Tubes type
The model of tubes installed in a tube or hybrid type amplifier (see "Element base"). The capabilities of the device largely depend on the lamps used in the design, including small details of the sound, not directly spelled out in the characteristics. In addition, this information allows, to some extent, to assess the overall level of the model. On the other hand, in fact, it can only be useful to extremely demanding listeners, attentive to every detail; most users, including audiophiles, will only need information about the type of tubes when they need to be replaced.
Signal-to-noise ratio (Main)
Signal-to-noise ratio when the amplifier is operating through the Main input. For more details on the value of the signal-to-noise ratio, see the relevant paragraph above, about the Main input — p. "Input to the amplifier (Main)".
Main input
The sensitivity and dynamic impedance of the amplifier when a signal is applied to the Main input.
Under the sensitivity of any input (except optical) is meant the lowest signal voltage at this input, at which the amplifier is able to provide normal nominal power values (see "Power per channel (8Ω)"). This parameter determines, first of all, the requirements for the signal source. On the one hand, the voltage provided by this source must not be lower than the input sensitivity of the amplifier, otherwise the latter simply will not give the claimed characteristics. However, a significant excess in voltage should not be allowed, otherwise the sound will begin to be distorted. More detailed recommendations on choosing an amplifier by sensitivity are described in special sources.
For any input other than optical, it is believed that the higher this indicator, the less distortion the amplifier introduces into the signal. The minimum level of input impedance in modern models is considered to be 10 kOhm, and in high-end devices it can reach several hundred kOhm.
