Noise when Playing music from computer to amplifier

MikeMl said:

Assuming that you have a stereo amp, you will need two isolation transformers. If you connect just one, there is still a DC Ohmic (Galvanic) connection between the chassis of the PC and the chassis of the audio amp. Isolation transformers work by breaking the Galvanic common-mode path, but letting audio pass through the magnetic flux in the transformer.

GLI=Ground Loop Isolator=Common-mode-path-breaker.

Click to expand...

Hi M,
I only have one isolating transformer and tried only one channel as a test, which didn't work.
Now it's connected without directly, and there are no noises. It's always difficult with intermittent faults.
C.

Hi,
Ok, the music now sounds fine, with no computer noises, it seems the problem cured itself.

Coincidentally around the same time period, we experienced static, when touching metal objects in the same room. This was completely independant, so across the room it would happen not near the computer or stereo. This also stopped at the same time.
Were they connected?
C

Yes. I bet you also got noise just before nearby cellphones or cordless phones started to ring too.

Did the weather change recently?

dknguyen said:

Yes. I bet you also got noise just before nearby cellphones or cordless phones started to ring too.

Did the weather change recently?

Click to expand...

Hi D,
It was frosty, and I suppose dry, now it's damp.
C.

camerart said:

Hi D,
It was frosty, and I suppose dry, now it's damp.
C.

Click to expand...

Yeah. My old, old computer in the basement was like that during the winter. Walking from the door up to the computer was enough to produce jumping sparks visible in daylight. I remember that I used to be able to hear them as well as phone calls. I eventually got sick of shocking stuff so I grounded my desk. But it's been long enough now that I no longer remember if I continued to hear phone calls through my computer.

Anyways, touching metal no longer producing noise might just be because of the weather. Less static build-up when it's damper. I'm dont think it it could actually be the cause of your speaker noise but who knows?

Any chance that there is a grounding problem in your AC power distribution system?

Here in the USA, where we have three-prong power cords, the green wire (round pin) always goes to the building ground system, which is not a current-carrying conductor. Here, the chassis of your desktop computer (including the RCA audio jack outside) is ultimately connected to the building ground. If your stereo amp has a three-wire line cord, so will its chassis be connected to the building ground. Any "noise" between the two ground connections will get into the audio stream. That is where the GLI could make a huge improvement.

MikeMl said:

Any chance that there is a grounding problem in your AC power distribution system?

Here in the USA, where we have three-prong power cords, the green wire (round pin) always goes to the building ground system, which is not a current-carrying conductor. Here, the chassis of your desktop computer (including the RCA audio jack outside) is ultimately connected to the building ground. If your stereo amp has a three-wire line cord, so will its chassis be connected to the building ground. Any "noise" between the two ground connections will get into the audio stream. That is where the GLI could make a huge improvement.

Click to expand...

Hi J and M,
While I was replying last, I had my hand on a radiator, and I could feel 'that' strange vibration that can sometimes be felt when something is connected to mains power. After a while, with nothing changed it stopped. Had I slowly discharged? I kept touching the radiator nuts, which are connected to ground.

Here in Britain, we have also three wires in our mains cables, the ground is connected to the central ground at the input cable from the street, and all of the metal piping, water and gas. This means my radiators are earthed to ground. I had my house rewired a couple of years ago.
C.

camerart said:

Hi J and M,
While I was replying last, I had my hand on a radiator, and I could feel 'that' strange vibration that can sometimes be felt when something is connected to mains power. After a while, with nothing changed it stopped. Had I slowly discharged? I kept touching the radiator nuts, which are connected to ground.

Here in Britain, we have also three wires in our mains cables, the ground is connected to the central ground at the input cable from the street, and all of the metal piping, water and gas. This means my radiators are earthed to ground. I had my house rewired a couple of years ago.
C.

Click to expand...

Yes, you have a leakage to ground somewhere. Some device (maybe your PC power supply) is giving a second path to neutral. That third cable should only
1) prevent the sign wave of mains power from "floating" to unreasonable values relative to earth.
2) be a path from chassis of grounded devices to the neutral cable in case a short or other fault occurs (and pops the circuit breaker or GFCI). This insures that the user himself does not create the path to earth when he touches the cabinet/chassis.

Although it is called "ground" wire, it is physically connected to the neutral bus bar in the breaker box and that is the better conductor if a short occurs. The lessor conductor is to earth and that conductivity depends on the soil conditions (conductivity, surface area, electrolyte level in the soil, etc).

The ground cable is not intended to be a second path back to neutral bus bar and such situations should trip a GFCI device if you have one. You'll need some help to diagnose. You may be feeling / hearing the ground loop only when the boiler system recirculating pump is running or some other device that does not run all the time.

Hi G,
My house was recently re-wired, with RCDs
My computer and power supply is also recently new.
The central heating and pump is old.

How is it best to chase the fault?

Thanks, C.