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cvenaccio

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I need help diagnosing a problem. I am using the M-Audio Onmistudio as a mixer for my synths. I have an Alesis QS7.1 and an Access Virus A. The Virus and Alesis are hooked up to the stereo inputs on the back of the Omnistudio via insert cables (Y-connector, 2 mono 0.25 inch to stereo 0.25 inch). The monitor out jacks plug into a stereo amplifier (Denon AVR-2600). I am getting the most God-awful feedback/ground/hum thing from the connection between the Alesis and the Omnistudio. There is no issue with the Virus.

At first I thought it might be the insert cable, so I switched the insert cables between the Alesis and the Virus and I still get the hum from the Alesis and the Virus is still fine. I even tried a single mono-mono cable and it hums.

I thought it might be a bad stereo in on the Omnistudio, but the Alesis hums on each of the 4 stereo inputs on the Omnistudio.

I then thought it might be the L/R out jacks on the Alesis, but I get no hum when I connect the Alesis directly to the amp.

I thought it might be a bad wall outlet, but I get the hum when I switch outlets.

I thought it might be the power cord, but get a hum after I switched that.

Both synths are about 2 feet from the Omnistudio and about 1 foot from the PC I am using for sequencing. I moved the Alesis so the PC and Omnistudio were 5 feet away and I still get a hum.

I've run out of ideas. I can't diagnose the issue. If there's a grounding issue with the Alesis, why don't I get a hum when I connect directly to the amp?
 
Are all these devices plugged into the same power strip or are they scattered across two or more outlets? Also you say you're using an insert cable. Are the inputs on the omni studio 1/4" stereo connectors?
 
What's a ground lift?

The alesis shares its outlet with a lamp. The other equipment is on strips from another outlet. The omnistudio has 1/4 inch stereo (TRS) plugs. I tried plugging the alesis on the same strip as all the other equipment, but I still get a hum.
 
Sounds like a classic ground loop. Get yourself a powerstrip with enough plugs to feed AC to all your gear and plug everything into it. Doing this gives you a "star" grounding set up and will probably make the hum go away. The ground lift mentioned would be something else to try. Some devices are equiped with one. You can also modify a cable with one. What it does is to lift or float the ground on an audio line to eliminate this type of problem.
 
I just noticed that the Virus and Waldorf (the two synths without the hum problem) have transformers on the plugs while the alesis has a regular 3 pronged plug.

I plugged the alesis on one of the strips with the other equipment, but it still hums. There isn't 1 strip holding all my gear. It's a strip plugged into a strip. The problem with finding 1 strip is that I have some 'wall wart' plugs that are really difficult to work with.

My amp and omnistudio are on the same strip. I get a hum when I connect my onmistudio and my alesis and not when I connect my amp and my alesis. Why is that?
 
Can I buy a groud lift and plug my alesis into it and then into the wall? Where do I get a ground lift?
 
cvenaccio said:
Can I buy a groud lift and plug my alesis into it and then into the wall? Where do I get a ground lift?
Click to expand...

Any hardware or electronics store.
 
You might have better luck, depending on your location, asking for a "3 to 2 prong adapter" - the two prong end usually will have a green wire dangling from it - don't attach this to anything, just plug the alesis or whichever device into the adapter, and the adapter into the power strip. If it doesn't help, power down and move the 3-2 adapter to ANOTHER unit, try each thing that plugs into the strip to see if any one makes a difference. Remember to TURN THE POWER OFF while making ALL these changes!

Make sure you run ANY audio cables as FAR AWAY from those "wall warts" as you can get them - some of these things can radiate hum for several FEET - Also, make sure and and ALL audio cables do NOT run close to and parallel to, ANY power cables... Steve
 
I bought a 2 to 3 prong adaptor and it worked beautifully. Thanks to all for your help.
 
As has been stated in other posts on this topic, make sure your equipment is in perfect operating condition when you do this. It can be hazardous.

If you should happen to have a loose wire that comes into contact with the metal chassis that electricity is going to crawl right up your arm the first time you touch the metal case.

Not to worry too much, equipment made these days is pretty solid. Just a heads-up for you. I have several noisemakers that have had the grounds lifted and I'm still here.
 
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