PA System Hum

Chuck Blake · From: West Virginia, USA

Was wonder will a Power Conditioner help to eliminate a hum we're having in our Band's PA System in certain venues!
We run a Mackie Non-powered mixer ProFx V.3, thru Mackie Powered 15" main speaker.

We either mic or go direct with all amps and use non-powered Peavey monitors, powered by a Crown amp.

Any ideas......
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Dave Grafe · From: Hudson River Valley NY

If it's only in certain venues and it's quiet otherwise I would first check the band setup in those venues:
The first is to make certain that everything that feeds the PA is plugged into the same power source thus the same grounding point.
If taking lines from wireless receivers, amps or keys all grounds should be lifted whenever possible.
A power conditioner that the whole band plugs into is a great idea, especially if it has a voltage monitor. A good one will filter hash in the line from nearby neon signs and electrical motors, it may not end the issues with noisy clubs but it will be a big step in that direction.

Bobby D. Jones · From: West Virginia, USA

Florescent lights or bad ballast in a florescent light can cause major problems.
If the building has a kitchen, Bad thermostats on deep fryers can cause interment problems with electronics.

Check the voltage in the problem building, A pole transformer with a short can cause high voltage and cause problems.

ajm · From: Los Angeles

From the OP: ".....a hum we're having in our Band's PA System in certain venues!"

Sort of eluded to in the previous responses, but the AC wiring in CERTAIN VENUES may be the problem.

I have a friend that does a karaoke service.
He has a powered mixer/turntables/desk/etc. He also has powered speakers.
Because of where everything is located when it's all set up, sometimes the desk and speakers end up using separate outlets.
Long story short, he had what sounds like the same problem in one particular venue.
It turned out to be a mis-wired AC outlet where the ground was swapped with either the hot or neutral.

If you have a mixer and an amp and powered speakers and whatever plugged in to various outlets this may be the problem.
Sometimes the wiring in bars, etc, especially old places, is not checked very closely.
You may have an outlet that has one of the phases/neutral
and the ground swapped.
You can buy an outlet checker for no more than $10-20 at Home Depot or Lowes or wherever.
They are stoopid simple to use. They usually plug right in to an outlet and have three lights on them that indicate the wiring. You don't need to be an engineer or a contractor to use it.
Before you use an outlet in a venue check the outlet(s) and make sure they are correct.

After that, if everything checks out, then it gets more complicated.

Chuck Blake · From: West Virginia, USA

Thanks for the replies. I have had side conversation on the subject of hum elimination or causes of an electrical hum and one of the clears suggestions was try to power all equipment from one outlet or circuit. I plan on trying this at our next play date. Most of our equipment is solid state with minimal electrical draw.
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Craig A Davidson · From: Wisconsin Rapids, Wisconsin USA

You can test two outlets and even if they both show ok on the tester you can still get hum if the ground wires are wired to opposite ground posts in the main box.
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Bill A. Moore · From: Silver City, New Mexico, USA

Code requires that all grounds terminate to a common buss in the entrance panel.
I used to tie all stage electrical, (except lighting), to a common circuit. Many of the old venues in my area are not up to code!

Craig A Davidson · From: Wisconsin Rapids, Wisconsin USA

But if you look there is a ground lug on both sides of the box. It's grounded, yes but if two outlets are on different lugs it can cause hum. Been there, done that, got the t-shirt, and the hat. So the best thing to do is connect from the same outlet and possibly use a conditioner.
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Bill A. Moore · From: Silver City, New Mexico, USA

The entrance panel, has both Neutral and Ground busses, which come together at that point. Extension or sub panels isolate all the Grounds and Neutrals to their respective buss bar which are electrically separated.
If the equipment ground is solid to the entrance ground, I don't see a way for it to induce hum. Now using a circuit that has a high load, (compressor), or as others have said lighting or thermostic controls could induce ripple in the powersupply.

