Vista external speaker humming feedback

[ourdill]

Hello,
im using an old compaq presario cq60 and i use an external amp/audio powered thro the headphone jack-i get a humming feedback noise although i use an inline ground loop isolater-i have reinstalled the sound card,butno different...although if i insert the jack into my phone for music i get none? can i change the way i feed the amp-ie:whith a usb connector or something--pls help this is driving my ears mad!!! thanks

Dill

 

[soundguruman]

The compaq has a 3 prong AC power plug.
Obtain the adapter that changes 3 prong plug into old style 2 prong plug.
This adapter is sold at the hardware store. OR at radio shack, etc... (link)
http/www.sears.com/shc/s/p_10153_12605_SPM5825157401P?sid=IDx20101019x00001a&ci_src=14110944&ci_sku=SPM5825157401
It costs about $1. This adapter disconnects ground from the computer chassis.
BUT the computer chassis is still grounded through the audio cable, to your receiver.
(I'm getting to that)
You see, there is more than 1 ground.
One of the grounds is coming from the 3 prong computer power plug...
Another is coming from cable TV, OR The receiver's power plug, OR a subwoofer power plug...
You see where this is going, you need to use adapters, as above, until all the grounds are disconnected, except ONE.

This is called a ground loop. It is caused when there are multiple grounds, instead of a single ground.
It is most common where cable TV is being used.
Disconnect cable from your entire system. Does the hum go away?

You can also use a cable TV isolation transformer. This goes between the cable service and your entire house. It disconnects the cable ground from your equipment.