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GK Microbass MB150E problem

R

rcfs1834

Jul 3, 2007
22
0
Portland, Maine
#1
I just received a new Gallien Krueger MB150E microbass combo. I noticed as soon as I plugged it in a "hissing" sound, it almost sounds like a it's a white noise generator. It's not a hum, which I'm familar with from my strat playing days, but an ambient hiss that I would put on if the neighbors were fighting and I wanted to sleep.

When I play I don't really notice it but when I stop playing it is noticeable. It's especially noticeable when I plugged headphones in to do some quiet praticing, the noise was unbearable through the headphones.

I've plugged guitar and bass amps into the outlet I'm using and no noise, so I don't believe it's bad power. I actually just had a guitar tube amp plugged into the same outlet yesterday and didn't notice any "hissing" sound. I've tried two different outlets and no difference. I've played with the controls and even set the controls to "walking bass" setting per the manual and no results.

I really like the amp, it's loud and light. But the noise issue is disappointing. Is this a known issue with the microbass amps? Any suggestions on how to fix this problem? Thanks.
 
#3
rcfs1834 said:
I just received a new Gallien Krueger MB150E microbass combo. I noticed as soon as I plugged it in a "hissing" sound, it almost sounds like a it's a white noise generator. It's not a hum, which I'm familar with from my strat playing days, but an ambient hiss that I would put on if the neighbors were fighting and I wanted to sleep.

When I play I don't really notice it but when I stop playing it is noticeable. It's especially noticeable when I plugged headphones in to do some quiet praticing, the noise was unbearable through the headphones.

I've plugged guitar and bass amps into the outlet I'm using and no noise, so I don't believe it's bad power. I actually just had a guitar tube amp plugged into the same outlet yesterday and didn't notice any "hissing" sound. I've tried two different outlets and no difference. I've played with the controls and even set the controls to "walking bass" setting per the manual and no results.

I really like the amp, it's loud and light. But the noise issue is disappointing. Is this a known issue with the microbass amps? Any suggestions on how to fix this problem? Thanks.
Click to expand...

I just got a new one myself after trying a couple over the past few years. No, it's not a common problem with this amp. Mine is very quiet and the only way I can get any noticeable hiss is to turn my bass volume way down, crank open the treble on the amp and push the volume controls wide open. This is not something that would ever occur in real world use. All the other Microbass amps I tried were equally quiet. As quiet as any of the best amps I currently own and quieter than many I've used before.

So, I'd say take it in to where you got it and have it checked out. Something is not right and it could be a simple fix.
 
#5
At least in my MB combo, the sound from the woofer is quiet. Some hiss appears when I activate the compressor. And there is mucho hiss in the headphone output. I have the schematics, and now my curiosity is piqued. I will investigate further.
 
#6
Thanks for the replies.

I did just email GK support to see what they say also. I'm still within the return window so I might just send it back and get another one to see if I still get the hiss.

It's very strange because I followed the manual's settings for "walking bass" and it still hisses just as loud as when I received it. When I change the controls the the hiss doesn't seem to be affected, it's a constant noise. Although the hiss is much more noticeable with the headphones than through the speaker.
 
#7
I have a MB150S and it hisses only when the limiter is engaged. When I'm at home practicing I don't use the limiter so it's not a problem to me. I've had this combo for 15 years now and as far as I can remember it has always hissed with the limiter on.

Cheers,

Dronnba
 
#8
I checked the schematic. The headphone output is driven by a pair of LM386 audio amp chips, which are noisy, but not noisy enough by themselves to produce unacceptably audible hiss (many assumptions went into this statement).

Since the two channels involve independent circuitry, it is unlikely that something "blown" would contribute equally to hiss in both channels.

My guess is that given the elaborate analog signal chain, so there might be a fair amount of noise built up. Still, it might sound quiet from the speaker, which simply has no high frequency response.
 
#9
I haven't tried mine, which is new, with headphones, but I get no noticeable hiss through the speaker even with extreme settings and when using the limiter. There has to be something wrong with the amp if he's ruled out bass, instrument cable and wall power.

I know I'm old and losing my hearing (so my wife says) but I can hear hiss when it's there. :)

The latest version of the MB 150 has been upgraded with better S/N ratio but I don't recall the older ones being all that noisy.
 
#10
If the hiss is in both the headphone output and the speaker output, the problem is probably in the preamp section and something is amiss with one of the filter caps somewhere. As Fdeck recognised above, the headphone output is drive by its own power amp chip, and taps the signal from preamp stage; it is independent of the poweramp stage driving the paragon speaker.

FYI, this particular 12" paragon has little response above 4 khz. Hiss is generally in the '5 - 7 khz' range and sometimes higher. If you have a sound clip it might help, as the caps in preamp sections sometimes filter off bleating squeals rather than 'hiss'. It might also be a dead or poor quality pot. The last device I had that had 'white noise' at idle was a Nady para EQ in one channel out of 5. It was a bad PCB pot. I disconnected it and lost than channel of EQ but also lost the white noise thus salvaging the unit. You may not have the option in the preamp section as it is effectively one signal chain as opposed to five bands of signals to be EQed.

So at this point, its all guessing.
 
#12
Wow, I haven't been on in over a week. Thanks again for the replies.

I've chatted with GK support and they didn't tell me either way if it was a defective unit or a known issue. I'm a little disappointed with their support, they ask a lot of questions but never had a solution. Even a "stumps us" reply would have been sufficient.

I have the same issue with the limiter that dronnba has. When the limiter is engaged I actually get a lot of hiss from the speaker as well as more hiss from using headphones.

I guess I'll exchange it and see if I get the same issue with the next one. Thanks.
 
#13
Yes, return it and get a new one. Check it out before you take it home.

Then write a letter to GK and tell them about the problems you had with their tech support. Write a real letter and send it in the mail.
 
#14
The headphone out is noisy, for sure. I sent mine back to GK for repair for that reason, right when I bought it, and was told, "sorry, it's at spec." So I don't use the headphones. Otherwise, I like the amp - nicely voiced.
 
#16
My MB150E is super old and has no hiss. That said, I have had nothing but good experiences with GK support, been using their amps for 20+ years and have broken my old 200MB a few times, but it is still kicking for another BABP that I sold it to.

I would do an exchange if you still can, but no worriers about sending it back to GK, they do great work.

Also, I see from your post that you have tried another cable, but if you have not tried other basses thru it, I would do that. Also having it close to a computer, TV, or other magnetic field might be an issue, never has been for me but.....
 
#18
Several comments mentioned reading the manual. The manual has several places where it's not accurate, such as the back on the new ones have a mono line out, but the manual says it's an stereo aux input. Also, several of the shown settings are not for EB but rather for DB. So if you find something in the manual that seems odd, email GK to find out. Not saying they are still putting the 1990 manual in the 2012 models, but I'd really make sure the specs are correct before doing anything drastic.
 
#19
Just got an MBS-III. Lovely sound, but, yeah, unusable with headphones (only realised when wanting to practise while visiting relatives) - horrible hiss. Also annoying that it's got a line out instead of an aux in (it's already got a DI - and, yeah, the manual says it's an aux in). I'll stick with it because the main thing I want it for is weight and sound (I didn't buy it to be a headphone amp :), but changeover from an SWR workingman's 12 hurts for funtionality (could do a couple of effective aux ins through passive/active line in, and FX - which effectively had volume control - bummer I can't use the GK to practise bass along with music from phone or metronome through headphones. Can't even practise with it just bass through headphones).
 

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