Mains filters
 

In article , Arfa Daily wrote:
Mains is full of crap anyway. Have you ever looked at it with a scope?
Sometimes it looks nothing whatsoever like those neat sinewaves in the
textbooks, but the power supplies in any electronic equipment running from
it will transform it, rectify it, filter it and stabilise it and thereby
turn it into clean DC for the electronics itself because that's what power
supplies do. Filtering the mains will have no additional benefit.

Rod.


That's what power supplies *should* do, Rod ! I've seen many linears in
lower end equipment, though, where the HF bypassing is poor, and spiky crap,
at least, does find its way onto the DC rails, and things like fridge stats
and room stats, and even next door's electric lawnmower motor, do cause
audible disturbance. In such cases, a surge plug or filtered plug or
combination of both plug, may prove beneficial. However, in general, I agree
with everyone else, that once you've got beyond the eighty quid TescoSonic
market, the input and power supply filtering easily take care of any mains
borne crap, and additional external filtering will be a waste of good beer
money.

Agreed. These mains "surge limiters" and "power conditioners" can only really
have a beneficial effect on the sound from equipment that is badly designed to
begin with, so the money might be better put towards upgrading to equipment
that works properly. Or beer of course.

Rod.

Mains filters
 

In article , Glenn Richards wrote:
The theory is sound anyway, if sticking an LCR filter across the mains
input does indeed reduce the noise floor.
Maybe it would be if it did, but it doesn't, so it isn't. It's nonsense.

That's why I said "if".

There isn't really an "if" at all. Sticking an LCR filter across the mains
input will not affect the noise floor in any way whatsoever, so this "theory"
isn not sound, being based on something that isn't true.

Rod.

Mains filters
 

In article ,
Stewart Pinkerton wrote:
Hmm. Switch off an inductive load like a motor on the same ring as an
amp and you'll hear it - or at least be able to measure the spike.

On the mains, certainly - not at the speaker terminals.

Depends on the power supply in the amp.

--
*A person who smiles in the face of adversity probably has a scapegoat *

Dave Plowman London SW
To e-mail, change noise into sound.

Mains filters
 

"Rich Wilson" wrote in message
...

"Glenn Richards" wrote in message
...
Rich Wilson wrote:

If you're going to upgrade your power cable you really ought to do it
all the way back to the substation, otherwise it's a bit pointless...

Well that was my initial thought... but apparently not.

In a conversation I had with a friend, we determined that power cables
are good at carrying low frequencies, and poor at carrying higher
frequencies. So RFI picked up at the substation won't make it to your
house, but interference sources in your house will cause RFI to reach
your kit.

What I want to know is how exactly the RFI gets through all the smoothing
capacitors and so on in the rectifier. I've got a little headphone amp
here with enough capacitance to not notice, say, a 2-second cutout in its
power supply, so I fail to see how any audible frequency could get
through.

Electrolytic capacitors generally have very poor characteristics at high
frequencies. This is why you will often find them bypassed with a small
value polyester or other film capacitor. A large electrolytic across a
supply as a smoothing cap will, as you say, happily supply the amplifier's
needs for a couple of seconds, but as far as RF goes, it may as well not be
there. Also, you're confusing RF with audio. A signal is not really
considered to be RF until it reaches 60 or 70 kHz or so. RF is of course,
not directly audible anyway, even if it gets into your amp, but if it had
enough level, it could conceivably drive early stages into non linearity, in
which case, its effect may become audible.

In contrast, although you might consider impulse interference from say a
drill motor, to be an audible frequency, the very fast rise times to high
peak amplitudes, will again bypass any electrolytics, as though they weren't
there, and may then become audible as ' interference '

Arfa

Mains filters
 

On Thu, 16 Mar 2006 14:40:00 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:


I am a grumpy old man - that is what keeps me so happy. Today it is
trying to snow, and I am about to go for a walk down to Sainsbury's to
get some food.

