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Thread: How to balance an unbalanced signal?

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    Question How to balance an unbalanced signal?

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    So im making my own pre-amp based on the INA217 IC, the thing is this, i have an unbalanced output from the pre-amp and i want to make a circuit to balance it, im guessing ill be needing a balanced output driver, but no idea on how to do it. Does anyone has a schematic of an already made circuit in order to balance this signal?, the other option is to balance the signal using an output transformer but i also have no idea on how to do this, i have some electronic skills but im no electronics engineer so any help you can offer will be much appreciated.
    Last edited by dualflip; 08-21-2008 at 11:57.

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    easiest way is take a duel op-amp and have input to one of the + and the other -... ground the unused inputs... the two outputs will be out from each other.... make sense???
    37.8% of all statistics are made up on the spot...

    hey give a guy some room... people are trying to evolve here... for crying out loud...

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    Yes, it does make sense, i was thinking of using a 5534 to do the job, but i finally decided for the THAT 1646 ballanced line driver, im planning on feeding the unbalanced signal into it and wire it according to the 1646 data sheet, now the question is: will it work?, BTW with a dual-op amp you mean something like the NE5532?

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    You can also do it with a small transformer with a center tap on the secondary.


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    Yes i also wanted to do that, using a transformer like the OEP A262A7E which is 1+1:1+1, and i dont know if its possible with the OEP A262A2E which is 1+1:2+2, but the thing is that i dont really know how to wire it. Heres the link of the data sheet: http://www.canford.co.uk/ProductResources/ig/2739.pdf

    Theres the wiring schematic, but i dont know how to wire it (exactly in wich tip will the unbalanced signal will go in, which pins does the balanced signal goes out, wich pins will be interconected, etc..)

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    There are many ways to ballance a Unballanced signal ,some are extremely easy and only need a couple extra parts and some are more complex....

    What I did with some of my INA217 Mic pre"s is built a Ballanced line driver useing a dual opamp ,Both opamps run at unity gain so .1% resistors are recomended to attain good CMMR...One opamp is non-inverted and one is inverted createing a ballanced output....

    Like in Figure 1 on this web page:

    http://sound.westhost.com/project51.htm

    Another way which I did on my latest INA217 is to use an Audio transformer...I had Two 1:1 Line transformers I salvaged from an old Akai 2 track recorded and used these on the outputs of the INA217...These do seem to color the sound a bit but it seems to add a bit of mojo to it...
    And with a Output transformer you don"t need a DC servo or output cap as the transformer blocks DC from the output....

    The last and the easiest way to ballance a unballance signal is a technique called "Impedance Ballanced"...in impedance ballanced systems there is no audio signal on the cold wire but the impedance on the cold wire to ground stays the same so you still retain good CMMR and a ballanced signal....This system only needs about 8 passive components to create a ballanced output (2 caps ,4 resistors and 2 ferrite beads)...If you use a DC servo you can probably drop the 2 Output caps...

    The schematic shown here uses a impedance ballanced output...

    http://www.jensen-transformers.com/as/as017.pdf

    You can copy the output section of the schematic and use it in your INA217 mic pre and get a very easy to build ballanced output....


    Good luck
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    Thanks for the input Minion i find it very helpfull
    Quote Originally Posted by Minion View Post

    Another way which I did on my latest INA217 is to use an Audio transformer...I had Two 1:1 Line transformers I salvaged from an old Akai 2 track recorded and used these on the outputs of the INA217...These do seem to color the sound a bit but it seems to add a bit of mojo to it...
    And with a Output transformer you don"t need a DC servo or output cap as the transformer blocks DC from the output....
    Could you explain how to wire a transformer?, i mean what goes into which pins and that, here is the schematic:

    http://www.canford.co.uk/ProductResources/ig/2739.pdf

    Im planning on using the A262A7E which is a 1+1:1+1 trafo, however i dont understand the connections to it, meaning where do i connect the output of the INA217, and where does the ballanced signal comes out. Also some times some of the windings have to be interconnected (dont know if to parallel secondaries and stuff like that), if you could solve this question for me it would be much apreciated.

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    I think i have a idea on how it is wired...

    most of the audio transformers I have wired up were either single primary and single secondary, or single primary Dual secondary or single primary center tapped secondary.... Yours looks like a dual primary and dual secondary with a ground tap (pin 9)....

    The way I see it you have a few options of how to wire it...

    You can wire both the primary and the secondary in series....
    (on the primary side the Ina217 Preamp output connects to pin 1 ,Pins 2 and 3 connect together ,and pin 4 goes to ground, On the secondary side Pin 5 goes to + out, pin 6 & 7 connect together and go to ground ,and pin 8 is - Output)

    You can wire both primary and secondary in Paralell...
    (Pin 1 and 2 connect together and connects to ina217 preamp output, Pins 3 and 4 go to ground, 5 and 6 connect together and are + output ,7 and 8 connect together and are - output , 9 goes to ground)..

    You can also use a combitation of Series and Paralell of each primary and secondary and you can also wire a switch so you can go from series and paralell on each winding...

    As for which wireing method is suitable for you I don"t really know but I would first try wireing both Primary/secondary in series and see how that sounds and go from there....

    Cheers
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    Thanks for the input everyone, you really helped me out, my pre-amp is now running and ballanced

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