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Amp noise!! What is causing it?

Robear22

Robear22

Sep 28, 2004
1,601
256
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Zion, Ill
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#1
I have a problem here that I hope you guys can help with. I have a Kustom Groovebass that I put in the shop because of an unusual amount of noise that I was getting. I was playing it in rehearsal and I heard my sound break up and the volume dropped. Then it came back but there was some noise coming from it. It was an electrical noise for all I know and it seems to come from the amp. I thought it was one of my basses but changing those produced the same result. I tried different instrument and speaker cables and nothing. Even with no instruments plugged in I got the hum. Sounds similiar to 60 cycle hum but louder. So I bring it home and try a different cab and same thing. So that is in the shop.

Then I try my backup head that I just got, a Behringer BX4500H and plug into my main rig(Avatar B212) and that head produces noise also. Not as loud as the Groove Bass but there is noise. A couple of weeks ago my rig was quiet but all of a sudden there is tons of noise. I do the same thing with the Behringer and bring it home and same thing I get noise. So I plug in my Yorkville XM200 into the Behringer return line bypassing the pre and the noise disappears. So I think that I got a noisy pre in the Behringer so I am returning it and getting a Hartke HA3000 for practice and backup. If this head gives me the same noise then what is the problem?

Also I messed with my Avatar B212 because I put the new crossover in it a couple of weeks ago and when I removed the plate the noise stopped for a brief second then came back on. But touching and moving the plate did not duplicate that response. I have no idea what is going on but it seems that all my stuff is acting crazy now. I would appreciate some input from you guys as to what you think it is or has anyone else experienced something like this. I remember that Tombowlus said in his reviews of the Groovebass that it is susceptible to noise issues. What can I do to improve this? I have not heard back from the repair tech yet.
 
#2
You have too many problems going on from too many sources to expect much of an answer sight unseen. This may or may not apply - did you plug all of the amps into the same outlet to test them? If so, check the voltage and ground of the outlet. Do you rehearse in a low-rent rehearsal space? I have seen some frightening wiring in some of those places. If you're lucky the problem will be in the external wiring and not in your heads and cabs. Otherwise it looks like you will have a few repair bills. Good luck.

Rick B.
 
#3
My amps reside in one of two places, my house and at church. I occasionally play out and when I did I got the same noise. The Behringer situation I feel is just a noisy amp because when I bypassed the pre-amp and used the Yorkville pre she was as quiet as a church mouse. When I did the opposite the noise returned. The Groovebass is a different animal though. Thanks for your response. Anyone else have an idea?
 
#6
Yes when I messed with the EQ the intensity changed especially when I adjusted the high and mid frequencies. I still heard it but not as clearly when I cut those frequencies. I can hear what I am playing but as soon as I stop playing I hear the hum. It was so loud that our sound tech thought it was coming from the PA. When I turned my amp down he gave me a look like "that was you!!??"
 
#7
i forget what its called, but if your preamp has a grounded plug, try an adapter that disconnects the ground or a short extention cord that does NOT connect the ground to the wall. might have a "ground loop".

like this
pRS1C-2266744w345.jpg


if the sound comes and goes, see if there is a refridgerator motor or some other heavy motor on the same circuit.
 
#8
Mcrelly said:
i forget what its called, but if your preamp has a grounded plug, try an adapter that disconnects the ground or a short extention cord that does NOT connect the ground to the wall. might have a "ground loop".

like this
pRS1C-2266744w345.jpg


if the sound comes and goes, see if there is a refridgerator motor or some other heavy motor on the same circuit.
Click to expand...

Ground loops occur only when there are other devices, with their grounds (or earths) connected through more than one path. You won't get a ground loop from just one device because there is no loop.

Don't use a ground lifting adapter or an extension cord that lifts the ground. That third prong on the AC plug is called a safety ground, and it's there to keep you or someone else from getting shocked or even electrocuted if something in the amp ever became damaged enough to allow the AC line to contact the chassis. It's rare, but it sometimes happens.
 
#11
Well I found the problem. It is my Behringer Dualfex processor that is sitting in the rack with my Groovebass. When I plug it in the noise starts. I don't know why this happens but maybe because both devices being on the same circuit are causing it to act up like that. I don't even have to turn it on, just plug it in and the noise starts. Now I need to get a new exciter. Maybe I will try the Aphex? Thanks Bob and McRelly for your replies.
 

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