Reading the schematic, it seems that the K4003 might support a fully differential configuration as-is. I’d connect hot to L, cold to R, and cable ground to the chassis (NOT signal GND). Likewise on the output side.
Has this been done? Can anyone foresee any problems?
If I were to put two of these boards in a single chassis thusly for balanced stereo operation, which transformer should I use? It’ll never be driving speakers, only headphones. Currently it’s a 120-ohm circumaural set, itself in the process of recabling for balanced operation.
Obviously enough, the PE conductor from the power cable should be connected directly to the chassis. Should the neutral line from the secondary side of the transformer also be tied to earth, or should it be allowed to float?