High frequency computer. - Page 1
Forum section: electronics / beginners

author: mwagz
author_rank: Newbie
timestamp: December 22, 2017, 08:46:59 pm
content: I am having a problem with my computer feeding high frequency into the wall outlet. If I test the frequency from another breaker I get the correct 60Hz. When I test from the same breaker or plug I get around 2kHz. Everything works fine, but it causes audio feedback in my soundsystem. Could it be caused by a combination of different electronics? Is there some sort of filter I could buy or make to remove the high frequency? Could it be a bad power supply? Or is that something that is normal.Thank you for any help/advice.

author: flynwill
author_rank: Regular Contributor
timestamp: December 22, 2017, 09:20:40 pm
content: I would be curious to know what you are using to measure "frequency".It is certainly possible that a defective computer supply could be injecting noise into the AC that would in turn cause issues with your audio gear, I would be very surprised if the amplitude of the noise were anything close to the 60 Hz mains voltage. It's far more likely your are seeing an issue with your measurement instrument.Do you have a positive correlation between the computer and the issue with the sound system (eg turn off or unplug the computer and the issues goes away). What is the nature of the "feedback"? a wine or hum? If so roughly what pitch?

author: mwagz
author_rank: Newbie
timestamp: December 22, 2017, 11:35:07 pm
content: I am using a old radio shack multimeter that has a frequency setting(cat. no. 22-168A). Checking other plugs that are on a different circuit it shows around the 60Hz. With the audio system it is a hum that almost sounds like a ground loop. When the pc is shutdown the high frequency goes away. Is is possible that it is interference between the computer and other electronics. On this circuit there is my computer, tv, audio system, router, modem, and a external hdd.

author: flynwill
author_rank: Regular Contributor
timestamp: December 22, 2017, 11:47:22 pm
content: You say:QuoteBut does the Hum go away if you just turn off the computer? Or do you need to unplug it?The meter is seeing noise from the computer power supply, but that probably isn't your problem if what you hear is 60/120Hz hum.Is the Audio output from the computer plugged into the audio system? If so the that you could be on the right track thinking it is a ground loop. I've had that issue in the past, the Antenna connection to the receiver was grounded, and so is the computer via the 3-prong on it's plug. In that case the fix was to fabricate an isolation transformer for the antenna connection.I suggest that you disconnect things one at a time from the stereo system (except the speakers) and see if the hum goes away at some point.

author: mwagz
author_rank: Newbie
timestamp: December 25, 2017, 01:02:19 am
content: With just the pc plugged into the wall I still get the high frequency in the lines. I only have to turn the computer off to get rid of the high frequency. It seams like the hum is still there with everything other than the audio system and pc connected. I can deal with the feedback from the audio, I am just worried about the high frequency killing something. Would it be best to replace the power supply with a high quality one? I imagine most people do not bother to measure the frequency at their wall outlet. I got curious and now I have this problem.

author: flynwill
author_rank: Regular Contributor
timestamp: December 25, 2017, 05:05:05 am
content: I wouldn't worry about the "high frequency" you are observing unless it actually start to interfere with something else (such as you have high-pitched whine in your audio gear). It is hard to say without putting a 'scope on the mains, but most likely it is just your cheap meter being over sensitive.The Hum is most likely a ground loop.

author: Raj
author_rank: Frequent Contributor
timestamp: December 26, 2017, 12:27:16 pm
content: 2khz will be high pitched...is it high pitch?and test by connecting a phone to the speaker with computer turned off.also,can you record the noise?