[Don[_3_]]

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

[Don Pearce[_3_]]

On Thu, 26 Mar 2009 18:46:04 GMT, Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

It only helps if there is a problem. Turn the audio gain up high with
no music playing, then switch the PC on. Do you hear noises? If not,
don't bother.

If you decide you do need ferrite, get the biggest rings you can
accommodate and put as many turns of coax through as will fit.
Position the ferrite close to the amplifier input.

For decently shielded cable, try some CT100, which is used for
satellite dish feeds. It is not terribly flexible so you won't be able
to drape it around easily, but it has 100% shielding, and won't let
anything in. It is also pretty cheap.

d

[Eeyore]

Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

Is it causing interference now ?


(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

I doubt the ferrites will help much, if at all since they're designed
primarily to stop emissions from noisy kit by placing them near to where
the cable exits the equipment.


(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

Can you use a larger diameter ? Professional audio cable is likely to be
far better shielded. Actually you can get it that dia but it tends to be
used by installers who buy it by the reel. Actually I know an installer
who'd have the stuff but he's here in the UK and your post appears to
originate from the USA.

Graham

[Richard Crowley]

"Don" wrote ...
At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

Not clear whether this is a theoretical question, or if you are curently
experiencing this electrical interference noise? If it is a practical
situation, mentioning some details might prove helpful.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

No it will not help no matter how many or where the ferrite beads are.
The reason is that any audio interference is *in-band*, at the same
frequencies as the desired audio signal. You canot filter out in-band
interference without also filtering out the desired signal.

The remedy is to move the cables away from the source of noise.
Use longer cables to avoid the problem spot(s). Use better cable
with better shielding, etc.

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

It would be easier to try simply using longer cable(s) to avoid the
problem spot(s).

[Adrian C]

Don wrote:
At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

If built properly to CE EMC guidelines (applicable in the UK), generally
your domestic PC and connected equipment should not be causing that type
of interference.

I run lots of Dell equipment around here next to a stack of Hi-Fi audio
components. No problem whatsoever with noise pickup, and if you've ever
taken one of their PCs apart you'll see a fairly serious job has been
done of shielding and filtering RF interference reaching to the outside
environment.

If home built (or it was built for you by a smaller manufacturing
fling-it-together concern) then you'll have to try some DIY cures. From
experience in working at an EMC testing facility - my number one tip is
sorting out these issues is this ...

Ensure that all grounding points on the motherboard are electrically
connected through conductive posts to the case (carefully avoiding parts
of those posts shorting out against any leadouts or components hanging
from the board). Plastic standoffs are a no-no.

Having just part of the motherboard grounded makes other bits attached
to it (including _all_ conductors on external cables) liable to pickup
and transmit the high frequency switching hash from the processor and
graphics circuits. In extreme cases, parts of the motherboard itself
will be singing like an aerial sending waves to be guided through
convienient slots in the case.

Similary, if you have an expansion cards attached to the motherboard,
ensure that the metal backplate of these cards is secure in being
grounded to the casework and that there are no rectangular gaps between
card and slot. You can get conductive meshed foam to fill the gap before
you screw the card in. Any other whole gaps in the case wider than a
couple of inches should also be screened across. There should be
conductive covers over unused drive bays for instance.

OK so, I'd start there first ... and then ye can implement further
measures from then on. Ferrites on external leads is an often used
tweak, but it is better in EMC terms to deal with the major problems
first at source of the noise and then move on.

--
Adrian C

[Dave Platt]

In article ,
Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

It can't hurt to try, but I'm not all that hopeful. Ferrites are
useful at blocking radio-frequency interference, but they won't do
very much (if anything) to block interference which is actually down
at the baseband-audio frequencies. If you're getting interference
from a CRT, it's likely that it's from the horizontal and vertical
sweep circuitry (and perhaps from modulations in the beam power), and
these signals are likely to be in the audio range.

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

If I recall correctly (possibly not) this sort of interference can
result either from pickup of the electrical field, or the magnetic
field (radiated from the interferer in either case). A shielded cable
helps keep out the electrical field (the more shield coverage the
better), but I don't believe it is as effective at keeping the
magnetic field out... at least, not at the low frequencies involved
here.

You might want to see if you can find some shielded twisted pair
cable, and make up some audio leads from that... use the pair for the
audio signal (connect both wires at both ends) and ground the shield
at one end only. Some people have reported better results with that
sort of cable.

You could try using a twisted pair, with a balun transformer at each
end.

Belden makes a lot of good types of audio cable stock - the
table at http://www.belden.com/pdfs/Techpprs/bavcadtp.pdf shows a
bunch of their part numbers for various sorts of A/V cable. Their
#1508A is a twisted pair with a 100%-coverage foil shield and a drain
wire. Might be worth experimenting with. #1883A is similar, and is
specified for use as an audio punchdown cable.

