Bass Amp / Cabinet troubles

[AwkwardLoudness]

Not very well grounded.

That's one common cause of dirty power. Sometimes an outlet's AC voltage will stray a bit far from 120V at different times of the day especially in a heavily industrial area.

 

[billfitzmaurice]

I went ahead and placed my head on top of a large pillow and placed it on a table some twelve feet away from the cabinet. I then proceeded to step firmly near the base of cabinet to test out our theory, and I am still hearing a distorted scratchy sound coming from the cabinet with each step.

Is the bass plugged in when you do this? A poor quality microphonic instrument cable could be the problem. A poor connection in the bass is also a possibility, as is a poor connection in the cab. Narrow it down by unplugging the bass. The AC power is not a factor.

 

[groovaholic]

Try using a normal 1/4" speaker cable.

Why I say this (when normally, I'd go with Speakon EVERY time) is that GK uses the pins on their NL4 connectors different than many.

Most manufacturers use 1+ and 1- for the + and - connectors, and leave 2+ and 2- unused. But GK amps and cabs use 4-conductors cables to do bi-amping, so 1+ and 1- typically go just to the woofer, while 2+ and 2- go to the horn.

If there's anything funky with your speaker cable, or with the full-range/bi-amp switch on your cab, you could have full-range signal at the horn, which would make a VERY nasty sound.

 

[KramerBassFan]

Try using a normal 1/4" speaker cable.

Why I say this (when normally, I'd go with Speakon EVERY time) is that GK uses the pins on their NL4 connectors different than many.

Most manufacturers use 1+ and 1- for the + and - connectors, and leave 2+ and 2- unused. But GK amps and cabs use 4-conductors cables to do bi-amping, so 1+ and 1- typically go just to the woofer, while 2+ and 2- go to the horn.

If there's anything funky with your speaker cable, or with the full-range/bi-amp switch on your cab, you could have full-range signal at the horn, which would make a VERY nasty sound.

wouldn't a full range signal just pop a horn, not make bad sounds?

 

[AwkwardLoudness]

I suggest tapping on the amp head without moving the cables around and listen for the scratchy sound. If no scratching is heard or exacerbated then move then jiggle the instrument cable and then the speaker cable. Hopefully, that would tell you which item is the culprit.

If the amp head is source of the scratchy noise, then take it to a reputable technician. If you let us know where you're located, then maybe someone here on TalkBass can make a recommendation.

 

[traindmunkie]

Hello Everyone!
I realize that this is an old post, but wanted to inform all of those who contributed to this discussion, as well as anyone who may be able to benefit from it in the future, that the problem with my cabinet and head making loud scratchy sounds when you tap the top of it has been resolved!
It was a couple of cold solder joints (broken solder connections). I took my amp in for repair, and it cost me about $115 + $5 for a couple of extra fuses. Thank you all for steering me in the right direction! Your help is greatly appreciated!
BTW for anyone living in the Denver Area, I took my gear into "Mars Amp Repair" in Englewood, CO. The staff was extremely knowledgeable, helpful, and extremely fair on pricing. I am very satisfied with the results, and would recommend them to anyone.
Thanks again Everybody!
-Traindmunkie (8=|)