In order to achieve maximum sound quality it is not sufficient to look at the front end. Also the design of the power amplifier should be considered. In that case we have to look at Watts, current and stability. And we should consider the phase pattern if two amplifiers are being used in a bi-amping configuration. Power amplifiers should have identical phase patterns/characteristics. And a preamplifier should well match the phase of the power amplifier. If not it is possible that a slight phase shift will limit the fidelity in the top of the frequency band and thus will inhibit the slam and the clean detailing of complex sound structures. You all know from experience that the same preamplifier functions better if connected to power amplifier X and does perform less well with power amp Y. There are a few things to consider:
• Maybe your amplifier has circuits with too much negative feedback and cannot deliver the energy with sufficient speed. • Maybe it is an amplifier with not enough energy storage and instead has a large toroidal transformer from which the energy is drawn. Those amplifiers are suitable for high efficiency loudspeakers and are not able to deliver constant energy to make lower efficiency loudspeakers with complex filters work properly, especially speakers with an efficiency of 85 to 87 dB, like Harbeth, several Avalon systems, etc. • Maybe you have high efficiency loudspeaker systems (93 to 106 dB) like Cabasse and Klipsch, and you are feeding them with heavy, prowerfull, high capacity amplifiers. Especially high efficiency horns need fast and neat power. • Another reason for dull sound can sometimes be the use of two bridged stereo amplifiers, one for the left and one for the right channel. As you know bridging generally gives dull sound.