WA22 - balanced or not - a never ending story.....
Here is what Jack Wu had to say about it:
The WA22 is a fully balanced amp, see diagram below.
The question here is that this amp is not fully balanced because the "amp with a single ended output stage directly connected to the XLR connectors.” It is not true. In an Output Transformer coupled design, the primary and secondary coils are isolated. Output stage and input stage are not connected and thus no cross-talk whatsoever can happen.
On the ¼” output, both channels have independent paths, see the black and red wires. If this wiring scheme applies to a Output Transformer Less design, the circuit will become single-ended. See the second diagram in #17, the v- would have to be a common wire to other channel. One must be carefull not to take reference from the wrong context to avoid all the misunderstanding.
Also, no phase splitter is needed because the source is XLR (balanced). As for the RCA input, only ½ of the input is used and the efficiency is roughly dropped 50%. In other words, the RCA input will not take advantage of this design. You must use a balanced source to get the best out of the WA22.
Hope that clarifies.