Speaker noise and thumping from AC power - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 12 Old 05-03-2016, 04:37 AM - Thread Starter
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Speaker noise and thumping from AC power

I don't know if this is the right place to post this, but I need some help solving an audio problem I am having.

I live in Nepal, and there is frequent 'loadshedding' here, which means the power goes out quite regularly. When the power is here, the voltage fluctuates quite a lot too. I have a whole-house servo type voltage stabilizer for these fluctuations and I have a whole house battery backup/inverter system.

When I am on the inverter, everything is great, no buzzing, thumping or anything. But when the city AC line is present, I get a thumping sound through my speakers as the voltage fluctuates, and the stabilizer responds.

Is this coming from the AC line or from the stabilizer itself? Is there any way to isolate my speakers from this? It is quite loud and annoying.
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post #2 of 12 Old 05-03-2016, 06:10 AM
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This is going to evolve into fairly complex power engineering pretty quickly; I'm not sure what sort of budget you have but you're best solution might be to contract a local electrical engineering firm to review your system and propose a solution.

How often is the thumping? Are the lights in your house effected at the same time?

I suspect the thumping is coming from your servo system as it responds to the AC fluctuations and comes on and off line. Do you have any specifications or model number on the device?

To give a better analyis you would need to provide long term readouts of your power line.

http://www.fluke.com/fluke/caen/Powe....htm?PID=80077
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post #3 of 12 Old 05-03-2016, 08:40 AM
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The obvious but expensive solution is to use an online UPS. That means you are always running the system from the UPS, and when the AC input is valid it uses it to charge the battery. There is no switchover. The cons are that the online UPS is always supplying power and so needs to be much more robust than an offline/standby type of UPS. Essentially it is powering your equipment 24/7 rather than turning on as needed.

An intermediate solution would be to try a point-of service UPS for the stereo that might better buffer the stereo from the line fluctuations. There's no guarantee it will perform better than your present system, but it might be a cheaper option if it works.

A different AVR or power amp might be less susceptible to power line variations (or might be more susceptible, alas).

No easy answers... Contacting a local resource as @clechien suggested is a good idea.

HTH - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #4 of 12 Old 05-04-2016, 04:57 AM - Thread Starter
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Thanks for the replies! Unfortunately, local solutions here are really not helpful as they are unskilled and not knowledgeable about this sort of thing. You should see the nightmare that passes for house wiring here.... I even dug out and installed my own grounding rod because the house's ground consisted of running a thin wire to the water pipes and wrapping it around it. I have actually done quite a bit to improve the house's wiring myself.

The voltage stabilizer is some handmade thing from India, as many things here are, so no model or anything on it. The thumping is quite frequent when it occurs - every few seconds. I have looked into online UPS solutions - they are quite large and expensive. Much larger than I need.

What about getting a small car inverter, small battery and a charger just for the speaker system? Do you guys think that would work? I would imagine the inverter needs to be sine wave?

I have taken to either shutting off the speakers completely when there is power or just using headphones, as they seem to be fine.
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post #5 of 12 Old 05-04-2016, 05:35 AM
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Quote:
Originally Posted by btkramer View Post
What about getting a small car inverter, small battery and a charger just for the speaker system? Do you guys think that would work? I would imagine the inverter needs to be sine wave?

I have taken to either shutting off the speakers completely when there is power or just using headphones, as they seem to be fine.
Have you tried a different amp?

In Theory.... If you could convert from AC to DC and then have a DC to DC isolator and then re-create the Sin wave, you should have clean power. Re creating that sin wave is tough though, usually it's a digitally stepped interpretation of a wave. Of course all of this is just so that the amp can convert back into DC power, but that's another topic.

Again, "in theory", getting a car battery charger, a 12 volt battery, and a car inverter could work to do this. I really really hate the ideas of car batteries in home use and I strongly recommend against this.

You might be able to use a computer power supply, take the 12 volt rail and throw that into the inverter and get AC power out the other side. A good computer power supply will have capacitors to smooth the power fluctuations and should be able to take the voltage fluctuations as they're build for 110/220 operation. Just watch out because a 1200 watt power supply is 1200 watts in total, you might only get 30 amps on a 12 volt rail = 360 watts. Plenty for any reasonable audio levels. You might get really ****ty audio though as computer power supplies are noisy.. BUT your AC powered amp might have enough filtration to clean it up again. the whole thing might just work!

