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Author Topic: Is this Balanced???  (Read 4260 times)

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Offline spiritman

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Is this Balanced???
« on: April 03, 2004, 11:51:43 PM »
I just took the sheild and the neutral together for pins 1-3. Is this true balanced? Or do I need to keep the shield and the neutral going to their own lug's?  Even if their at the same potenial?

Offline sickrick43

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Re:Is this Balanced???
« Reply #1 on: April 04, 2004, 01:48:41 AM »
Sheild should be on pin one, and seperate from gnd.  Shield also serves to cut down on emi/rfi induction into cables in noisy environments.  Sheild & gnd should be kept seperate.

At some point gnd is grounded to chassis, which keeps devices at the same potential and eliminates ground loops or floats.  Sheild is usually grounded to chasis right at the connector (and in the case of mic's, to the case of the mic itself), which again puts the cases at ground and keeps dangerous voltages off equipment.  Lifted grounds are a safety hazzard - and you ain't LIVED until you've taken an arc off a microphone onstage -usually from someone putting a ground lift plug on the console, because they're too damn lazy/stupid to find the source of the buzz in the system.

Rick
4 Track & CD Live Rig: TLM-170's->V3->SD-744T  CDLive->TC Finalzer Express->Tascam CDR-900SL

24 Track Rig: Audix D6/D2/D4/I5/SCX1-C/O->Whilrwind SPC82 ISO Splitters->DigimaxLT's->Alesis HD24 (Lucid GenX192 Master Clock)

Canon 1Ds MarkII - 16-35/2.8L - 24-70/2.8L - 70-200/2.8L IS - 180/f:3.5 Macro - 550EX Flash


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Offline Sean Gallemore

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Re:Is this Balanced???
« Reply #2 on: April 04, 2004, 03:38:39 AM »
looks "unbalanced" to me

Offline spiritman

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Re:Is this Balanced???
« Reply #3 on: April 04, 2004, 03:49:38 PM »
OK, But the wire I have from AudioQuest. King Cobra. Its shielded with foil then there is a "drain" wire. I thought that they were the same, because they look like they touch one another. But my OHM meter showed me different, Time to break out the soldering iron!!! Thanks....

Offline Marc Nutter

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Re:Is this Balanced???
« Reply #4 on: April 04, 2004, 10:47:59 PM »
Cool picture spiritman,

While it sounds like you already got all the info. you needed to make a balanced cable, I though this could help.

A balanced circuit uses a differential amplifier which outputs signal based on the difference between pins 2 and 3. These should have equal impedance in reference to ground (pin 1) (Nothing you can do much about when you are making cables, unless you are the manufacturer).  

For the audio circuit to be complete it must have a return path.  Hence a positive outgoing voltage on 2 will complete the circuit through a return on 3 and vice versa.

For the noise rejection to function optimally, the differential amplifier should see equal and opposite information on each incoming wire and each should have equal impedance to ground. The jumper from 1 to 3 sacrifices this.

All told, pins 2 & 3 must be connected on each end of the cable for it to be balanced.

When making cables for portable systems (like our rigs), pin 1 will usually be connected on both ends as well.  The jumper between 1 and 3 is not going to work well. At the very least, you would lose 6dB of output.  I think it would actually be a more substantial problem than that but I’ve never tried it.
 
As sickrick said, the shield is an extension of the AC ground and only serves to keep the chassis of the various boxes at the same potential.  However, no audio signal should be carried on shield—only noise which we hope won’t make it into our signal.  Still, go ahead and connect it to the xlr on each end of the wire.

Sounds like quite a party sucking AC off a mic due to some jackass with a ground lift.  Sure solves the hum problem but those things quickly make for dead (or at least very angry) musicians.

Long story short, use twisted pair shielded wire and solder all wires on each end to their own respective point.

Marc
« Last Edit: April 05, 2004, 08:28:39 AM by Marc Nutter »

Jason B

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Re:Is this Balanced???
« Reply #5 on: April 04, 2004, 11:06:43 PM »
Sheild & gnd should be kept seperate.

Except when going from a balanced connector on one end of the cable to an unbalenced connector on the other, ie XLR to RCA cables. Then ground and shield should be tied together at the unbalanced end.

Offline spiritman

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Re:Is this Balanced???
« Reply #6 on: April 04, 2004, 11:09:02 PM »
Here is the poop...... I'll rewire them on monday. Thanks for clearing up my blind spot!! 8)
Sorry for the double post but my attachment didn't mack the trip the first time. So see next post. OK?
« Last Edit: April 04, 2004, 11:13:09 PM by spiritman »

Offline spiritman

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Re:Is this Balanced???
« Reply #7 on: April 04, 2004, 11:11:16 PM »
Here is the poop...... I'll rewire them on monday. Thanks for clearing up my blind spot!! 8)

Offline Marc Nutter

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Re:Is this Balanced???
« Reply #8 on: April 05, 2004, 08:43:19 AM »
Sheild & gnd should be kept seperate.

Except when going from a balanced connector on one end of the cable to an unbalenced connector on the other, ie XLR to RCA cables. Then ground and shield should be tied together at the unbalanced end.

This is a common practice but also one of the bigger debates in the installed sound industry.  I work with a company that insists on landing the shield only on the input side.  Others, like Bill Whitlock of Jensen Transformers, make very strong arguments for always landing on the output, usually connecting to both, and NEVER connecting only on the input side.  As the cable may go XLR>RCA or RCA>XLR, you may not always connect the shield to the RCA side.

For tapers in the field, the arguments would be the same and since we don't have the problems of grounded AC power cables connecting our equipment, we usually can land on both ends without the fear of ground loops.

