Listening to headphones creates, on many recordings, an unnaturally wide soundstage. I decided to play with the idea of 'crossfeed' whereby some deliberate crosstalk is introduced between the two channels. With transformers its jolly easy to do - just create an extra winding with the right number of turns then put this winding in series with the main output of the opposite channel.
In the picture I've done this with some EP17 ferrite cores and added a DPDT changeover switch to A/B between the original and crossfed version. The crossfeed factor I've gone for is 25%. It works in practice in that there's a more natural presentation without any 'extreme' stereo effects (almost a kind of phasiness on some recordings). But sometimes I enjoy the 'all around' effect so switchable is the name of the game
Trafo winding details as follows - primary 500T of 0.1mm, two secondaries first 120T 0.21mm, second 40T 0.21mm.
Made a second one as a colleague liked...