ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3   Go Down

Author Topic: 60 HZ hum, only in Backline Amps - on same power as Sound System  (Read 11195 times)

Jerome Casinger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 278
    • Castle Rock DJ and Sound

So I was stumped last night.  New venue, shady power to say the least, but had a dedicated distro for sound/lights.  I have been running my rig for 3 years now In the area and never had an issue. (QSC KW, X32).  Last night the Bass Amp and Guitar amp had a hardcore 60 hz buzz....flipped ground lifts and it got better but was still horrendous.  Moved them onto my power so we were running on the same circuit....no change to there amps. 

I had a slight hum in the PA, was odd, as I turned on a sub it was there, when I turned the other it disappeared.  When the gig was over (everything powered down, bar cleared out), you could hear the 60hz hum big time from an AC unit or Ice Machine or something big time, luckily the band heard it as well at that point and realized it wasn't my gear (I was a fill in sound guy, they didn't have the issue a month or so ago when they where there).

I ran through what I new how to do....could an appliance introduce "noise" somehow into the entire power grid?  Is there a way to check that?  Or is there anything I could have done.

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17176
  • Hickory, Mississippi, USA
    • Resotune
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #1 on: July 04, 2015, 01:53:55 PM »

Guitar pickups sending high impedance instrument level signal around in a high magnetic hum field will generally pick up hum.

JR
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3361
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #2 on: July 04, 2015, 02:09:42 PM »

Active or passive DI boxes? Lots of cheap active DI boxes don't have an isolated pin-1 so they can send 48-volt power across the pin-1 lift. Also, there are imported DI boxes with rather crappy transformers that don't do well at lifting grounds. If pulling out the XLR cable from the DI box stops the hum/buzz, then stick a mic in front of the offending amp and get on with the show. Sound check is no time for mental exercises. Just get it done and run...

Also, check to make sure your XLR cables don't have a pin-1 to shell bond. If they do and you're plugged into a DI with a metal XLR jack, that bond will be in parallel with the DI's ground lift and stop it from lifting properly.

Jerome Casinger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 278
    • Castle Rock DJ and Sound
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #3 on: July 05, 2015, 11:12:32 AM »

No DI's on either.  The guitar cab was Mic'd, and the Bass amp had it built into the head but had the hum without anything plugged in.  When he would unplug the bass the hum was ridiculous.

Active or passive DI boxes? Lots of cheap active DI boxes don't have an isolated pin-1 so they can send 48-volt power across the pin-1 lift. Also, there are imported DI boxes with rather crappy transformers that don't do well at lifting grounds. If pulling out the XLR cable from the DI box stops the hum/buzz, then stick a mic in front of the offending amp and get on with the show. Sound check is no time for mental exercises. Just get it done and run...

Also, check to make sure your XLR cables don't have a pin-1 to shell bond. If they do and you're plugged into a DI with a metal XLR jack, that bond will be in parallel with the DI's ground lift and stop it from lifting properly.

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Online Online
  • Posts: 23744
  • Wichita, Kansas USA
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #4 on: July 05, 2015, 11:30:25 AM »

I'm suspicious of the distro or something plugged into it.

Stuff hums because something is grounded that shouldn't be, or isn't grounded that needs to be.

Could be defective back line amp, mis-wired extension cord or power drop box, or outlet on the distro.  Only takes 1 to create problems.
Logged
"If you're passing on your way, from Palm Springs to L.A., Give a wave to good ol' Dave, Say hello to progress and goodbye to the Moonlight Motor Inn." - Steve Spurgin, Moonlight Motor Inn

Geoff Doane

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 954
  • Halifax, NS
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #5 on: July 05, 2015, 01:18:13 PM »

I'm suspicious of the distro or something plugged into it.


Ground and neutral swapped at some point, or just connected together, has been know to cause problems like that.

GTD
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3361
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #6 on: July 05, 2015, 08:19:21 PM »

Ground and neutral swapped at some point, or just connected together, has been know to cause problems like that.

GTD
But that usually requires a ground-loop path, such as a DI to XLR connection, to make it hum. As mentioned previously, this sounds like magnetic coupling. I've heard this happen when the stage was built over top of a large conduit passing building power. Did you happen to notice if the hum changed when the guitar necks changed orientation on stage? When they line up with a power conduit they can hum, but when at a 90 degree angle the hum usually nulls out. Interesting problem...

Jerome Casinger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 278
    • Castle Rock DJ and Sound
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #7 on: July 06, 2015, 12:14:38 PM »

The GTR player said he noticed a difference in his positioning.  I should have went and investigated what it was in the back at the end of the night that was making the hum (annoying).  At that point it was 230am and my focus was elsewhere, but it was distinctly coming from the back of the bar.  Sounds like if I have to go back there I will be doing some more investigating prior.  I just didn't expect to walk into such an issue so didn't have enough time to do much more troubleshooting than switching power to different circuits.

But that usually requires a ground-loop path, such as a DI to XLR connection, to make it hum. As mentioned previously, this sounds like magnetic coupling. I've heard this happen when the stage was built over top of a large conduit passing building power. Did you happen to notice if the hum changed when the guitar necks changed orientation on stage? When they line up with a power conduit they can hum, but when at a 90 degree angle the hum usually nulls out. Interesting problem...

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17176
  • Hickory, Mississippi, USA
    • Resotune
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #8 on: July 06, 2015, 01:58:52 PM »

The GTR player said he noticed a difference in his positioning.  I should have went and investigated what it was in the back at the end of the night that was making the hum (annoying).  At that point it was 230am and my focus was elsewhere, but it was distinctly coming from the back of the bar.  Sounds like if I have to go back there I will be doing some more investigating prior.  I just didn't expect to walk into such an issue so didn't have enough time to do much more troubleshooting than switching power to different circuits.
An old school neon light sign could make some noise...

If the position of the guitar player changes the noise it may not be related to conducted power noise, but the general noise field in the room. (I think I already suggested this in an earlier post).

JR
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Online Online
  • Posts: 23744
  • Wichita, Kansas USA
Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #9 on: July 07, 2015, 10:15:11 AM »

The GTR player said he noticed a difference in his positioning.  I should have went and investigated what it was in the back at the end of the night that was making the hum (annoying).  At that point it was 230am and my focus was elsewhere, but it was distinctly coming from the back of the bar.  Sounds like if I have to go back there I will be doing some more investigating prior.  I just didn't expect to walk into such an issue so didn't have enough time to do much more troubleshooting than switching power to different circuits.

If that's the case then I'll walk back my idea about a wiring problem or defective gear...  But with inductive interference the guitarists usually find out quickly that there is a positional aspect to it and helps with identifying the cause.
Logged
"If you're passing on your way, from Palm Springs to L.A., Give a wave to good ol' Dave, Say hello to progress and goodbye to the Moonlight Motor Inn." - Steve Spurgin, Moonlight Motor Inn

ProSoundWeb Community

Re: 60 HZ hum, only in Backline Amps - on same power as Sound System
« Reply #9 on: July 07, 2015, 10:15:11 AM »


Pages: [1] 2 3   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.037 seconds with 24 queries.