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Transformer Based Balanced Output & Impedance
Transformer Based Balanced Output & Impedance
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Old 11th June 2013, 03:51 PM   #11
m00dawg is offline m00dawg  United States
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Hmm actually that might work but I'm not 100% on that and I have had coffee today already That sounds like it might work since it's sort of turning L/R into a balanced L + R of sorts?

Good point on the line level vs mic. I can switch between mic and line as far as that goes. The goal of the balanced output is really cases where the cable length is real long, and the added benefit of isolation. Trying to be more up on impedance matching but I'm no expert in it for sure.
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Old 3rd July 2013, 03:26 AM   #12
m00dawg is offline m00dawg  United States
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Join Date: Aug 2012
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Originally Posted by Pano View Post
Sure, glad to help!

I was doing something similar a few years back - extracting the difference signal from L, R and did it with a transformer. You should contact Edcor to see if they have something like that already, that is not in the catalog. Just let them know that you want the difference signal (not sum) from 2 inputs. They can probably supply what you want for not much more than the price of the mixing transformers. Let them know you want line level to line level (1:1) if possible.

It would be nice if they had this as a regular catalog item.
Well, the tranny I ordered wasn't exactly to the above spec. It has one input and two outputs, doh.

BUT I read around the Interwebz and, man, I almost had this going last night on my own, but if I connect L to +, R to - and GND to CT, I basically have a case where only the differences pass through the tranny. So, on the other side, I then just have regular +, - and an isolated GND. I've attached a simple schematic of how it's hooked up.

If I play the same content on both L and R, the tranny only gives me the difference, which isn't much (some audio leaks through given non-ideals). But if I play music only on the left, now the difference is the left minus the common noise, as that's getting cancelled out.

The only concern I have is that the GB speaker gets real quiet when I plug it into the transformer. I'm not sure if I need a resistor across the + and - (I've seen that in some balanced designs on the output side) or if it's an impedance mismatch or what. The audio on the output side is loud as when not using the tranny.

I'm not sure if this is correct or if I may be risking doing harm to my GB as a result but it works and, actually works better than simply emulating the original noise cancelling design. I think it's because the resistors looked to be doing some weird harmonics and, with the single tranny, I don't need to use them (as I don't need to sum any inputs).

Curious as to what folks might think. Using one tranny vastly improves my design and, apart from the attenuated volume on the GB's own speaker output (which isn't an issue so long as it's not risking any electronics in the GB), this seems to work well.
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