*** THESE IDEAS ARE JUST RANDOM THOUGHTS I'M HAVING. NO LIABILITY IS IMPLIED OR EXTENDED. ***
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post #6 of 12 Old 05-04-2016, 06:26 AM - Thread Starter
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I haven't tried another amp, but it would be difficult to do as its an all-in-one system, as pretty much everything is here, unfortunately. I have been looking into getting some stuff imported, but its really expensive with the shipping and customs.

I like the computer supply>inverter idea. I'll give that a try. I have a decent spare computer supply here I can try it out with. Need to find a decent small inverter now...

Thanks for the input! I'll let you know when I've got it sorted. Might be a few days....
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post #7 of 12 Old 05-04-2016, 06:34 AM
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Maybe an isolation transformer to the amp, the best i saw cheap was only 2amp recently, depends on your current draw needed
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post #8 of 12 Old 05-04-2016, 06:40 AM
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Or could be as simple as a capacitor in the amp not filtering out ac line noise properly, or too much draw resulting in device being underpowered?
Hopefully it's just a simple thing, i admire the challenges your facing there
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post #9 of 12 Old 05-10-2016, 06:08 PM
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I use a hybrid approach.
I have non-online UPS's and a AC-DC-AC regenerator from PS Audio.

I did an analysis of the power-quality in my home last year.

Here were the results:

Incoming dual leg AC:



One leg of Incoming AC:



PS Audio PPP power conditioned socket (AC-DC-AC power regenerator):



The Fluke is displaying the waveform correctly. Normal wall-socket AC power has 2% to 5% distortion in it.

CyberPower 2200VA Puresinewave UPS on battery-power (non-online type):


Not to shabby for running off of battery-power.
This feeds my PPP if / when the power goes out.
Or when gets really nasty, which it never has THUS FAR.

As you can see the PS Audio stuff is not snake oil, it does clean the AC for people who have massive power stability problems. The only downside is that they don't have battery reserve power. They are also expensive.

You might be better off with a ~1000watt server-grade PC power-supply an pure-sinewave inverter.
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post #10 of 12 Old 05-11-2016, 03:19 AM
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Is the thumping caused by powerline sagging or is it caused by short dropouts/sags causing switch overs to the inverter.
If the latter is the case you might be able to set a lower threshold voltage to prevent unnecessary switch overs.
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post #11 of 12 Old 05-21-2016, 04:03 AM
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Quote:
Originally Posted by BassThatHz View Post
As you can see the PS Audio stuff is not snake oil, it does clean the AC for people who have massive power stability problems.
I'm curious, is there a noticeable audible improvement whilst using all that equipment versus not using it? I'm not suggesting the equipment is snake oil (I bet it would solve the OPs problem) but the first of your pictures showing the incoming AC waveform doesn't look too bad to me (I've seen much worse), are you saying you can hear (in an ABX test) the difference between the original and the slightly improved waveform? I'm skeptical.

I'm sure the equipment would work wonders on a truely messy/distorted AC waveform but I bet a majority of people who use such equipment don't actually need it because their incoming AC is clean enough (to not make an audible difference) and they buy it for the same reasons they buy overpriced speaker cable. Even cheap AVRs are pretty resilient to minor waveform distortion, much more than the audiophile industry would have you believe. And any digital audio processing (e.g. a HTPC) is far less susceptible to powerline waveform distortion, its really only power amplifiers that are the issue and _might_ need some power conditoning.

To the OP:
I would suggest an isolating transformer and a full-regeneration AC conditioner. If you want to save some money and have some DIY fun, the car battery/charger/inverter solution you suggested would work quite well, but it would be a fire safety nightmare (I've considered it myself, used 12v power amplifiers designed for car-audio can be had for pennies). If you do go this route, put inline fuses EVERYWHERE on the 12v system.
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post #12 of 12 Old 05-21-2016, 04:38 AM
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Distortion on ac power lines is the least you should worry about. In a competent amplifier design this is not a problem.


In black is the typical current draw with a bridge rectifier into a load with buffer elco's.





http://electronics.stackexchange.com...r-ac-frequency

Last edited by Frank Derks; 05-21-2016 at 09:09 AM.
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