My amp may be dying

Rimshot · #1 02-07-2011, 01:43 PM

I have a GK MB2-500

It has developed a "fuzzy" sound in addition to the normal tone being sent (when playing notes, not a constant sound). I do not believe it's the speakers nor is it cables or the bass.

Any ideas? Is it fixable? Time for a new amp?

Your help is greatly appreciated.

RickenBoogie · #2 02-07-2011, 01:53 PM

If it's new, use the warranty. If it's not covered, you need an amp tech. How do you know it's not the spkrs?

Rimshot · #3 02-07-2011, 01:55 PM

I've tested it with multiple cabs.

I bought it used about a year ago here on TB so no warranty.

Phalex · #4 02-07-2011, 01:57 PM

I had a similar situation on my head a year or so ago. I thought one of the speakers in my 410 was blown, or had a loose mounting screw. The cab turned out to be fine, so I brought my head to a guy I know that does repairs.

Turned out to be a dirty tone pot. He sprayed a bunch of contact clearer on stuff and it's worked fine ever since.

If you fiddle with the control pots on the amp does it crackle?

scottbass · #5 02-07-2011, 01:57 PM

Quote:

Originally Posted by RickenBoogie

How do you know it's not the spkrs?

/\ This. The symptom you described could be caused by the amp itself or the speaker. Unless you've tested it with a different cabinet, you don't know. It's probably not the amp-to-speaker cable or jacks. If they were bad, you would get a scratchy or intermittent sound.

EDIT:

Quote:

Originally Posted by Rimshot

I've tested it with multiple cabs.(

Given this new info, yeah, you need someone to look at your amp if you're not comfortable doing it yourself.

gregoire1 · #6 02-07-2011, 03:09 PM

I had this problem, happened on both my cabs, turned out to be a dying battery in my active bass. (you may have already eliminated this).

Lowbrow · #7 02-07-2011, 06:01 PM

Quote:

Originally Posted by Phalex

I had a similar situation on my head a year or so ago. I thought one of the speakers in my 410 was blown, or had a loose mounting screw. The cab turned out to be fine, so I brought my head to a guy I know that does repairs.

Turned out to be a dirty tone pot. He sprayed a bunch of contact clearer on stuff and it's worked fine ever since.

If you fiddle with the control pots on the amp does it crackle?

+1 I once almost replaced speakers that I thought were blown when all I was hearing was a dirty pot.

With the amp plugged into the speakers and set at an audible volume, turn each pot (all of them in turn, one at a time) and see if you get a crackle.

If you don't have contact cleaner on hand, you can often clear out the dirt by flicking the pot back and forth a gazillion times until it works itself loose. You'll hear when it's gone. And you will be so happy.

Rimshot · #8 02-07-2011, 07:10 PM

GENIUS! It was the High-Mid pot.

See, THAT'S why I come here. (well, that and the carrots)

Thanks a million...or at least $499.00 plus tax, shipping and handling.

Wes Whitmore · #9 02-07-2011, 09:03 PM

Some of the problems I have been having with my MB2/500:

1. I get a crackle that happens when I pluck a string. The volume varies and cuts out. It does it with different basses and instrument cables. I took a brush to the efx loop and input jacks, but maybe it's time to try some spray cleaner.

2, Fan - When it kicks on, it's RPM is all over the place. It goes up and down quickly, sometimes running constant for a couple of seconds, then slowing down or turning off. It comes on when I have the volume all the way down and the bass turned off sitting on the stand. The fan can be on, and I can hit the mute button or -10db pad and the fan shuts off. It's never even warm to the touch.

3. Fan noise through speakers - When the fan runs, I hear a buzz noise related to the fan RPM through my cabinet. It doesn't do this out the DI. It makes sense that the buzz goes away when the turn the volume down, and gets loud when I turn the volume up.

3. Basses that don't clip the input of my MB200 clip the MB500 quickly. I have to use the pad on the MB500, but not the MB200. This causes me to have to work the volume harder, and the higher I go, the hissier the amp gets.

4. I can't get the volume to 3 o'clock like the manual says without it sounding like an FM radio in between stations. Tons of hiss...

I send it my Factory Repair Form, that was sent to me through email, some 33 days ago...I have sent followup emails since with no response. I'm pretty patient, but I'm giving up on this one. Besides, I am so happy with my MB200 that I don't have a pressing use for it right now. If my MB200 fails, I'll drag out the 400RBIII...

Wes

And I · #10 02-19-2011, 07:00 PM

Quote:

Originally Posted by Rimshot

GENIUS! It was the High-Mid pot.

See, THAT'S why I come here. (well, that and the carrots)

Thanks a million...or at least $499.00 plus tax, shipping and handling.

same thing happened with my MB2-500 for the first time today. static/scratchiness when i play a note. it cleared itself up with no real intervention on my part... i just tried all the knobs, and the hi-mid pot is making a little bit of crackling noise when i turn it up and down... can i get some wd-40 into this thing on my own? or will i mess it up if i open it up?

and Wes, as for your #4 above, forget about it. you don't need to keep the master at 3... turn the master to 10 o'clock, dial in the tone you like on the gain knob, and adjust the master to suit your volume needs. i got that advice here, and the amp sounds better with the gain a bit higher and master a bit lower.

KramerBassFan · #11 02-19-2011, 07:32 PM

Do NOT use WD-40!!!!

That is meant for moving metal parts... use contact cleaner. for Electronics.

And I · #12 02-19-2011, 07:42 PM

thanks for the tip

GrowlerBox · #13 02-19-2011, 09:29 PM

A completely different source of random crackling I discovered yesterday, to my utmost embarrassment, was a loose connection in a speaker cable I had rewired to Speakon connectors. I hadn't trimmed the 4 wires (it's a GK 4-way cable) all to quite the same length, so a couple were slightly bunched up. Trimmed them back, re-connected it, et voila! No more crackle. I'd had visions of returning my newly acquired RH450 to the US (from NZ), or paying an arm and some other appendage for repairs locally, thus negating the savings I made from importing it. Disaster, or at least inconvenience, averted.

And I · #14 03-01-2011, 07:27 AM

so the crackling in my amp is definitely not the high-mid, or any other of the pots. the thing is just dying... the boost channel is fine. but the regular channel sounds staticky and swooshy even with the mute switch on. if i push gently on the knobs i feel it give a little bit and it either temporarily stops or changes the character of the static. i opened the case and i see that the main board with the knobs attached is actually not attached to the chassis by anything other than the knobs themselves. there are two screw holes in the board and the chassis, but no screws in them... is this by design? or did i get humped by buying the floor model? the thing has served me well for 2 years and maybe the fact that i can't find a carrying case for it has something to do with its present condition... but still... this sucks.