Noise from piece of equipmet

[joshzz]

We have a piece of equipment that gives off a small hum. It's the Energy Onyx Codec.

If I disconnect the line-out plug from the unit going into our computer, we have no problem. We seldom use it though we are planning to use the unit once per week in the future.

We've trying grounding it better etc., but it's a noise maker.

I would like to keep the plug going (1/4" inputs going in the sound card) in the computer but need to somehow disable it without actually physically disconnecting it. Appreciate your help! josh

 

[Tom Wells]

Hum into other equipment? regardless of line selected or output level?
Could be enough rf intermodulating the hum into the output.
Power supply should have a a .01 cap between the AC lines, or one from each side of the AC line to power supply internal common point. Caps must be rated well well above line voltage.
This RF bypassing is often not included since most users won't suffer.
You don't say if there's rf there...AM, FM?

I had a low rough noise injected into the AM audio (even with ALL audio lines disconnected) after a new automation computer/power supply.
I had to disconnect the ground plug for that power supply only, the whole system is still earth grounded, but
the power supply (AC side) for that one computer simply CANNOT be grounded or noise results.
2 previous computers in the same audio job and location had no such issues.

 

[Jasonce66]

Depending on the sound card, this may be a classic hum loop issue... Some sound cards "pretend" to be real balanced inputs, like the M-Audio cards, but they are not really. If you're depending on a pre-made cable, you'll be in trouble. If you're not sure the card is a real balanced input, make a cable with a mono 1/4 plug to go into the sound card, that goes to an XLR on the codec, with Pin 1 on the XLR going to shield, and pin 3 going to the center conductor (yes, I know this is unbalanced)... if you have other devices that this codec output goes to, make sure you wire them carefully. If you want to bridge a balanced input device across the connections on the output of the codec, you should have no trouble, as the (+) and (-) inputs to the balanced device (a console input, for example), never get connected to shield at any point in the wiring.

Remember, it is easy to get a balanced input to accept an unbalanced output, and it is easy,(at least with modern equipment) to drive an unbalanced input from a balanced device, but care has to be given to the wiring.

ALWAYS wire an input, regardless if it is a transformer or transformer-less coupled input as if it IS a transformer coupled input, meaning, no input should EVER be left floating. If it is not signal, connect it to the shield. At the output-end of an input wire, it is usually good practice to just connect the (+) and (-) without connecting the shield.

On outputs, the opposite is true, if you want to use an active balanced output as an unbalanced output, connect to shield and the positive output only. Don't ever connect an + or - pin to shield as these usually have signal on them that will get shorted to ground, usually with bad results.

In your situation, the problem arises when the ground is connected at one end, and goes into one of the balanced input pins on the other end (or likewise is connected to the (+) and (-) at the output), without also being connected to shield. This sets up the "hum loop" because the balanced input gets it's signal path through another source, say the AC lines between the equipment. A pre-made cable, can potentially do this, and if other combinations of equipment are connected to the same output, they can produce similar results, because even if both the sound card and the codec are balanced, maybe someone else made a wiring error that caused shield to get connected to the (-) wire, for example? If your signal comes from the codec and shield is not connected and you're expecting to get an unbalanced tap somewhere at the studio, you may need to connect the shield at the codec.

One time I saw an excellent tutorial in an old Arrakis console manual on how to combine different types of equipment, and the method works flawlessly. I wish I had the illustration for every engineer, because it will save you hours of headaches just like this. What I said above is a verbal description of what I saw in that illustration. I hope it makes sense to you.


If you cannot solder your own connectors onto wire, I'd suggest finding someone to help you, as this is a VERY fixable situation... you should be able to create a noise-free signal from the codec.

 

[Jasonce66]

Never used one... probably a good bandage if you don't/can't solder or use a punch tool on a 66 block, wire cutters or needle nose pliers. Rarely have I found, short of a real audio isolation transformer (unfortunately the guy who used to manufacture them is now gone) is anything like this going to totally eliminate the ground loop. Proper wiring techniques are probably your strongest defense - and cost a lot less.

If wired properly, you should never (and I have never) need one of those. I have built up DOZENS of studios, and done massive consolidation projects of up to 10 stations into one building with hundreds of pieces of equipment shared by multiple studios. I'm not saying that something like this isn't worth a shot... it is a tool... your mileage may vary.

These are available at Guitar Center, I noticed, so at worst, you could take it back if it isn't effective.

Good Luck.

 

[SRP]

Jason - with all due respect - tone it down a bit, dude. We don't need to be lectured and honestly, most of us couldn't care a whit about how many studios you've built.

As for the OP's problem - it may be an internal grounding problem within the computer itself. And THAT can't be fixed by soldering connectors.

 

[Jasonce66]

Actually it can be totally eliminated by proper wiring practices... That is the truth. A repeatable truth as certain as ohms law itself. If the computer has a wiring issue, then making a cable that properly interconnects the equipment will TOTALLY eliminate the problem.

The wiring between the equipment must satisfy the path requirements for the signal, or yes, the external influence of things like AC wiring will be a factor. Any one of about 20 editions of the NAB engineering handbook agree with my suggestion, and so does the Mackie 1604VLZ3 manual on page 28 - (they also suggest some other alternatives for tough situations, which won't work for situations where multiple equipment pieces are concerned, but worth a try)... In this fellow's situation, it sounds like he may have more than one piece of equipment playing a factor in the hum issue, thus, wiring is very crucial, and making sure all of the grounds are connected properly, and to the right things, is most likely the key. If he has the shield of his unbalanced sound card (also would be the same potential as the computer's case) connected only to pins 2(-) and 3(+) of his console and then connected to pin 1 on another piece of equipment, for example, then yes, he would have a wiring issue that is fixable and I can imagine why there is hum. Unplugging the sound card would tend to make you think the problem is in the computer, which it is, but not in the way you think.

