On Sun, 22 Nov 2015 08:48:57 +0000, Eiron
wrote:

On 22/11/2015 07:57, Woody wrote:
"Phil Allison" wrote in message
...
Brian-Gaff wrote:


With the proliferisation of mobile devices running on the mobile
phone
network its getting increasingly a annoying to listen to things on a
good
old fashioned or even new fangled radio, without the noise occurring
at some
point. Even from next door one can get it getting into the audio
chain.
Anyone know if there is an easy way to stop it.



** There is no easy way.

In the old days a few
capacitors got rid of Radio China or Vatican City, but due to the
high
frequencies of the phones and the spiky nature of the handshaking
noise,
this seems not to work much. What is the mechanism. they cannot be
tuned to
the r frequencies, so is it just straight diode type detection due
to the
huge signal level?



** At a range of a few metres, the induced signal is hundreds of
millivolts.
Rectification by a non linear component produces a small DC level and
when the RF signal is 100% amplitude modulated at an audio frequency
causes the buzzing noise. GSM phones are the worst.


Low level circuits like turntables, microphone inputs etc, seem to
be the
worst, but I've also proved my Denon is picking it up from its
speaker
cables.


** The standard technique is to reduce RF energy entering a device via
input and output leads by making sure the shields are grounded to the
metal case right at the connectors. A 10nF ceramic cap wired direct to
chassis from the ground pin of the connector normally does the trick.
The same can also be done with both speaker terminals.

I helps if all co-axial signal cables have woven shields.

If the device does not have a metal case, you are outta luck.


... Phil


For once I would agree with Phil, and there is one other point.

Many hi-fi components these days only have a two core cable with just
one, hopefully the amplifier, having three core. Aside from any safety
issues this means that many sources can only achieve proper signal and
unit screening through the braid/screen of a signal cable which can
make the whole unit at the distant end from the amplifier act as an
aerial especially if, for any reason, the cables are long.

Decoupling does work and in many cases will help, save that the
average user doesn't even know what a soldering iron is let alone
which is the hot end. IME the one connection that has most effect is
the longest aerial of all, the loudspeaker leads. In many cases
putting a loop or two the speaker cable through a ferrite ring will
kill the interference dead, but have you tried buying ferrite rings
these days? At one time they were easily obtained and in many
varieties but now - lets us say rocking horse manure comes to mind.

Try the CPC website. No **** but dozens of ferrite cores.
Or visit your local tip and pick up an old PC with ferrites
on the motherboard and in the PSU.

I replaced a shorted 10nF cap on the output of my Yamaha amp recently.
It sacrificed itself to save the amplifier from a nearby lightning strike.

Decent screened cables help. Many phono leads have no more than a
dozen or so very fine copper strands for screening - in fact all they
do is just about carry the ground. For fixed wiring that doesn't
require flexibility, go for CT100 - the stuff used for satellite
downleads. It uses copper foil as well as wire to achieve 100%
screening.

Additionally, killing the common mode currents induced by high level
RF fields is a good idea. Ferrites slipped over audio and power cables
will prevent the ingress of ground currents, which only need a small
series impedance to be turned into signal voltages.

As for two mains wire vs three. This is absolutely vital. Only one
component - and the amplifier is a good choice - should carry a mains
earth connection. Everything else should ground via the signal leads.
Unless your audio is balanced pair, any other arrangement will lead to
ground loops and consequent hum.

Lightning protection - All my audio gear is powered from a single
mains extension strip in which I have incorporated three large MOVs, a
gas discharge tube, two Y1 caps, a Y2 cap and a common mode choke.
Everything is pretty much proof against lightning surge. The antenna
feed grounds at the star point from this strip before continuing to
the receiver.

Do all this, and your audio system should be proof against pretty much
anything.

d

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