One question that comes up about the Dreadnought 1:1 toroidal isolation transformer is, since we are using the transformers in an application with bi-directional signals, will the SDA signal be imbalanced. The answer is no. Although there is a small difference in output between the primary to secondary and secondary to primary directions, the difference is inaudible, on the order of fractions of a dB.
This subject was first discussed in posts 62-71 of this thread...
...and again in posts 167-174 of this thread...
and most recently in posts 11-18 of this thread:
When I measured the left and right stereo and dimensional outputs of the Y236906 800VA transformer in 2008, there was a few percent difference in the outputs of each direction, but it certainly could not be considered as an "imbalance".
In terms of dB, the differences in voltage amplitudes between channels are:
0.12 dB stereo, 0.26 dB dimensional.
0.38 dB stereo, 0.39 dB dimensional.
With all of the things going on in a stereo sound field, most people would not (or cannot) notice a difference of 0.1 dB to 0.4 dB difference in sound level between channels.
Consider that any isolation transformer, even the one used with the original AI-1, will have a small difference in output when comparing primary to secondary direction and secondary to primary direction. This is unavoidable since a 1:1 isolation transformer must include a small step up function to account for transformer losses. It is unavoidable that a signal going in the secondary to primary direction will see a small step down function. However, the output differences between directions should be (and are) inaudible and should be (and are) within the range you would expect from differences in amp channels and differences in loudspeaker drivers and crossover components. The difference between the outputs of each direction will also vary with frequency. Table 2 shows the output voltage differences according to direction among the original AI-1, 800VA Dreadnought, and 1000VA Dreadnought. The SDA circuit operates from 1600 Hz down.
Figure 1. Left to right: original Polk AI-1 Non-Common Ground Interface, 800VA AI-1 Dreadnought, 1000VA AI-1 Dreadnought.