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Dealing with dirty power/grould loop issues

B

Bob Palmer

Apr 17, 2013
112
1
#1
Hey all,

Both in my home studio (100 year old house with dubious wiring), and in some small bar gigs (with equally dubious wiring) I have had issues where my small PA (a pair of Kustom 50 watt speakers) pick up significant humming/etc.

In the case of my home, it's definitely (or at least mostly) ground loop related, since if I use a two prong adaptor (which I know is a no-no, but wanted to troubleshoot), most of the hum goes away.

That being said, some other things I have seen:
- If I get my active bass too close to the amp (or my PC), I start getting feedback issues
- In one venue, I was hearing their crappy jukebox tunes echo through my PA speakers, even witn no connection other than to the wall outlet.

So my question is, what should I pick up to help mitigate these issues? Not looking to break the bank, so something that gets me 90% there at a (relatively) low price point would be great.

Thanks as always!
Bob
 
#3
You probably don't have "dirty power" issues, and no power "conditioner" is likely to help, even one with a substantial price tag.

The issue in a so-called "ground loop" usually boils down to what are actually "pin 1 problems" as well as questionable gain structure.

So in addition to the Kustom powered PA loudspeakers, you also have an amp and a PC. Feedback when you bring your bass close to the amp is understandable, but it's really unusual to get feedback through a PC. Can you elaborate on what exactly is feeding back in that situation?

In the situation where you heard the juke box music coming out of your loudspeakers, can you describe what else was in the system and how it was all hooked up? That could help us figure out what was picking up the interference and where.
 
#4
Thanks for the reply!

For the juke box situation, we had the PAs and two mics plugged in (Shure 58's) - but between sets everything was powered off - yet I was hearing their music resonating pretty clearly through my speaker, and a couple of times we had some horrific humming coming through (I think in that case we turned the PAs off because I was afraid of damage, turned them back on again, and eased back to the same volume level we had before the horrible humming kicked in).

The PC one, it was definitely weird... if my Ibanez 505 got too close to my computer, I hear a loud hum from my amp - if I backed it off, it would diminish (example would be leaning forward to turn the volume up on a backing track playing on the PA) - seem to have the issue less with my Stingray.

My major problem now is that if one of my PA speakers is plugged into the same power strip as my PC or Mac, I get a staticky buzzy noise, which vanishes if I use a plug adapter, but ideally I'd like to fix the problem right. Ideally with some piece of gear that does not break the bank :)


Bob Lee (QSC) said:
You probably don't have "dirty power" issues, and no power "conditioner" is likely to help, even one with a substantial price tag.

The issue in a so-called "ground loop" usually boils down to what are actually "pin 1 problems" as well as questionable gain structure.

So in addition to the Kustom powered PA loudspeakers, you also have an amp and a PC. Feedback when you bring your bass close to the amp is understandable, but it's really unusual to get feedback through a PC. Can you elaborate on what exactly is feeding back in that situation?

In the situation where you heard the juke box music coming out of your loudspeakers, can you describe what else was in the system and how it was all hooked up? That could help us figure out what was picking up the interference and where.
Click to expand...
 
#5
Side note, I am hooking to the PA from my audio input using a pair of 1/4" plugs (stereo output via a pair of 1/4" outs, so one to each PA speaker's line in). My left PA speaker is fine - my right (plugged in with the PC) is the problem child. I could in theory run these to alternate power strips, but would be interested in something that solved the problem given I've had nasty noise/feedback issues with these at a live venue before and would not mind killing two birds with one stone.

Thanks again!
Bob
 
#6
Bob Palmer said:
Thanks for the reply!

For the juke box situation, we had the PAs and two mics plugged in (Shure 58's) - but between sets everything was powered off - yet I was hearing their music resonating pretty clearly through my speaker, and a couple of times we had some horrific humming coming through (I think in that case we turned the PAs off because I was afraid of damage, turned them back on again, and eased back to the same volume level we had before the horrible humming kicked in).

The PC one, it was definitely weird... if my Ibanez 505 got too close to my computer, I hear a loud hum from my amp - if I backed it off, it would diminish (example would be leaning forward to turn the volume up on a backing track playing on the PA) - seem to have the issue less with my Stingray.

My major problem now is that if one of my PA speakers is plugged into the same power strip as my PC or Mac, I get a staticky buzzy noise, which vanishes if I use a plug adapter, but ideally I'd like to fix the problem right. Ideally with some piece of gear that does not break the bank :)
Click to expand...

Are you sure you were getting jukebox music through the PA loudspeakers when they were powered off? That seems unlikely.

