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Author Topic: Ying outputs, was I really that wrong?  (Read 6386 times)

Geoff Doane

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Re: Ying outputs, was I really that wrong?
« Reply #30 on: January 22, 2016, 02:34:18 pm »

So if you have two balanced outs and you want to make a mono connection that sums them together, could you not use only pin 1 and 2 from the left send and then use only pin 3 from what would be the right side? The connections in the outputs would then never technically be in direct connection with each other. The balanced input at the speaker or amp would sum the signals together as normal right? The impedance would not harm the outputs either as it would just be like dropping a hot or cold pin. Or is this crazy talk? 

JR and I have had this discussion before.  :)  I don't think either one of us convinced the other we were right.

What you suggest will work (I've done it extensively in an installation), but there are too many "gotchas" to assume you can get away with it all the time.  First of all, you need to know that ALL the inputs and outputs will be "balanced", and the outputs have to be simple transformerless outputs with no circuitry that tries to mimic a transformer.  Impedance balanced outputs also don't work.

In my particular case, I was dealing with racks of distribution amplifiers that drove the + and - outputs with individual op-amps.  I could take + from the left, and - from the right into a differential input, and get a mono sum (with no gain or loss, if the signals were identical) of the two signals.  The beauty of this scheme is that it can be done with just simple wire.  No resistors, pad boards or other gack to lose signal or degrade the output impedance.  If the DA outputs are 30Ω per leg, you can still drive 1000 feet of cable.  Probably not a good idea to try that after you've added 1KΩ of series resistance with a passive combiner.

Unfortunately (depending on your point of view), simple active outputs with no cross connection are increasingly rare these days, because they usually don't tolerate having one side connected to ground gracefully.  Connecting a "balanced" source to an unbalanced destination is likely far more common than trying to combine two signals.  I actually stole the idea from the schematic for a piece of broadcast processing gear.  It was a stereo processor, but had left, right and mono outputs.  In that era, it would be very unlikely to encounter any equipment that didn't have a differential input.

GTD
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Luke Geis

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Re: Ying outputs, was I really that wrong?
« Reply #31 on: January 22, 2016, 03:27:56 pm »

I know ^^^^^^^^^ I was being rhetorical and facetious. Fuel for the fire........

I brought it up only because the theory supports it under specific conditions. I don't have such a cable and don't intend to ever make one. I also don't condone others to make one.
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Mike Caldwell

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Re: Ying outputs, was I really that wrong?
« Reply #32 on: January 22, 2016, 05:34:49 pm »

And this is "why" I have one these.

Luke Geis

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Re: Ying outputs, was I really that wrong?
« Reply #33 on: January 22, 2016, 08:11:32 pm »

Now one of those^^^^^^^^^^^ I do have
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David Sturzenbecher

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Re: Ying outputs, was I really that wrong?
« Reply #34 on: January 23, 2016, 01:43:56 am »


Now one of those^^^^^^^^^^^ I do have

Best looking resistor box I have ever seen!


Sent from my iPhone using Tapatalk
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Mike Caldwell

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Re: Ying outputs, was I really that wrong?
« Reply #35 on: January 23, 2016, 07:56:40 am »

Best looking resistor box I have ever seen!


Sent from my iPhone using Tapatalk

The Whirlwind box is a transformer isolated combiner.

Luke Geis

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Re: Ying outputs, was I really that wrong?
« Reply #36 on: January 23, 2016, 07:40:31 pm »

mine indeed is.
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Re: Ying outputs, was I really that wrong?
« Reply #36 on: January 23, 2016, 07:40:31 pm »


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