Any idea on why this flip-flop in preamp design? Afterall, neither transformers nor capacitors are new technologies – why such a major change in design approach?
@captc2 By using coupling capacitors, the preamp, although balanced, was unable to support the balanced line standard also known as AES48 (which is a connection standard, also defines how the grounds are connected). There is no such standard for single-ended operation FWIW.
When coupling caps are used, the ground becomes part of the circuit return path, which means the ground is involved with the signal. This opens the preamp to ground loops, something that isn't supposed to happen with balanced operation.
A transformer OTOH easily supports the standard. This is beneficial as it allows the preamp to drive longer cables and to reduce interconnect cable artifact.
Historically speaking one of the founders of BAT was a customer of ours; evidently the BAT designer took inspiration from our designs- at the time we were the only manufacturer in high end audio using a circuit called the Circlotron. We obtained a patent for its use at the preamp level and I suspect they didn't want to get involved with infringement; our patent allowed for a reliable direct-coupled output that supports AES48. So they used coupling caps but lost a lot of the benefit of balanced operation since the standard wasn't supported. I suspect this move is to reclaim that benefit- transformers are very good at this sort of thing.