He needs to go through all connections and make sense out of what he has, do a little research, and try fixing it. Understanding how signals flow over ground paths on unbalanced, and across + and - inputs on balanced devices are very instrumental for devising a strategy to solving this problem. So, yes, a proper wiring scheme is exactly what will fix this problem.

Lifting the ground on the computer, video monitor or inductively isolating them (what this gadget does) is the alternative that was suggested - probably not safe as these devices typically do not provide an high enough instantaneous current path to maintain the safety of the ground on the equipment. It is probably a good solution for a temporary situation, like a live sound gig - (if your station has proper ground straps in the studios, and lightning protection throughout, this method will upset the protection your systems provide).

With his current configuration, the computer's ground is indeed a hum injection point into the current path of the audio signal, so eliminating the injection point with the gadget would somewhat fix the problem... then he will have other factors causing noise later on, like moving the wheels of his chair across the carpet, causing pops and cracks in his audio, for example. This is because the device still allows the computer chassis to be part of the current path of the audio signal... although it's path isn't completed through the AC line... see what I mean?

So, Connecting the grounds through the audio wiring properly causes the audio currents to have ONE path (and that NOT through the computer's chassis, where it can pick up electromagnetic energies, due to it's shear physical size, or static discharges or other current producing influences-all producing some form of interference).

It is usually better to do it right the first time and not compromise. The adapter is a compromise, which has its place in some situations.

 

[Tom Wells]

Jason - with all due respect - tone it down a bit, dude. We don't need to be lectured ...

Not sure if there was editing in this thread or not, but I thought I saw Jasonc66 reference being a grad of
Valpo Tech, and then I surely understand why Jasonce66 sounds preachy.
Read an old RCA transmitting tube manual someday, or any or the words of FE Terman.
Anyone who graduated from Valpo Tech will naturally come across to some as preachy.
It's just not imaginable in modern terms, how they taught... let's put it that way.....

It's NOT about preaching, it's just an honest info download for ones' consideration.

(Ask Jasonce66 about when "dropping one's keyring" becomes the Zenith of emphasizing a lesson)



But back to the noise, in my case it was NOT hum. It was more like white noise, yet with lots of rich low frequencies, not at all extending
up into the range that would be perceived as hiss. Vey strange. So now everythng is tied back to the common point for DC earth ground,
except for that ONE automation computer AC-side of the power supply.

I've run into a lot more ground loops at work (in printing) than I ever have with rf/radio audio here at home.

 

[Jasonce66]

Oh, well, that is different... and a reason for that one too... You find out about these things when you design and manufacture your own mic pre-amps. Depending on the input, you may have a floating pin on your line input, or to the line input, both pins may appear shorted or really close to ground potential. If the line input circuit is capacitively couple (most are) then the capacitor is going to generate a nice bold white or pink noise like signal. Another thing that causes this is a lot of DC offset on the output of the suspect device. Anything more than 1 or 2mv per pin to shield is suspect. The output chip may be bad (probably a 5532, if I know one of Bernie's designs) or the mic/line input is funky.

Try a distribution amp if you can get your hands on one, or capacitively isolate them (add like a 4.7uf 16 volt cap in series on both pins)

 

[SRP]

Anyone who graduated from Valpo Tech will naturally come across to some as preachy.
It's just not imaginable in modern terms, how they taught... let's put it that way.....

I understand, Tom. But this isn't Valpo Tech. Not all of us want to be preached to.

 

[Tom Wells]

Anyone who graduated from Valpo Tech will naturally come across to some as preachy.
It's just not imaginable in modern terms, how they taught... let's put it that way.....

I understand, Tom. But this isn't Valpo Tech. Not all of us want to be preached to.

Yes, I'm agreeing, and suggesting it's NOT preaching, but a confidence born in a unique place.
I hear the same echoes, and hear my own opinions reflect the same conviction.
I don't think any of Jason's post suggests that there can be no other considerations to the noise scenario,
but establishes important considerations for all installations.

There are several specific individuals who can be blamed for passing on this "VTI instructor" outlook.
I wouldn't trade the perspectives I learned there for anything in the world.
Just can't begin to express it in words...

 

[Jasonce66]

Thanks Tom... Certain techniques tend to lend themselves well to repeatability... ohms law is what it is... if it weren't, the world would certainly still be in the dark ages and alchemists would still rule our understanding of the mystic.

Fortunately, the dozens of tough studios I've rewired and cleaned up, have always turned out good, if not better than expected, for the given selection of equipment I had to work with. There must be some repeatability to these techniques in the real world, or I'd still be working on the first one it total futility.

A nice little radio shack test speaker (amplified) with a 1/8th inch plug cord made up with a pair of alligator clips is a handy device to determine where noise is in fact coming from. Only problem I end up having is I leave them turned on and end up running down the battery. : Radio Design Labs makes a real expensive one with a calibrated VU meter, but I've always gotten along with the cheapie radio shack box... if I blow it up on a high voltage circuit, no real money lost. It has enough sensitivity to make a judgment call about the noise floor of the equipment in question, once you know what position on the thumbwheel gives you the proper sensitivity. A good three digit voltmeter is also important, especially for tracking down a DC offset problem that could be making hum and noise. If the output is close enough to one of the supply rails in voltage, you will get a lot of buzz and a loud pop when you plug in or unplug. Saturated, or partly saturated transistors make wonderful hiss producers.

Good luck to all electron herders!