|
|
New webpages on mains filters
Hi,
Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
New webpages on mains filters
Jim Lesurf wrote:
Hi, Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. Slainte, Jim From endless searching through catalogues, it seems to me that most commercially available mains filters are aimed at trying to stop equipment *transmitting* crap onto the mains rather that stopping it getting in to equipment though I guess reciprocity applies to at least some degree. Cheers ian |
New webpages on mains filters
Ian Bell wrote:
Jim Lesurf wrote: Hi, Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. Slainte, Jim From endless searching through catalogues, it seems to me that most commercially available mains filters are aimed at trying to stop equipment *transmitting* crap onto the mains rather that stopping it getting in to equipment though I guess reciprocity applies to at least some degree. Cheers ian I should also have said that my experience with linear supplies is that there is a huge amount of crap on the mains from laptop SMPSUs and the like that falls squarely in the audio band. RFI filters are not effective in the audio band of course. Cheers Ian |
New webpages on mains filters
"Ian Bell" wrote
I should also have said that my experience with linear supplies is that there is a huge amount of crap on the mains from laptop SMPSUs and the like that falls squarely in the audio band. RFI filters are not effective in the audio band of course. I agree that there's plenty of audio-band crap on the mains, but not from SMPSs, which generally work at frequencies well above the audio band. AF crap is either harmonic distortion of the mains waveform, or comes from commutator motors and the like. AF crap shouldn't be a problem with a linear PSU. The transformer will remove common-mode noise, whilst the filtering on the rectified output (which you need anyway to remove mains-frequency ripple) will eliminate the rest. David. |
New webpages on mains filters
In article , Ian Bell
wrote: Ian Bell wrote: Jim Lesurf wrote: Hi, Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. From endless searching through catalogues, it seems to me that most commercially available mains filters are aimed at trying to stop equipment *transmitting* crap onto the mains rather that stopping it getting in to equipment I'd agree that dealing with problems by 'silencing' the source is - where possible - probably better that having to protect each individual 'victim'. though I guess reciprocity applies to at least some degree. You sometimes have to be careful with reciprocity when people start playing with ferrite devices. :-) An advantage of fitting suppression at (or near) the source is that it helps cut down on the number of possible routes by which interference might then distribute itself. Alas the problem in practice may sometimes be from sources outwith your control or even being able to locate them. I should also have said that my experience with linear supplies is that there is a huge amount of crap on the mains from laptop SMPSUs and the like that falls squarely in the audio band. RFI filters are not effective in the audio band of course. Yes, although that does depend to some extent on the type of filter and RFI. So for example the use of ferrites as common mode chokes can work down to relatively low frequencies as they discriminate in a way that lets them pass the wanted mains (or loudspeaker signal) more easily. But that doesn't help much if the interference isn't common mode. You may also need to use a loop of ferrite as a 'cm choke' rather than a simple clip-on chunk so as to get a large enough inductance. Snag here is the absence of useful measured data on the details of how much any given commercial filter rejects. I didn't comment on approaches like 'coating the wires with ferrite' as I think some cable makers say they do. That struck me as a perhaps dubious, and probably pointless exercise. Too little ferrite and too easily saturated by the mains power, I suspect. Must admit I also wonder about using VDRs as it occurs to me that in some cases they may *draw* current to them which otherwise may have gone elsewhere. Unfortunately, I've not found a lot of reliable measurements on these matters that show what tends to happen, and how often, in domestic UK situations. I did find some data on wall socket impedances, but with no guide to how consistent this was from one house to another! Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
New webpages on mains filters
BadJokeYou Should Be Working For Toyota!/BadJoke
On Thu, 25 Mar 2010 11:51:42 UTC, Jim Lesurf wrote: Hi, Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. Slainte, Jim -- Regards, Galen ------ There are only 10 kinds of people in the world. Those who understand binary and those who don't. |