In honesty, though, distance is your best friend in this case.
Near-field interference drops off very sharply as a function of
distance (I *think* it tends to fall off as the fourth power of
distance from the source) and keeping the cables a couple of feet
further from your equipment may eliminate the problem or reduce it to
the point where it is not harmful. If you have to add a few extra
meters of cable to accomplish this, do it - the audio degradation from
the extra wire will be negligible.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[Sjouke Burry[_2_]]

Don Pearce wrote:
On Thu, 26 Mar 2009 18:46:04 GMT, Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

It only helps if there is a problem. Turn the audio gain up high with
no music playing, then switch the PC on. Do you hear noises? If not,
don't bother.

If you decide you do need ferrite, get the biggest rings you can
accommodate and put as many turns of coax through as will fit.
Position the ferrite close to the amplifier input.

For decently shielded cable, try some CT100, which is used for
satellite dish feeds. It is not terribly flexible so you won't be able
to drape it around easily, but it has 100% shielding, and won't let
anything in. It is also pretty cheap.

d
One thing that worked for me, is an extra (short,thick)wire between
the case of the audio amplifier and the case of the computer.

[John Larkin]

On Thu, 26 Mar 2009 18:46:04 GMT, Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)


Not the same situation, but adding this ferrite...

ftp://jjlarkin.lmi.net/Ferrite.JPG

dropped the RF sensitivity of this gadget (a thermocouple signal
conditioner) about 30 dB.

My competitor's box, from Oxford Instruments, could be shut down from
across the room with an old GR signal generator and a pigtail antenna.
Ours was around 30 dB better without the ferrite, 60 with.

John

[Richard Crowley]

"John Larkin" wrote ...
Not the same situation, but adding this ferrite...

ftp://jjlarkin.lmi.net/Ferrite.JPG

dropped the RF sensitivity of this gadget (a thermocouple signal
conditioner) about 30 dB.

My competitor's box, from Oxford Instruments, could be shut down from
across the room with an old GR signal generator and a pigtail antenna.
Ours was around 30 dB better without the ferrite, 60 with.

Indeed. But thermocouples rarely have high-frequency response
even reaching 1Hz, so essentially anything AC is "out-of-band". :-)

And in situations where the interference is caused by the input
circuitry responnding to the RF, then ferrite beads/cores can be
helpful.

[Kevin McMurtrie[_2_]]

In article ,
Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

You probably don't need them. Computer equipment has many localized
switching power supplies running in the 10A range. Even a very solid
ground plane will have some RF noise on it. Better computers feed
peripheral connectors through ferrite blocks to fix this. Cheap or
compact computers may rely on a ferrite cylinder over the cable.

There should be no advantage to putting ferrite beads on cables passing
near the computer. If it does, there's probably something broken.

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

Get the specification for the shield coverage. Musical instrument
cables are about 95% copper coverage plus 100% conductive PVC coverage.

--
I will not see your reply if you use Google.

[Eeyore]

Sjouke Burry wrote:

One thing that worked for me, is an extra (short,thick)wire between
the case of the audio amplifier and the case of the computer.

That will likely help depending how the equipment was designed with regard
to grounding strategy.

Graham

[Eeyore]

John Larkin wrote:

Not the same situation, but adding this ferrite...

ftp://jjlarkin.lmi.net/Ferrite.JPG

dropped the RF sensitivity of this gadget (a thermocouple signal
conditioner) about 30 dB.

Philips / Ferroxcube ? I used one of those plus some Y caps to get a piece
of kit through EMC regs that was just 'marginal' without them.

Those dual hole ferrites are a real boon.

Graham

[Don[_3_]]

On Fri 27-Mar-2009 03:39, Kevin McMurtrie
wrote:

In article ,
Don wrote:

At home, I often use some screened audio leads which carry
speech signals at about 100 to 200 mV. The leads may carry
one or two signals (mono or stereo) and may be about 1m or 2m
long. They are not balanced.

Sometimes it's unavoidable but my audio lead has to pass near
a PC and also about 6 inches below and in front of a CRT
display. I want to avoid electrical noise interfering with
the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If
so, then at which point on the lead is the best place?
(Source, destination, where lead passes near causes of
interference). Is it better to use more than one ferrite?

You probably don't need them. Computer equipment has many
localized switching power supplies running in the 10A range.
Even a very solid ground plane will have some RF noise on it.
Better computers feed peripheral connectors through ferrite
blocks to fix this. Cheap or compact computers may rely on a
ferrite cylinder over the cable.

There should be no advantage to putting ferrite beads on
cables passing near the computer. If it does, there's
probably something broken.

(2) For a given max outer lead diameter of about 3mm (maybe
4mm), I guess some audio leads are better at intereference
shielding than others. I'm in the UK; is there a type of
decently shielded audio leads you might recommend without
getting into really expensive stuff. (I can add the
connectors.)

Get the specification for the shield coverage. Musical
instrument cables are about 95% copper coverage plus 100%
conductive PVC coverage.


