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Ground loop master thread
Old 6th November 2019
  #1
Here for the gear
 

Ground loop master thread

So I've been doing studio work for a while now and I'm now moving to live work. I usually dealt with noise on instruments by attaching a wire to the bridge or any other place attached to the circuitry of the instrument or cable to mine or the player's skin. I know about instrument shielding and grounding and have a general idea about grounding but it's all still sorta magical nonsense to me. Now that I'm moving into live sound on a cheap mixer, the ground loop thing is getting on my nerves because there are alot of opposing opinions all over the place so I came here to ask for some help. Here's what I want to know. Anyone with knowledge of electricity and dealing with ground loops and such, I'd be very grateful were they to chime in because I'd like to know the science too, not just how to fix it but anyone, feel free to help, talk about your experiences and so on. I'm desperate.
So here goes:
1) Starting from the building's source of power and circuit breaker. I've heard that studios usually ask power companies for an isolated line to remediate 'dirty' power. Obviously this isn't always practical for someone doing live sound but I'd like to know what that's about. I also read about these devices called GFCIs that I think attach to circuit breakers and there are some that are shrunk and in a different form as to attach directly to an outlet. Do GFCIs in a circuit breaker help with ground loops?

2) At the outlet side of things, the outlet version of GFCIs, Power Conditioners with RFI and EMI filtering, 'Ebtech's Hum Canceller', what should we employ here when the buildings power quality is beyond control?

3) After the outlet, moving on to the mixer and audio cables and so on. DI boxes and hum eleminaters on everything? Pseudo balanced cables on some things? Shielded cables help right? Why are audio gear manufacturers so DUMB ABOUT WIRING. There's a compliance standard right? I feel like that's never followed. Found this white paper (a term for something that's well established and could be called a standard) on interconnection between audio gear. Showed all the wiring that should be employed and a sigh of relief came as years of confusion over gear and microphones that misbehaved with mixers was resolved.

4) Beyond all guitars being shielded, grounded and having working, noise free equipment (depending on their inherent designs ofcourse [noise cancelling bass pickups anyone? Glenn Fricker taught me that one]), if there's anything past this point that's important I may have missed, feel free to mention.

Thank you to anyone who even read this far whether you have advice or stories to give.
Old 9th November 2019
  #2
Here for the gear
 

Bump
Old 1 week ago
  #3
Here for the gear
 

Found solutions to the problem but will someone please explain this for us normies
Old 1 week ago
  #4
Lives for gear
 
avare's Avatar
 

Quote:
Originally Posted by GoldenH2O View Post
Found solutions to the problem but will someone please explain this for us normies
Why do you not at least identify the white paper so we know your level of knowledge?

Put your questions clearly, not buried in paragraphs.
Old 1 week ago
  #5
Gear Maniac
 

1. Find the source/sources of the noise

2. Come up with a solution to fix the noise.

3. don't attach anything to peoples skin. FIX the issue don't bandade it.

There are ALL kinds of reasons you can have issues. If you are doing livesound with your own gear and noise issues pop up at different locations then the issues if probably something in your gear.

Just recently I was working with a church that had 2 issues.

1. Ground loop via laptop connection and
2. RF noise via VGA projector cable

A DI box with ground lift fixed the loop and a new hdmi cable with sheilding fixed the noise issue, now the sound is pristine!

SO step one is to figure out where the noise is coming from.

Blessings
Old 3 days ago
  #6
Here for the gear
 

This is what I came up with until I can speak to other electicians and audio engineering practitioners. I spoke to someone at my power company which powers 99% of people where I live and the guy said that they don't provide isolated power lines but the conversation which ensued was insightful. He said that companies and individuals with sensitive equipment actually employ CFGIs as a first line of defense to regulate power and prevent any spikes. Now that's not always possible so the next line of defense is the outlet. A power conditioner, the likes of Furman or anything on par with or higher quality with EMI and RFI filtering is gonna kill hum from things like power amps and mixers. Get two if you can because some are susceptible to blowing up to save gear. May clean up hum from your instruments and mics too but I'd recommend ensuring those are at the very least grounded and shielded first. If they aren't/can't be and you still have hum even with or without a good power conditioner you can use DI boxes and hum cancellers between mixer and devices/instruments. Also be sure to use the right cables (instrument and speaker cables are different) and quality ones at that.

