Why the Hell...

[Elspode]

...do both of our laptops make a hideous 60 cycle hum when I have the headphone output plugged into the stereo while the laptop in on mains power? WTF's up with that shit?

[jinx]

Are they HPs?

[Elspode]

One is. The other isn't. I think I've found a solution onlne...

http://www.radioshack.com/search/ind...0isolator&sr=1

[tw]

Originally Posted by Elspode

One is. The other isn't. I think I've found a solution onlne...

If a ground loop exists, then you have currents flowing into and out of the computer that should not happen. Hum would be a symptom of a defect. A real isolator would only help to identify that defect. This isolator is unlikely to eliminate hum in unpowered headphones. That defect also may be a symptom of a serious human safety issue.

A simpler solution (solution only to identify the problem; not yet fix it) would be a three prong plug to two prong receptacle adaptor. Another solution (again we are not yet ready to fix anything) is to try both computers is another building.

To have that hum means a current is flowing into the computer on one path and out on another. AND that current must not be flowing where it can create a hum.

Also not provided are other connections to that computer. To identify a failure, first list everything connected to the machine. Not just other peripheral connections. Are headphones powered or unpowered? If powered, then that too is another connection.

If may be something trivial. But it could also be the canary in a coalmine. Better is to identify the problem first before fixing it. The isolator is typically used when ignoring symptoms of a much larger problem.

[Cicero]

This is a grounding adapter. Be advised.
http://www.radioshack.com/product/in...ductId=2104010

[Elspode]

Power supplies on both computers are plugged into a grounded plugstrip which is in turn plugged into a grounded outlet. So the system is grounded. The only other connection is from each computer's headphone out jack to L/R line ins on a receiver/amp.

I have also bypassed the plug strip and plugged the computers directly into the wall socket with the same result. In reading up, ground loops aer not completely unknown, hence, the existence of the device I posted. I am quite familiar with 60 cycle hum in audio gear. DI boxes, for example, usually have a 'ground lift' setting, and other audio gear, such as mixer boards, usually have a polarity invert switch which does essentially the same thing.

I'm just kinda baffled why it is happening in two separate laptops, yet does not occur in anything else which comprises the audio path (stereo, tv, etc).

[tw]

Originally Posted by Elspode

Power supplies on both computers are plugged into a grounded plugstrip which is in turn plugged into a grounded outlet. So the system is grounded. The only other connection is from each computer's headphone out jack to L/R line ins on a receiver/amp.

I have also bypassed the plug strip and plugged the computers directly into the wall socket with the same result.

So you have speculated that the computer is grounded. OK. That is the hypothesis. Now, where is your experimental evidence that is also required before a fact can exist. Nothing yet says the system is grounded.

Requested were a few experiments in the previous post. Without experiment results, then nobody knows that the system is grounded.

Meanwhile you have a receiver/amp that you did not mention? The sentence is vague. Is the computer headphone wires (both left and right) connected to the input of a receiver amp? Is it the same receiver amp that makes a hum for both computers? Does this amp also have the necessary three prong plug? Where is this amp powered?

Rationing facts does not help with the diagnosis. Because you hope the receptacle is a ground (and you don't say which type of ground) does not mean anything is actually grounded.

If the Radio Shack isolator does something between a computer headphone jack and the power amp, then something is defective in one of those two items (more probably the amplifier) OR a wiring problem exists.

Currently everything is only speculation because none of the experiments have been performed and suddenly new facts such as the amplifier are discovered. Nothing connected to any USB port? No network or modem cable? Is that an RCA jack connection to amp input from headphone output? With numerous AC power connections, the system is more complex meaning the three prong to two prong experiment must be performed for each item singly and all other permutations. And testing the entire system in another building remains useful information.

[barefoot serpent]

ferrite core noise suppressors on the headphone cable?

[smoothmoniker]

Maybe it's the sound of a thousand tiny angles beating their wings?

[dar512]

Would those be acute or obtuse angles?

[Cicero]

From what I have read Elps. It is specific to certain kinds of laptops. Some, do not do that. I do not know why.Of course this is what I have read on other forums so I do not know the validity of that either.Sorry I couldn't be of more assistance.

[Elspode]

TW, in his usual inimitable way, is making a good point. Namely, that the wall socket into which things are plugged may not in fact be grounded, despite the fact that it has a grounding hole, and everything that goes into is grounded. I will investigate further. Part of my investigation will be to try the same setup with a different audio device.

Configuration, TW, is: Miniplug from computer headphone output jack to RCA L/R in Receiver/Amp Aux inputs. Single cable, no adaptors, miniplug male to RCA L/R males.

[tw]

Originally Posted by Cicero

From what I have read Elps. It is specific to certain kinds of laptops. Some, do not do that.

Which is all directly traceable to various and different types of power connection designs. Also directly traceable to some electronic failures that would never be apparent until a second problem exist or some unique design is used.

It comes right back to basic school science. One generates hypothesizes based upon intimate knowledge of fundamental theories. Then one does experiments to convert that hypothesis into a fact.

Using the 'three prong to two prong' receptacle adaptor is one experiment. A more expensive experiment is the Radio Shack isolator. Moving the entire setup to another building is also an experiment because some buildings (not just the receptacle) could account for that hum.

That concept of hypothesis and experiment is why we teach people in science how to even understand politics. A concept that many forget if not tested by doing - such as by repairing things. We don't repair things to save money or time. First and foremost, we repair things to learn. For some, that means relearning a junior high school science concept - hypothesis and experimentation.

Reading that it is specific to certain laptops says little. If those writers knew, then why did they not also say why? Let me tell you from experience – because most who ‘know’ electrical solutions don’t even know how electricity works AND because Elspode’s problem is often created by something simple but quickly gets complex when trying to find it.

[Elspode]

Mostly, I just want it to go away without time consuming experiments, and I'm willing to pay the reasonably modest fee for the (hopeful) solution.

[tw]

Originally Posted by Elspode

Mostly, I just want it to go away without time consuming experiments, ...

The experiments are neither time consuming nor too complex. For example, simply put that 'three prong to two prong' adapter on each power cord, power on, and learn what happens. Posting that last reply took longer.

Paying in Radio Shack for that adaptor or the isolator is too much money. The adaptor on computer and test. The adaptor on power amp and test. Adpator on power strip with both units powered from that power strip ... and test. Move system to another building and test. Only then can any reply here post something useful.

The concept is quite simple. Every wire inside every cable is a possible 'hum' conductor. For hum to occur, one wire must carry hum current in and another carry hum current out. If any one wire is found to be a 'hum' carrier, then half of the problem is known so a reply can suggest a solution, or a reduced number of suspects exist.

Suggested was the easiest and fastest way to solve these type problems. The fact that you don't know what is being targeted suggest you do not yet know how quickly this can be done and that learning occurs only after performing these simple experiments.

Assumed is 'boxes' are powered by three prong connectors - correct? Also assumed was power strip is only a power strip - not a surge protector.