Your info about shield coverage reminds me that I once heard
someone guess that shielded twisted pair would make good audio
cable. Any views on using that?

[Richard Crowley]

"Don" wrote ...
Your info about shield coverage reminds me that I once heard
someone guess that shielded twisted pair would make good audio
cable. Any views on using that?

Twisted pair (whether shielded or not, as the situation dictates)
is a great way of reducing noise *IF* you have equipment (and
especially at the destination/input end) that has a *balanced*
input circuit. If your (still unidentified) equipment has only un-
balanced connections, then using twisted pair over such a short
distance is likely not worth the effort to try it. Moving the cable
away from the noise source is a *much more likely* method of
remedying your problem.

[Don[_3_]]

On Thu 26-Mar-2009 19:44, Richard Crowley
wrote:

"Don" wrote ...
At home, I often use some screened audio leads which carry
speech signals at about 100 to 200 mV. The leads may carry
one or two signals (mono or stereo) and may be about 1m or 2m
long. They are not balanced.

Sometimes it's unavoidable but my audio lead has to pass near
a PC and also about 6 inches below and in front of a CRT
display. I want to avoid electrical noise interfering with
the audio signal.

Not clear whether this is a theoretical question, or if you
are curently experiencing this electrical interference noise?
If it is a practical situation, mentioning some details might
prove helpful.


It is essentially a theoretical question. I want to avoid later
hearing artefacts and/or distortions in the audio due to
interference.

I find such audio problems are not always apparent at first, so
it's not just a matter of trying it and hearing it. For example,
for several months I did not hear the artefacts a particular
flash memory recorder I have was adding to its recordings. In
this case the problem was bad design rather than interference
and it was creating "birdies" at a very low level on one of the
stereo channels.

It needed the right audio material and right listening equipment
used to make those artefacts apparent.


(1) Would it help to clip some ferrite on the audio lead? If
so, then at which point on the lead is the best place?
(Source, destination, where lead passes near causes of
interference). Is it better to use more than one ferrite?

No it will not help no matter how many or where the ferrite
beads are. The reason is that any audio interference is
*in-band*, at the same frequencies as the desired audio
signal. You canot filter out in-band interference without
also filtering out the desired signal.

The remedy is to move the cables away from the source of
noise. Use longer cables to avoid the problem spot(s). Use
better cable with better shielding, etc.

As I mentioned before, there are times when the cable can't
easily take another route so I am interested in the better
shielding appraoch which you mention.

Unfortunately, many web sites merrily say that almost any wire
will do for a short run of audio cable. I am not so sure!


(2) For a given max outer lead diameter of about 3mm (maybe
4mm), I guess some audio leads are better at intereference
shielding than others. I'm in the UK; is there a type of
decently shielded audio leads you might recommend without
getting into really expensive stuff. (I can add the
connectors.)

It would be easier to try simply using longer cable(s) to
avoid the problem spot(s).

[Don Pearce[_3_]]

On Fri, 27 Mar 2009 02:28:47 +0100, Sjouke Burry
wrote:

One thing that worked for me, is an extra (short,thick)wire between
the case of the audio amplifier and the case of the computer.

Not a great plan as it creates a ground loop. OK, it is working
against a line level signal so it won't be desperately serious, but it
is still technically the wrong thing to do. Making the ground of the
signal wire as good as possible is the right thing.

d

[Mr.T]

"Richard Crowley" wrote in message
...
"Don" wrote ...
Your info about shield coverage reminds me that I once heard
someone guess that shielded twisted pair would make good audio
cable. Any views on using that?

Twisted pair (whether shielded or not, as the situation dictates)
is a great way of reducing noise *IF* you have equipment (and
especially at the destination/input end) that has a *balanced*
input circuit.

In fact good quality balanced audio cable usually is shielded twisted pair.
But not exactly the same as similar computer cable since the requirements
are a little different.

MrT.

[Lostgallifreyan]

Don wrote in
:

Unfortunately, many web sites merrily say that almost any wire
will do for a short run of audio cable. I am not so sure!


That will be an antidote to the audiophools that insist of oxygen free silver
or whatever it is they insist on now.

The advice here someone gave on using satellite feed cable is good, it's very
well screened. The other thing is to use star network ground schemes for the
audio, and to keep digital and analog grounds separate if you can, and where
possible, used balanced audio signal lines. Major studios do this, as do many
home studios since the practise has been frequently described in Sound On
Sound and similar magazines. As they specialise in handling mixed signals
from a large range of gear, you can be sure their methods are good. If you do
this you'll likely not need to worry if digital and audio cables run side by
side, though it's still wise to minimise that, don't tempt fate..

[Richard Crowley]

"Don" wrote ...
As I mentioned before, there are times when the cable can't
easily take another route so I am interested in the better
shielding appraoch which you mention.

