam handy but I didn't end up needing it because my amp never rattled. I am not sure if this is because of the SUS-4 mounts or if I just got lucky. For that matter though, the chassis never rattled in the head cabinet either. I can see the internals though through a slight air gap now if I look into the front at the right angle. I suppose I could install some foam across the front between the chassis and the top of the cabinet but I figure that the gap could be left alone for some additional ventilation to help keep the amp cool and keep the SUS-4 mounts from being stressed.