405-2比405好得多的原因..........
The only significant shortcoming of the original 405 was its inability to drive at full power into low impedances — and the impedance dips of many nominally '8 ohm' speakers presented difficulties here. The new 405-2 features bigger, output devices, which can safely handle the increased power dissipation into lower impedance loads. As a result, the protection circuitry has been 'backed off', allowing a continuous power of 150 watts into a 5 ohm resistive load (cf. 6 ohms for the 405-1) and 100 watts into 3 ohms — as opposed to 25 watts into 3 ohms for the 405-1.
To sum up, the 405-2 scores very highly as a serious and long term investment at the 100+100 watts level — perhaps more highly in this respect than any other power amp.
At the same time, reservations are still in order as regards its suitability for driving high power into speakers presenting a 'difficult' load, especially if their nominal impedance is well below 8 ohms, which is perhaps more often the case with professional, as opposed to domestic speakers.
以上全文出自 http://www.muzines.co.uk/articles/quad-405-2-amplifier/1255