Lacking any additional details, in general I believe you will find
that aproach to be fruitless for a situation as you describe. The
best shielding and/or filtering known to modern technology won't
protect a low-tech piece of consumer equipment from overwhelming
EMI at short range. You are seriously underestimating the value
of distance in reducing interference. Good luck.

[Lostgallifreyan]

"Mr.T" MrT@home wrote in
:


"Richard Crowley" wrote in message
...
"Don" wrote ...
Your info about shield coverage reminds me that I once heard
someone guess that shielded twisted pair would make good audio
cable. Any views on using that?

Twisted pair (whether shielded or not, as the situation dictates)
is a great way of reducing noise *IF* you have equipment (and
especially at the destination/input end) that has a *balanced*
input circuit.

In fact good quality balanced audio cable usually is shielded twisted pair.
But not exactly the same as similar computer cable since the requirements
are a little different.

MrT.




The shielding is often better. If you're running fixed balanced audio lines
it might be worth using. As far as I know, the main thing with audio lines is
they're made to meet a wide demand for strong and flexible cables with soft
coverings.

Given that audio uses a low output impedance into a high input impedance, it
doesn't matter what the impedance of the cable is, if it's a balanced line in
a twisted pair inside a foil sheath, it's ideal, so long as it's not flexed
to damage point. What is NOT a good idea is using audio cables for S/PDIF and
other high speed digital transfers.

[PhattyMo[_2_]]

Don wrote:
At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?


I usually use one at each end of the cable.

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

Something with good shielding.Be it some kinda of pro audio
cable,instrument cable,or a good old fashion coaxial cable.

[Eeyore]

Don Pearce wrote:

Sjouke Burry wrote:

One thing that worked for me, is an extra (short,thick)wire between
the case of the audio amplifier and the case of the computer.

Not a great plan as it creates a ground loop. OK, it is working
against a line level signal so it won't be desperately serious, but it
is still technically the wrong thing to do. Making the ground of the
signal wire as good as possible is the right thing.

All audio equipment should adopt balanced working which would evade all
such problems. The cost is minimal other than replacing the damned useless
RCA 'phono' connector.

Graham

[Eeyore]

Don wrote:

Your info about shield coverage reminds me that I once heard
someone guess that shielded twisted pair would make good audio
cable. Any views on using that?

There are very many types of construction of shielding. The best consist
of at least two layers.

Twisted pairs will only significantly help if your equipment is
balanced.

Sorry, but this isn't something 'consumer audio' vendors give a damn
about. They're only interested in liberating as much cash from your
pocket as possible with inferior technology compared to what pros use.


Graham

[Don[_3_]]

On Fri 27-Mar-2009 23:34, Richard Crowley
wrote:

"Don" wrote ...
As I mentioned before, there are times when the cable can't
easily take another route so I am interested in the better
shielding appraoch which you mention.

Lacking any additional details, in general I believe you will
find that aproach to be fruitless for a situation as you
describe. The best shielding and/or filtering known to modern
technology won't protect a low-tech piece of consumer
equipment from overwhelming EMI at short range. You are
seriously underestimating the value of distance in reducing
interference. Good luck.


I do understand (as John Larkin posted in this thread) that
distance is my friend ~ to the power 4!

However, sometimes distance is hard for me to control. Even if I
extend the length of the lead and try to reroute it the lead may
still have to run close to potential sources of interference
especially where it has to approach a device such as a PC to
terminate its run.

On a related topic can I ask this ... if I have a stereo source
then is it much better to use a twin cable in which each core
has its own shielding than a cable in whch both cores are
together and inside a single shielded?

[Richard Crowley]

"Don" wrote ...
I do understand (as John Larkin posted in this thread) that
distance is my friend ~ to the power 4!

However, sometimes distance is hard for me to control. Even if I
extend the length of the lead and try to reroute it the lead may
still have to run close to potential sources of interference
especially where it has to approach a device such as a PC to
terminate its run.

Alas, I don't see that you have any practical alternative. No
amount of filtering, shielding, or magic cable is half as effective.

On a related topic can I ask this ... if I have a stereo source
then is it much better to use a twin cable in which each core
has its own shielding than a cable in whch both cores are
together and inside a single shielded?

Probably not. Many of us regularly use "twisted pair" shielded
for L/R stereo. I just finished building eight 50-ft stereo mic
cables with "star-quad" cable which has no shielding between
the L/R pairs. I anticipate no significant issues with that practice.

[Lostgallifreyan]

Don wrote in
:

On a related topic can I ask this ... if I have a stereo source
then is it much better to use a twin cable in which each core
has its own shielding than a cable in whch both cores are
together and inside a single shielded?


Yes. Small losses due to capacitance rarely matter in this case so close
individual screens are good, and even over longer runs it's mainly an
attenuation of higher frequencies well beyond those for audio except in runs
of a hundred metres or more where it might best be considered differently.