I should also be 'grumpy' at this point. We had water coming through a
ceiling on Monday due to snow melt getting in via a flat roof. Currently
looking out at occasional showers of rain/snow/sleet and seeing if the
large tub behind one speaker is going to get any more contents...

Had some plastic sheeting tacked over the roof as a temporary measure this
morning, so keep yer fingers crossed that it helps!

Despite the above, at present I don't feel grumpy, but if we get more
floods I may decided to feel less cheery than usual...

Slainte,

Jim

You ought to try being grumpy - it really can be great fun.

d

Pearce Consulting
http://www.pearce.uk.com

Mains filters
 

"Glenn Richards" wrote in message
. uk...
Just a quick straw poll...

What are people's opinions of mains filters, upgraded power cables
etc?

Have been doing some investigation and there may actually be
something
in this. Not talking Russ Andrews style £250 mains cables here, more
like sticking a plug with a filter onto a standard IEC lead, and
possibly using one of those Masterplug RFI filtered 4-way blocks.

Has anyone done any serious experimentation on this? I did hear a
quite
convincing demonstration at the Sound & Vision show in Bristol a few
years ago, but the mains there is probably a lot dirtier than your
typical home installation.

What myself and a few others have figured out is that the level of
RFI
introduced onto your ring main by something like the switching PSU
in a
typical PC is quite high.

Opinions, people?

--
Glenn Richards Tel: (01453)
845735
Squirrel Solutions
http://www.squirrelsolutions.co.uk/

IT consultancy, hardware and software support, broadband
installation

If you are suffering clicks, pops and bangs that are mains borne then
it is better to cure the source than to try to filter the destination.
Very little in terms of such noise is radiated - it needs to be very
close to do so, and surprisingly little is mains borne.

Contentious statement? Not really. Mains cable like any cable has
resistance and inductance which, small though it is, will tend to
dampen the leading edge of a spike and it is that leading edge that
generates the click pop or bang. As an example, the most effective way
of reducing ignition interference on a petrol engined car is to fit
spark plugs with integral resistors. Those resistors in series with
the inductance of the HT cable form a damped circuit which kills
multiple frequencies generated by the leading edge of the spark.

Most electrical noise comes from arcing of opening contacts when a
thermostat supplying an inductive load opens. The most common causes
are fridges and freezers, boiler and room thermostats, washing
machines and dishwashers, and switches feeding (perhaps surprisingly)
fluorescent lights especially the PLE variety.

If you know what you are doing and if you can get access to both side
of a thermostat then a varistor or voltage dependent resistor across
the contacts will kill the arc dead. Where PLE lamps are concerned an
incandescent bulb in parallel will work, albeit at some cost to the
original intention of using that type of lamp! Even if you cannot get
at the thermostat, a 13A plug top with a varistor inside it plugged
into the same outlet will often be enough.

If you cannot cure the problem at source the filtering at the hi-fi
may be the only answer. The 'parallel' plug filters that Russ Andrews
sells at ridiculous prices contains just a couple of varistors, as
indeed do the 'spike protected' trailing distribution blocks. Again
often use of such a dis block, or even the plug top with a varistor in
the same outlet will be enough.

If the source is un-fixable and it is near to the hi-fi then a filter
plug may work. These usually contain a toroidially wound choke with
capacitors either side of it and varistors to kill the spikes. One
that I have used regularly over the years is that made by Bowthorpe
and available for about £30 from the likes of CPC, Farnell, or RS.
Again this is what Russ Andrews sells for three figures (without a
decimal point!)

For those that do understand electricity and/or electronics and
haven't yet discovered it, get hold of a copy of Russ Andrews'
catalogue. Interesting (wide-eyed?) reading!


--
Woody

harrogate3 at ntlworld dot com

Mains filters
 

In article , Glenn Richards
wrote:
Jim Lesurf wrote:

That mains filters may be useful if you are having a problem with
audible 'clicks and pops' from the mains, and can't suppress them at
source.

What about inaudible RF interference, for example from a PC PSU?

