Jump to content

AC mains filters - how do they work ? how to choose one ?


thoppa

Recommended Posts

Hi,

I have noticed, by switching amps and power supplies about, that there is noise in my system that can only be coming from the AC power coming from the wall.


So I'm looking for a better mains filter but I don't know how they work, what to look for, and why some are recommended for power amps and some are not (something to do with dynamics and the filtering....).


Anybody help me out ?


Cheers,

Tom

Link to comment
Share on other sites

I know a lot of people use power conditioners and filters. I simply use good power strips from different outlets and TOTALLY eliminate noise by not overloading. Flourescent lighting is bad about giving an "AC" hum. Isolating the amps from the preamps power source has usually taken care of the noise problems. No sense adding high dollar items when the fix can be simple.

HarryO

Link to comment
Share on other sites

Thanks !

Unfortunately, I already have tried your suggestions. No difference. Boo hoo. You have a good supply - lucky dude !

My supply is being affected by the house wiring, my neighbours and the grid generally. I could ask the neighbours to switch everything off but that's not gonna make me popular at the next BBQ.

It isn't loud at all and I am definitely being fussy, but if I can reduce it that would be very satisfying. I think I have to get a simple filter for spikes and noise - for about 8 amps (2KW) max I reckon.

Cheers,

Tom

Link to comment
Share on other sites

They make very good industrial line filters (directional) for your 120/220voltac line home inputs but they are very expensive. They are used for computer rooms and electronic areas. They were mainly designed to remove electronic generated noise and to prevent the noise from contaminating the power grid.

JJK

Link to comment
Share on other sites

When I bought my power strips I bought them at a Computer shop. They were about $24.00 each. I bought 4 of them. The manufacturer of the strip guaranteed no damage from spikes or surges for an amount of up to $50,000.00 if my equipment was damaged. They are also filtered. It may be why mine work. I get no noise at all through them. I live in an apartment with 12 units. I do get noise through my sons system in his room. It doesn't have the strips I use on my system. I have one strip not being used and I will install it now and start my "diagnostics" and test his system with and without the Power strips. I'll let you know if the last strip works. I'm curious now.

HarryO

Link to comment
Share on other sites

I use APC computer battery power backups.

The protector provides an uninterrupted power supply (UPS) as well as automatic voltage regulation (AVR).

Safeguard against power fluctuations or surges that can damage hardware. This device is rated to protect against surges of up to 420 joules.

The device features eight outlets.

The one I use was an extra from work but it has already saved me from 3 power blinks. I hate to think what I might have lost!

If you had one of these you could disconnect the ups from the wall and run on battery power for a couple minutes. If you still hear the sound it is not the mains.

Link to comment
Share on other sites

I have one strip not being used and I will install it now and start my "diagnostics" and test his system with and without the Power strips. I'll let you know if the last strip works. I'm curious now.

HarryO

Curiosity killed the clicks....let me know if it works and what the make and manufacturer are please !

Thanks,

Tom

Link to comment
Share on other sites

what doess the noise sound like?


is it coming from your speakers or your the transformers of your equipment?



Hi !

It's a bit weird really, it sounds like someone miles away is running a water pump ; I can hear the pump faintly whirring and water softly whoosing. It is very quiet and I only hear this with my ear right against the speaker.

I'm not in the habit of listening so close (dur !) but I was trying out comparsions re my bi-amping and DAC testing and during this I switched back to my old Onkyo and noticed the exact same noise. So I tried my Sony - same noise. In fact the noise is the same between very different amps (2 class AB, class T) and power supplies (linear and smps) and inputs (DACs, soundcard, DVD etc) it only varies in volume and slightly in tone. I even went to the extreme of shorting out the inputs on one amp's circuit board so it was a closed circuit amplifying nothing - and yes, you guessed it - same noise.

The quality of the noise changes slighty when I switch on the bathroom ( flourescent ) light so I'm as sure as eggs are eggs that is coming out of my wall.

I am going to try out a Chinese-made power filter bar designed for audio over the weekend but because I don't know how these things work I won't know how it is affecting my amps - noise may go - but this might just be a dirty great big capacitor that doesn't discharge fast enough to supply an amp's transient demands so quality might be affected.

Any idea how they work ?

Cheers,

Tom

Link to comment
Share on other sites

I use APC computer battery power backups.

If you had one of these you could disconnect the ups from the wall and run on battery power for a couple minutes. If you still hear the sound it is not the mains.

Hi,

Well I don't have this but you have given me an idea ! Thanks ! I have just realised my class-T amps will run from a car battery. I will give it a try tomorrow morning.....thanks.

