Hum going to FOH

[Big Benner]

Hello fine people of TB,

I have a questions regarding a gig I did last weekend that involves a clean sound from my bass amp but a hum going to FOH through the DI. I’ll try to give all of the details.

Here’s the setup:

- EBMM bass (fresh battery & set up)
- into BOSS TU-2 tuner & LMB-3 limiter powered by a 1 Spot
- into a Markbass 102P combo amp with Traynor 2x10 extension speaker cab
- with an XLR cable plugged into the DI out of the Markbass with a Pre EQ signal being sent (the Pre EQ and GND Lift switches were in the Out position).

Both the 1 Spot & the Markbass amp were plugged into a power bar that was taken off of the AC receptacle on Stage Left.

The sound coming from the amp was great, quiet & clean - no hum. As soon as the sound man (my keyboard player) got the PA up & running he noticed a hum coming from the PA - this showed on the mixer meter lights as well. I pressed the Ground Lift switch to the In position and the Hum got noticeably louder. The PA was plugged into an AC receptacle on Stage Right.

The sound man had other things to set up, so to experiment I took out my APHEX Punch Factory out of my "Backup" bag and replaced my pedal board set up:

- EBMM bass
- into APHEX Punch Factory powered by 1 Spot with an XLR cable plugged into the DI out of the pedal.
- ¼” out of pedal into the Markbass 102P combo amp (Amp DI no longer being used).

Same issue running through the PA. My amp was clean but there was a hum coming through the PA. I tried all of the switches on the APHEX and nothing worked to get rid of the hum.

Because 95% of the bass sound to fill the room was coming through my bass rig, we put a mic in front of it using the same XLR cable that was off of the DI(s) and finally we had a clean sound going to the PA.

Anyone have any ideas of what was causing this? I thought I had a fairly simple bass setup, where was this hum being caused from?

Didn’t think of it at the time but if I took the 1 Spot out of the equation and used the 9v batteries (either in the BOSS pedals or the APHEX), do you think this would have made a difference?

Thoughts?

 

[s0c9]

Most hums in a PA are due to ground loops..
they can be a b*tch to track down, but can often be caused by stage circuits NOT having a common ground.. that can be compounded by FOH being run on ANOTHER circuit with a different ground.
If this occurs are multiple venues, I'd be concerned about something in the rig.
If it's just the one.. the simplest approach maybe the solution you already have - and the hum may not even be your problem.

When I encounter this issue (as I do at some venues), the first thing I do is disconnect the DI XLR cable on the back of my amp.
If the hum goes away.. it's me. If it remains, it's not.
Changing your power source might correct it...

 

[rjd5974]

I had the same exact problem...constant hum at multiple venues through the PA despite clean sound coming from my bass. Went crazy trying to change every little thing to track down the problem. It happened with different basses, and even with different amps. I switched out every cable in my chain one by one to try to figure it out to no avail. I finally purchased one of these and it completely eliminated the problem. Before spending any money though, make sure it's not just that one venue.

Amazon.com: Whirlwind ISOXL Line-Level Isolation Transformer, 3-Pin XLR Male/Female Connectors: Electronics

 

[Rick Auricchio]

Most hums in a PA are due to ground loops..can often be caused by stage circuits NOT having a common ground.. that can be compounded by FOH being run on ANOTHER circuit with a different ground.

This.

I'm always careful to run the entire band from a single outlet until I know the venue has properly wired outlets with good grounds.

I've played two venues where we had to run the PA on an extension cord to the same outlet as the band. The problem was worse during damp and rainy days!

 

[micque]

I've played places that had bad grounds, even one place that had no grounds, was a bad hum all nite, and be carefull, if you have no ground and a fault occurs, you can become the missing ground, no fun dancing the power jig with madame electron ! ( experience talking )

 

[s0c9]

I've played places that had bad grounds, even one place that had no grounds, was a bad hum all nite, and be carefull, if you have no ground and a fault occurs, you can become the missing ground, no fun dancing the power jig with madame electron ! ( experience talking )

Everyone should spend the < $10 and invest in one of these types of devices.
I test ALL outlets before hooking up the power! One never knows!
Sperry Instruments GFI6302 GFCI Outlet Tester - Multi Testers - Amazon.com

 

[Zooberwerx]

I had the same exact problem...constant hum at multiple venues through the PA despite clean sound coming from my bass. Went crazy trying to change every little thing to track down the problem. It happened with different basses, and even with different amps. I switched out every cable in my chain one by one to try to figure it out to no avail. I finally purchased one of these and it completely eliminated the problem. Before spending any money though, make sure it's not just that one venue.

Amazon.com: Whirlwind ISOXL Line-Level Isolation Transformer, 3-Pin XLR Male/Female Connectors: Electronics

How does it work? IOW, what is it actually doing? I'm somewhat familiar with mod'ing the connections on a conventional balanced XLR cable.

Riis

 

[dheafey]

I'm not a huge fan of direct outs from amp heads or even preamp pedals (Queue dozens of "mine works fine" replies. ;-)). Open the device up and a rare few are transformer isolated. Even more rare do they use a decent transformer. My signal to the board comes from a Radial JDI (Jensen transformer) at the end of my pedal chain (Pitch Black->Sansamp BDDI->Empress Compressor->JDI). Power could still be a concern, as others have mentioned. I plug into the same power source as the on stage IEM mixer.

 

[rjd5974]

How does it work? IOW, what is it actually doing? I'm somewhat familiar with mod'ing the connections on a conventional balanced XLR cable.

I can't tell you the technical details of how it works, but you plug it into where ever your direct out is, and then the sound guy puts the XLR into it. All I know is it eliminated the problem entirely when nothing else worked.

 

[Gravedigger Dav]

I don't personally know this to be true, but I had a sales dude at GC dissuade me from a 1 spot. He said they can induce the hum. Reading your posts, that seems to be the common thread, if I didn't misread or not read part of what you said.

 

[dheafey]

I don't personally know this to be true, but I had a sales dude at GC dissuade me from a 1 spot. He said they can induce the hum. Reading your posts, that seems to be the common thread, if I didn't misread or not read part of what you said.

I'd heard the same which is why I ended up with a Snark SA-1.

 

[ak56]

How does it work? IOW, what is it actually doing? I'm somewhat familiar with mod'ing the connections on a conventional balanced XLR cable.

Riis

I can't tell you the technical details of how it works, but you plug it into where ever your direct out is, and then the sound guy puts the XLR into it. All I know is it eliminated the problem entirely when nothing else worked.

It's a simple 1:1 isolation transformer between the input and output XLR's, with no ground connection between the two sides.

 

[Zooberwerx]

It's a simple 1:1 isolation transformer between the input and output XLR's, with no ground connection between the two sides.

Thank you. When viewing the product via the link above, they also suggest this:

Amazon.com: Whirlwind Lifter: Musical Instruments

It disconnects pin one to isolate the ground.

Riis

 

[s0c9]

Thank you. When viewing the product via the link above, they also suggest this:

Amazon.com: Whirlwind Lifter: Musical Instruments

it disconnects pin one to isolate the ground.

While this is fine in-line on a low-z level signal, I think it should be said that DO NOT GROUND lift your amps.. especially if they are tube amps! You will become the ground.. that can get you killed!
Likewise, if you touch a mic with your lips and get a "tingle".. you have an errant ground somewhere.. GET IT FIXED !

 

[rtslinger]

I use this Boss Noise Suppressor works great