Bad hum from Audigy card when connected to Home A/V.

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ShorewaySaint

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Dec 30, 2005
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I read as many posts as I could first and now my eyes are getting blurry. I have had the card for 5 years and it always has worked well. When connected to my 3way computer speakers (with subwoofer) sound is perfect. I recently ran a circuit through my attic to my home stereo to play mp3's and as soon as I connect the sound card there is a low frequency hum that would drive you crazy! I plug my Nomad to the circuit and it is perfect. Is there something I need to know about grounding the sound card and the stereo together to avoid a ground loop?
 
I used Quad Shield Coaxial Cable (Left and Right) about 50 feet with keystone faceplate adapters to convert "F" plug to RCA at the wall. This is what professional Home Theater installers use. The cord from sound card to wall is 18" stereo mini plug to split RCA. The patch cable from wall to home stereo is a standard 3' RCA. The hum is similar to a ground loop I used to get when installing car stereos. It has been a long time since hearing that but it is the only explaination. Portable nomad player has no noise and when I unplug the mini from the sound card there is no noise. I am wondering now if one of the jumpers on the sound card might be a ground lift? I am certainly not going to lift the ground on the entire computer! After the holiday I may be able to figure that out, I was hoping someone had already been through this?
 
This is normally caused by the PC (Power Supply) voltage that is being picked up by the A/V receiver. With the Nomad, because it is DC (Battery Operated) you shouldn't have the issue. I would recommend using a Ground Loop Isolater for RCA plugs as it comes into the A/V receiver. This should fix the problem. You can pick them up at Radio Shack or a Car Audio Shop. :)
 
That is my next step. Still wondering if this is typical of anyone else connecting a computer to a stereo on a different electrical circuit? Thanks everyone for your thoughts
 
Yeah, this will happen if the PC and audio componentry are on different wall circuits. It is as you have noted a ground loop. The easiest and cheapest solution will likely be getting the powered devices onto the same power circuit. I might try running an extension cord to the PC from the outlet that the A/V eqipment is plugged into.

Hang in there, just keep trying stuff till you figure out what makes it go away. It isn't impossible to fix but this kind of thing always freaks people out.
 
I have now had the chance to look at ground loop isolaters and it seems that they are specific to car audio in that they block DC voltage. I would still like to try it but I dont want to drop a lot of cash on it yet. I can tell you that even if I use the audio out from my motherboard the same exact hum is still present. Oh well maybe a new dedicated power circuit to my computer and stereo isnt a bad idea!
 
do both your Audio card and your Reciver support a fiber optic audio cable, becuase that eliminate any electrical differencials as they are non conductive. Thats whay i use and i am loving it. Just a thought.
 
Well after that last post I got all excited about the fiber optic thing knowing that my audigy supports it, however after pulling my av receiver I found that it does not. I will post to confirm or denounce the ground loop isolater which will be my next easiest option if I find one cheap.
 
Sorry I'm a week late.

What happens is the following.

Each of the parts you use PC and Receiver have different PSUs.

They introduce noise (yes low freq ~50/60 hertz) plus a DC shift, specially in the computer that has a switching power supply (using PWM, diodes and capacitors). PWM introduces noise too, very High freq but should produce harmonics. Another problem about the computer PSU is that it works much like an AUTOTRANSFORMER and not like a TRANSFORMER (look at what it is in Wikipedia, but basically the Autotransformer has one line input straight to the output (intended to be Neutral pole of the AC input as long as your electric wiring is OK and you are plugging in the right way //unless the AC (PC or RCV) plug does not have a specific side// and the other line is LIVE)

You can do this check. Touch PC chassis and hold the RCA/miniplug with the other hand. Will "feel" the power running through you.

So the best you can do is this:

1) Install a ground connection (it's a large copper bar buried in the soil 10 feet under //at least//) (you should have it already, then check it)

2) Verify the wiring of the ground gets to both the PC and Receiver

3) Do a specific (this is my current setup) wiring from the copper bar (I don't know the name in english, sorry) and attach to Receiver chassis (it has a specific bolt for it, or it has to be connected to the ground in the FM antenna input (a "fork" like symbol, but upside down)

|
|
__|___
/ / /

And attach it to the computer chassis (remove a bolt from the PSU on the outer side of it. Do a circle with the cable or soldier a terminal to the cable and then bolt it. Screw it hard (no bad intentions here) so the copper or the terminal scratches the chassis and is firmly pressed to it and no oxide will form between them and will keep good electrical connection.