Tom

Link to comment
Share on other sites

Tom,

The manufacturer is unknown. It is a grey 6 outlet strip with trip reset, on/off, phone line in and out, cable in and out, and the power cord is almost 7/16" thick and about 4' long with an inline 1 1/4" barrell approximately 2" long. All I can find on it is a model #. 53200msa made in China.

I've waited all day and overnight and haven't noticed any noise since the change in the kids room. I usually hear the noise from my upstairs neighbors vacuum cleaner. No static and no tv interference noticed since the putting the strip in either.

This morning I took the strip out and did notice some occasional interference from what may have been a Microwave oven. Just a guess but I could hear my upstairs neighbor walking overhead in the kitchen. It lasted about 2 minutes. I've been doing tests using can openers, vacuum cleaner, jigsaw, (I've been building motorboards in my apt for my "Wallrus". No complaints from the neighbors yet!) and the strip eliminated the noise from the vacuum and can opener. Noise showed up without the strip.

To be fair I did the same tests using a Belkin SurgeStrip (trademark) and the same noises also went away.

I replaced one of the 53200msa strips with the Belkin Surge strip and the results were the same except for the can opener. I did get interference with the can opener with the Belkin. Not very scientific but a difference noticed through the can opener when I switched out strips.

Next I switched out the strips on my left channel amp. I inserted the Belkin in place of the 53200msa and i did get some previously unnoticed "tube hum" from the left channel. I switched back and the hum was gone. Enough proof for me.

I will go down the street to the PC shop this afternoon and have them search my purchases and try to find the brand I am using.

This apartment has aluminum wiring 40 years old. We received a notice last month about space heaters. I don't know if it has an effect on noise or not.

Updates later.

HarryO

Link to comment
Share on other sites

"It's a bit weird really, it sounds like someone miles away is running a water pump ; I can hear the pump faintly whirring and water softly whoosing. It is very quiet and I only hear this with my ear right against the speaker."


Of the three, hum, buzz, or hiss, can your noise be considered a hum?

Intresting that the tone of the noise changes when you turn on ligthing that uses ballasts.

You system is picking up reflected inductance.  This can include apppliance motors that are in your house hold and other house holds on your local step down transformer.  Other factors are light dimmers, switching power supplies in SAT and Cable recivers, computers, power supplies for game consoles, microwaves, and even power supplies used to charge cell phones.  This reflected inductance interfere's with transformer operation used in DC power supplies.   

It would be helpful to know the variations in your household voltage levels during peak and non peak usages.

This used to be rare and only found on industrial sites, but with more and more use of non-resistive devices in the home, this type of noise is on the increase.

Before getting into the fix.  repeat yor test after disconnecting all the devices of the type I mentioned.

Send me an email, if I miss your response to this thread.









Link to comment
Share on other sites

I switched back and the hum was gone. Enough proof for me.

I will go down the street to the PC shop this afternoon and have them search my purchases and try to find the brand I am using.

Hi,

Thanks for posting this. You have so much spare time ! Lucky man....

I have tried to do some research on power filters and I have discovered two basic types - ones that use a transformer to isolate and others that use regulators to produce a pure sine wave. Apparently the second type is better for audio as the former don't react fast. Any idea what your Belkin and no-brand use ?

Cheers !

Link to comment
Share on other sites



Of the three, hum, buzz, or hiss, can your noise be considered a hum?

Intresting that the tone of the noise changes when you turn on ligthing that uses ballasts.

You system is picking up reflected inductance. This can include apppliance motors that are in your house hold and other house holds on your local step down transformer. Other factors are light dimmers, switching power supplies in SAT and Cable recivers, computers, power supplies for game consoles, microwaves, and even power supplies used to charge cell phones. This reflected inductance interfere's with transformer operation used in DC power supplies.

It would be helpful to know the variations in your household voltage levels during peak and non peak usages.

This used to be rare and only found on industrial sites, but with more and more use of non-resistive devices in the home, this type of noise is on the increase.

Before getting into the fix. repeat yor test after disconnecting all the devices of the type I mentioned.

Send me an email, if I miss your response to this thread.

Thank you so much - very informative ! Sound (sic) advice too !

It's hiss but not a pure tone hiss. 50cm from the speakers it's quite inaudible. I also notice that my neighbours' light switches (I think) cause tiny clicks that are not so tiny with the volume up.

My laptop uses smps power, as does the external hard disk so I switched these off and played audio from the 80Gb internal drive and ran on the battery. No real difference. I can also power the amps from a motorcycle battery but as yet I haven't had a chance to do this. They have smps or linear supplies - I have both. I also have a 5V/12V 60A/60A supply intended for servers - it is super smooth with surge protected output etc but its fans are so noisy it's impractical. It was gift from a friend who works in a company over the border. A great bit of kit but sadly unused. I digress. The DAC is a linear supply (sadly not toroidal so while looking inside I started thinking about replacing it...one thing at a time ...). Anyway, I'll play around and let you know.

