It also has massive heatsinks for cool, reliable performance. An AC power detect circuit, which ensures that the amplifier outputs shut down first when AC is removed. This will guard against any thumps or pops that could otherwise occur, potentially damaging speakers when power is cut to the amplifier. Differential input buffers to eliminate ground loop hum coming from the power amp. The Velocity 250 takes what those first models provided to a whole new level.
Every tube amplifier has some amount of output impedance due to the output stepdown transformer.
Conversely, solid state amplifiers have little or no output impedance, because the speaker terminals are connected directly to the output devices. This difference in impedance is the primary reason why the two types of amplifiers sound differently. As the control is turned clockwise, the effective impedance increases and sounds more like a tube amplifier's output stage. But with the Velocity 250, you still get the full rated output delivered to the speaker. What this means for you is that you get an amplifier that will react differently with each speaker cabinet you use with it, just like a tube amp would do.