Conrad Johnson
Evolution 2000 Zero Feedback Power Amplifier
The Evolution 2000 was a genuinely unique design drawing on the many year's experience conrad-johnson had with both vacuum tube and solid-state circuits. The EV2000 uses MOSFETs for output devices and vacuum tubes for the input stage making the EV2000 a truly hybrid design. It was a straightforward response to the challenge of producing a true zero-feedback power amplifier. Since only square-law valves are deployed in the EV2000, only second order distortion products are produced. Odd order distortion components, which are most noticeable and objectionable to the human ear, are virtually non-existent. Triode vacuum tubes were selected to provide all of the voltage gain. Current gain is provided by two stages of complimentary MOSFET source followers, the final stage consisting of five-pairs of high current devices for a nearly unlimited capacity to deliver current into reactive loudspeaker loads. High current delivery was facilitated by a massive, oversized, dedicated power transformer (nearly 50 lbs.) used for the solid state output devices. The MOSFET output stage eliminated the bandwidth limitations and phase shift associated with output transformers, and at the same time achieved a much lower output impedance than would be possible with a vacuum tube output stage.
The EV2000 offered the tonal integrity of the finest vacuum tube amplifiers combined with the speed and detail of superior transistor designs. Individual voices and instruments are faithfully reproduced and remain tightly focused on the soundstage no matter how complex the musical passage.