You might lose signals to the other line causing crosstalk and reduced stereo
width in much shorter runs if the channels are not screened from each other.
It might not be significant but if for any reason you want one to be silent
while the other is at full bore (studio effects and panning), it really pays
to screen them separately.

[Archimedes' Lever]

On Thu, 26 Mar 2009 20:20:39 +0000, Adrian C wrote:

If built properly to CE EMC guidelines (applicable in the UK), generally
your domestic PC and connected equipment should not be causing that type
of interference.


You must not have seen the 'window equiped' PC cases all over the place
now.

[Archimedes' Lever]

On Thu, 26 Mar 2009 20:01:00 -0700, John Larkin
wrote:

dropped the RF sensitivity of this gadget (a thermocouple signal
conditioner) about 30 dB.


Wouldn't that be 'raised the PARD rejection factor'? :-]

Because if it isn't periodic or random, and you know where the source
is, the solution would be closer to the source.

[Archimedes' Lever]

On Sat, 28 Mar 2009 02:21:15 GMT, Don wrote:

On Fri 27-Mar-2009 23:34, Richard Crowley
wrote:

"Don" wrote ...
As I mentioned before, there are times when the cable can't
easily take another route so I am interested in the better
shielding appraoch which you mention.

Lacking any additional details, in general I believe you will
find that aproach to be fruitless for a situation as you
describe. The best shielding and/or filtering known to modern
technology won't protect a low-tech piece of consumer
equipment from overwhelming EMI at short range. You are
seriously underestimating the value of distance in reducing
interference. Good luck.


I do understand (as John Larkin posted in this thread) that
distance is my friend ~ to the power 4!

However, sometimes distance is hard for me to control. Even if I
extend the length of the lead and try to reroute it the lead may
still have to run close to potential sources of interference
especially where it has to approach a device such as a PC to
terminate its run.

On a related topic can I ask this ... if I have a stereo source
then is it much better to use a twin cable in which each core
has its own shielding than a cable in whch both cores are
together and inside a single shielded?


Get a new vid card that has HDMI out. Take the audio from the PC thru
that.

Upgrade...

[Ben Bradley]

In
sci.electronics.components,alt.engineering.electri cal,sci.electronics.design,rec.audio.tech,
On Thu, 26 Mar 2009 18:46:04 GMT, Don wrote:

At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

I agree with (most) the other posters, ferrites are unlikely to
help with a direct baseband audio signal being injected, and perhaps
the easiest solution is use a longer cable that doesn't go as close to
the CRT.

I'm thinking you could use audio transormers (which itself may be
sensitive to the CRT's deflection coils from several feet away) at
each end and run a balanced cable between them. "Star Quad" type
configuration would be best to minimize/cancel interference. But all
that gets expensive.

Another "expensive" idea - replace the CRT with one of the
new-fangled flat-panel display things, surely they generate less
interference, and they also take up less space.

Or move the CRT. Get a few phone books and/or encyclopedias to put
under it and lift it up, just a few inches may help.

[[email protected]]

On Mar 27, 11:24*pm, Archimedes' Lever
wrote:
On Sat, 28 Mar 2009 02:21:15 GMT, Don wrote:
On Fri *27-Mar-2009 23:34, Richard Crowley
wrote:

"Don" *wrote ...
As I mentioned before, there are times when the cable can't
easily take another route so I am interested in the better
shielding appraoch which you mention.

Lacking any additional details, in general I believe you will
find that aproach to be fruitless for a situation as you
describe. The best shielding and/or filtering known to modern
technology won't protect a low-tech piece of consumer
equipment from overwhelming EMI at short range. *You are
seriously underestimating the value of distance in reducing
interference. *Good luck.

I do understand (as John Larkin posted in this thread) that
distance is my friend ~ to the power 4! *

However, sometimes distance is hard for me to control. Even if I
extend the length of the lead and try to reroute it the lead may
still have to run close to potential sources of interference
especially where it has to approach a device such as a PC to
terminate its run.

On a related topic can I ask this ... if I have a stereo source
then is it much better to use a twin cable in which each core
has its own shielding than a cable in whch both cores are
together and inside a single shielded?

* Get a new vid card that has HDMI out. *Take the audio from the PC thru
that.

* Upgrade...- Hide quoted text -

- Show quoted text -

FOR ONCE I SEE YOU AS YOU SEE OTHERS - IDIOT

I AM PROTEUS

[[email protected]]

On Mar 26, 2:46*pm, Don wrote:
At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. *The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. *They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. *I
want to avoid electrical noise interfering with the audio signal. *

(1) Would it help to clip some ferrite on the audio lead? *If so,
then at which point on the lead is the best place? *(Source,
destination, where lead passes near causes of interference). *Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. *I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

WHAT WHERE THE AUDIO LEADS SCREENED FOR COCAINUM OR STEROIDS?

