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Super loud hum through PA..HELP!

rjd5974

rjd5974

Nov 16, 2014
19
8
52
#1
So over the last month or so I've encountered a huge problem when going through our PA. I get a very loud hum that comes from the mains of the PA..however the sound out of my amp is totally clean. This is way more than the low level 60 cycle hum that you can get from some pups..it's obnoxiously loud to the point we can't put me through the PA directly and we've been micing my amp. It happens at every venue we play also, so it's not a specific venue problem.

I feel like I've tried everything to solve the issue.

I've changed every cable along the way, including the power cable to the amp, cables to the bass, different DI cables, etc.. We've tried switching me to a different channel in the PA. I even thought maybe my amp had a ground issue so I brought a different amp to another gig and the problem persisted.

I've tried coming directly from the amp heads, from the line out on a Zoom B3..no difference.

OK..maybe it's the bass...tried a different bass and the problem was still there. And these are Lakland and Modulus basses..so not junk instruments.

The only thing I haven't been able to change is the PA system, because we travel with it...but it does it only to me, not the other instruments.

One thing that did work was putting me into a DI box. This gave me a clean sound out of the PA which also helped me rule out the bass as the problem. However, as soon as we tried to go from the thru to my bass amp the hum returned. That sound guy ended up feeding me direct and somehow ran a line out from the snake and into my amp to get sound out of my amp and that worked as well..but I couldn't connect to the thru on the direct box without getting the hum. Our usual sound guy doesn't know what he did though..so he can't replicate that set up.

The only thing I can possibly point to is the PA as it's the only thing that hasn't changed in this situation. It's a nice PreSonus PA, but who knows.

Any feedback or things to try is totally welcome as I'm at a complete loss.
 
#3
Humbled said:
Sounds like a ground loop to me. Does your DI have a ground lift one it? ...Or buy (or make) a Pin 1 lift to put on the output of your DI feed to the snake. Or try an XLR in-line Isolation Transformer on the output line of your DI feed.
Click to expand...

All of this exactly.

It's a ground loop in your line out. See if the amp had a switch first (ground lift).

As with any technical question on a forum, it's best to give as many details as possible. What kind of amp? When did it start doing this? Etc. It will be much easier to help if we can Google up the pdf of a manual. Or perhaps many here will have experience with that same amp and problem.
 
#4
Wait, so you have tried taking your amp completely out of the chain and running from the Zoom to the board? Now it's getting weird. And you don't hear it through the amp, but you hear it in the FOH even if you aren't running the amp at all and running through the Zoom instead?
 
#5
Thanks for the info guys...has done it through multiple line outs though. Directly out of my TC Electronic head...directly out of my Euphonic Audio Iamp head..and directly out of a Zoom B3. The TC and EA heads have ground/loop switches but no dice.
 
#7
Wait, so you have tried taking your amp completely out of the chain and running from the Zoom to the board? Now it's getting weird. And you don't hear it through the amp, but you hear it in the FOH even if you aren't running the amp at all and running through the Zoom instead?
Click to expand...

Yes..that's what's confounding me.
 
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#8
BazzTard said:
I would suggest trying an active and a passive DI. Sometimes one will stop noise where the other didn't.

Use the ground lift. Make sure the amp is on a separate circuit to the PA and your pedal(s).

Is your bass active? If so, it could be the pre-amp.
Click to expand...

Yes..both basses I tried are active. Bad pres on both basses? Not likely.
 
#9
Have you tried multiple channels in the snake? Multiple channels on the board itself? Have you tried bypassing the snake altogether and running directly into the mixing console channel(s)? Channels on boards and snakes go "bad" all the time.

With this happening no matter what combination of basses and gear you use, the problem then is most likely further down the chain. The odds of multiple bass heads or multiple basses suddenly having technical issues are slim to none.
 
#10
two fingers said:
Have you tried multiple channels in the snake? Multiple channels on the board itself? Have you tried bypassing the snake altogether and running directly into the mixing console channel(s)? Channels on boards and snakes go "bad" all the time.

With this happening no matter what combination of basses and gear you use, the problem then is most likely further down the chain. The odds of multiple bass heads or multiple basses suddenly having technical issues are slim to none.
Click to expand...

I know we've tried different channels on the snake. I'm not sure about different channels on the board. I'm pretty clueless when it comes to live sound so when you speak about running directly into the console channel I'm not sure exactly what you mean, but read the stuff I wrote in my original post about when I went into a DI box...is that what you mean? I went straight DI and that worked fine, but as soon as I came out of the thru to get some volume to the amp for stage volume the hum returned. The sound guy somehow ran a line out of the snake and into my amp to get me volume and that took the hum away..but I couldn't go out of the thru.

So is an isolation transformer worth trying? I've been hesitant to throw money into stuff when I don't know what in the hell is going on.
 
#11
rjd5974 said:
Yes..both basses I tried are active. Bad pres on both basses? Not likely.
Click to expand...
true, most unlikely.

I would start by hiring a different PA for one gig or a rehearsal.

I'm totally stumped by the clean signal to the PA from the DI but hum in the thru output. Try a passive DI if the one you used was active. Both will work with active basses,but might solve the hum.


Hmmm, hang on, you've tried a different HEAD, but you haven't tried a different cabinet yet have you?

Try a different cab.
 
#12
I wouldn't try the transformer yet.

OK, so a snake is pretty much an "extension cord" for each channel on your board. For every hole in the box on your stage, there is a corresponding hole on the back of your mixing board. Every hole in the snake box has a plug on the other end that sticks into (usually) the channel with the same number as on the box on stage. So, snakes go bad all the time. People are usually pretty rough on the cords rolling them up.

Try running any or all of these combinations (the different amps and DI boxes) directly into a channel on the board itself (no snake). If you still get the hum, try running your bass into the channel of something that you know for a fact did not hum before. In other words, if the kick drum channel has zero hum, plug your bass (via a DI box) directly into that. If it doesn't hum, you have taken both the bass and the DI out of the equation. Then try lining from your amp directly into the same channel. No hum? It isn't the amp. And so on......
 
#14
BazzTard said:
true, most unlikely.

I would start by hiring a different PA for one gig or a rehearsal.

I'm totally stumped by the clean signal to the PA from the DI but hum in the thru output. Try a passive DI if the one you used was active. Both will work with active basses,but might solve the hum.


Hmmm, hang on, you've tried a different HEAD, but you haven't tried a different cabinet yet have you?

Try a different cab.
Click to expand...

Yeah..my TC Electronic is a combo...the EA is not, so I had to pair the EA with a cab when I brought it out.
 
#16
Probably going to live with micing the amp for now before I try to buy an isolation transformer or Passive DI. We've got a gig the first weekend in February at a place with a house PA, so I'm interested to see what happens when I plug into that.
 
#17
Have you tried connecting the DI out on your amp to the snake through a mic cable with the shield completely disconnected from one of the connectors? The ground lift on the DI will disconnect the amp's pin 1 from the cable shield, but if the connector shells are tied to the mic cable shield, the board may still "see" the chassis of your amp and make a ground loop.

This could still happen if you use a separate DI; the chassis of the DI is connected to the chassis of your amp through the hi Z cable shield and you can't cut that shield and have it still work. You *might* have a problem with your amp; if there is stray AC voltage on your amp chassis then that's what is causing the loop to be noisy.
 
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