"Eeyore" wrote in message
...


David Looser wrote:

It's not necessary to go to full balanced to get over earth loop
problems,
differential inputs connected to unbalanced outputs achieves the same
thing.

An unbalanced output with equal value resistors in the hot and cold signal
lines
( the cold going to equipment ground ) and a seperate screen IS balanced.

Balanced in terms of impedance, not balanced in terms of signal voltage (and
hence it's ability to cause crosstalk in adjacent circuits). So I don't
think it correct to say it IS balanced. Having said that it is a perfectly
satisfactory arrangement for short runs and one I have used often.

Normally just called 'impedance balanced' it provides almost all the
advantages
of full-blown active balanced outputs. With a few more resistors it can
even
'ground sense' and overcome hum caused by non-equipotential equipment
grounds.

Not quite sure what you mean by that, a differential input naturally
overcomes hum caused by non-equipotential equipment grounds. This was made
very evident when a piece of video equipment of mine which has a
differential, unbalanced 75R co-ax input was fed from a video line which,
due to confusion about which is the neutral and which the earth pin on an
EP4 mains connector, was referenced to mains neutral, not earth. The
equipment worked fine with but the merest hint of a hum bar on the picture.

A differential ( balanced ) input takes a couple more resistors to make
than an
unbalanced one.

Indeed.

PLUS the XLR is an excellent connector compared to the RCA.

True, though a lot bigger and more expensive.

David.

In article , David Looser
wrote:
"Eeyore" wrote in message
...


David Looser wrote:

It's not necessary to go to full balanced to get over earth loop
problems, differential inputs connected to unbalanced outputs
achieves the same thing.

An unbalanced output with equal value resistors in the hot and cold
signal lines ( the cold going to equipment ground ) and a seperate
screen IS balanced.

Balanced in terms of impedance, not balanced in terms of signal voltage
(and hence it's ability to cause crosstalk in adjacent circuits). So I
don't think it correct to say it IS balanced. Having said that it is a
perfectly satisfactory arrangement for short runs and one I have used
often.

The potential pun problem with the above is that its behaviour depends on
if both source and destination are 'externally' grounded or not. If they
both have their signal 0V levels connected to a mains 'earth' then any
return current will tend to pass back via the mains earth, not the ground
return of the 'allegedly balanced' connection.

That also means that if you remove the mains grounds from both then you
force the return via the connection. In such a case the above sort of
meaning for 'balanced' means the result would be 'current balanced' even if
you didn't bother to have the magic resistors in the ground return path.
:-)

All told, therefore, I'd personally wary of telling anyone that the system
described was 'balanced' without very carefully explaining the caveats.
:-)


PLUS the XLR is an excellent connector compared to the RCA.

True, though a lot bigger and more expensive.

Well, Lemo and others have also made all sorts of 'excellent' connectors -
often at high prices. Can be very useful in lab or industrial applications.

But I'm not sure that means it makes sense to choose the most expensive for
a simple task like a domestic audio connection that is fairly short. :-)

Above said, I do recall a salesdroid at an audio show who was working for
Levinson. Their amp at the time had Lemo plugs. He proudly showed how "good
the electrical contact was" by pulling at the lead to show this would not
pull out the plug.

The reality, of course, is that the plugs in question have slide-locking
collars so have teeth that engage to prevent the plugs falling out if
someone trips over the cable. This ensures they stay in the socket (unless
you pull the plug sleeve itself to disengage the teeth). But that won't
guarantee an *electrical* contact if there is some other problem like
tarnish. Still, I'm sure it impressed the punters who'd never seen such
plugs before and didn't know what they were actually designed for. No
doubt if someone was paying Levinson prices the cost of a few Lemos was not
a deterrent... ;-

Fun, this engineering lark, isn't it. :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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In article ,
Jim Lesurf wrote:
Above said, I do recall a salesdroid at an audio show who was working
for Levinson. Their amp at the time had Lemo plugs. He proudly showed
how "good the electrical contact was" by pulling at the lead to show
this would not pull out the plug.

The reality, of course, is that the plugs in question have slide-locking
collars so have teeth that engage to prevent the plugs falling out if
someone trips over the cable. This ensures they stay in the socket
(unless you pull the plug sleeve itself to disengage the teeth). But
that won't guarantee an *electrical* contact if there is some other
problem like tarnish. Still, I'm sure it impressed the punters who'd
never seen such plugs before and didn't know what they were actually
designed for. No doubt if someone was paying Levinson prices the cost
of a few Lemos was not a deterrent... ;-

Lemos are normally used where the connector will be removed and replaced
frequently - things like radio mics and studio cameras which don't have a
recorder on board. And *very* good they are too - and so they should be
given the cost. But totally OTT for domestic audio - unless you indulge in
bar room bragging like so many here do. Decent phonos are perfectly
adequate for an unbalanced connector. And the plug doesn't make much
difference since it's the socket 'spring' which grips the centre pin.
Assuming they both have decent corrosion resistant plating.

--
*I didn't fight my way to the top of the food chain to be a vegetarian.

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