Replacing Op-amps used for Balancing with Transformers

I see op-amps used all the time for unbalancing (at the input) and balancing (at the output) in pro-studio gear. Usually the op-amps are running at unity gain, so what's to stop someone from tossing in a 1:1 transformer to replace the op amp? I have a feeling it's got something to do with the impedence of the op-amp output right? The op-amp has got a super low output impedence, while a 1:1 xformer will have a secondary impedence that is the same as what it sees at it's primary right? So would one need to replace an un-balancing op amp with a xformer AND a unity gain op amp??

Ian

hey Ian

i think that the opamp is not only for balancing/unbalancing but acts as a buffer amp as well. someone else can probably explain this in more detail. i'm no guru, but i was just thinking about this in the car today, so i am curious to hear some replies.

-AL

You will need a good opamp, either a discrete opamp or an opamp plus a current buffer to drive the transformer well. Transformers like to see 0 impedance on their inputs to give you their lowest distortion and their best low frequency transfer. You can hang a transformer off an ordinary opamp with less than spectacular results. Here is an example of an opamp supplemented with a high current capability buffer.
http://mysite.verizon.net/res75okq/sitebuildercontent/sitebuilderfiles/compositeNE5534LT1010.gif