It really can sound and feel just like a tube amp.
The Rocktron Velocity 300 Rack Power Amp was designed in a joint effort between Rocktron and integrated circuitry design engineer Derek Bowers. The Velocity 300 is the first commercially available amplifier to be based on current-feedback technology. This technology provides extremely high-speed, wide-bandwidth amplification. The bandwidth of the power amp section is considerably higher than typical amplifiers based on voltage feedback designs therefore providing much more punch and definition than previous designs have allowed for.
Another of the Rocktron Velocity 300 power amp's innovative features lies in the reactance simulation circuitry (controlled by the front panel "Reactance" control. At the minimum setting of the reactance control, the Velocity 300 will provide the added punch and improved transient response of the high-speed current-feedback design. As this control is turned up, the Velocity 300 will begin to simulate the interaction that takes place between the tube amplifier and the guitar speaker cabinet.
In addition to the high-speed current-feedback design, the Velocity 300 also incorporates Rocktron's unique "Speaker Reactance Simulation" circuitry. This concept is unprecedented in a solid-state amplifier and yields the much-sought-after sound of the most impressive tube amplifiers without the added maintenance and cost and weight of a tube amp. In addition, the Velocity 300 has “Definition” controls to give you that little bit of edge you need to bring your playing out in the mix. It also has automatic short circuit protection, which detects problems and shuts down the amplifier before any internal damage can be done.
While other amplifier manufacturers seem to concentrate solely on the harmonic characteristics of the tube itself (and how to recreate them in a solid state circuit), Rocktron suggests it still lacks the tube sound. When put to the test and compared directly with the most popular tube amps, these solid state designs still sound cold and thin.
At the maximum setting of the reactance control, the Velocity 300 will instead sound like a tube amplifier, simulating the interaction between a tube amplifier and a guitar speaker cabinet. The resulting sound is much warmer and fatter, and when compared directly with a tube amp, is virtually indistinguishable.