Apart from the pickups, John Birch applied a single-knob bass-cut/treble-cut tone control at all his instruments, equivalent to the controls at 1940/50 Epiphone Electar guitars and early 1950 Gretsch guitars with DeArmond Dynasonic pickups.
All standard guitars like the J1, J2 and SG models are switchable for mono, stereo and anti-phase-mono operation, wired to a stereo phono output connector.