60Hz hum question...can it be that easy?

Lutz · 21st June 2008

Hi all,
I feel like I may be asking a very easy question....but sometimes it's best to bounce these things around, especially when it's a 'new to me' kind of problem.

Here is my scenario. I have been to a school to optimize their set up for the kids theater performances, as well as their band performances. I managed to get them sounding 10 times better than before I came in to do the work, except 1 thing. .....
The first day I went in the system was silent, no hum in the mains at all. I came back 2 days later to set their main EQ, and finish working on their set up. and there was the buzz as soon as I powered up. Nothing had changed from the previous visit...well at least in the sound setup. This leads me to believe there is likely some other piece of equipment on the same circuit (likely in the cafeteria kitchen) had been plugged in recently. On top of that, this is an old, historic building, likely with some layers of creative electrical work within the walls that could have 60hz ghosts coming in and out at any given time. So......
I have the whole rig balanced, that is not an item of issue (aside from any design errors on the manufacturers part). The amp on its own doesn't produce any hum- it's when I connect the house EQ to the amp. The next step, in my mind, is to find something like the HUM X to insert before the power bar that hosts every units AC. Would I be correct in assuming that this type of device will filter out the 60hz ground loops that come and go on this AC line? It almost seems too easy....

Thanks in advance for any input you may have.

blim · 21st June 2008

Quote:

Originally Posted by Lutz

The next step, in my mind, is to find something like the HUM X to insert before the power bar that hosts every units AC. Would I be correct in assuming that this type of device will filter out the 60hz ground loops that come and go on this AC line? It almost seems too easy....

I would love for someone who has used Hum-X to tell us how effective it is. I'm no electrical expert, but I agree -- the thing seems too good to be true. I mean, I've heard of studio owners who have torn up an entire building, spending thousands of dollars trying to find and get rid of a ground loop. Why would they have done this if a simple $90 device could have taken care of the problem?

aussie_techie · 21st June 2008

have you tried lifting the ground between the foh rack and amp rack?

dbbubba · 21st June 2008

Un-plug every input source one by one to see if the hum goes away.
If anyone with a D.I. input plugged into the wrong place as far as AC goes it will give you hum.
We do a GIANT high school production each year where we take in a full concert rig.
We have our full 200A distro which includes mains, F.O.H., monitor world, full backline power and several other 20A legs for stuff like video.
EVERY year a kid manages to plug into the outlets on the stage instead of the backline legs from our distro. HUMMMMMMMM

If it isn't from an input look for anything from lighting world that might have been introduced and is sharing your power.
On ALL of our shows we have lighting separate from audio and video.
ALWAYS

The problem WILL NOT be something on the line causing trouble unless there is something like a SCR dimmer or something extra plugged in.

There is a ground loop and you will just have to hunt it down.
You'll learn something when you do find it.

Look for extension cords without ground lugs.
Look for stuff plugged into outlets that they shouldn't be plugged into.

I promise that someone moved something, changed something or added something in the AC system.

chris319 · 21st June 2008

See if they can show you the building's ground rod.

stagefright13 · 21st June 2008

Plug EVERYTHING audio into the same circuit. And make sure it isn't shared with microwaves and other stuff. Use one big cord. And try different sockets if you don't have a power map.

Lutz · 21st June 2008

Great, thanks so far for all the help! Just curious though, if anyone has used products like HUM X ? If it can resolve issues like this, wouldn't it save a lot of time and effort?

t_chance · 25th June 2008

I had a coffee house where I could never get clean power. I tried other isolation in line, with no luck. I stopped at my local audio store and they had the hum-x and sold it to me on the premise that if it didn't work I could return it. It did the job, and I have used it in other venues and would not give it back. I think I paid $80 for mine and it was worth every penny.

huub · 26th June 2008

Quote:

Originally Posted by dbbubba

If it isn't from an input look for anything from lighting world that might have been introduced and is sharing your power.
On ALL of our shows we have lighting separate from audio and video.
ALWAYS

Lighting...

drpro · 27th June 2008

As I write this I am about to start work on a Brooks and Dunn concert that we are shooting for GAC. During setup yesterday they had a nice 60hz coming thru the PA system. I asked them about it and they said they just live with it. So even the big boys have the problem.

