Question for GK MB-150 folks

[Marc Piane]

Let me start off by saying I really dig this amp. Very portable and I have been really happy with the sound I'm getting.

I have a two regular gigs where the drummer gets pretty loud. This is not in a bad way. They are both fully capable of really great quiet playing. Whenever we play club dates and they can play out a bit they do. I'm totally cool with that. I have had no problems keeping up volume-wise but I'm definitely close to maxing that little guy out.

Here's the problem/question. There are two notes, D and Eb, that cause a rattle that gets on my nerves a bit. This is only at high volumes and only those two notes so I doubt the speaker is the problem. Has anyone else experienced this? Has anyone found a solution?

Thanks. M-->

[eadg57]

M-

I know just what you are talking about; mine buzzes on a low G.

On another forum, this was brought up. Several posters thought that the cause was a change/deteriorization of the foam gasket material that seals the metal box. Some players pulled theirs apart and reinstalled the material; other (like me) let it go. I understand that there are many, and different size screws, so the project was laborious.

I convinced myself that at high levels, no one else could hear the buzz anyway.

[Greg Clinkingbeard]

I also believe the rubber seal between all the panels is the problem. Black latex caulk is the fix. Also, the screws may need to be tightened. Mine didn't rattle until just before it maxed out, but I sealed it up anyway.

If the seal on a cabinet DESIGNED to be sealed goes bad I think it should be fixed.

[Marc Piane]

Do I need to take anything apart for this?

Are we talking bathroom caulk?

[fdeck]

Get a friend to help. Try squeezing on different parts of the amp while you play the offending tones. Both of you wear earplugs for this.

I once got a rattle in my GK due to the circuit boards resonating. It was an exercise in frustration to diagnose. Eventually I traced it to the power supply bridge rectifier, which I fixed by squeezing in a piece of rolled up bike innertube. Of course you have to be extremely careful with such a fix, as there are safety concerns to address.

If you tighten screws, do it gradually. Those are machine screws threaded into sheet metal, and the threads are easy to strip out.

[Marc Piane]

I think I'm going to try the caulk thing. Seems easy enough plus it'll give me an excuse to actually use the caulking gun I bought for a bathroom project a few years back. Just curious if there are any other opinions out there.

[pjleo]

I have opened the back of my gk mbs several times with no problems.
It can be a little tough getting off because of the sealer...
just take your time and ease it up with a paint scraper or thin screwdriver etc.....I would use a good quality silicone caulk as opposed to latex / acrylic....good luck.

[Marc Piane]

Thanks for all the suggestions. Yet another victory for TBDB. I tried fdeck's suggestion and isolated the vibration. I played a bit and got an idea of the general location. It does seem to be the grill. I then tapped on the grill and found the exact spot.

I'm going to do the caulk thing later today. I looks like the previous owner did some caulking already so I am just going to do the spot in question. I'll keep everyone posted. M-->

[Marc Piane]

In case anyone was wondering.

I isolated the vibrating sound in question to the grill on the front of the amp and more speciafically to where it meet one of the sides. Instead of removing everything I just took off the grill, packed the sides with caulk and replaced it. I then filled the screw holes wth caulk and replaced the screws. Last I ran a bead down both sides.

It seems to have worked. The amp no longer vibrates when tapping the grill. I have played though it a bit, no vibrations. I have a gig tonight so that will be the real test but so far so good. Thanks everyone.