Mains filters
 

In ,
Jim Lesurf typed:
In article , Jo
wrote:
In , Arny Krueger
typed:


Most power amps already have chokes in series with their output
terminals.
As they should. The Texan didn't.

A snag here is that some designers feel that an output choke
increases the HF o/p impedance and degrades the sound. Classic
example being the older Naim power amp designs which just used a 0.22
Ohm resistor...

... and then may require about 10microH of lead inductance to be
stable. :-)


Yes, this brings us back into the topic of "but can humans really hear the
difference ?" that occupies many threads. I wonder how much extra impedance
is added to the output circuit at audio frequencies by the addition of RF
chokes ? The formula for inductive reactance is simple and for a 100uH choke
I get:

XL=1.3K at 2MHz and 13 Ohms at 20KHz which would seem to be a significant
contribution to the impedance of an amp output circuit...

....BUT if a decent common mode type bifilar wound filter choke is used the
effective inductance in the speaker circuit would be much less than this and
so any degradation of the audio signal would be negligible....or would it
:-)

Jo

Mains filters
 

In article , tony sayer

wrote:
In article , Jim Lesurf jcgl@st-
and.demon.co.uk writes


Well TAXIS are FM these days and you wont hear them, you might get a
bit of hum.

Old bill is fast going off to Airwave TETRA and you will not hear him
at all!...

You may do,,, ;- The TETRA mobiles are pulsed, so may produce AM
envelope demod of the data pulses if they find enough nonlinearity in a
suitable place.

If U reckon U can decode the TETRA old bills using Jim, then there would
be a lot of people very interested in that!....

Afraid I can't as I don't have the details of the encoding. But that isn't
required simply to detect the pulse power envelope. :-)

Indeed, you may recall some 'health scares' about TETRA that were fuelled
by its pulse profile - although those who panicked at the time had the
details wrong so were worrying about nothing much. If interested, have
a look at

http://www.st-and.demon.co.uk/temp/tetra.html

Note that although the base stations probably don't normally pulse, the
mobiles probably do, both to save energy and to reduce slot conflicts.
The point of the above page was to show that 'health' worries about
the *base stations* was probably groundless. Locally, we had all kinds
of stories about 'Cows not giving milk', etc, when TETRA bases were
installed - in fact before they came into actual acive use. :-)

A distinction to be made is one that (surprisingly) in my experience
often escapes people in the military, etc, who deal with encrypted or
spread spectrum comms. The payload data may be unreadable, but the actual
signals are easily detected, and often easily indentified in terms of class
of system. Alas, it seems easy for people to assume that the information
being encrypted as being the same as the actual transmission being
undetectable. Tain't so.

For the above reason you could, if you wished, easily detect when the Bill
are transmitting and even say where from... Technically, not particularly
difficult. Indeed, I've done this sort of thing for other (legal) reasons
in the past... :-) Knowing what they are saying would be more
difficult.

For similar reasons, locating, jamming, etc, of mobiles is much easier than
actually listening to the message payload/content.

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
 

Serge Auckland wrote:

He had a Ferrograph F307 amplifier...

Wow! I've got one of those sat up in the loft... picked it up for about
a fiver at a car boot sale many years ago (came with an AM/FM tuner and
a set of rather ropey speakers).

Sounded lovely, until the PSU blew up... smoothing caps went and took
out one of the bridge rectifiers. Managed to salvage a couple of much
newer caps, same value, similar size, from a dead Cyrus amp (was
terminal, beyond economic repair).

Apart from the crackly volume pots it's still working fine. Lovely bit
of kit, that was.

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

IT consultancy, hardware and software support, broadband installation

Mains filters
 

Stewart Pinkerton wrote:

If your opinion is that filtering won't make a difference, state your
opinion, avoid personal insults, and let civilised debate commence.
It won't, if your gear has decent RFI rejection, as it certainly
should. Moral of the tale - avoid 'high end' gear from back street
companies with no real engineering ability.

I'd hardly call Arcam a "back street company"...

[usual tirade of personal insults snipped]

Anyway, been doing some testing today with interesting results. Will
write up a summary and post when I've got a bit more time to spare...

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

IT consultancy, hardware and software support, broadband installation

Mains filters
 

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

Hello Glenn. A couple of days ago, I popped in for 30 secs to an audio
demo at a local dealership to take him some audition material. He was
demonstrating a mains filter unit. He had a tunable RF gadget with a
small inbuilt speaker which he plugged into a wall socket. Radio
transmissions and very loud hash could clearly be heard. Then he
plugged the gadget into one of the filtered outlets. Silence.

