GK MB112: White noise coming only from speaker (only power is plugged into amp)

slapnthebass

slapnthebass

Dec 1, 2011
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Durham, North Carolina, USA
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#1
Just some preemptive notes...
1) I've done a search through Talkbass and nothing similar came up for me. Hopefully I didn't miss anything that already cover this. I'd hate to be that guy, haha.
2) I'm gonna take it over to a shop to have it looked at, but figured I'd scrounge up some advice here to supplement it.

Alright, down to the point.
I've had my MB112 combo for +2 years, no issues so far. (Love this thing!) Today, I set myself up with it and turned it on to discover what I would describe as "white noise," and it wasn't there yesterday or ever before...

So I did the obvious checks:
-Play the bass and see if it sounds as it should. Sounds great as usual! But with persisting background noise.
-Turn the bass' volume control all the way down. Noise is still there.
-Turn the amp's volume control all the way down. Noise is still there.
-Tweak the amp's EQ controls and see if the noise changes. No dice.
-Unplug all input/output cables except the power cable. Noise is still there.
-Try other power outlets. Nope, still there.
-Try another power cable. Still there.
-Try another rig. No noise!
-Try the MB112 again. IT'S BACK.

Here's where it get interesting. I thought to try the headphone output, to see if the speaker mutes properly and if the noise will be present in the headphones. It mutes, and no noise in the headphones!
But unplugging the headphones unmutes the speaker and suddenly the noise reappears.


TL;DR: Noise is isolated to the speaker itself. The noise itself sounds similar to the fuzzy noise that you'd hear between broadcasting radio stations. It's noticeable enough to be a nuisance.

If anyone has any advice or has had this issue, I'd really like to hear from you. Thanks in advance.
 
#2
Does the amp have an effects loop? If so connect a signal cable from the send to another amp to see if the noise is there. If no connect the signal cable from send to return and see what happens. If the noise is gone you have dirty switched on the effects loop jacks. Connect a dummy plug into the return to see if the noise disappears. Let us know the results of these tests.
 
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#4
BassmanPaul said:
Does the amp have an effects loop? If so connect a signal cable from the send to another amp to see if the noise is there. If no connect the signal cable from send to return and see what happens. If the noise is gone you have dirty switched on the effects loop jacks. Connect a dummy plug into the return to see if the noise disappears. Let us know the results of these tests.
Click to expand...

This specific combo does not have an effects loop, however tobias3469's advice did get me thinking it may be an issue of dust settling into one of the inputs. The only thing that makes me believe otherwise: I don't hear the noise when using the headphone output. Hypothetically, I'd think I should probably be hearing the noise through headphones too if the noise is resulting from one of the inputs being dirty.

Only way to find out is to test it, so I'll be taking some canned air to the inputs ASAP. I'll keep you guys posted. Keep the advice coming!
 
#6
Hey all,

Was wondering if I could open this bad boy up because I am having the same exact issues as the original post, like EXACTLY the same issues.

I went a head and gave it the ole' Homer Simpson and whacked the hell out of the top of it, and no more buzz! This might be a good solution for today's playing, but is there anything I could do to stop this issue once and for all?
 
#7
Without (correctly) identifying the cause, a real solution will be challenging. It will be a tough diagnosis for a tech too.
 
#10
HoagieSlayer said:
Right. But you'd think the fact that it goes away when plugging in the headphones, and whacking it fixes it, then it must be a wiring issue with the speaker itself, no?
Click to expand...
Not necessarily (and even more likely not in this case), because it depends on how the headphone signal is routed and generated (there are several ways to do it), and it may be an interconnection within the amp, a mechanically defective component, a small piece of conductive debris sitting on top of the PCB causing intermittent leakage that got disturbed by the "pounding", etc.
 
#11
I had the very same noise problem on a 6-7 year old MB200 that recently had the power amp board replaced. The whooshing white noise started yesterday. I plugged in headphones to see if the problem was in the preamp board, then unplugged them. That actually fixed it! Must have been a dirty contact at the jack. Thanks guys!
 
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