Back in the heyday of hi fi, I had a very nice Tandberg amplifirer with a
torroidal transformer and lots of inputs and outputs, unfortunately, it was
based on din sockets and their parameters, but it seemed to work fine to
me, until that is during a quiet bit in a particualarly evocotive bit of
film music, I head Sk cs 1 to brown leader repeated sevveral times then a
one sided conversation about a problem on a boat.
Try as I might with capacitors ferrites mains filters on everything every
night in the summer this q guy would be there at some point with cryptic
conversations.
Eventually, I unplugeed every input and found that the only way to not get
it was to plug in the phones and remove the speaker plugs, bot of them.
As I say nothing worked. Asked Tandberg and they said basically their
systems all passed the radio interference specs so it has to be the
transmitter. I talked to at the time one of the gov deps that policed this,
they told me it was allocated to the local sea cadets and they would check
and get back to me. They of course said in about a month later that all the
installations passed to test.
So there you go, nobodys fault but it still happened, I lived with this
for about a year and then got a local shop to bring around a Pioneer
recever with more capapbilities than the tandberg to check at the allotted
wiching our and silence. No problems.
I gave him the tandberg and got a nice cheap price on th pioneer, That
thing lasterd for years. The only issue it had was short lived dial lights
in a pretty blue, but he gave me a handful of bulbs and though they were a
pain to get at we kept it going for years. A transistor went noisy in the
turntable circuit, a quick trip to get an equiv from tandy sorted that out.
Then a noisy electrolytic in the power amp. The next issue was the dil
string broke which was the staart of its demise many many years later I have
to say.
Now I've had a Denon receiver for many years and its only issue is that I
can no longer see the digital frequency and I had to clean the speaker relay
contacts a couple of times.
Its gothuge fets in it and sounds better as well. Sloight hum now but its
probably electrolytic dry out.
Brian

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"Phil Allison" wrote in message
...
Jim Lesurf wrote:



The Armstrong 626 I had refurbished recently was an early version. These
were prone to clicks, etc. The first impression might be that they were
getting in via the mains.



** Nearly everyone imagines that pops and clicks heard through stereo
systems as appliances are switched on or off MUST arrive conducted via mains
wiring.
But this is only rarely the case, iron transformers and other PSU components
do a thorough job of blocking RF energy arriving that way.

The source of the energy is the arc that briefly forms when a mains switch
opens - or closes and then bounces. Much like a spark transmitter, RF energy
from the arc is then radiated by the active and neutral wiring carrying
current to and from the switch.

There can be a fair bit of power involved too, particularly when the load is
inductive - like a fridge compressor or washing machine motor. The arc's
energy's spectrum spreads from audio frequencies right up to the top of the
VHF band interfering with radio and TV reception too.

So the actual path is through the air and into audio signal cables (ie RCA,
microphone, DIN and speaker leads) where the RF energy can then enter
directly into sensitive audio circuitry. In the case of speaker leads, it
enters via the NFB loops in output stages.

With well screened cables, the bursts of RF energy are picked up and travel
on the shields, dissipating harmlessly IF these are grounded to each chassis
right where they enter and leave equipment. Most makers know this while some
appear not to and so allow RF to come right in the door.

Many domestic appliances have RF suppression components across their
switches and this IS the best solution - but some do not plus the components
can fail due to age.

IME adding EXTERNAL (ie plug in) suppression devices to offending appliances
rarely helps and adding one to your stereo system never does.


.... Phil