YOU SHOULD USE SHEILDED CABLES INSTEAD "DON"

I AM PROTEUS

[Eeyore]

Kevin McMurtrie wrote:

Get the specification for the shield coverage. Musical instrument
cables are about 95% copper coverage plus 100% conductive PVC coverage.

Not all are mage the conductive plastic, but yes you can get it. You can
also get aluminium film shields over a lapped one. Double shields too for
that matter, one lapped in one direction, the other in the opposite.

Graham

[Archimedes' Lever]

On Sat, 28 Mar 2009 06:27:11 -0700 (PDT), wrote:

On Mar 26, 2:46*pm, Don wrote:
At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. *The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. *They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. *I
want to avoid electrical noise interfering with the audio signal. *

(1) Would it help to clip some ferrite on the audio lead? *If so,
then at which point on the lead is the best place? *(Source,
destination, where lead passes near causes of interference). *Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. *I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)

WHAT WHERE THE AUDIO LEADS SCREENED FOR COCAINUM OR STEROIDS?

YOU SHOULD USE SHEILDED CABLES INSTEAD "DON"

I AM PROTEUS


They ARE shielded, you ****ing idiot!

They use the word "screen" for our word "shield" in the UK.

Not that you have enough brains to grasp that fact.


Quoted from original poster:

"At home, I often use some screened audio leads..."

[Don Kelly[_2_]]

Ben Bradley wrote:
In
sci.electronics.components,alt.engineering.electri cal,sci.electronics.design,rec.audio.tech,
On Thu, 26 Mar 2009 18:46:04 GMT, Don wrote:


At home, I often use some screened audio leads which carry speech
signals at about 100 to 200 mV. The leads may carry one or two
signals (mono or stereo) and may be about 1m or 2m long. They are
not balanced.

Sometimes it's unavoidable but my audio lead has to pass near a PC
and also about 6 inches below and in front of a CRT display. I
want to avoid electrical noise interfering with the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If so,
then at which point on the lead is the best place? (Source,
destination, where lead passes near causes of interference). Is it
better to use more than one ferrite?

(2) For a given max outer lead diameter of about 3mm (maybe 4mm), I
guess some audio leads are better at intereference shielding than
others. I'm in the UK; is there a type of decently shielded audio
leads you might recommend without getting into really expensive
stuff. (I can add the connectors.)


I agree with (most) the other posters, ferrites are unlikely to
help with a direct baseband audio signal being injected, and perhaps
the easiest solution is use a longer cable that doesn't go as close to
the CRT.

I'm thinking you could use audio transormers (which itself may be
sensitive to the CRT's deflection coils from several feet away) at
each end and run a balanced cable between them. "Star Quad" type
configuration would be best to minimize/cancel interference. But all
that gets expensive.

Another "expensive" idea - replace the CRT with one of the
new-fangled flat-panel display things, surely they generate less
interference, and they also take up less space.

Or move the CRT. Get a few phone books and/or encyclopedias to put
under it and lift it up, just a few inches may help.


Recalling an old trick/cure with low mv level magnetic pickups for
record players - use two conductors inside a shield and ground the
shield at one end only to avoid a ground loop. It works well for
60/120Hz and I see no reason for it not to work at audio frequencies.
No guarantees but it is worth a try.


--
Don Kelly

remove X to reply

[Don[_3_]]

On Sat 28-Mar-2009 17:50, Salmon Egg
wrote:

I have seen this thread for a while without reading it.
Because of it longevity I will throw in my 2¢ without even
knowing what has been written in the past.

All the ferrite beads do is add lossy inductance to the common
mode propagation along the vague transmission line formed by
all of the conductors in parallel against free space and the
surrounding environment. It is the equivalent of winding the
cable on a transformer core. Ordinarily adding these beads
will help primarily in two situations.

1. The receiving device is sensitive to common mode signals.

2. There is regeneration or parasitic circuitry that could
cause oscillation to break out,

In the former, the inductance "chokes" the common mode. There
are other ways of handling the problem. For example, coupling
the audio signal, through an audio transformer to the
receiving device will prevent the common mode signal from
being transmitted.

For the latter, the beads introduce loss and change other
circuit parameter. That may be enough to suppress oscillation.

If you can, understand what is going on rather than merely try
anything.

Bill


Hi Bill, thanks for the detailed info. You're right that I was
guessing about the idea of using a ferrite without really knowing
the theory! :-)

I was making my assumption based on my observation that all the USB
leads which have come with my dictation machines or MP3 players
have a plastic "blob" on them.

I was told this blob is a ferrite and that it's purpose is to
prevent trouble from interference. I didn't get told if the blob
prevented "incoming" intereference affecting the signals on its
lead or, alternatively, if the "blob" limited "outgoing"
interference being generated by using the lead. From what you say,
I guess the idea of the blob containing ferrite is incorrect.

