@johnss The pin 2 inverted and pin 3 non-inverted is a European thing. Most US manufacturers use pin 2 as non-inverting. Using the ’hot’ and ’cold’ nomenclature can be confusing since both pins carry a signal of equal weight (’cold’ often refers to ’ground’, which in this case it is not).
Again, we introduced the MA-1 with balanced inputs in 1987 and followed that with the MP-1 in 1989. But we did make an earlier OTL that had very limited production that we call the ’campfire’ amp, since the power tubes are arranged in a circle around the driver circuit. Those amps only had XLR inputs; no RCAs at all and the earliest of them was built in 1984.
All these products were fully differential and balanced internally. So a few years earlier than you suggested in your post.
@wesselc As best I can make out, Accuphase didn’t make any balanced line products for home use until about 1989. If you know of something earlier, I’d be interested. A couple of years ago I serviced a single-ended solid state preamp they made in the 1970s. It was built very well but no electronics will last 100 years without service; that unit was in desperate need of new filter capacitors in its power supplies!