With this done, only will have hum at higher volumes on the receiver (-30 dB and up).

PS: Here's what I've done since my house have that installed but not wired:

a) Put a special wire 2,5mm^2 of section straight from ground to my room.

b) Put a plug into the wall to take AC power. from there to a 10AMP thermic protection, from there to many different outlets bolted in a piece of wood. (german Stucko, american, european standards and 220->110V transformer)

c) Put many terminals to ground wires all bolted togheter (ground input, ground to outlets, ground to PC chassis, ground to Receiver chassis, ground to multi-standard-outlet, ground to stucko)

D) LAST BUT NOT LESS IMPORTANT: Did assembled all the outlets corresponding to standards and checked all the cables (yes, the 3 pins cables from outlet to the equipment) to be correctly wired (some where not) and checked to have them all plugged in the same way //neutral wire (black in USA, cyan in Europe, to neutral pin) live wire (red in USA, brown in Europe) to live pin//

I have used this setup to connect my PC and receiver at home, and to connect my PC and a 8IN/8OUT external audio card to a Behringer 2442A console for recording purposes. It does work.

EDIT: Forgot to mention that the best you can do, if you have the chance, is to get a optical SPDIF. There is no electricity involved.
 
I would disagree in that if the ground loop is truly eliminated there will be no hum at any volume.

Case in point, my own system. PC is connectd to home theatre system, front channels have 600W each. While PC is source but with no music playing I can turn the volume all the way up and only hear white noise. There is absolutely no audible hum.

I think you may have said this in your story but it really all boils down to maintaining a solid single point ground. It is a common theme in electronics. You will even see ham radio guys talking about the single point ground in their ham shacks. Why? It seems to work.
 
I would disagree in that if the ground loop is truly eliminated there will be no hum at any volume.

Case in point, my own system. PC is connectd to home theatre system, front channels have 600W each. While PC is source but with no music playing I can turn the volume all the way up and only hear white noise. There is absolutely no audible hum.

I think you may have said this in your story but it really all boils down to maintaining a solid single point ground. It is a common theme in electronics. You will even see ham radio guys talking about the single point ground in their ham shacks. Why? It seems to work.
Click to expand...

I would disagree if you say you've read carefully:

"With this done, only will have hum at higher volumes on the receiver (-30 dB and up)." <-- In original post.

My dad has been doing ham radio for more than 20 years.

Your 600Watt equipment sounds like a big lie, but that's another story I will not follow up.
 
whatever bud. maybe you need to get your dad to set your stuff up if you are getting ANY hum. Maybe that is the person who should be posting solutions here too since it seems you are trying to give advice about a problem you haven't even been able to solve yourself.

PS what makes you think I am lying about my sound system? I am looking at a set of 2500W (bridged) amps to replace the 600Wer's as they don't seem to be enough to drive my main speakers to my satisfaction. Believe what you want, but soon with the new amps you will be able to hear my system whether you like it or not.
 
i get no hum at just about any volume, but then gain i am using fiber optic :). and it would seem this has turned into a "my stereo will explode my ear drums faster than yours" thread.

Just go with fiber optic and all your ground issues go away, for the most part.
 
Here is an update, I have wired my stereo and computer to the same outlet to avoid ground loop No Luck. I have plugged my wifes computer to the stereo to see if the noise is unique to my system, and it still persists. With heavy extention cords I plugged my stereo into an outlet across the house that I know has a good ground (new circuit) and the noise is louder through the added power extention cords. I will continue to keep you all up to date. Next try will be grounding cases together like in a professional sound system... it will be difficult through the wall though!
 
For the single point ground to work you must star pattern every ground connection and I do mean everything that electrically is part of the system. This includes external modems, printers, powered speakers, monitor, etc. Just one little overlooked path is all that is necessary.

One thing to try is Plug the PC + monitor into the same outlet as the stereo, and make sure there are NO peripherals other than bus powered mouse and keyboard plugged into it. Under these conditions do you still get hum? When the star pattern ground topology is truly followed the hum will have no choice but to disappear.