Dave Grafe · From: Hudson River Valley NY

Bill A. Moore · From: Silver City, New Mexico, USA

Dave, for that to happen, you would need a poor connection in either the grounds or neutral circuits. Yes, a ground lift function is a workaround for a problem, but if all equipment is properly grounded, there can be no potential. It would be easy to check for high resistance, but any other equipment using the same circuit should be also experience problems.

Bob Sykes · From: North Carolina

Let's assume a facility wiring is compliant with the NEC and not degraded. Normally the "third wire" safety ground conductors have no voltage or current...in a perfect world...

Usually amplifiers and PA are powered by branch circuits (one circuit feeding multiple outlets/devices). Now let's assume the circuit(s) our sound system is plugged into also powers other devices/outlets. If these devices cause large surge currents/voltages (as mentioned previously), they will appear at the outlet(s) powering the sound system. These "surges" and "sags" are usually transient events on the AC Hot and Neutral which can present as audio pops and clicks.

If our branch circuit also powers modern electronics then noise can be induced on the third wire safety ground conductor with a continuous pulse repetition frequency of 60Hz which presents has hum or buzz.

Modern electronics generally have some sort of AC input line filtering which essentially dumps undesired noise voltages onto the safety ground conductor. These signals are small (milliVolts) but that's enough to be a problem when it's across an unbalanced audio input. There's no safety issue or code violation here. Just noise.

A solution (already mentioned above) is to power all the PA from the same outlet. Any ground voltage differences would then be due to the connected sound equipment and not other devices on the same facility branch circuit. Balanced audio interconnects are also more immune to this type of noise.

The above scenario is called "conducted noise". Radiated noise caused by electromagnetic fields is an entirely different rabbit hole but often coexists with conducted EMI.
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Dave Grafe · From: Hudson River Valley NY

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Yes, the ground loop issue is ubiquitous if bands don't pay attention to grounding at a single point. This point unfortunately falls on totally deaf ears among many musicians. I often find it hard to convince people to simply power from a single power strip/outlet - or ideally, my Furman voltage regulator (not a power conditoner), which I make every effort to plug into the same outlet that the PA is powered from. I try to avoid having to lift grounds. But at least if that is required, it should be done correctly - it is an even bigger mistake to lift every single ground, especially with old tube amps in the mix. And yes, I see this.

Of course, eliminating ground loops does not fix every possible noise problem. If house wiring is incorrect; or there is heavy noise on the line (which the Furman generally cleans up pretty well); or there is heavy stray electromagnetic radiation, these need to also be dealt with. A cheap Radio Shack style outlet tester and VOM are required equipment in my gig bag. But heavy electromagnetic radiation into single-coil pickups is the hardest nut to crack. I can deal with single-coils on guitars because their orientation relative to the noise field can be easily adjusted. But I've all but given up on them for pedal steel.

As far as so-called 'power conditioners' go, I find the typical musician-grade device no more useful than a good power strip. But a serious voltage regulator like the Furman AR-1215 can be very useful, if used in conjunction with other good practice as outlined above and in earlier posts. I've had mine since the 90s - it's out of production, but there are newer versions. The good - they work pretty well if used as intended; the bad - they are on the heavy side and not cheap like a typical 'power conditioner'.

Bill A. Moore · From: Silver City, New Mexico, USA

Dave, I think we're talking about different "ground loops". It is critical in the signal chain to keep them at bay, but usually lifting the shield at the equipment end of long cable runs takes care of most problems. Equipment grounding shouldn't be an issue as all modern equipment also filters the power supply, and all grounds will be at the same potential. Remembering electrons travel at the speed of light, I don't think 50-100 feet more wire resistance could cause any audible voltage potential.
I was an EV dealer in the 80's, and did several fixed installation install and upgrades, and often did have to chase down hum. If the AC is the cause of the hum, Chuck might get the venue to let him check his system while turning on/off different circuits at the venue to eliminate their contribution. (One venue here I was able to quiet the noise by swapping the power leg to the bandstand!) I believe the 5HP walk-in motor was the culprit, and since the problem was resolved, the owner was also happy.

Dave Grafe · From: Hudson River Valley NY

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