Hum from the line-out

If your computer and your stereo are each individually grounded, connecting them may result in a "ground loop". The most obvious symptom of a ground loop is a low a frequency hum from the speakers.

I'm not an electronics expert, but I know that sometimes the grounding that exists in a Cable TV cable can cause this. If you have a Cable TV cable connected to your stereo, try temporarily disconnecting it. If the hum disappears, I think Radio Shack may have an inexpensive fix. (Maybe someone else can provide specifics.)

If you don't have a Cable TV cable connected to your stereo, then perhaps a "three pronged plug" grounds one of your stereo components or you have the stereo plugged into its' own surge protector/line conditioner. See if disconnecting/bypassing the component or surge protector eliminates the hum.

If the above doesn't help, post back. There are some forum regulars who have good electronics knowledge and they may have your answer.

The "ground loop" hum is a prime cause.  If the stereo amp is grounded (has a ground plug) use a "ground lifter" adapter on the AC power plug and see if that fixes it.  If it does then it is definately a ground loop problem (difference in potential of the grounds in the PC and the stereo).  A note of caution, when you remove the AC ground from one device there is a potential for safety and you must make sure you are always connected to the other device to maintain a ground.  If you disconnect the PC, remove the AC power ground lifter (adapter) from the stereo system before using it.

Another cause is the cable.  Althouigh you checked the cable, you need to make sure it is a good quality shielded cable, not a "speaker" cable which is not shielded.  Some cheaper "shielded audio cables" will tend to have poor shielding and can have hum problems.  The interface cable should be approx 20 ft or less, longer cable lengths can have signal and fidelity loss and even hum depending on how they are run.  Although shielded audio cable is used, still keep it away from AC power lines.

What input are you using on the stereo?  Do not use the "phono" input, use an aux, tape, CD, etc input and make sure you are inserting the cable connector(s) fully on both ends.  Also try a different input on the stereo and see if that makes a difference. 

Here's my audio interfacing artilce, it may also help.  Link

I tried all suggestions including: Unplugging cables (TV and Modem), checking/changing power sources, not using phono input, everything....  Still get the hum

PFBF,

Sorry none of that worked.

I did a little searching and found the following additional suggestions for troubleshooting ground loop problems. (If both the computer and the receiver are really humless when not connected together, I can't think of any other reason for the hum.)

If possible, plug the stereo and the PC into the same wall connector (using a surge protector). Generally, a typical AC outlet can easily handle both a stereo and a PC. - As a first (minimal) test, you might try disconnecting/unplugging everything that isn't necessary and just plug the receiver and computer into the surge protector.

If it's not possible to plug the stereo and the PC into the same circuit, if the stereo has an AC plug that can be reversed, try inserting it in the opposite orientation. - Yeah, I know, this sounds really silly. But, there is a legitimate basis for trying it, even if/when it doesn't work.

I'll search around a little more.

Message Edited by blueshift on 12-17-2003 11:38 PM

As I do guitar and P.A. system amp repair, hum problems are a major concern of musicians.  Most of the time it is a ground loop (difference in potential of the grounds in two devices) and lifting the ground on one of them will take cre of the problem.  There's a product, "Ebtech hum eliminator" which can be inserted in the signal line between two devices that will also lift the ground.

However, the second most common reason for hum is either bad or poor quality signal (shielded) cables.  One common source is the "imported" guitar cords that use plastic molded connectors.  First the cable is usually of inferior quality and very poor "shield" or ground wire and second the plastic connector ends are not shielded and AC hum can be induced at the connectors. 

Working with PC's, I've also come across several cases of audio hum either to or from external audio devices and along with cheap cables I've found several that did not thave the mini (1/8") stereo plugs fully inserted into the jack. 

The last and least common problems are with the physical jacks on either the PC's sound card/module or the remote unit. 

No more hum thanks to you two guys....You were right about the ground loop.  I could not find where the problem was coming from (I tried everything), so I went the isolator route.  The Ebtech was a little expensive, so I checked out Radio Shack's site, found one for $14.95 and went out and picked it up.  It did the trick.  Thanks again!

PS  I play guitar and always had at least some hum, depending on how I hold the guitar.  Would one of these things eliminate guitar noise (60 cycle hum) as good as it is doing for my computer/stereo?  I guess I can try for myself.

 

Thanks for posting back on your success. Not only will it be helpful to others with this problem, but also, everyone likes to hear about a Happy Ending.

Happy Listening!

A lot of guitar "hum" is caused by the pickups.  You need "hum bucking" pickups to minimize it.  Many guitars only have single coil pickups and they will tend to hum.  I have a Telecaster with the stock pickups and it will hum, depending on where it's located in reference to the amp.  Some Gibson's (and others) do have humbuckers but many also argue the single coils have a better sound.  But, I have Bill Lawrence humbuckers on my pedal steel and they are considered by many to be the top of heap as far as pedal steel guitar pickups.