How to filter noises from mains power

[gnd]

I seem to have problem with inpulses from mains power leaking into my studio. I can hear them as clicks and pops. They get into recordings.

Any switching of lights, fridge, plugging and unplugging devices, all of this is heard in my studio as quiet (and sometimes not so quiet) pops and clicks.

All studio electricity is by design on separate mains phase. Even studio lights are not on the same mains phase as equipment. So I guess noises are not coming through mains live, but through mains ground, which is common to all three phases.

Is there a way to filter this out. Any suggestion how to deal with this?

...

 

[JohnRoberts]

Perhaps it isn't coming through the ground.. maybe it's RFI (radio).

Figure out where it's getting into your gear and adress it at the entry point(s).

JR

 

[SonsOfThunder]

You didn't say what country you are in in your profile. That's VERY important in a situation like this in order to know what electrical codes apply to your particular locale...

Could be RFI...in that case could you move the device that is causing noise to an outlet that is physically farther from the studio equipment? I have never tried to t-shoot that way before.

My experience says it might be the shared ground. If you are in the US, NEC says you can use a separate "technical ground" for all of your equipment.

Check this article on Tech Gnd. Ignore all the babble about balanced power. Note what they say about tying to the regular mains ground and also about isolated-ground outlets if you are using conduit...Verry important!

Talk to an electrician who knows something about this in you area.

HTH!
Charlie

 

[gnd]

Thank you, Charlie.

I had people from power distribution come today, to check their cabling. All is fine from their side, so problem must be in the house.

I also contacted electrician, who is specialized for ground installations, and he will come and do some measurements tomorrow.

Regarding rules for separate "technical ground", I'm from Europe.

I hope that the expert coming tomorrow will be able to provide some solution. As it is now, my studuo is too unreliable for any serious recording.

thnx.

...

 

[Guest]

What is the condition of your earthing stake?

 

[gnd]

[quote author="uk03878"]What is the condition of your earthing stake?[/quote]

Yes, this is a good question. My house earthing is basically coming through city power distribution cable. There is a few meters of zinc coated iron rod burried in the ground together with city cable, just before city cable enters into house's external distribution box, but is in sandy earth, and not very deep, so it is probably almost useless. There is no separate grounding.

I read there should be two or three copper bars (or zinc coated iron bars) burried in ground, at some distance, connected and so on. There is nothing like that in my house, so I guess I'll have to make it.

I'm not into going all arround the house with a copper wire, that seems too much. But I could hammer three 2meter long iron zinced tubes (water distribution tubes of some 3 or 4 cm diameter), connect them together and use this as a ground.

I will wait and see what will this local expert recommend tomorrow.

There is also a chance, that there are some electrical machines in other parts of house, which are on the same electrical phase as my studio equipment. In my part of the building I took care to separate one phase for studio, but who knows what happens with that same phase in other parts of building. So it may be that problem is not only in ground, but also in 240volt signal.

If pulses are in mains signal, then it can be filtered out with some filtering units, is it? Would UPS help? Or those special filtering extension cables?

...

 

[mikka]

You may need a separate copper earth stake just for your studio wiring. My brother is an electrician and I recall ..... it was surprising how deep the earth stake had to go to get good connection. Let us know how things work out.

 

[gnd]

[quote author="mikka"]You may need a separate copper earth stake just for your studio wiring. My brother is an electrician and I recall ..... it was surprising how deep the earth stake had to go to get good connection. Let us know how things work out.[/quote]

Here is some news.

People from power distribution were here two days ago, and all is fine with their line. Beisides three mains phases and neutral, they provide also separate wire for ground. Therefore they say that separate grounding is not necessary, because they provide proper grounding. They measured their lines, and all is fine.

Today came experts for grounding, and they measured impedances both at outside distribution box, and in studio. They said that all is fine, within normal readings.

So I guess ground is fine. I must be getting impulses from machines, which may be on the same power phase in other parts of building, or maybe even from neighbours.

Expert mentioned, that I may try filtering my mains power. He didn't know exactly what condensers to use. He also recommended, that I try to connect equipment through UPS.

Basically I will have to play arround a bit, I guess. I will not do it now, too busy. But will try in near future. I think mostly it will be guesswork, hoping for some solution. I may also try kicking thre rods in the ground, and connect them to mains ground.