David

21st June 2008	#1
Lutz Gear interested Joined: Apr 2007 Location: Montreal Posts: 7 Thread Starter	60Hz hum question...can it be that easy? Hi all, I feel like I may be asking a very easy question....but sometimes it's best to bounce these things around, especially when it's a 'new to me' kind of problem. Here is my scenario. I have been to a school to optimize their set up for the kids theater performances, as well as their band performances. I managed to get them sounding 10 times better than before I came in to do the work, except 1 thing. ..... The first day I went in the system was silent, no hum in the mains at all. I came back 2 days later to set their main EQ, and finish working on their set up. and there was the buzz as soon as I powered up. Nothing had changed from the previous visit...well at least in the sound setup. This leads me to believe there is likely some other piece of equipment on the same circuit (likely in the cafeteria kitchen) had been plugged in recently. On top of that, this is an old, historic building, likely with some layers of creative electrical work within the walls that could have 60hz ghosts coming in and out at any given time. So...... I have the whole rig balanced, that is not an item of issue (aside from any design errors on the manufacturers part). The amp on its own doesn't produce any hum- it's when I connect the house EQ to the amp. The next step, in my mind, is to find something like the HUM X to insert before the power bar that hosts every units AC. Would I be correct in assuming that this type of device will filter out the 60hz ground loops that come and go on this AC line? It almost seems too easy.... Thanks in advance for any input you may have.

21st June 2008	#6
stagefright13 Lives for gear Joined: Apr 2006 Location: Pennsylvania Posts: 1,221	Plug EVERYTHING audio into the same circuit. And make sure it isn't shared with microwaves and other stuff. Use one big cord. And try different sockets if you don't have a power map. __________________ Stagefrightrecords.com

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21st June 2008	#3
aussie_techie Lives for gear Joined: Jan 2004 Location: Perth, Australia Posts: 2,709	have you tried lifting the ground between the foh rack and amp rack?

21st June 2008	#4
dbbubba Banned Joined: Sep 2005 Posts: 7,099	Un-plug every input source one by one to see if the hum goes away. If anyone with a D.I. input plugged into the wrong place as far as AC goes it will give you hum. We do a GIANT high school production each year where we take in a full concert rig. We have our full 200A distro which includes mains, F.O.H., monitor world, full backline power and several other 20A legs for stuff like video. EVERY year a kid manages to plug into the outlets on the stage instead of the backline legs from our distro. HUMMMMMMMM If it isn't from an input look for anything from lighting world that might have been introduced and is sharing your power. On ALL of our shows we have lighting separate from audio and video. ALWAYS The problem WILL NOT be something on the line causing trouble unless there is something like a SCR dimmer or something extra plugged in. There is a ground loop and you will just have to hunt it down. You'll learn something when you do find it. Look for extension cords without ground lugs. Look for stuff plugged into outlets that they shouldn't be plugged into. I promise that someone moved something, changed something or added something in the AC system.

21st June 2008	#5
chris319 Lives for gear Joined: Jun 2007 Location: West Hollywood, USA Posts: 1,492	See if they can show you the building's ground rod.

25th June 2008	#8
t_chance Gear maniac Joined: Aug 2005 Location: St Paul MN Posts: 162	I had a coffee house where I could never get clean power. I tried other isolation in line, with no luck. I stopped at my local audio store and they had the hum-x and sold it to me on the premise that if it didn't work I could return it. It did the job, and I have used it in other venues and would not give it back. I think I paid $80 for mine and it was worth every penny.

27th June 2008	#10
drpro Gear Head Joined: Mar 2008 Posts: 70	As I write this I am about to start work on a Brooks and Dunn concert that we are shooting for GAC. During setup yesterday they had a nice 60hz coming thru the PA system. I asked them about it and they said they just live with it. So even the big boys have the problem. David