TVC preamps: good or bad?

I don't know if they introduce colorations and aberrations, but they do seem to be very transparent and quiet and don't appear to be much bother by impedance matching issues that you sometimes get with resistor based passives. Some folks with pretty good equipment seem to swear by them, especially the Bent units and those made with S&B transformers.

I'm curious and a bit confused about these as well. On the one hand these transformer based units seem to offer much the bonuses of passives, without the impedance issues of passives. On then other hand, some tube manufacturers are willing to deal with impedance issues to avoid using transformers. Some of those same manufacturers claim that transformers introduce phase issues. What's the real story?

I currently have Promitheus Audio Reference C-core TVC and I can confirm that this unit is extremely transparent and extremely quiet. Soundstage definition and resolution is the best I've heard in any system at any price. Each instrument has its own well defined space. Dynamic contrast is top notch. This TVC doesn't have the midrange magic that tubes provide, but it gets pretty close.

This is the top-of-the-line TVC that Promitheus Audio makes, so I don't know how their other units compare to this one. From what I've read, these TVCs don't work well on systems where there is not enough gain. I don't have that problem at all. The sound is already too loud if I pass the 1 o'clock mark.

Regards,

iSanchez