Ground loop hummmmm......

krizrox · Post by **krizrox** » Wed May 15, 2002 1:11 pm

Not one to give up easily, I tried attacking this problem yesterday to no avail.

Ground loop humm from Pulsar 2. Monitored with headphones from headphone out jack on mixer.

Running analog out into a Mackie 1604VLZ mixer. Nothing else connected to mixer or PC. Both PC/monitor and mixer connected to same AC source. Nothing else connected. Not even the printer or phone line. Analog cables very high quality (even tried another set). Analog outs into any 2 channels on mixer.

Ground loop humm.....

Cured problem by connecting AC adapter to mixer AC cord (disabling ground connection). When I tried using the same AC adapter on the PC AC line cord, it had no effect. Tried a second mixer. Same problem, so I'm sure it's not the mixer.

Tried every possible solution known to man including swapping PCI slots, BIOS settings, msconfig'ing everything away.

Wat the heck?

Any ideas?

With the AC adapter on the mixer, sounds beautiful. No humm and quiet. But don't want to leave it that way for safety reasons. Checked continuity from mixer to PC case. Zero ohms. What am I missing?

Kamurah · Post by **Kamurah** » Wed May 15, 2002 3:20 pm

Lift the ground and be happy.

I know the fear you have. I know the manuals say not to do it.

Every audio engineer I ever talked to curses grounding plugs...because different companies ground their gear differently.

They all lift the grounds.

I do too.

In fact, the first thing I do when I get a new piece of gear is rip out that ground plug.

Now my UPS *IS* grounded. The rest are not.

I don't know of another way to do it short of buying an islolated transformer.

Cheers

subhuman · Post by **subhuman** » Wed May 15, 2002 3:27 pm

Yup, sometimes lifting ground is the only way. In one installation, there was a groundloop between the powered monitors, and the mixer, even with nothing else plugged in! Creating our own special audio cables with ground lift cured the problem...

remixme · Post by **remixme** » Thu May 16, 2002 2:26 am

Sometimes midi cables can be the cause of ground loop hum. Have you got any of those connected?

I'm assuming your using unbalanced connections.
I can upload a diagram of cables with ground lift if you want.

Fede · Post by **Fede** » Thu May 16, 2002 3:56 am

That theory of ground loops isn't much clear for me, I didn't understand what exactly can be cosidered as a ground loop and what cannot

For example, the connection of a stereo channel from soundcard to amp is made with two cables both carring ground that is the same for them, isn't it a ground loop?

- sorry for bad English, I hope you understand-

I learned by many attempts that reducing redundance of ground wires helps very much against noise when modifying the electrical wiring of my guitar (a Fender Stratocaster

). In that guitar I noticed doubled contacts made with the help of the internal shield (congrats to Fender for this!) and since I removed unuseful wires it is really less noisy.

Can you explain me when this problem occours and what is the physical explanation?

Thanx
(Strato)Fede

w_ellis · Post by **w_ellis** » Thu May 16, 2002 4:15 am

Here's a couple of articles I found on Sound on Sound's web site. I'm sure there are several others besides which might help.

http://www.sospubs.co.uk/sos/1994_artic ... loops.html
http://www.sospubs.co.uk/sos/jan02/articles/faq0102.asp

Cheers,
Will

Krabat · Post by **Krabat** » Thu May 16, 2002 2:08 pm

If you dont't want ot lift the Electric ground, cut the ground of the audio-connection. It's safer and should work. Do you have any antenna connected? Sometimes they are grounded, too.

Regards

krizrox · Post by **krizrox** » Thu May 16, 2002 3:27 pm

Appreciate the feedback. Absolutely nothing attached to the mixer or the PC other than a monitor and the stereo instrument cables from the analog outputs to the mixer.

I forgot about the monitor though. That was still connected to AC with the standard AC cord. Maybe explains why the adapter didn't work on the PC

Still, very wierd. Just can't bring myself to lift the ground connection on the mixer. Would hate to kill a client

Thanks all!

remixme · Post by **remixme** » Thu May 16, 2002 11:48 pm

Call a qualified electrician, they will be able to wire up your studio in such a way to eliminate ground loop, they might ground lift the mixer but earth it somewhere else.

Also like subhuman suggested try using special cables that cancel ground loop hum, you can make them yourself the articles that Will Ellis mentioned above will tell you how.

bassdude · Post by **bassdude** » Fri May 17, 2002 5:57 am

Don't lift the ground in the mains cord. As Krabat says, lift the ground in the audio interconnection cables.

Another good site for info:-
http://www.rane.com/library.html

This is a good doc to have handy:-
http://www.rane.com/note110.html

Krabat · Post by **Krabat** » Fri May 17, 2002 9:28 am

Forgot to mention a transformator (german: Trenntrafo). I'ts an AC/AC 230V/230V Device which lifts the ground safely.

Regards

Fede · Post by **Fede** » Fri May 17, 2002 11:28 am

bassdude, what a huge amount of knowledge on that Rane site!
there's enough material to write an Audio-pedia!

bassdude · Post by **bassdude** » Fri May 17, 2002 4:01 pm

Stratofede,

Yeah! I stumbled across that site ages ago and I've kept the link handy. It's really good! That note110.pdf (Sound System Interconnection) is especially good if you need to make up your own cables without causing problems.

Cheers.

krizrox · Post by **krizrox** » Sun May 19, 2002 9:03 am

Hey - very cool links bassdude. Thanks!

DJATWORK · Post by **DJATWORK** » Sun Jul 28, 2002 8:33 pm

May be there is any noise in your electric line. Tehre are AC Filter (a brand: TRANSPARENT) that eliminates that noises.

You can try your Ground connection to be sure that its not broken at any point.

I know a case of a musician (not death) but severally burn in his right hand because of a GUITAR and a MIC that touched the strings and was ground lifted. It was in the school wich I had study "Sound Technical". Thats ironic because they teached me not to lift ground...

DJATWORK

DJATWORK · Post by **DJATWORK** » Sun Jul 28, 2002 8:36 pm

(Sorry, repeated message)

<font size=-1>[ This Message was edited by: DJATWORK on 2002-07-29 03:12 ]</font>