New webpages on mains filters
In article ,
Brian Gaff wrote: Personally, I'd love to shove some crap into the mains for a few days to clobber these power line adaptors so the idiots scap them and I can listen to short waves again. Could you have a decent external aerial fitted? I have one feeding my Quad AM3, and SW reception is pretty good. -- *Marathon runners with bad footwear suffer the agony of defeat* Dave Plowman London SW To e-mail, change noise into sound. |
New webpages on mains filters
Jim Lesurf wrote:
Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. I know you wanted to keep it simple, but I wonder if you've missed the big issue? If you consider real components rather than idealised inductors and capacitors, then the picture has another dimension. The range of frequencies that can be considered to be RFI is so great that parasitics may be just as important as the nominal component values. Consequently, a real filter will be effective at some frequencies, but not others, across a broad spectrum. You don't show that what rolls off at some frequency may well roll back on higher up...then off, then on again, etc. As a result, every RFI filter has a particular profile of protection. Every consumer mains outlet has a particular profile of threat, which will change over time. It's like fitting a key to a lock, when the keys all look the same and the lock is unknown and frequently changed. Keeping *all* noise out is too unlikely to consider...perhaps the best you can hope for is, by chance, to defeat particular problems with your particular equipment in your house. Ian |
New webpages on mains filters
David wrote:
I agree that there's plenty of audio-band crap on the mains, but not from SMPSs, which generally work at frequencies well above the audio band. AF crap is either harmonic distortion of the mains waveform, or comes from commutator motors and the like. Just because SMPS "work at frequencies above the audio band" doesn't mean they don't also produce audio-frequency noise. A SMPS with a fixed switching frequency can easily employ a mains input filter that targets that frequency, although it isn't so easy to deal with all of its harmonics. It's likely that its PFC boost converter, if it has one, has a different problem. It tries to ensure that current drawn by the supply is in synchronous proportion to the mains input voltage. This is problematic in the face of the large following capacitance which is trying to drag the current out of phase. It's errors appear in terms of phase and amplitude, so harmonic distortion is a likely outcome. A large number of mains harmonics fall within the audio band. Also to take into consideration is how the SMPS is regulated, and what it does when under or over-loaded. It could be that it operates in bursts, and the frequency of bursts could be within the audio spectrum. AF crap shouldn't be a problem with a linear PSU. The transformer will remove common-mode noise, whilst the filtering on the rectified output (which you need anyway to remove mains-frequency ripple) will eliminate the rest. Sounds fair enough. Why is it a problem for Ian Bell, though, I wonder? It's a problem for my AVO valve tester, which only rectifies the grid voltage, and does no smoothing at all. There's a simple European standard for mains harmonic distortion from consumer equipment. It allows a fair amount, IIRC. They don't appear to have taken my AVO into consideration. Ian |
New webpages on mains filters
Ian Iveson wrote:
David wrote: I agree that there's plenty of audio-band crap on the mains, but not from SMPSs, which generally work at frequencies well above the audio band. AF crap is either harmonic distortion of the mains waveform, or comes from commutator motors and the like. Just because SMPS "work at frequencies above the audio band" doesn't mean they don't also produce audio-frequency noise. A SMPS with a fixed switching frequency can easily employ a mains input filter that targets that frequency, although it isn't so easy to deal with all of its harmonics. It's likely that its PFC boost converter, if it has one, has a different problem. It tries to ensure that current drawn by the supply is in synchronous proportion to the mains input voltage. This is problematic in the face of the large following capacitance which is trying to drag the current out of phase. It's errors appear in terms of phase and amplitude, so harmonic distortion is a likely outcome. A large number of mains harmonics fall within the audio band. Also to take into consideration is how the SMPS is regulated, and what it does when under