Perhaps the blob does not contain a ferrite but something else? So
I dug around and got this interesting web page.
http://www.bitpim.org/help/

QUOTE "This cable has a blob half way along the cable
that converts from USB to serial and then connects to
the serial interface in the phone. The chip inside the
cable is a Prolific 2303 and this is how your operating
system will report it. It is marked as for the LG VX1/10
but works fine on the VX4400. /QUOTE

There's a chip in their blob? WOW. Well I never use my blob
leads! I use just ordinary USB leads and there seems to be no
problem.

Admittedly in this case the lead carries *digital* signals which go
to the USB port. By contrast, I had been asking about *analogue*
audio on a shielded lead going into the line-in socket of a PC (or
perhaps going to some other device).

(a) So what is really in the blobs in my leads? (EG on my Olympus
WS-331M) The above link talks about conversion to serial but I
don't think my blobs would need to do that.

(b) Whatever is in the blob, would one of those help reduce
interference on my intended longer leads because the leads will run
near equipment and will carry analogue audio signals?

[Baron[_3_]]

Don wrote:

On Sat 28-Mar-2009 17:50, Salmon Egg
wrote:

I have seen this thread for a while without reading it.
Because of it longevity I will throw in my 2¢ without even
knowing what has been written in the past.

All the ferrite beads do is add lossy inductance to the common
mode propagation along the vague transmission line formed by
all of the conductors in parallel against free space and the
surrounding environment. It is the equivalent of winding the
cable on a transformer core. Ordinarily adding these beads
will help primarily in two situations.

1. The receiving device is sensitive to common mode signals.

2. There is regeneration or parasitic circuitry that could
cause oscillation to break out,

In the former, the inductance "chokes" the common mode. There
are other ways of handling the problem. For example, coupling
the audio signal, through an audio transformer to the
receiving device will prevent the common mode signal from
being transmitted.

For the latter, the beads introduce loss and change other
circuit parameter. That may be enough to suppress oscillation.

If you can, understand what is going on rather than merely try
anything.

Bill


Hi Bill, thanks for the detailed info. You're right that I was
guessing about the idea of using a ferrite without really knowing
the theory! :-)

I was making my assumption based on my observation that all the USB
leads which have come with my dictation machines or MP3 players
have a plastic "blob" on them.

I was told this blob is a ferrite and that it's purpose is to
prevent trouble from interference. I didn't get told if the blob
prevented "incoming" intereference affecting the signals on its
lead or, alternatively, if the "blob" limited "outgoing"
interference being generated by using the lead. From what you say,
I guess the idea of the blob containing ferrite is incorrect.

Perhaps the blob does not contain a ferrite but something else? So
I dug around and got this interesting web page.
http://www.bitpim.org/help/

QUOTE "This cable has a blob half way along the cable
that converts from USB to serial and then connects to
the serial interface in the phone. The chip inside the
cable is a Prolific 2303 and this is how your operating
system will report it. It is marked as for the LG VX1/10
but works fine on the VX4400. /QUOTE

There's a chip in their blob? WOW. Well I never use my blob
leads! I use just ordinary USB leads and there seems to be no
problem.

Admittedly in this case the lead carries *digital* signals which go
to the USB port. By contrast, I had been asking about *analogue*
audio on a shielded lead going into the line-in socket of a PC (or
perhaps going to some other device).

(a) So what is really in the blobs in my leads? (EG on my Olympus
WS-331M) The above link talks about conversion to serial but I
don't think my blobs would need to do that.

(b) Whatever is in the blob, would one of those help reduce
interference on my intended longer leads because the leads will run
near equipment and will carry analogue audio signals?

Yes the blob located near to one end of the lead is there to stop
radiated interference from the lead. Yes it is a ferrite tube.
Note "From" not to.

--
Best Regards:
Baron.

[Don[_3_]]

On Thu 26-Mar-2009 21:26, Dave Platt
wrote:

In article ,
Don wrote:

At home, I often use some screened audio leads which carry
speech signals at about 100 to 200 mV. The leads may carry
one or two signals (mono or stereo) and may be about 1m or 2m
long. They are not balanced.

Sometimes it's unavoidable but my audio lead has to pass near
a PC and also about 6 inches below and in front of a CRT
display. I want to avoid electrical noise interfering with
the audio signal.

(1) Would it help to clip some ferrite on the audio lead? If
so, then at which point on the lead is the best place?
(Source, destination, where lead passes near causes of
interference). Is it better to use more than one ferrite?

It can't hurt to try, but I'm not all that hopeful. Ferrites
are useful at blocking radio-frequency interference, but they
won't do very much (if anything) to block interference which
is actually down at the baseband-audio frequencies. If you're
getting interference from a CRT, it's likely that it's from
the horizontal and vertical sweep circuitry (and perhaps from
modulations in the beam power), and these signals are likely
to be in the audio range.