So to recap, this should be your starting point after CFGIs and/or isolated power lines.

1) Start with the speakers (and power amp if you're not using an active system) and the mixer/audio interface. Connect them together using instrument cables from the mixer to the power amp and speaker cables from the amp to the speakers. If in doubt check the manuals. Turn on the mixer first with everything zeroed out, gains set at minimum and master volume set at -inf. Turn on the power amp. Turn the volume up on the power amp. Is there hum or high frequency noise? White noise or 'air' is fine. At higher volumes, that's expected in some systems but a serious high frequency buzz which is very different than air is most likely due to an internal component issue with either the amp or the speakers. Double check on reference quality monitoring headphones. Is the HF buzz still there? Get yourself a return or do some research. Worst case scenario is you're gonna have to try a resistor or capacitor of some sort installed into a cable to bleed off the high frequencies. Now let's assume you have low frequency hum. Touch the power amp chassis. Does it go away? Touch the mixer with it's volume still down. It might go away but to a slightly lesser extent or vice versa. The one that makes it go away completely when you touch it is the problem. Turn the mixer's master volume up to unity but make sure the preamps are turned all the way down. You might get more air but you shouldn't get more hum. If you do, it should be extremely minor compared to chassis hum and that's okay. This is more often than not just the mixer warming up the signals but again it should be really really quiet even with the power amp and mixer turned up. Repeat the process of touching each device again making notes of what's hum and what's not. This process allows you to gauge what's a ground hum and what's just electronic noise. Use a power conditioner with EMI and RFI filtering to negate these problems. Experiment with only the mixer on the power conditioner and connecting the power amp direct to wall and vice versa as lots of people say that some power conditioners degrade signal integrity of power amps. If all else fails you could try using a hum canceller between mixer and power amp or power amp and speaker or both.

2) Ground and shield instruments if possible. Noiseless pickups especially on basses or single coils are also a great option for starting at the source. Use high quality shielded cables for everything except when going from power amp to speakers as mentioned earlier. Mics, especially cheaper ones can be a pain. Some of them are flat out wired wrong and require resoldering either the mic itself or making (or buying) a pseudo balanced cable. It's handy to have a pseudo balanced cable lying around anyway for contingency's sake. Gates also work really well for worst case scenarios. Now would be a great time to mention that one of my favourite YouTube audio engineers, Glenn Fricker, makes a wonderful gate pedal called the Cockblocker that is super high quality.

3) So some devices may not be easy or even possible to ground or shield. Or maybe you've grounded and shielded everything and you wanna take things further to achieve total silence in your system. This is where DI boxes and hum cancellers come in. This is another place where you wanna go for quality at least for the most important signals. An active DI on something like a bass. Even checking for DIs specific to instrument types. They should all have one thing in common though. A ground lift switch. This is where the magic happens. Hum cancellers do the same thing as DI boxes but are usually always hum cancelling and output a ground lifted signal on the 1/4 inch outputs which alot of DI boxes won't do. This makes hum cancellers ideal for some situations where you need those specific ins and/or outs.

Now listen to your system. Hear that? Neither do I. Worth it? Debatable. The broadcast guy might not care as long as he gets his SNR right but the studio owner might lose his mind trying to preserve dynamics, frequency range and overall signal integrity by using all the above, transformers and gold plated cables and connectors. I think it'd be great if we could do a direct test of a fully electrically treated system versus one that isn't to hear the difference. People have mentioned using just one of these steps can be day and night so it'd be interesting to hear. Let me know if there are any steps you agree or disagree with or steps you think should be added or removed. Cheers.
Old 2 days ago
  #7
Here for the gear
 

Btw here's the white paper on interconnection of gear that I was talking about. It has a PDF download available at the end of the page. It's really insightful. I was shocked when checking some of these. Definitely a gift to anyone who works in audio.

https://www.rane.com/note110.html
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