ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: Unbalanced line level run  (Read 3800 times)

Bradford "BJ" James

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 392
Unbalanced line level run
« on: February 11, 2016, 02:35:20 PM »

A venue with an install that I service is requesting canned music from a central location be routed to another small system in a banquet type room in another part of the building. There is an existing unbalanced shielded cable making the approx 100' run between the 2 systems. I planned on pulling a new run of balanced line, but thought I would ask here first if there is any new technology or tricks I could use to make the existing unbalanced line work.
Cheers,
BJ
Logged
Proud Canadian dealer for Danley Sound Labs, A&H, Yamaha, QSC, Yorkville and more.

Rob Spence

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3513
  • Boston Metro North/West
    • Lynx Audio Services
Re: Unbalanced line level run
« Reply #1 on: February 11, 2016, 04:24:24 PM »

What kind of cable exists? Is it audio coax? 50 ohm or 75 ohm coax?

What is the budget? Converting to Madi & back could do it but could be expensive unless you have, for example, a Soundcraft desk with stage box?


Sent from my iPad using Tapatalk HD
Logged
rob at lynxaudioservices dot com

Dealer for: AKG, Allen & Heath, Ashley, Astatic, Audix, Blue Microphones, CAD, Chauvet, Community, Countryman, Crown, DBX, Electro-Voice, FBT, Furman, Heil, Horizon, Intellistage, JBL, Lab Gruppen, Mid Atlantic, On Stage Stands, Pelican, Peterson Tuners, Presonus, ProCo, QSC, Radial, RCF, Sennheiser, Shure, SKB, Soundcraft, TC Electronics, Telex, Whirlwind and others

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16833
  • Hickory, Mississippi, USA
    • Resotune
Re: Unbalanced line level run
« Reply #2 on: February 11, 2016, 04:42:18 PM »

In general there is a strong chance that different grounds spaced 100' apart will not be the same voltage (the same ground won't be the same 100' away).

The signal integrity of a line level signal inside shielded cable could be decent (depends on the environment, i.e. how much noise the shield has to absorb). The fun begins when you attach grounds together at the far end.

An isolation transformer that keeps the two grounds floating should help.

An active differential (or balanced) receiver that has enough resistance between the two grounds that little current flows even from a voltage difference, and the signal can be grabbed differentially from the output of the shielded cable. Since the cable is there already, you can measure between the receiver ground, and shielded cable ground, with VOM on AC volts before connecting them to get a sense of how much hassle to expect. 

Sending the signal as hot as you can then perhaps pad it down at the receiver which may attenuate ground errors too.

Most modern gear has some sort of differential input so you can try these cheapest first, to most expensive. It seems pulling new wire is likely the most expensive solution.   

JR
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3380
  • Isle of Wight - England
Re: Unbalanced line level run
« Reply #3 on: February 12, 2016, 02:44:37 AM »

An isolation transformer as John suggests plus keeping the signal level high in the cable, even a loudspeaker or headphone output level would help as long as the transformer at the other end, possibly with an attenuator, can bring the level back down to suit the input.

I would personally do it the same way as my isolating transformer for connecting i-things and laptops.  I have a 12VA mains transformer with 230v and 12v windings.  The headphone outputs L and R are summed with resistors into the 230v winding and the 12v winding goes to pins 2 and 3 of the input.  It works perfectly.  It was constructed in a hurry with what I had to hand but I have never felt the need to replace the transformer with a proper transformer designed for audio (although I now have a pile of the Peavey CS input transformerss spare).  I figured that if it could run at 50Hz it wouldn't be lacking in bottom end for audio.


Steve.
« Last Edit: February 12, 2016, 02:49:59 AM by Steve M Smith »
Logged

Caleb Dueck

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1453
Re: Unbalanced line level run
« Reply #4 on: February 13, 2016, 10:04:10 AM »

100' isn't far, if this is an install, pull new. 
Logged
Experience is something you get right after you need it.

James Hicks

  • Newbie
  • *
  • Offline Offline
  • Posts: 24
Re: Unbalanced line level run
« Reply #5 on: March 01, 2016, 09:59:11 AM »

A venue with an install that I service is requesting canned music from a central location be routed to another small system in a banquet type room in another part of the building. There is an existing unbalanced shielded cable making the approx 100' run between the 2 systems. I planned on pulling a new run of balanced line, but thought I would ask here first if there is any new technology or tricks I could use to make the existing unbalanced line work.
Cheers,
BJ

Assuming it wouldn't take as much time to test as it would to simply pull a new cable, I think I'd just hook it up and see what happens.
Logged

Scott Holtzman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 6425
  • Ghost AV - Avon Lake, OH
    • Ghost Audio Visual Systems, LLC
Re: Unbalanced line level run
« Reply #6 on: March 02, 2016, 03:26:05 AM »

Assuming it wouldn't take as much time to test as it would to simply pull a new cable, I think I'd just hook it up and see what happens.

Why would you have to pull new wire?  Just put a pair of line interfaces (transformers) at either end.

Logged
Scott AKA "Skyking" Holtzman

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks

Bradford "BJ" James

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 392
Re: Unbalanced line level run
« Reply #7 on: March 02, 2016, 11:17:41 PM »

Scheduled this in today. Hooked it up as is, and it worked fine with no hum. I'm really surprised at this. Past experience has not shown this to be a favourable solution.
Thanks for the tips and suggestions everyone.
BJ
Logged
Proud Canadian dealer for Danley Sound Labs, A&H, Yamaha, QSC, Yorkville and more.

Joseph D. Macry

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 425
  • Austin TX
Re: Unbalanced line level run
« Reply #8 on: March 03, 2016, 03:24:31 PM »

Scheduled this in today. Hooked it up as is, and it worked fine with no hum. I'm really surprised at this. Past experience has not shown this to be a favourable solution.
Thanks for the tips and suggestions everyone.
BJ

I once had to install an "iPod" line (unbalanced stereo, using shielded mic cable) to run from floor pocket in a Gym out to the sound closet across the hallway. I said that I hate to run unbalanced that far (maybe 80 feet), but the school district Technology guy said it will work fine.
Then I found out the electricians ran the conduit to the wrong side of the gym, and now the run is over 400 feet going around the entire gym. Aaarrgh!
Amazingly, it worked well, with no hum. Technology guy is all "Told ya so."
Logged
Joseph Macry,
Austin, TX

ProSoundWeb Community

Re: Unbalanced line level run
« Reply #8 on: March 03, 2016, 03:24:31 PM »


Pages: [1]   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.092 seconds with 25 queries.