(2) For a given max outer lead diameter of about 3mm (maybe
4mm), I guess some audio leads are better at intereference
shielding than others. I'm in the UK; is there a type of
decently shielded audio leads you might recommend without
getting into really expensive stuff. (I can add the
connectors.)

If I recall correctly (possibly not) this sort of interference
can result either from pickup of the electrical field, or the
magnetic field (radiated from the interferer in either case).
A shielded cable helps keep out the electrical field (the more
shield coverage the better), but I don't believe it is as
effective at keeping the magnetic field out... at least, not
at the low frequencies involved here.

You might want to see if you can find some shielded twisted
pair cable, and make up some audio leads from that... use the
pair for the audio signal (connect both wires at both ends)
and ground the shield at one end only. Some people have
reported better results with that sort of cable.

You could try using a twisted pair, with a balun transformer
at each end.

Belden makes a lot of good types of audio cable stock - the
table at http://www.belden.com/pdfs/Techpprs/bavcadtp.pdf
shows a bunch of their part numbers for various sorts of A/V
cable. Their #1508A is a twisted pair with a 100%-coverage
foil shield and a drain wire. Might be worth experimenting
with. #1883A is similar, and is specified for use as an audio
punchdown cable.

That's a great chart. I printed it out. I found my chosen suppliers
didn't have several of the leads or even list Belden reference
numbers in the same format as the table. Is the chart out of date?

After seeing your chart I went here.
http://www.belden.com/03Products/03_...logSection.cfm

The Belden range is bewildering. Even the guides to cables are
bewildering! For example:

Cable Finder Guide (780k)
http://www.belden.com/pdfs/03Belden_...Cable_Finder_G
uide/02CableFinderGuide.pdf

Residential Cables (1.2MB)
http://www.belden.com/pdfs/03Belden_...Residential_Ca
bles/21Residential_Cables.pdf

It's too much!


In honesty, though, distance is your best friend in this case.
Near-field interference drops off very sharply as a function
of distance (I *think* it tends to fall off as the fourth
power of distance from the source) and keeping the cables a
couple of feet further from your equipment may eliminate the
problem or reduce it to the point where it is not harmful. If
you have to add a few extra meters of cable to accomplish
this, do it - the audio degradation from the extra wire will
be negligible.

[Eeyore]

Don wrote:

On Sat 28-Mar-2009 17:50, Salmon Egg
wrote:

I have seen this thread for a while without reading it.
Because of it longevity I will throw in my 2¢ without even
knowing what has been written in the past.

All the ferrite beads do is add lossy inductance to the common
mode propagation along the vague transmission line formed by
all of the conductors in parallel against free space and the
surrounding environment. It is the equivalent of winding the
cable on a transformer core. Ordinarily adding these beads
will help primarily in two situations.

1. The receiving device is sensitive to common mode signals.

2. There is regeneration or parasitic circuitry that could
cause oscillation to break out,

In the former, the inductance "chokes" the common mode. There
are other ways of handling the problem. For example, coupling
the audio signal, through an audio transformer to the
receiving device will prevent the common mode signal from
being transmitted.

For the latter, the beads introduce loss and change other
circuit parameter. That may be enough to suppress oscillation.

If you can, understand what is going on rather than merely try
anything.

Hi Bill, thanks for the detailed info. You're right that I was
guessing about the idea of using a ferrite without really knowing
the theory! :-)

I was making my assumption based on my observation that all the USB
leads which have come with my dictation machines or MP3 players
have a plastic "blob" on them.

I was told this blob is a ferrite and that it's purpose is to
prevent trouble from interference. I didn't get told if the blob
prevented "incoming" intereference affecting the signals on its
lead or, alternatively, if the "blob" limited "outgoing"
interference being generated by using the lead. From what you say,
I guess the idea of the blob containing ferrite is incorrect.

Oh it contains ferrite ok. Its job to stop emissions coming *out* of the
apparatus.

Graham

[Adrian C]

Archimedes' Lever wrote:
On Thu, 26 Mar 2009 20:20:39 +0000, Adrian C wrote:

If built properly to CE EMC guidelines (applicable in the UK), generally
your domestic PC and connected equipment should not be causing that type
of interference.


You must not have seen the 'window equiped' PC cases all over the place
now.

Yup. For _whole systems_, CE is a labelling thing of little concern to
consumer end users, and rules are openly ignored in the light of history
that there really hasn't been a successful string of prosecutions in the
UK on EMC rule compliance for PC assemblers, for a long time, if ever.

For commercial use in business, and supply of component assemblies made
for eventual construction of systems for end users, EMC certifications
and compliance are more found important and are often demanded in
purchasing and import orders together with all the other legal safety
stuff.

However the testing (and passes) of assemblies may be specific to a
certain (and sometime fraudulent) system configuration available at the
moment, which may not be all that relevent to the final users use!

Some read CE as 'Chinese Export' and take no further interest in
independant verification of these tests ...

I quit that job a long time ago now, thankfully. ;-)

--
Adrian C