If it is inaudible, why would it be worth worrying about? :-)

If you wish, you can check this simply by using something like a spectrum
analyser to the relevant output. You could use a an AC meter/DVM, but may
then have to use a filter if you want to avoid simply measuring the 'hum'
from unit's own PSU or ground loops.

I know all about the regulations... but I've opened enough of these
things up to know that they often radiate like a spark transmitter.

Well, I've also developed instruments in research labs, for people like the
NPL. Designed to make wideband measurements down to levels suitable for
defining national standards. In general, mains interference from personal
computer power supplies wasn't a problem even at level many orders of
magnitude below what would ever be audible from audio kit.

What *did* cause problems at times is radiated fields from CRTs, but even
this tends to be low level these days, so if the equipment it correctly
made this should not be a problem.

Bottom line remains, though, if you can hear an effect then by all means
buy and fit a filter. Indeed, like myself, there is no harm in buying a
cheap RS/Maplin one simply for the feeling that it makes assurance doubly
sure. :-)

Ideally, though, the audio equipment is well enough designed to
prevent such problems being audible.

In an ideal world, yes... but even kit like my Arcam stuff is still
built to a budget. I've had long conversations with R&D bods from
companies like Arcam, Meridian etc at hi-fi shows, and they're always
cursing the beancounters... "we wanted to put more RFI filtering in, but
budget constraints meant we had to make sacrifices" etc etc.

Design engineers will always tend to worry about such things. :-)

However even 20+ years ago, it wasn't rocket science to be able to make
a PSU and amplifier that rejected mains noise fairly effectively. Can't
recall ever hearing any such pops, etc, from the amps I designed since I
simply spent some time on sorting this when developing them. Nothing
special or unusual in this so far as I am concerned.

The reason design engineers worry about this is there will always be some
cases of ultra-severe problems, so you have to decide "how much is
enough". But if they know their job, they'll have been aware of how
much noise can be expected, and deal with it in pretty much all cases.

The test is open to you. If you can hear clicks and pops, or buzzes, when
no music is playing, then try a cheap mains filter... If not, up to you to
decide to fit one purely for 'peace of mind'. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Mains filters
 

In article , Serge Auckland
wrote:


The avoidance of mains-borne clicks or equipment lock-ups is the main
function of domestic mains filtering. All other suggestions of
improvements in the sound are snake-oil, put about by those selling
expensive filtering items.

I would agree with the above.

FWIW If you are worried about 'RF' then you should also worry about
interference which is directly radiated into units. e.g a mobile phone in
the same room as the audio system, coupling in via the speaker leads. A
mains filter will have no effect on this. Hence it is the kind of thing the
designer should have considered...

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Mains filters
 

In article , Rich Wilson
wrote:


What I want to know is how exactly the RFI gets through all the
smoothing capacitors and so on in the rectifier. I've got a little
headphone amp here with enough capacitance to not notice, say, a
2-second cutout in its power supply, so I fail to see how any audible
frequency could get through.

Alas, if only it were that easy. :-)

Two examples of snags the designer should have dealt with:

1) Large electolytic caps (as normally used as reservoirs in a linear PSU)
will have self inductance and resistance that means they stop acting as a
capacitor - probably somewhere below 10MHz. Hence for RF 10MHz they may
do nowt.

2) The RF may enter via leads, then radiate around inside the box, neatly
bypassing any filtering. :-)

In each case the RF "might" then be rectified by a device inside the amp,
or combine nonlinearly to down-convert into the audible range.

The point, though, is that the designer should know about such things, and
know how to deal with them. The normal result being no audible effects to
bother the user. This was hard many years ago, but devices and techniques
developed, so that even 20 years ago, it was largely tractable.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Mains filters
 

"Jim Lesurf" wrote in message
...
In article , Iain Churches
wrote:


It's a beautiful sunny day here. I am just off for a morning walk down
to the sea with the Airedale.

Didn't Warfedale make them? Why aren't you taking *both* speakers for a
walk?... :-)

Even one is quite a handful:-) It is mounted on four legs, one of which it
insists of lifting periodically - resulting in a high dampness factor:-)

Iain