Passive mode:
From Michael Fremer's review:
http://www.stereophile.com/content/ypsilon-pst-100-mkii-line-preamplifier
"While I listened in both active and passive modes, the latter's output, even with the attenuator well down from its 0dB maximum level,
was more than enough to drive my Musical Fidelity Titan amp and my relatively sensitive Wilson Audio MAXX 3 speakers In passive mode, there was literally nothing but the silver relay and the step-down transformer between the incoming signal and the interconnect to the power amplifier. The PST-100 sounded about as close to the source as can be imagined.
All sources, analog or digital, were steps more transparent, three-dimensional, and closer to sounding "live"—or at least closer to the source going directly to the amplifier—than I've otherwise heard in my listening room."
BTW, curiously, he could literally hear no difference between passive and active mode. There goes the theory that an "active" preamp is an essential
part of of a high end system.