Was the hum when your bass was close to the PC in addition to the feedback? Did you perhaps have the bass feeding into the computer and the computer loudspeakers turned up when it fed back?

Does the other PA loudspeaker also buzz when you you plug it into the same outlet strip as the PC or Mac, or only one of them? What sort of AC/mains plug do your PC and Mac have?
 
#7
Bob Palmer said:
Side note, I am hooking to the PA from my audio input using a pair of 1/4" plugs (stereo output via a pair of 1/4" outs, so one to each PA speaker's line in). My left PA speaker is fine - my right (plugged in with the PC) is the problem child. I could in theory run these to alternate power strips, but would be interested in something that solved the problem given I've had nasty noise/feedback issues with these at a live venue before and would not mind killing two birds with one stone.

Thanks again!
Bob
Click to expand...

Bob, do you always use the same loudspeaker for left and the same one for right?

A feedback issue would indicate that something's turned up way too loud. If your bass is feeding back, then sound from the loudspeaker is somehow strong enough to either get picked up directly by the bass pickups or to excite a string and keep it vibrating indefinitely (think Jimi Hendrix).
 
#8
Before you go dropping big money (especially over priced Monster anything) on a fancy power conditioner try this.
[Invalid or Expired Link Removed] If the problems went away when you lifted the ground this will fix it without lifting the ground. For what it is it's over priced, but it's not hundreds of dollars either.
 
#9
Believe it or not, yeah RE their juke resonating in my speakers (their juke routed through the house PA, and the power in this place was pretty sketchy). when I first heard it I immediately powered down the PA speakers, and was surprised that I could still hear it (a low volume, but still.. if you were next to the PA stand you could clearly hear it).

Was mostly hum, without playing... just proximity and I'd start hearing humming coming through - but mostly on the Ibanez 505, never had an issue with the passive basses.

Both speakers exhibit the same behavior. Basically I have two giant power strips on each side of my work area, that go directly to power outlets, with the PC and Mac plugged right into the power strips (and the PA speaker in the same strip)

Thanks again :)

Bob Lee (QSC) said:
Are you sure you were getting jukebox music through the PA loudspeakers when they were powered off? That seems unlikely.

Was the hum when your bass was close to the PC in addition to the feedback? Did you perhaps have the bass feeding into the computer and the computer loudspeakers turned up when it fed back?

Does the other PA loudspeaker also buzz when you you plug it into the same outlet strip as the PC or Mac, or only one of them? What sort of AC/mains plug do your PC and Mac have?
Click to expand...
 
#10
Bob Palmer said:
Believe it or not, yeah RE their juke resonating in my speakers (their juke routed through the house PA, and the power in this place was pretty sketchy). when I first heard it I immediately powered down the PA speakers, and was surprised that I could still hear it (a low volume, but still.. if you were next to the PA stand you could clearly hear it).

Was mostly hum, without playing... just proximity and I'd start hearing humming coming through - but mostly on the Ibanez 505, never had an issue with the passive basses.

Both speakers exhibit the same behavior. Basically I have two giant power strips on each side of my work area, that go directly to power outlets, with the PC and Mac plugged right into the power strips (and the PA speaker in the same strip)

Thanks again :)
Click to expand...

Bob, in what way is the power sketchy? Have you measured the voltage or anything?

I really doubt that the jukebox audio comes in through the power line. Your powered loudspeakers's power cord inlet is not an audio input. At first you said everything was powered off and you heard sound, and later you said it was all on and then turned off.

When you say "mostly hum," are you referring to when you were also getting feedback? Or is that a different issue a different time, or something?

Can you perhaps start all over with your descriptions? You've added information that either contradicts what you said before or is a different situation than what you'd described. Tell us what you have in your system(s) and how they're hooked up. Try to be as accurate and complete as possible, OK?

Do you know what kind of AC/mains plug(s) your PC and Mac use?
 
#11
Sketchy as in really old looking wiring, junction boxes bolted to the floorboards, etc. Anyhoo, for clarity RE sound from the PA. Two 50 watt speakers daisy chained with an XLR cable, two mics hooked into it. Each plugged into a separate outlet at the venue, venue has their own speakers for the juke. When our first set was over, I noticed music coming from the PA speakers (despite being powered off). Very low volume (as in, you had to be next to them and you would notice it). Our drummer who also does live sound was pretty perplexed as well.