I won't be checking the mains voltage. The first amp I built many years ago was great but the power supply shorted to the case when I was moving it - the shock made my hands grab the case even tighter for a second or so before the amp and I parted company with some force. I laugh about it now but wouldn't wanna do anything that might make the last few bits of hair I have on my head fall out.

I have a Chinese LongYu power thingamy on loan. I am still testing this with various connections and I'll post about it tomorrow. Gotta work today ! Shucks...

Cheers

Link to comment
Share on other sites

"I have tried to do some research on power filters and I have discovered two basic types - ones that use a transformer to isolate and others that use regulators to produce a pure sine wave. Apparently the second type is better for audio as the former don't react fast. Any idea what your Belkin and no-brand use ?"

There are a few more types as well as issues to be mindful of.

a. voltage regulator - goal is to maintain a constant voltage

1. Types that use a DC to AC converter. These have batteries that charge. The battery actually runs a DC to AC converter which powers your equipment. The battery has a defined period of run time once AC power is no longer available at your wall outlet. Less expensive ones do not generate a true sine wave, and as a result, limit amplifier dynamics.

2. Types that use a variable trasnformer - the transformer has a multi-tapped primary and secondary winding. A computer determines what the turns ratio should be to maintain a constant voltage. These can be noisy as the transformer armature rotates to new positions as voltage changes occurs. Another version uses a capacitor to change the reactance of the transformer based on the load placed on the unit. These are really brown out devices. They have a narrow range of operation usally +- 10% of line volatege.

b. line conditioner - goal is to remove or reduce interference and noise

1. types that use isolation transformers. Basiclly a 1:1 transformer. Whatever comes in is what comes out. reduces noise by isolating your equipment from the house mains. consideration is that you need to determin your voltage ampere requirements and get a properly sized unit.

2. types that use balanced isolation transformers. This is simular to item b1, but uses a transformer with a center tap on the secondary side. The ground refernece is moved to the center tap. Voltage gets converted from 110 - 0 to 60 - 0 - 60. The result is that noise gets cancelled due to the way the device inverts the +60 and -60 to get 120. Same conderations about sizing as item b1.

3 types that use inductors and capacitors. This is much like a crossover network. Inductors and capacitors are use to change the path noise takes and causes it to be diverted to ground. The way this works results in an insertion loss that cuase performance issues with power amplifers, resulting in poor dynamics. More expense ones uses multiple stages of low insertion loss circuts that minimize the effect it has on amplifier dynamics.

c. surge protector - goal is to capture spikes that can damage your equipment.

1. types that use solid state devices like MOV's. These are basiclly differnet grades of power strips that contain banks of MOV's designed to capute surges. The MOV's have a hit life. The more they are hit, the shorter their life. On more eloaborate surge protecotrs, an indicator will tell you if the MOV's are no longer working. If yor surge protector does not have an indicator, best bet is ether to replace the surge protector yearly, or have someome replace the MOV's.

Link to comment
Share on other sites

There are a few more types as well as issues to be mindful of.

So it's quite straightforward then eh ? :-) Thanks for posting this info - it is just what I was trying to find out and gives me a much better idea.

I haven't had a chance to use the battery cos I finished off my bi-amping today. I'm really not convinced about bi-amping in the real-world but I didn't try the active route so maybe that's why.

The power filter I borrowed is a line conditioner designed for hi-fi, it says. It has turned the 'odd' noise into a slightly quieter but pure hiss only, which I trust is the system. I haven't heard a click all day even though the neighbours have been in and obviously switching stuff on and off as usual. It seems to work so I'll probably buy one - they are about US$50 which seems pretty reasonable. There's a website :

http://www.chongqinglongyu.com/product.asp

But altavista babelfish can't translate the data page and the English tab doesn't work so it's not much help. Like so many things made in China, the assembly and finishing is poor. I had a bit of a shock when I connected up the cap to the tweeter today - the compression driver does not fit flush to its mounting on the horn because the horn moulding is just a few fractions of a millimeter too big over a bout a third of its outer diameter, so it sits at an angle of maybe 10 degrees and ther plastic surround bends to allow the screw to fully tighten. Both speakers had the identical problem so obviously the factory die is out of spec. I doubt it affects sound output though. Anyway, says made in China on the back of the speaker. I had a pair of Dynaudios once - they said 'carefully made in Denmark' on the back.

Zeiss have recently tried to produce a 16-80 lens for Sony in China but the lens' release has been delayed by six months because apparently Zeiss were not satisfied with the quality control in China and so moved production to Japan. Lens comes out in March.

http://www.ecat.sony.co.jp/alpha/lens/lens.cfm?PD=24680

Cheers,

Tom

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...