The Eureka has a Class A transformer-coupled Preamp. Power amplifiers are classified primarily by the design of the output stage and are designated Class A, B, AB, D, G, or H. In a Class A preamp, the output circuits are always on for the entire cycle of signal swing or the bias current flows at all times. As a result, Class A preamps have the most linear design, with no crossover distortion, and they deliver purer, clearer, and more musical results than the Class AB designs that are found in many preamps. Eureka contains a Class A discrete input buffer followed by a dual-servo gain stage. This yields ultra-low noise and wide gain control, allowing you to boost desirable signal without increasing unwanted background noise.