On Sun, Jun 06, 2010 at 05:18:53PM -0700, Niels Mayer wrote:
> On Sat, Jun 5, 2010 at 2:48 PM, <fons@email-addr-hidden> wrote:
>
> > But calling such an output a 'fully balanced output' is
> > stretching the truth - describing it as such in a spec
> > or sales literature would be a plain lie.
>
> You mean like M-audio?
> http://forums.m-audio.com/showthread.php?869-delta-1010-balanced-jack-query
> ... I'm sure http://behringer.com does it too.
It's not a technical matter. What I object to is
marketeers redefining a technical term that has
(even if by tradition only) a well defined meaning
to something of lower quality, for their own greedy
purposes.
If you ask anyone with some real background in audio
engineering, a 'true balanced output' means a transformer.
(case #5 in my previous post).
One step down is an 'electronically balanced output (either
#2 or #3).
One more down is am 'impedance balanced' one (#1).
What the marketeers try to do is to confuse their customers
by abusing these terms.
> For quasibalanced OUTPUTS, however, I disagree that it is a lie. It
> really is a balanced output. If you do a
> Einstein-relativity-gedankenexperiment except instead of riding an
> elevator you're riding the balanced cable, it is clear that without a
> reference point (which is what a true differential input would provide
> -- a non-reference point) this output is exactly like having both (+)
> and (-) side of the differential pair actively driven;
No, the output still has a reference point.
And even for a 'quasi floating' ouput (#3) the floating
range is limited by the output voltage range of the amps.
Which means it's of limited use. It requires the same, or
almost the same ground potential at both ends of the cable.
In that case even an 'impedance balanced' system will work
well. If you can't rely on a common ground of some sort,
the only thing that will work is a tranformer. Try driving
100 km of telephone line (from an OB van to a continuity
studio) with anything else. The chances that it will even
survive are minimal.
> Your #5 is best represented by
> http://www.dself.dsl.pipex.com/ampins/balanced/balfig6.gif (
> http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm )
> " Simplified diagram of a quasi-floating balanced output, with its
> essential trim control for output symmetry."
No, that would be #3. For #5 you need a transformer.
> In terms of implementation, I like using
> http://www.rdlnet.com/product.php?page=54 (RDL STA-1 active
> transformer pair) to implement the "quasi-floating balanced out" from
> a computer. The can float w/r/t their power supply.
As far as I can read the specs, the output is not isolated from
the input nor from the power supply. It's just allowed to float
in a very limited range. This again is #3.
Ciao,
-- FA O tu, che porte, correndo si ? E guerra e morte ! _______________________________________________ Linux-audio-user mailing list Linux-audio-user@email-addr-hidden http://lists.linuxaudio.org/listinfo/linux-audio-userReceived on Tue Jun 8 00:15:03 2010
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