May be a very useful device if you happen to have such an RF
detector/demodulator/amp connected to the mains and you want to cut down
the noise it makes without bothering to unplug it. ;-

The unit was about 4U in height, and had ten mains outlets on the rear
panel.

I was there for only a few seconds, (car parked on a yellow line) The
dealer has promised me some literature.

The gain, etc, of the device used to produce audible noises from the
'mains' might help.. . :-)

AIUI though, most decent audio equipment isn't actually designed
specifically to demodulate and amplify mains interference. Perhaps he
avoided demoing with audio equipment as the main (pun) result might have
been to warn people not to buy that specific item of equipment. :-)



I think we had better not pursue this line, Jim. The power amp
demonstrated was a Krell which was being compared with a
Conrad Johnson. He phoned me this morning to say he took two
orders for the CJ.

Regards to all
Iain

Mains filters
 

Thus spake Jim Lesurf:
Snipped
Indeed, you may recall some 'health scares' about TETRA that were
fuelled by its pulse profile - although those who panicked at the
time had the details wrong so were worrying about nothing much. If
interested, have
a look at

http://www.st-and.demon.co.uk/temp/tetra.html

Note that although the base stations probably don't normally pulse,
the mobiles probably do, both to save energy and to reduce slot
conflicts.
The point of the above page was to show that 'health' worries about
the *base stations* was probably groundless. Locally, we had all kinds
of stories about 'Cows not giving milk', etc, when TETRA bases were
installed - in fact before they came into actual acive use. :-)

A friend was using Tetra radios as a constable on his beat in Skegness more
or less from launch. He reported no personal health issues but related
several anecdotal stories of scrambled brains. IIRC, the poorest aspect was
the pass-through onto the mobile network wasn't brilliant therefore was
easier to use his mobile.

A distinction to be made is one that (surprisingly) in my experience
often escapes people in the military, etc, who deal with encrypted or
spread spectrum comms. The payload data may be unreadable, but the
actual signals are easily detected, and often easily indentified in
terms of class of system. Alas, it seems easy for people to assume
that the information being encrypted as being the same as the actual
transmission being undetectable. Tain't so.

For the above reason you could, if you wished, easily detect when the
Bill are transmitting and even say where from... Technically, not
particularly difficult. Indeed, I've done this sort of thing for
other (legal) reasons in the past... :-) Knowing what they are
saying would be more difficult.

For similar reasons, locating, jamming, etc, of mobiles is much
easier than actually listening to the message payload/content.

The current use of the radio spectrum of allocating certain frequencies to
particular purposes makes it a no-brainer to know if that band is in use.
However, if UWB/SDR/Cognitive Radio ever reaches the ether, it will be
virtually impossible or very difficult to pull out military, emergency,
mobile, TV etc, etc from one another, ever before one can even contemplate
decrypting anything. If CR ever happens, it will be incremental, probably
with holes all through the spectrum for non-hopping radio. I can't see a
future humble radio hopping from DC to light either - just too expensive for
the intended purpose. Propagation characteristics are hardly even from DC to
light either. It will certainly make the whole spectrum a hell of a lot more
efficient, once regulators & the military can grasp the concept of loosing
fixed bands but retaining priority of use, security etc

--
Basically, I hate people who preface nearly every sentence with the word
'basically'!

Mains filters
 

Thus spake Arny Krueger:
Snipped
The last time through, a low-cost reduced-sound-quality format won the
reissue race: MP3. The moral of the story is that the much-demeaned
CD format was actually overkill.

Yup. The "you've never had it so good!" era of CDs (yes, I know this is
disputed by a few) maybe a thing of the past where we all have to put up
with 128k MP3s as the de facto standard & take a reduction in quality that
99% of consumers will be perfectly happy with. As for DVD-A or SACD, I've
never seen them in a retail outlet - not that I frequent them that often as
I prefer not to get ripped off. As for Blu-Ray or equivalents - region
coding for music anyone?

My Rotel will play HDCD discs but finding anything I want to actually listen
too is the challenge. I guess at the licensing fee being to high - better to
make a little money often than too much rarely. Goes to show that there's
still room for capitalists with brains to understand their chosen market.

As for the lost opportunity that digitised music could have brought to the
music industry...