Any ideas for DIY mains filtering? Is it done with capacitors? Any special capacitors? Any special circuits? I guess such circuit would be fairly simple, few capacitors and maybe resistors, maybe a coil, is it? Maybe somebody has such schematics to share?

thnx

...

 

[Guest]

Did you read this?
http://www.groupdiy.com/index.php?topic=1838&postdays=0&postorder=asc&highlight=earth&start=0
especially the book advice?

And there are a few threads here on power conditioners

 

[W DeMarco]

I have read a bit about using balanced AC in the studio. I have also heard this is a good idea for cleaning up you mains. Its a bit exspensive so you might want to find some alternatives.

http://www.equitech.com/articles/bpng.html

Good article by equitech.

Another might help you organize your electric needs

http://www.equitech.com/support/tpb.html

And finally this one covers grounding in a non balanced power and a balanced power system.

I have also heard talk about hospital grade outlets being helpful as well.

Will

 

[gnd]

I hammered three 2meter metal pipes into ground, connecting them to mains ground.

Pulses in mains improved, they are quieter, and more on bass, more like a "pop" instead of "click". Noise is still there. I have plenty of noise in my ground, I think it is probably from numerous switching PS in seven studio computers. If I scope ground near computers, it is all spikes up to megahertz's, basically white noise made of tiny pulses. Grounding doesn't seem to help with this noise.

I read articles on equitech.com. I may try DIY balanced power for my mixer, and see how it works. Equitech speaks about 16dB or more noise improvement. Thats huge. But I will DIY, equitech is expensive, and 120V only. :idea: I'm planning on ordering smaller (300Watt) toroid 1:1 trafo with bifilar secondary winding, and do some experiments. I will put some DIY RF filtering on it too. :wink: That shouldn't cost me more than 50euro. If it turns out a success, I will order a big toroid for entire studio wiring.

I think worst source of noise in ground are all those computers I have connected. Maybe it would be best to feed all my computers through balanced power, to remove the switching noise they put back in ground. Then I could feed all my racks with usual power, since switching noise will be out, and ground will be preety clean.

What do you think of this? Any suggestions?

 

[Samuel Groner]

If the computers are really your problem (can't you switch them off temporarily to check?) I'd rather think about replacing the computer PSUs with something better. Fixing the cause is allways better than curing the ills.

Samuel

 

[gnd]

[quote author="Samuel Groner"]If the computers are really your problem (can't you switch them off temporarily to check?) I'd rather think about replacing the computer PSUs with something better. Fixing the cause is allways better than curing the ills.

Samuel[/quote]

I did some switching off of computers. I turned off six, then scoped between mixer PS chasis and mains ground. This is what I get:

http://84.255.203.119/noise/scopenoise1.JPG
http://84.255.203.119/noise/scopenoise2.JPG
http://84.255.203.119/noise/scopenoise3.JPG
http://84.255.203.119/noise/scopenoise4.JPG
http://84.255.203.119/noise/scopenoise5.JPG

This is the major noise I was observing. What am I looking at?

Turning on computers one by one starts filling the noise between those periodic noise bursts, and adds some variety to shape of bursts too. But those bursts remain visible and prominent.

If I unplug mixer PS and measure at the cable, noise bursts are still there. Actually they are everywhere, wherever I measure.

Now, unplugging things, I'm starting to think about where to take my refference ground from. It gets a bit confusing, because I don't know where is clean ground, and where is ground with noise. Any idea how to get me a clean refference ground?

How to troubleshoot this?



...

 

[mikka]

Just thoughts...... running a UPS permanently hooked up on your computers may help ....

.... a big isolation transformer or two for your other gear.....?

I wonder if some local industry could be causing those square waves.

 

[gnd]

[quote author="mikka"]I wonder if some local industry could be causing those square waves.[/quote]

Those are not actually square waves, but spike noise bursts of some 6ms length, appearing with 100Hz repetition frequency. In previously posted photos from my scope, every next picture is more zoom into those noise bursts.

Since they are in frequency of rectified 50Hz mains (twice 50Hz = 100Hz), maybe they come from some weak power supply. Maybe some weak rectifier diodes somewhere, or bad bypass caps... Maybe from those cheap external power adapters that some units use... Is this possible?

