Tweakers' Asylum

Thanks! I've wanted to verify that I don't have one, and

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Terry P

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In Reply to: Re: What does a "ground loop" sound like? Hum? -nt posted by pkell44 on March 18, 2006 at 18:00:30:

I don't. However, every so often I get a similar hum from my amp. It is intermittent and not present very often. I suppose it could be related to the quality of incoming mains power?

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That would be DC on your AC... - Al Sekela 11:19:17 03/20/06 (2)
Your AC power voltage can become distorted from a pure sine wave if some other user connected to the local power feed uses something that draws a lot of current for only part of the AC wave. One possible cause would be a hair-dryer set for partial power.
Audio equipment with toroidal transformers can hum if the toroid is fed some DC along with the AC. DC causes the transformer core to saturate during part of the AC waveform and one result is a mechanical 60 Hz hum. Older rectangular transformer designs seem to be less sensitive to this problem.
- Al - you da man ! Thanks! - Terry P 12:07:32 03/20/06 (1)
  My wife and I did an experiment where she first ran her blow-dryer at full power and then on the "warm" setting. The warm setting (partial power) resulted in hum from my amp, just as you said above.
  What's interesting is that the same hum has intermittently occurred when there is no one in the house but me, meaning that it is initiating from one of my neighbors' houses and then traveling over to our house. The houses are very close together.
  - Yup. Sometimes several houses are fed from the same - Al Sekela 15:00:08 03/21/06 (0)
    power company transformer. Could be your neighbor using a hair dryer.
Re: Thanks! I've wanted to verify that I don't have one, and - pkell44 10:21:13 03/20/06 (0)
Doubtfull that the 60 Hz. hum is riding in on your mains. 60 Hz hum is usuallty due to a ground fault(s) such as a ground loop or faulty grounding. Start by cleaning the grounds of all your RCA's, male & female, with a good cleaner such as De-Oxit. If that doesn't eliminate it try re-solding all your ground connections on all the components in the unit that is generationg the hum : it could be a cold solder joint that intermittently conducts properly. My tread mill began start-stop action and I finally traced it to an R in the control pcb with a joint so cold that one lead easily pulled out of the board. After re-soldering the R the treadmill runs faster than I can. Intermittents are very vexing and difficult to locate. It takes great fortitude to find them.
Happy Hunting !

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