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Author Topic: Balanced outputs to unbalanced amps Sebastian Binz Film Handler Posts: 32 From: Cologne, Germany Registered: Nov 2007 posted 02-25-2008 06:37 PM                     Since the search feature didn't bring up sufficient results, I would like to ask this question here again: The outputs of our processor (JSD-80) are balanced, but our amps (Dynacord PAA series) only have unbalanced inputs. What is the best way to wire this type of setup? thank you for your comments [ 02-26-2008, 05:53 AM: Message edited by: Sebastian Binz ]  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-25-2008 06:49 PM                     Download this - page 29  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-25-2008 08:30 PM                     In order to know how to best wire it up, one needs to know the output design of the USL device...is it true balanced or "quasi-balanced." A true balanced output can have one leg tied to reference and merely shift the entire signal above reference...just like a transformer output. Quasi-balanced (all too common by midiocre designers) merely provide an inverting opamp to create the "-" terminal from the plus terminal. If you connect a true balanced output to an unbalanced input, your signal level should remain constant. If you neglect to connect the "-" terminal of the output, the signal level should drop considerably. If the output is quasi-balanced, then connecting the "-" terminal to the low/E of the unbalanced intput shorts it out, in effect. You are better off just ignoring the "-" on the output in this case and treat the output of the quasi-balanced output as nothing more than an unbalanced output with an extra terminal. It will play 6dB lower than if you had a balanced input but should work otherwise. Ideally, one should place something like a high-quality audio transformer in line to effectively make the inputs of the amps balanced. You will get the maximum signal transfer with the maximum noise isolation. The only potential downside is if low quality transformers are used you will color the sound some. Steve  |  IP: Logged Sebastian Binz Film Handler Posts: 32 From: Cologne, Germany Registered: Nov 2007 posted 02-26-2008 05:59 AM                     Thanks for your replies, maybe Clint Koch can answer the question of the real or quasi-balanced outputs? A tech I talked to just recommended to connect + to tip, - to ring and leave the shield floating on the amp's end. Is there a chance to damage anything by doint this? *I take the phone joker*  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-26-2008 08:29 AM                     Again, unless you know what the output design is, the advice you received was, at best, questionable. If the USL output is quasi-balanced, then you are shorting out one opamp and not providing a proper reference the + side of things so you will likely get oscillation and other unpredictable results that will vary over time. Steve  |  IP: Logged Sebastian Binz Film Handler Posts: 32 From: Cologne, Germany Registered: Nov 2007 posted 02-26-2008 05:02 PM                     I actually found something in the XD10P's manual: In the drawing F208 on page 75 of the manual the drawing recommends to connect + to + and - in connection with the shield on the amp's end to "com". (whatever is meant by "com"?)  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 02-26-2008 05:36 PM                     quote: Sebastian Binz A tech I talked to just recommended to connect to tip, - to ring and leave the shield floating on the amp's end. Is there a chance to damage anything by doint this? That's correct, just do that way, you won't have any problems!  |  IP: Logged Clint Koch Phenomenal Film Handler Posts: 1435 From: San Luis Obispo, CA, USA Registered: Feb 2002 posted 02-27-2008 11:40 AM                     The outputs are balanced, not quasi balanced.  |  IP: Logged Nathan Tarpley Film Handler Posts: 12 From: Crystal Lake, IL Registered: Sep 2007 posted 02-27-2008 11:54 AM                    Taking this question a step further... Lets assume you have a processor with true electronically balanced outputs, such as the DFP3000, and all of your amps have balanced inputs. How do you best interface a monitor that only has unbalanced inputs into this system? Ideally you would like to maintain the balanced interface between the processor and amps, but wouldn't grounding the "-" terminals effectively unbalance them? Nathan  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-27-2008 12:12 PM                     Yes, you can not introduce an unbalanced monitor in this situation. Your choices are to replace the monitor (much preferred) or to add transformers (or suitable active circuitry) to the inputs of all of the channels of the monitor, or use a distribution amplifier on the various channels to feed each independantly. Steve  |  IP: Logged Nathan Tarpley Film Handler Posts: 12 From: Crystal Lake, IL Registered: Sep 2007 posted 02-27-2008 02:39 PM                    What about leaving the "-" unconnected on the monitor input and only using the "+" and the shield? Nathan  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-27-2008 10:00 PM                     That won't necessarily work...it all depends on the output design. If the output truely emulates a transformer type balance, then connnecting only one terminal will not provide a complete circuit, tieing the shield or no. Odds are, you will get SOME signal flow as the gound is in there, somewhere and if it is "balanced" then it is likely in the middle. But truely, hooking balanced out to unbalanced in should just be plain avoided. Steve  |  IP: Logged Sebastian Binz Film Handler Posts: 32 From: Cologne, Germany Registered: Nov 2007 posted 02-29-2008 05:16 PM                     Thanks for your help guys, the system is running with great performance. The only issue we are experiencing (which is more annoying than an actual issue) is sound from the RS232 connection between a desktop PC and the processor. It only appears upon hitting the "connect" button in the software until you tell the program to disconnect. You can literally hear the bits and bytes. We have tried several approaches to this issue, including different wire routing, unplugging the non/sync inputs which are coming from the same pc, and additional grounding of both the processor and the pc, with zero results.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 02-29-2008 06:53 PM                       Begging the question, but is the desktop always connected to the JSD-80? Is this only for setup, or for alternate content video? I have seen laptops inject noise when plugged into the wall to keep the battery charged while running a DVD. Once running on batteries alone the noise stopped. You might try an experiment with a UPS to provide isolation from the power plug.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 03-01-2008 12:18 AM                     Also, remember that all peripherals attached to the computer can inject noise. I recently had a ground loop from a video projector plugged into the VGA out of a laptop... unplug the VGA, hum went away. --jhawk  |  IP: Logged

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