Edwyun, take a look at my review on the Bent Audio Tap linestage, it will provide a great amount of information on this topic. Hope this helps.
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Passive linestages can be very good if the rest of your system is up to the task. And a well designed TVC is the best of this breed. First, you must determine your amp input sensitivity and voltage gain, speaker sensitivity, source output impedence and voltage. If all these are "passive friendly", you are good to go.
What you will hear with a TVC over a resistor based passive is a very slight bloom in the midrange not unlike tubes. But you give up no ground in transparency or detail. The bass is also more solid and defined like that of an active linestage.
I lived with and loved a TVC for several years. Only recently have I gone back to an active preamp due to an amp upgrade that neccessitated it.
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.
Clio99, no: there is just one set of ICs to connect, from the switchbox to the attenuators (one per channel). Each attenuator has a very short cable coming out of it with an RCA connector: that's what you plug into the amps. By the way, the attenuator module looks just like the old MC stepup that you can see on the Bent Audio website. The top is a bit different but you can see on the picture the cable coming out of the module and the RCA input on top (there's actually another RCA which can be used as secondary output, to go into a subwoofer).
Clio99, yes of course, you might be right, and I haven't compared this little piece of cable with other cables so I can't say that it couldn't be improved upon; so far I haven't found any fault to it. However, as I mentioned in the previous post, there is an additional RCA output on top of the module, if one doesn't want to use the cable that's already there. I haven't used that output yet, but will try to do it before I send the unit back.
By the way, on the same subject, John wrote me the following:
"The 2nd output on the module is there to address EXACTLY this concern. I ran into this years ago with my old Bent Units. On the new TAP the main switch box/controller will have a dedicated separate and buffered (to take it out of the signal path) subwoofer output. The 2nd output on the module is there in case you want to use a particular cable from module to amp. I do find it kinda funny in a way - since the cable is shorter than the internal wiring in other pre-amps (it's only about 5 inches long - no jokes please......) and really in essense that internal wiring that would be inside - but you see it. It is actually a very custom cable I make up by hand - its a weave of OCC copper around a center core then insulated with natural cotton - very decent and more involved than internal wiring in any pre-amp I have seen!"
Thanks for the clarification Edwyun.
In fact, I'm using a S&B passive. I prefer this to a ladder type resistor based unit -- which, OTOH is cheap to make (the S&B TVC is expensive); Both of the above where better than the basic rotary switch equivalent; I preferred relay switching than the mechanical, rotary, counterpart.