The one area of agreement is that if the cables don't tranmit hum and buzz into the signal, and do transfer signal, it is good. : )

Marc

Offline spiritman

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Re:Is this Balanced???
« Reply #9 on: April 05, 2004, 11:31:08 AM »
Soooo, Is there a one "standered" for this?   ;D I know I have see both.    In this app. I am going from a sound card in my PC (ECHO Layla24) - to my pre (ADCOM GFP750)  then to my powered speakers {this wire} (dynaudio B15A)
So I am unbal. from my ECHO to the Adcom then bal. to the Dyn's
I thought I should term. both ends of the bal. cable..........
I also need to rewire from my ECHO to My Adcom... to stay bal.  

Offline Marc Nutter

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Re:Is this Balanced???
« Reply #10 on: April 05, 2004, 11:55:30 AM »
Soooo, Is there a one "standered" for this?   ;D I know I have see both.    In this app. I am going from a sound card in my PC (ECHO Layla24) - to my pre (ADCOM GFP750)  then to my powered speakers {this wire} (dynaudio B15A)
So I am unbal. from my ECHO to the Adcom then bal. to the Dyn's
I thought I should term. both ends of the bal. cable..........
I also need to rewire from my ECHO to My Adcom... to stay bal.  

Hi spiritman,

I would terminate both ends initialy.  If there is a hum or buzz, I would disconnect the shield (pin 1) on the receive side (the one connecting to the input of the next device (your speakers in this case).

While on the subjects of buzzes (no, not that kind), NEVER use a ground lift as it is a SEVERE SAFETY ISSUE, and try to plug in all devices to a common power service outlet or power strips going to one outlet (both outlets on the same box is okay), unless you are pulling more than the outlet breaker can handle.

Marc

Offline spiritman

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Re:Is this Balanced???
« Reply #11 on: April 05, 2004, 05:13:08 PM »
OK, I broke down and called Audio Quest. He said to use one each of the three conductors for each pin! In fact that is why there is three. I rewired all 8 conn. today. WOW I can hear the diffence. Much better stereo image, no buzz at all. Even with the pre maxxed!  8) Thanks for the help!!

Offline sickrick43

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Re:Is this Balanced???
« Reply #12 on: April 06, 2004, 05:35:53 PM »
In theory, the sheild to connector shell, carries stray currents, EMI/RFI/etc., that would be induced into signal conductors (by "waves-of-force" "cutting" through the wire).  It happens more often at Radio Frequencies.  Putting sheild to chassis ground, shunts this to earth ground (as long as a ground lift is not used).  If a ground lift is used, then "safety ground" is floating, and can be anything from 0A to very high currents.  (CURRENT KILLS not voltage)

What you commonly see is guitar amps with "lifts", and when the guitarist touches a microphone that is properly grounded, his BODY completes the circuit, and the "floating" ground that is carrying an actual voltage (for whatever reasons) is what gets carried (from the amp, thru the guitar, thru the GUITARIST, the mike can, to chassis ground in the console).  Most gear has a "ground bus" that all grounds are tied to.  Gear with multiple ground points, usually suffer corrosion or a loose nut, and that's what causes the buzz - a ground lift will lift EVERYTHING, so everything is floating (and in turn seeking a GROUND to complete the circuit).

I had a number of clubs I've worked in, bring in electricians to go through the entire system.  PA gear on one circuit, lighting gear on another, backline on another - with a ground bond that ALL circuits get strapped to (I usually have them drive a ground stake (8 foot copper rod) into the dirt outside, and wire it to a 10 guage strap).  All the buzzes go away.  In most small clubs, it's the dimmer packs from the lighting system, that cause buzzes.

We did a 3 week safety course in Navy Electronics school, covering proper grounding.  On ships it's real important, as the entire ship is grounded.  If a piece of gear is "floating" anything else you touch can be hazardous to your health.  I've gotten enough "electro-shock therapy" from bad grounding to avoid it whenever possible.

Sorry for the rant, it's really not a safety issue in portable recording, but properly constructed cables can make all the difference in quality recordings...

Rick
4 Track & CD Live Rig: TLM-170's->V3->SD-744T  CDLive->TC Finalzer Express->Tascam CDR-900SL

24 Track Rig: Audix D6/D2/D4/I5/SCX1-C/O->Whilrwind SPC82 ISO Splitters->DigimaxLT's->Alesis HD24 (Lucid GenX192 Master Clock)

Canon 1Ds MarkII - 16-35/2.8L - 24-70/2.8L - 70-200/2.8L IS - 180/f:3.5 Macro - 550EX Flash


"this isnt a dramatic bitchy exit, its just time to go." - Big Ray (queen of the dramatic bitchy exit)

Offline Marc Nutter

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Re:Is this Balanced???
« Reply #13 on: April 06, 2004, 07:38:30 PM »
+T for the expanded explanation rick.

Recently, I spent some time with Bill Whitlock of Jensen Transformers (mentioned above).  He's lately carrying the well earned moniker of "the father of grounding and shielding."

He rigorously impresses open everyone the same rap you share about grounds lifts.  A deviation from the thread but an extremely important issue.

Be Safe  :)

Marc

Offline digital-havok

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Re:Is this Balanced???
« Reply #14 on: April 16, 2004, 09:27:30 PM »
I make a lot of these cables everyday at work for a lot of the audio equipment I work with.

I usually use 22awg Beldon 8451 wire.  Is this a recommended wire type for recording. btw, i use it for XLR's RCA ect...

Just curious.


 

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