Subject: [USR-TC] The Balanced vs. Unbalanced discussion/definition...

From: Jeff Mcadams <[email-masked]>
Date: Wed, 03 Jul 2002 17:31:08 +0000

OK...this is probably rather off-topic, but there were a couple of
different people participating, and it might be of interest to some, so
feel free to delete if you're not interested.

Talked (via email) to my uncle who works for Sweetwater Sound
(http://www.sweetwater.com) and owns his own sound studio on the side,
about the use of the term "balanced" in audio gear.

He said that the term wasn't precisely defined (gee, sounds like the
data world!), but that in his opinion it didn't require a ground line to
be considered a balanced signal.  He basically said that virtual every
cable type that you'll run across in audio work *does* have a ground
line (sometimes, its also the shield), so its kinda a moot point, but
that its not strictly required.  Indeed, he pointed out that it can be a
*bad* thing to have ubiquitously connected ground lines in audio work.

He pointed out that the local ground of one piece of equipment may not
be the same as the local ground of another piece of equipment, so since
they are both grounded through their AC line, connecting the ground line
between the two pieces of equipment can result in a voltage and waveform
across the ground line, which can result in a hum in the signal.

He mentioned that the way they avoid this problem in his studio (plug:
DSL Studios, http://www.dslstudios.com...hosted by IgLou ;) was to have
every connection between different pieces of equipment run through patch
bays.  Each piece of equipment has its own ground (through the AC line),
and the patch bay itself (a passive piece of equipment) is also ground,
but that the ground line in the cable is *not* connected to the ground
of the patch bay.  This ensures that there is no continuous ground
connection between two different pieces of equipment and avoiding a
ground loop.

FWIW, he pointed out the use of the balancing concept at
http://www.equitech.com...specifically "balanced power", ie, rather than
having a hot line at 120VAC and a ground, you have two hot lines at
60VAC, but in opposite phase.  When the power supplies in the equipment
run by this looks at the two lines, it still sees 120VAC, but the
opposite polarity of the lines means that the "reactive currents" coming
back out of the power supply end up cancelling each other out, resulting
in a significant noise reduction.  I found it interesting that there's a
third field where balancing is used.

Anyway...this is probably way more than most of you wanted to know, but
I found the mental excursion interesting, hopefully others have found
the discussion enlightening as well.

Let me know if anyone has questions, if I can't answer them, I'll get
better answers from my uncle...he's *quite* knowledgeable about audio
production.  :)
-- 
Jeff McAdams                            Email: [email-masked]
Head Network Administrator              Voice: (502) 966-3848
IgLou Internet Services                        (800) 436-4456

---

From: [email-masked]
Date: Thu, 04 Jul 2002 02:24:34 +0000

Hi all
 
To my knowledge this isn't  a question of ground or not.
A twisted pair cable is for example a balanced cable but a coaxial cable is un-balanced.
When a TP cable is subjected to interference both wires are affected equally which means that the interference doesn't effect the signal at the end.  When a coax cable is subjected to interference the outer conductor will be more affected than the core which means that more of the interference will be affecting the signal at the end.
 
Pls correct me if I'm mistaken or don't remember correctly :)
 
Regards Johannes Rognvaldsson
Electronic technician

	-----Original Message----- 
	From: Jeff Mcadams [mailto:[email-masked]] 
	Sent: mið. 3.7.2002 23:30 
	To: [email-masked] 
	Cc: 
	Subject: [USR-TC] The Balanced vs. Unbalanced discussion/definition...

	

	

	
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From: Brian Becker <[email-masked]>
Date: Sat, 06 Jul 2002 03:39:05 +0000

I knew I should have re-read my post before hitting send...but I was
late for leaving for the Cardinals v. Dodgers game (Cards won 3-2).
Anyway, had I spent a more "editor" time, I would have said: 
Just as a comment...IN THE AUDIO WORLD balanced is...

I'm actually an EE/CompE by degree and I have NO MEMORY of EVER studying
this. Guess that explains that 2.74 GPA! :)

Brian

Brian Becker
President, Poplar Bluff Internet, Inc. http://semo.net
P.O. Box 190 | Poplar Bluff, MO 63902 | 573.686.9114

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of Dave Martin
Sent: Thursday, July 04, 2002 11:45 AM
To: [email-masked]
Subject: RE: [USR-TC] The Balanced vs. Unbalanced
discussion/definition...

>AHHHH!!  So which one is it??
>
>There has to be an EE on this list somewhere.

Guilty as charged.  Balanced signalling transmits a signal over a 
pair of conductors (usually referred to as "+" and "-") with opposite 
polarity in order to eliminate "common mode" distortion from external 
electromagnetic sources.  EMF is induced equally in each of the two 
conductors and is cancelled out (to the extent of the common-mode 
rejection offered) at the receiving end of cable.  No shield is 
technically required (unshielded twisted-pair [UTP] ethernet cabling 
is one example), but is often used, especially on analog (e.g. audio) 
cabling.

>Charles
>
>--
>Charles Sprickman
>[email-masked]
>
>
>On Thu, 4 Jul 2002, Brian Becker wrote:
>
>>  Just as a comment...balanced is required to have a ground and a
shield
>>  to be defined as balanced. Of course much of the audio gear can
survive
>>  if the ground and shield are the same signal, but it is not part of
the
>>  spec and all major recording studios will utilize separate and
distinct
>>  paths for the ground and the shield to reduce the level of noise to
its
>>  minimum.
>>
>>  I am "Artist Formerly known as Brian Becker" with Benson Music
Group,
>>  Nashville, (Christian Rock) and spent many hours working with top
>>  studios in Nashville & Houston...they would laugh at the thought of
>>  combining ground and shield.
>>
>>  Brian Becker
>>  President, Poplar Bluff Internet, Inc. http://semo.net
>>
>>  Home of TotallyFabricated.com Software & Web Design
>>    http://TotalScrutinizer.com - Tech Support Just Got Easier!
>>
>>  POBox 190 - Poplar Bluff, MO 63902 - 573.686.9114
>>
>>
>>  From: [email-masked]
>>  [mailto:[email-masked]] On Behalf Of Jeff Mcadams
>>  Sent: Wednesday, July 03, 2002 6:31 PM

-- 
------------------------------------------------------------------------
Dave Martin                 Netcetera, Inc.            [email-masked]
                       "May the Foo be with you"
------------------------------------------------------------------------