Probably I will need to unplug everything on my studio mains phase. This will be fun.... But I need to find good refference for ground first. Any suggestions? Maybe a thick cable directly from house distribution box (where mains fuses are)? Or maybe a thick cable directly from my new outside ground rods? What would be best reference ground?

I will order one DIY isloation balanced transformer (bifilar toroid), and do some experiments.

...

 

[mikka]

Woops... I meant square waves as a description.... bad choice of words around here ... I believe big electrical equipment over 1km away could be enough to cause surges that generate similar..... Can you check for those "spikes" at your meter? I know you said it had been checked .... but it might be worth doing yourself.

I'm not an expert ... just awake .... :green: I hope others can chip in with more useful info.

I would use the stakes that you put in as your earth reference. Might help to get a hose out and wet the ground for half an hour where each stake is driven in...... just to ensure you have a good ground for your work.

Those cheap external power supplies could be at partial fault. The ones I've used only have a plastic case..... no shielding. A few people have mentioned those things have caused noise in their studio. I'm wondering about your lights also. Flourescent? I guess you're gonna have to turn EVERYTHING off and see if it's there to begin with.

At least you're not alone. Many others have been through similar .....

 

[Samuel Groner]

I'm not sure how relevant the measurement you posted is--these are simply current pulses from rectifiers and would manifest itself as hum/buzz and not clicks or pops as you described it. Any linear PSU does generate these sort of spickes (both as radiated magnetic field and transmitted voltage in the mains).

First off all I'd check which pice of audio equipment is most sensitive to the effects.

Samuel

 

[gnd]

[quote author="Samuel Groner"]I'm not sure how relevant the measurement you posted is--these are simply current pulses from rectifiers and would manifest itself as hum/buzz and not clicks or pops as you described it. Any linear PSU does generate these sort of spickes (both as radiated magnetic field and transmitted voltage in the mains).

First off all I'd check which pice of audio equipment is most sensitive to the effects.

Samuel[/quote]

So those spikes are from PSU's. Would they affect audio noise floor? If yes, how to reduce them? Possibly RF filters and isolation transformers will not help with this, because they are not filtering ground, but live and neutral wires?


Otherwise I have somewhat given up on solving clicks and pops. :sad: They are just too random, and usually too rare. I'm observing it for weeks, and cannot figure out some pattern. Sometimes it is just fine several hours, and sometime I get several clicks one after another within few minutes.

While trying to solve clicks, I came upot this hum/buzz pulse noise. If it is increasing noise level of my system, I would really like to reduce it, since this noise is present all the time. Clicks and pops I can eventually avoid with some luck in timing, or some post editing if really critical.

...

 

[gnd]

Once I started digging into noise of my system, there seem to be no end to it. I'm moving from one thing to another, and slowly removing problems.

Computers are a horrible place for audio cards. For a last two days I was trying to find a source for noise appearing on my recorder computer emu1212m. It was few frequencies, 120Hz and 140Hz, with numerous overtones up to 1kHz, over 30dB above normal noise floor. At 1kHz noise was cut off, and above there was just quiet noise at -150dB.

I found solution. Emu 1212m has 2 cards, one digital and one analog. My analog card was next to Yamaha DS2416 card, and there was some interference, which showed on 1212m as tones. I moved the card to another PCI slot, and tones are almost gone. I'm thinking of putting some shield between cards, maybe piece of metal wrapped in plastic, and isolated to chasis....

It is amazing what can all go wrong inside this computers.... Good I isolated at least this one.

And regarding clicks and pops, I think I isolated problem too. It is connected to electric cooker in another apartment. It seems, that cooker in on same phase as my studio. Any switch on cooker creates click in my system. :? Fun, is it? Especially mixer is sensitive to it. I will try filtering and balanced power - I ordered isolation transformer already. As last measure I can move my studio mains to another mains phase.

I still need to locate source of 50Hz hum on my mixer. I'm sure I will get it, sooner or later. But thats probably mixer's internal ground problem. Ground bus is thin wire, almost 1m long. I may rewire it to star.

...

 

[SonsOfThunder]

Glad to know you are making progress though it is one small step at a time. Be persistent!

Peace!
Charlie