A note on inverters. Most of them, especially the cheap ones, do not have "true sine wave" output. (very similar to how our gear "samples" an analog signal and reproduces it as audio later) They use a method of creating an approximation of a sine wave that is basically square waves in steps. For most AC powered devices, this is not an issue. However, sensitive electronics can exhibit side effects from the simulated sine. Hand tools and heating devices are not bothered by it at all and run perfectly fine.

On the house electrical system ground. You can check for corrosion and loose connections. I've seen rods that looked perfectly fine be totally corroded in the ground due to acidic soil conditions. Sandy soil tends to have the higher resistance since it dries out so quickly and doesn't have good conductance period. If you are eliminating possibilities, certainly have an electrician with the proper equipment come and check the ground. An ohm meter is NOT the proper gear for checking a rod to ground connection. You need a ground resistance tester and the test needs to be done according to the instructions. Pouring water on it simply makes it wet unless the ground is totally dry, it will probably do very little to remedy the problem.

I don't believe you are going to find the problem in the electrical system of your house. If the hum was 60 hz, I might say it was possible, but the sound is higher in pitch and freq.

Since it's a tower computer, you can't run on battery to do this next test. But I think you will likely find the issue inside the computer. Since everything else you have done to eliminate the issue from outside, through the cables and the peripheral gear has not found the issue.... I'm starting to think you will need to dig in to the internal components, likely starting with a power supply swap. The switching power supply in the computer operates at a much higher frequency than the 60hz line..... and you mentioned that the freq was 300 something..... It's been a while since I looked at the specs on the switching power supply....

(pause) I went to google to see what I could find on switching power supply freqs..... not too much info on this topic but in one site I did see that some of the switching power supplies have a frequency of "several hundred hertz"...a little bit vague.....however, as I recall from my past studies, the freqs were in the 300 to 400 range in the supplies I was working with. Easiest thing would be to get a new supply and swap it out. Get one rated for more than the computer needs.

Last edited by Guitarhacker; 09/22/14 04:36 AM.
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