Ghostrider hit upon one negative aspect of transformer coupling i.e. the potential for non-linear frequency response errors to be introduced into the signal path.
As far as signal paths go, transformer coupling is equivalent to running the signal through an interconnect that is hundreds of feet long. This is due to the amount of wire that the signal must pass through on both the primary and secondary sides of the transformer.
The fact that the signal is NOT directly coupled and is only linked via the magnetic flux of the transformer also opens the door to signal degradation. I would also imagine that the potential for increased susceptability to RFI becomes more of a factor in heavily populated areas.
Transformers can also run into saturation, which is not much of a problem when dealing with line level signals. None the less, a transformer coupled design is both tougher to design and more likely to suffer bandwidth related distortions than a capacitor or direct coupled design.
Isolation can be improved with a transformer but the capacitance must be kept down to a bare minimum. In most cases, any fluctuation that the transformer runs into on the secondary side due to irregular loading conditions will be passed back into the primary side of the transformer. The effects of the loading irregularities may be reduced but they are still there and the circuit on the primary side still has to deal with them.
I can continue on but will some it up by saying that there is no "golden goose" when it comes to audio circuitry design. They all have their ups and downs. As such, it is not so much what topology or design that one uses, but more of how well that design is implimented and the quality of parts used. Sean
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