Is naturally occuring ground loop noise common?

Is it correct to assume all equipment makes a noise similar to ground loops even if properly grounded?  When I crank my output of my compressors I get very low frequency humming. Even on my Neve I get it.  I'm not certain if it's something to look into or just record with lower output so its not as obvious during playback.  I have seen pro guys working in Logic and SloTools with audio wave files that are miniature compared to mine. Is that because they are avoiding this very problem? Again, this stuff can play with the mind... is the hum worse today or are the variables like outputs slightly higher than the other day when I recorded and it all seemed so much more quiet?

abecedarian said:

Is it correct to assume all equipment makes a noise similar to ground loops even if properly grounded?

Click to expand...

No.

It is rare for gear to be completely free of mains power related noise, but in well executed designs it is generally kept  down in the dirt (below the hiss).

When I crank my output of my compressors I get very low frequency humming. Even on my Neve I get it.

Click to expand...

How clean is the source? Are you listening to a muted input, or open microphone?

  I'm not certain if it's something to look into or just record with lower output so its not as obvious during playback.

Click to expand...

Both... you want to confirm your system is clean, and operate at decent gain structure to avoid your noise floor be it hiss or hum.

I have seen pro guys working in Logic and SloTools with audio wave files that are miniature compared to mine. Is that because they are avoiding this very problem? Again, this stuff can play with the mind... is the hum worse today or are the variables like outputs slightly higher than the other day when I recorded and it all seemed so much more quiet?

Click to expand...

Identify where the hum is getting in,,, It could be poorly shielded cables or interface related, whihc is relatively easy to fix, or inside your gear, which can be harder to exorcise.

Everything has hiss if you turn it up far enough, but it does not need to have hum.   

JR

One thing you might also want to take into consideration, is that there might actually be a ground loop! especially if you are using a console and the device is being fed from and then back into the console.

Thank you, John, Abe for your responses.  There was no mic plugged in and it turned out the humming was louder than the hiss.  This wasn't present days ago when I first plugged everything in.  The difference was the rack.  Once I screwed everything in to the rack ears, the hum came about. 

Every piece of gear should have one path to ground to avoid ground loops and hum.

There can be many different sources of ground loops.

Chassis ground through racks and other equipment, xlr grounds and power grounds.

Try buying rack isolation screws and wrap them in teflon tape and use washers on both sides of rack ears, or remove gear from racks all together. I've seen custom wooden rack rails with gear slightly spaced to avoid touching each other.

cut or lift xlr grounds on one end of each piece of balanced gear that is interconnected. Cutting the Input side is preferred but cutting the output will work too.

Properly designed gear will ignore multiple external ground paths. You should not need to lift grounds with professional gear.

JR

JohnRoberts said:

Properly designed gear will ignore multiple external ground paths. You should not need to lift grounds with professional gear.

JR

Click to expand...

+1

JohnRoberts said:

Properly designed gear will ignore multiple external ground paths. You should not need to lift grounds with professional gear.

JR

Click to expand...

How does it do that?

Out of the Blue said:

JohnRoberts said:

Properly designed gear will ignore multiple external ground paths. You should not need to lift grounds with professional gear.

JR

Click to expand...

How does it do that?

Click to expand...

Ground-loop noise comes when the current induced in the loop is allowed to enter the audio ground of the equipment. In order to achieve that, the connection between Pins 1 of the XLR's and the ground lug of the mains cord or receptacle must be as solid as can be, and the audio ground must be connected to the chassis ground in only one point.
That's the short of it; now you can spend your whole life working this out.

That's why there are 3 wires inside XLR cables. 2 for the audio and 1 for the ground, So you have your hot and cold water pipes, and a sewer line.

As long as the ground noise currents are kept out of the audio lines, the pure audio is extracted as the simple difference between the two.

Some old 3 circuit gear, did not handle pin 1 (ground) properly and allowed those shield and ground currents to corrupt the audio, but modern properly designed gear will ignore external ground voltage nonsense. In fact lifting grounds will make the shielding less effective and could add noise. 

Google "pin 1 problem" to find several white papers on the subject.

Note: 2 circuit wiring shares shielding with an audio wire, so will never be as pure as professional interfaces.

JR

Back in the 1970's when I bought my copy I don't recall it being very expensive.

JR

JohnRoberts said:

Properly designed gear will ignore multiple external ground paths. You should not need to lift grounds with professional gear.

Click to expand...

That is the whole truth of audio device interconnection.

The rest is commentary.

Now go study it.

-a

JohnRoberts said:

That's why there are 3 wires inside XLR cables. 2 for the audio and 1 for the ground, So you have your hot and cold water pipes, and a sewer line.

Click to expand...

I would like to encourage people not to use the term 'ground' when talking about pin1 because it makes people immediatley think of 0V which is the last thing we want. Pin 1 is a shield or screen; it is an extension of the chassis.

CHeers

Ian

I think it's the other way around.
Nothing wrong in calling ground the chassis, and thence Pin 1.
But the 0V rail is not always ground. In particular in a double-insulation piece of gear.
In French, we have three different words:
Terre for ground
Chassis for metalwork ground
Masse for 0V rail
It's supposed to make things much clearer, but in fact many people take one for the other, just like women with left and right.

abbey road d enfer said:

I think it's the other way around.
Nothing wrong in calling ground the chassis, and thence Pin 1.
But the 0V rail is not always ground. In particular in a double-insulation piece of gear.

Click to expand...

And in double insulated gear the chassis is not ground either. The point is that the screen is always meant to be the chassis. You might sometimes connect the chassis to safety earth (if available) and you might sometimes connect 0V to safety ground but there is no reason to call the chassis ground.

Cheers

Ian

Sorry about my semantic indiscretion but after decades of design, I never confuse ground with 0V. It is always a sewer system for sundry noisy currents and never a single voltage.  I recall one install product I did with a screw terminal labelled "ground" that had to pass a 50A ground bonding test to the line cord ground pin (I hope it is Ok to call that ground). I could have called the screw terminal something else and avoided the wrath of UL, but I decided to beef up that ground path inside the product to pass the full safety test. Working at UL must be a little fun sometimes, catching people's products on fire, or whatever.

Pin 1 in XLRs is not a safety ground per se, and may not be labelled ground to avoid UL testing like i encountered, but there is no reason it couldn't be, since it should be a low impedance to chassis ground, and ultimately to mains ground in grounded line cord, single insulated, grounded chassis pro gear. Enough musos, get shocks from this path  to ground (pin 1 to mic handle), while I consider this a safety fail in the other gear (typically a guitar amp)  that is supplying the rouge voltage.

Confused yet?  I know there are some alternate opinions about optimal treatment of pin 1 so argue among yourselves. We have discussed this before in other areas of this web forum.

JR

JohnRoberts said:

Confused yet?  I know there are some alternate opinions about optimal treatment of pin 1 so argue among yourselves. We have discussed this before in other areas of this web forum.

JR

Click to expand...

I agree, all I was suggesting was using the word screen or shield for pin1 rather than ground as the former more accurately reflect its intended function and the latter simply adds to the already prolific confusion.

Of course, when it comes to phantom power, all bets are off.

Cheers

Ian