I've tried two passive solutions in my system - a Bent Audio TVC with copper transformers and a built-in resistor attenuator in my Audion Silver Night. I've tried various configurations: I've used the Bent with five different amps, both tube and solid-state, and I've tried the Audion nude, with the Bent and with a couple of actives. This has been done on two different speaker systems, both of them efficient and high-res. The source is a balanced AN DAC, with quite low output impedance and sufficient, though not excessive output voltage.
The conclusions that have remained relatively consistent across most configurations are:
- The Bent was sonically problematic in all my configurations. It's very smooth, but robs enough dynamics and detail to make the sound boring.
- The tube preamps I've tried (Canary and Audion) have better dynamics than the Bent, but equivalent detail and higher noise. They tended to be more fun to listen to, but were more coloured (warmer).
- The resistor attenuator in the Audion sounds quite good nude. Putting the Bent or one of the tube preamps in front of it mucked up the sound in various ways.
- The joker in the deck is the solid state Tom Evans Vibe/Pulse. I tried it with three amps, and it produced better sound than any of the others. It even improved the sound of the Audion amp when driving its internal attenuator. Imprevements were in the areas of bass and treble extension, dynamics, detail, neutrality and transparency. The downside of course is that it is two to four times the price of any of the others. I ascribe the superiority of the Vibe to its higher output current and lower output impedance.
So, a passive can be better than a medium-high quality line stage (the case with the Audion's attenuator), or it may be worse (like the Bent). A very good preamp is likely to exceed the quality of a passive because of its current and impedance advantages.