Re the home setup - just the usual three prong power plugs on everything, PC to power strip, power strip to wall outlet. Right now, if I turn on a PA speaker plugged with a standard three prong power plug into the same strip as my PC, I get loud buzzing/humming/white noise which increases with the PA's volume, but stays constant regardless of what the line level volume going into it is (so if I turn the PA speaker down low, and crank the PC's volume and the volume on my audio interface, I drown out the hum). Additionally, if I record the sound to the PC via the audio interface and just use the speakers as monitors, it does not record any of the nasty humm/buzz, so it's purely an artifact of the speaker output (which makes sense).

Buzzing/humming occurs with both speakers, significantly more pronounced if they are on the same power strip as the PC that the audio interface is attached to (which is also the output device for the monitor speakers)

Hope that makes sense :)


Bob Lee (QSC) said:
Bob, in what way is the power sketchy? Have you measured the voltage or anything?

I really doubt that the jukebox audio comes in through the power line. Your powered loudspeakers's power cord inlet is not an audio input. At first you said everything was powered off and you heard sound, and later you said it was all on and then turned off.

When you say "mostly hum," are you referring to when you were also getting feedback? Or is that a different issue a different time, or something?

Can you perhaps start all over with your descriptions? You've added information that either contradicts what you said before or is a different situation than what you'd described. Tell us what you have in your system(s) and how they're hooked up. Try to be as accurate and complete as possible, OK?

Do you know what kind of AC/mains plug(s) your PC and Mac use?
Click to expand...
 
#15
"Voodoo" is an apt name for a power "conditioner" manufacturer. ;)

When you play live, plug the two powered loudspeakers into the same outlet or outlet strip.

In your home setup, do you get buzzing if the PC and Mac are not hooked into it and not turned on?
 
#17
Yep. primarily with the PC/Mac on. side note - got a couple of the Hum X plugs and that has wiped out the issue

Bob Lee (QSC) said:
"Voodoo" is an apt name for a power "conditioner" manufacturer. ;)

When you play live, plug the two powered loudspeakers into the same outlet or outlet strip.

In your home setup, do you get buzzing if the PC and Mac are not hooked into it and not turned on?
Click to expand...
 
#19
Bob Palmer said:
Thanks for the reply!

For the juke box situation, we had the PAs and two mics plugged in (Shure 58's) - but between sets everything was powered off - yet I was hearing their music resonating pretty clearly through my speaker, and a couple of times we had some horrific humming coming through (I think in that case we turned the PAs off because I was afraid of damage, turned them back on again, and eased back to the same volume level we had before the horrible humming kicked in).

The PC one, it was definitely weird... if my Ibanez 505 got too close to my computer, I hear a loud hum from my amp - if I backed it off, it would diminish (example would be leaning forward to turn the volume up on a backing track playing on the PA) - seem to have the issue less with my Stingray.

My major problem now is that if one of my PA speakers is plugged into the same power strip as my PC or Mac, I get a staticky buzzy noise, which vanishes if I use a plug adapter, but ideally I'd like to fix the problem right. Ideally with some piece of gear that does not break the bank :)
Click to expand...

How are the cables routed? Are they laid parallel to or draped over speaker wires for the juke box? If that uses 70V speaker output, it can contribute to picking up the sound.

Staticy, buzzy sound is usually from a computer's screen or power supply. Try moving the computer farther from any sensitive devices, like mics, guitar pickups, etc.

You want all of your equipment to be on the same circuit. If any external items are plugged into your PA, make sure they're on the same circuit. This can be a problem in an older home or a bar, because these kinds of places don't necessarily have dedicated circuits for anything- they often share one with freezers, coolers, neon lights, cash registers and others. Once you plug a PA in, the circuit can be overloaded, causing additional problems- voltage often drops before breakers pop. If you have ground loops, Jensen Transformers are about the best for isolation. They're expensive, but they work. EbTech's HumX work, too. I have even used Radio Shack (I prefer not to) and PAC ground loop isolators when RCA connections are used. The PAC are designed so they provide a 1 or 1.25dB increase in level, which is good if hiss is present, along with the hum. Proper level setting is still necessary, though.

If the lights dim or flicker when the wind blows, the fridge kicks on or maybe the furnace/AC starts, the wiring should be checked- it may be as simple as the connections to the cable from the pole, outside. I have seen these go bad and cause this kind of problem, at my parents' house. Once they were replaced, everything was fine.

However, a 100 year old house probably has what's called 'knob and tube' wiring and if you decide to have an electrician change or connect to the same circuit, you need to know that the electric code calls for this kind of wiring to be disconnected and abandoned, including removing as much as possible to keep it from being used in the future.
 

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