No Idea. You may want to check out some of the panels they use for damping PC's.
Best,
E
Best,
E
Make a trasnformer hum 101
So this comes up repeatedly and I wanted to share this with you.
Sometimes perfectly good transformers mechanically hum. Often this is caused by having DC on the line. This is kind of a weird concept so let me take it step by step.
Normally a good AC line has a neutral which is essentially at ground potential, and a "hot" which we say is 120 VAC. That is, it has a sinusoidal waveform which repeats at 60 Hz (for America) or 60 times/second. The magnitude of the complete swing is measured in RMS. It’s an average which allows us to easily determine power dissipation. What this really means is that the voltage "swings" from about +85V to -85V. This is also called Peak to Peak or Vpp. An RMS measuring multi-meter will correctly say 120VAC, but if you look on an oscilloscope you will actually see the very top and very bottom of the waveform at around +- 85 V.
It is possible to have DC, AC or both on a conductor. In an incoming power line however it is NOT desirable to have anything but AC. What’s odd is that stupid little power supplies and dimmer switches can actually take an otherwise fine power line and distort it by adding DC to it.
This happens for a couple of reasons
Consider a dimmer or laptop power supply that only takes current during the positive cycle. With a little resistance on the line, this pulls down the maximum positive voltage. Say from +85Vpk to +83Vpk, but the negative swing is still -85Vpk. Congrats, you’ve just added -2Vdc to your waveform. To make matters worse, these supplies may take current only for very short periods of time, causing the waveform to distort far from sinusoidal, and adding harmonics, or high frequency noise, to the incoming power where none existed before.
It is this DC voltage that will make otherwise fine functioning transformers develop a mechanical hum in the laminations.
The point I wanted to make is that these power supplies don’t really inject noise, so much as slurp power unevenly, causing a host of possible audible or visible effects.
Everything I’ve written here is scientifically verifiable with models, measurements and test gear, however it does not automatically justify spending $50k on power conditioners. How much of a problem you have and how much it’s worth to solve is entirely up to the music/movie lover.
I hope this is helpful,
E
Sometimes perfectly good transformers mechanically hum. Often this is caused by having DC on the line. This is kind of a weird concept so let me take it step by step.
Normally a good AC line has a neutral which is essentially at ground potential, and a "hot" which we say is 120 VAC. That is, it has a sinusoidal waveform which repeats at 60 Hz (for America) or 60 times/second. The magnitude of the complete swing is measured in RMS. It’s an average which allows us to easily determine power dissipation. What this really means is that the voltage "swings" from about +85V to -85V. This is also called Peak to Peak or Vpp. An RMS measuring multi-meter will correctly say 120VAC, but if you look on an oscilloscope you will actually see the very top and very bottom of the waveform at around +- 85 V.
It is possible to have DC, AC or both on a conductor. In an incoming power line however it is NOT desirable to have anything but AC. What’s odd is that stupid little power supplies and dimmer switches can actually take an otherwise fine power line and distort it by adding DC to it.
This happens for a couple of reasons
- Some amount of impedance/resistance on the wire to the transformer, and through the transformers.
- A power supply that ONLY takes from one or the other voltage swing.
Consider a dimmer or laptop power supply that only takes current during the positive cycle. With a little resistance on the line, this pulls down the maximum positive voltage. Say from +85Vpk to +83Vpk, but the negative swing is still -85Vpk. Congrats, you’ve just added -2Vdc to your waveform. To make matters worse, these supplies may take current only for very short periods of time, causing the waveform to distort far from sinusoidal, and adding harmonics, or high frequency noise, to the incoming power where none existed before.
It is this DC voltage that will make otherwise fine functioning transformers develop a mechanical hum in the laminations.
The point I wanted to make is that these power supplies don’t really inject noise, so much as slurp power unevenly, causing a host of possible audible or visible effects.
Everything I’ve written here is scientifically verifiable with models, measurements and test gear, however it does not automatically justify spending $50k on power conditioners. How much of a problem you have and how much it’s worth to solve is entirely up to the music/movie lover.
I hope this is helpful,
E
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- 18 posts total
SMPS have bad rap from crude computer applications. Jeff Rowland uses extremely quiet SMPS (cleaner than linear power supplies). Advantage of SMPS is that it can operate from AC and DC (tolerates presence of DC) while many operates from wide voltage range. In addition they are line and load regulated, while linear supplies in power amps are not. |
dweller 1,377 posts 02-27-2017 6:46pm 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 yourhttp://www.diyaudio.com/forums/solid-state/2080-dc-filter.html Most 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. // 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. . |
- 18 posts total