or over-loaded. It could be that it operates in bursts, and the frequency of bursts could be within the audio spectrum. AF crap shouldn't be a problem with a linear PSU. The transformer will remove common-mode noise, whilst the filtering on the rectified output (which you need anyway to remove mains-frequency ripple) will eliminate the rest. Sounds fair enough. Why is it a problem for Ian Bell, though, I wonder? Indeed, it is probably not anything to do with the linear supply itself. Here's the scenario. I am measuring the noise from a mic pre. Its input is balanced and shorted and anyway the gain control is turned down to zero so there's no chance of pick up at the input. Output is unbalanced with a source impedance of about 800R feeding a battery operated Lindos MS1 which is connected to the laptop via a serial link. The Lindos has a built in speaker so you can actually hear any noise present. With the laptop running on batteries the output noise is close to -80dBu as expected and sounds like hiss in the speaker. Turn on the laptop PSU though and the reading rises to -40dBu and you can hear a high pitched whistle in the speaker. Cheers Ian |
New webpages on mains filters
"Jim Lesurf" wrote in message ... Hi, Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html Jim, I think it might also be worth mentioning that when earth referenced filters - i.e. caps. etc. from Live and Neutral connected to Earth, that there is a potential safety issue and that the Earth should never be disconnected. How many old-timers have disconnected the Earth on a scope looking to stop loops and found that the chassis floats up to half the mains volts - albeit limited in current- but still enough to give a bit of a tingle. IIRC, HP scopes in particular at that :-) Happy listening Mike |
New webpages on mains filters
"Jim Lesurf" wrote in message ... Hi, Just to let people know that I have just put up a couple of new pages that explain the basics of how mains RFI filters work. The aim being to allow readers to decide which type of filter - if any! :-) - might be most appropriate if they have a problem with RFI. The first page is at http://www.audiomisc.co.uk/mains/filters1.html and that has a link icon at the end to take you to the second page that deals with ferrite and VDR devices and their use. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html Sorry - pressed the 'Post' key too fast: That should read "IIRC, HP scopes are particularly good at that" |
New webpages on mains filters
On Fri, 26 Mar 2010 17:45:55 -0000, Ian Bell wrote:
Here's the scenario. I am measuring the noise from a mic pre. Its input is balanced and shorted and anyway the gain control is turned down to zero so there's no chance of pick up at the input. Output is unbalanced with a source impedance of about 800R feeding a battery operated Lindos MS1 which is connected to the laptop via a serial link. The Lindos has a built in speaker so you can actually hear any noise present. With the laptop running on batteries the output noise is close to -80dBu as expected and sounds like hiss in the speaker. Turn on the laptop PSU though and the reading rises to -40dBu and you can hear a high pitched whistle in the speaker. That's a standard ground loop problem typical of laptops. James. -- http://www.jrpmusic.net |
New webpages on mains filters
James Perrett wrote:
On Fri, 26 Mar 2010 17:45:55 -0000, Ian Bell wrote: Here's the scenario. I am measuring the noise from a mic pre. Its input is balanced and shorted and anyway the gain control is turned down to zero so there's no chance of pick up at the input. Output is unbalanced with a source impedance of about 800R feeding a battery operated Lindos MS1 which is connected to the laptop via a serial link. The Lindos has a built in speaker so you can actually hear any noise present. With the laptop running on batteries the output noise is close to -80dBu as expected and sounds like hiss in the speaker. Turn on the laptop PSU though and the reading rises to -40dBu and you can hear a high pitched whistle in the speaker. That's a standard ground loop problem typical of laptops. James. Yes and no, because it does not go away if I disconnect the serial cable. Also, if I pull the mains cable out of the laptop PSU so there can be no ground loop, the whistle is still there and you can hear it change pitch and disappear as the PSU dies. Not only that, the PSU mains cable is a double insulated two pole type so there is no ground connection to loop. I strongly suspect the SMPSU is putting crap straight onto the mains. Cheers Ian |
| All times are GMT. The time now is 02:09 PM. |
Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.0.0
Copyright ©2004-2006 AudioBanter.co.uk