The new Bent passive indeed is/will be using autoformers. I've had the chance to sample the first prototype recently (I still have it for a few days) and it is really wonderful: completely transparent at any volume setting, dynamic and excellent at micro detail. It is actually very close to a direct connection, as I checked myself (with low volume music!). I've spent the last 4 months trying all kinds of resistor-based potentiometers (or attenuators) and they all messed up the signal--the difficulty here of course is to find the right resistor impedance to match the source impedance; but in my experience even Vishays (which are by the way vastly overrated) are no good for that application. As is said above in one of the threads, passives will not necessarily work in every system. In my system, it works really well with the Audio Note 3.1x balanced DAC and the CIAudio monoblocks; but finding the right setting with the WrightSound phono preamp (which has volume controls) is not easy, precisely because that preamp has a high output impedance; then, I suspect that the volume controls on this preamp are passive, which means that if they are not bypassed, one gets two passive devices in the circuit--not good! I also experimented with a Hagerman Trumpet and that works extremely well (the Trumpet has almost the same output impedance as the AN DAC).
The main difference between this new Bent passive with the older TVC is that the switchbox and the attenuator modules are now separate: this allows having the switchbox near the source and run long interconnects to the attenuators if needed, because the attenuator modules are set very close to the amps--useful if your sources are not close to the amps, obviously. John estimates that the new units will be ready in a few weeks.