I don't expect connecting the cases with a wire will be your solution but it is a data point and you should still try it, for the scientific knowledge and for the fact that you should never trust anonymous internet bozos like myself.

I have been where you are. It can be frustrating. Hang in there. Trust me when I say there exists a configuration that works, you just haven't found it yet.
 
Quite simply I use large custom power strips from my office with digital correction (verister technology?) I have one on my computer that everything is plugged to and one at my stereo that everything is plugged to. I basically used a heavy guage extension cord to carry the computer power strip to the outlet the stereo was plugged in and then reversed the extension cord to carry the stereo power strip to where the computer was plugged in. Same noise no difference?

I know that when securing rack mountable signal processors in a PA rack there are isolation tabs to use that will elliminate noise but I dont understand the science of it. I had 5 units installed I would turn one off at a time untill the noise went away then I would isolate the chassis of the noisy unit from the rack rail with the isolation grommets.. no more noise!

In my situation now the frame grounds are not touching. In theory with the above example I will introduce more noise by grounding frames together? I have not yet been able to try anymore experiments.
 
Based on your description it sounds like you have done about as well as you possibly can with getting the grounds into the "star" configuration I was describing. One last suggestion on that note though: I think I might try bypassing the fancy power strip with a normal one once to make sure it wasn't throwing an unknown into the equation.

In theory with the above example I will introduce more noise by grounding frames together?
Click to expand...

That is just my theory, and is based on results I had when I was in a similar situation. Please keep in mind sometimes subtle differences in equipment can cause seemingly major differences in what works. What has worked for me is not going to necessarily work for the next guy unless nothing in our setups is different. So in other words don't let me stop you from trying everything you can think of. The theory is there to help come up with reasonable things to try. What works is what is important and fitting theory to a problem is always much easier once you have identified what the issue REALLY is. Often it is much quicker to try to solve an issue like this through trial and error testing that it is to try and model the system and be proficient enough with theory to solve it. The best approach is almost always a combo of theory and testing.
 
I seem to be having a similar problem to the original poster but my setup and 'debugging' has given different results... can someone shed some light on this?

(I live in an apartment)
I have my PC setup on one power strip and am running a 2.5mm stereo cable from the line out on my Asus A8N-E onboard sound to a single power strip setup consisting of a Logitech Z-5500 with an HDTV. Using the option of multiple stereo inputs, I have the line from my PC and a RCA<->2.5mm stereo audio line from the TV hooked into the Z-5500. When the sound input is set to the TV, there is no hum. However, when the sound is set to the PC, there is a notable hum.

Here are the scenarios of what I tried but kept the hum going:
- Unplugged power to TV
- Turned TV off
- Switched between back/front panel ports on PC

The only way I was able to cut the hum was to break the connection between the TV and Z-550

I think I'm missing the key element here that causes this hum. I also noticed that when I drew the audio from my laptop instead, the hum was not there. I am guessing that the aforementioned ground resolution is worth a try but why does it work fine when the TV connection is not there then?

Any explanations will be like 'wow'.

Thanks.
 
the tv could be for some reason causing intereferance. The only sure fire way to make sure there is no hum is to use fiber optic audio connections since no electricy is used. or it could possibly be the cab;e it self or the connections. how high quality of a cable is it ?
 
I have completed the dedicated AC circuit to the computers and stereo and the noise was still there! I then knew it was coming from the sytem itself, I believe it is noise on the 75 ohm coaxial cable line plugged to my vcr/tv. If I isolate the Tv system from the audio system no noise but then I cant use my surround sound while the computer is plugged in! I now have to figure out the best way to ground the cable signal? I have seen the grounded cable blocks but I dont understand where to use it except for where it comes into the house for safety from lightning? I am making progress though.
 
If you've already tried making custom cables then do some diagnostics before proceeding. Move your hi-fi to next to the computer (or other way round) and then see if the hum is there with the short distance cable. If it is, then you have that ground problem. If it's not, you will at last realise that there is NO WAY to get good sound THREE ROOMS AWAY. The furthest I would use cables is about 7m, making sure they are good quality etc...

My friend's Linn Classik drives two B&W 602's in the same room, and it sounds great (awesome speakers!!!), but running the cable to his living room (2 rooms away) with the same awesome B&W's it sounds crap, and that's with good quality speaker cable.

I know it's not the same, but seriously, you can't expect good sound over that much cable.
 
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