Hum/Feedback with Bass DI

[crijan]

This may be in the wrong forum, depending on what the likely root cause turns out to be but since there's so much involved I'm guessing this is as good a forum to start as any.

Saturday night I was playing at a very reputable club with a nice sound system. First band finishes playing with no problem, I go to set-up and use the same Passive Behringer DI box that the first band used. I was also plugged into the same power outlet.

The PA was getting a loud hum from the bass DI signal, but I was getting no hum through my amp. As we were in a hurry to get started, we didn't quite get to check everything and eventually we just mic'd the bass cabinet and went on with the show.

All bands before and after ours were able to use the Passive Behringer DI box with no problem.

Here's my setup and then I'll follow with the things we did check/swap out.

Fender Jazz V --> AKG WMS 40 Pro Wireless w/Guitar Bug ---> Boss DTR-2000 Rack Tuner ---> Aphex Punch Factory Compressor ---> Aphex Bass Xciter ----> Boss Bass Overdrive (ODB-3) ---> Passive Behringer DI ----> Ampeg SVT-VR ----> Avatar 2x10 / Avatar 1x15 (4 Ohm total load)

So we disconnected the wireless and tried a cable from the bass, no help. Then we replaced the 1/4" cables into and out of the Passive Behringer DI, no help. Then we switched to the DI on the back of the Ampeg SVT-VR, no help. Then we mic'd the cabinet and played the set as we'd already wasted too much time. The mic used the same XLR cable to the snake as the DI.

All pedals were powered with a Voodoo Lab Pedal Power II. All power connections, including the Voodoo Lab, were run through a Furman M-8 Power Conditioner.

This is the same setup I've always used, with two exceptions. One, the SVT-VR is new and has only been used on the last two gigs. Two, the last time I used the SVT-VR, the passive DI was plugged in front of my effects chain (by the sound techs that didn't realize I would need those effects in the front of house).

Again, I never got this hum through my bass cabinets.

Any ideas on stuff I can try before my next gig? I don't want to go in and have the same problem.

 

[bassman1185]

First off, that doesn't sound like feedback at all. Feedback is when a certain frequency is amplified too much, which causes resonation at that same frequency, which causes it to be amplified more, which causes more resonation, which causes more amplification, etc. What you're describing is humming.

It's probably caused by one of two things: 60 cycle hum or a grounding issue.

You said that you're playing a jazz. Did it keep humming if you ran both pickups at the same level? Single coil pickups are known to do this, and if there is a lot of interferance in the room, it will be more pronounced. However, if this were the case, you would hear the hum through your amp as well, so my guess is that it's a grounding issue. There should be a button or switch on the DI box labeled "ground lift." If it happens again, try messing with that.

 

[crijan]

I play both pickups on my jazz at full volume to eliminate any single pickup hum.

I'm pretty sure they checked the DI to make sure it's ground was lifted.

Basically, I'm looking for anything in my gear that could have caused a problem.

I sort of wonder if there's something with the SVT-VR, but I don't know if it's possible for something connected to the 1/4" output of the DI to cause a problem with XLR output.