dweller 1,377 posts 02-27-2017 6:46pm
So a dedicated line from the panel will never cause hum? Can another line sharing the panel bleed noise into the dedicated line? How can we get a perfectly hum free power line? Can an aging grounding bar cause noise? Inquiring minds want to know...
So a dedicated line from the panel will never cause hum?
Hum? As in a 60Hz ground loop hum heard from the speakers? Even a dedicated branch circuit if improperly installed or using the wrong type of wiring geometry for the branch circuit wiring can cause a ground loop hum. Especially if more than one dedicated branch circuit is used and the branch circuit wiring is long in length.
As for a mechanical vibration, hum, heard from a power transformer I doubt a dedicated branch circuit would directly be responsible for the hum. I can’t see how it could stop it, or prevent it.
All transformers hum to some degree. Some more than others. A few things that make them vibrate, hum, louder than normal are, too high of a mains voltage, being overloaded beyond their manufacture’s rating, in the case of an EI transformer loose laminations, or DC offset on the mains. I have heard lighting power transformers in an older office building hum loudly, more than normal, running hotter than they should, due to a heavy concentrated load of personal computers, that are fed from the power transformer. The power transformer may be only running at 80% of its full load KVA rating. So what is the cause? Harmonics. All them damn switch mode power supplies found in the PC computer found at every desk.
Toroidal transformers of a decent size, as found in power amps for example, are susceptible to mechanical hum caused by DC on the mains. Some manufactures that use a toroidal power transformer in their power amps may employ a DC blocker circuit inside the equipment on the AC lines before the power transformer.
Quote from Nelson Pass:
If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.
The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.
You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +.
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.htmlMost common things found in the home that can cause DC on the mains.
Hair dryers. Especially the high wattage hair dryers that are set to the medium heat setting.
Electric space heaters that have a reduced wattage setting example, 1500/900 watt that are set on the lower wattage setting.
Cheap lighting dimmers. Here I think it depends on the connected load to the dimmer.
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Can an aging grounding bar cause noise?
As in equipment ground or as in main system, "Grounding Electrode System" ground of the electrical service?
As for the safety equipment ground a loose or corroded connection can add a series resistance in the equipment ground. The resistance can cause a difference of potential to exist from one equipment ground to another. A good example is a difference of potential from a CATV provider's coax cable shield to the safety equipment ground at the mains wall receptacle. If the CATV is connected in any way to an audio system using the wall receptacle safety equipment ground there is a very good chance of a ground loop hum problem.
In most cases the problem is an improperly grounded CATV cable provider’s Coax cable shield. Or it could be a loose or corroded connection at the CATV grounding block. But it can also possibly be a loose or corroded branch circuit wiring safety equipment ground connection.
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